Showing 1–50 of 77 results for author: Cai, M

Measurement of the cosmic ray nickel energy spectrum from 10 GeV/n to 2 TeV/n with the DAMPE

Authors: F. Alemanno, Q. An, P. Azzarello, F. C. T. Barbato, P. Bernardini, X. J. Bi, H. V. Boutin, I. Cagnoli, M. S. Cai, E. Casilli, J. Chang, D. Y. Chen, J. L. Chen, Z. F. Chen, Z. X. Chen, P. Coppin, M. Y. Cui, T. S. Cui, I. De Mitri, F. de Palma, A. Di Giovanni, T. K. Dong, Z. X. Dong, G. Donvito, J. L. Duan , et al. (123 additional authors not shown)

Abstract: Nickel, one of the most stable elements alongside iron, is the most abundant heavy element beyond iron in cosmic rays. With DAMPE's excellent charge resolution and broad energy range, a high-precision energy spectrum provides valuable insights into the acceleration sources of heavy nuclei and their propagation through the interstellar medium. In this analysis, we report the direct measurement of c… ▽ More Nickel, one of the most stable elements alongside iron, is the most abundant heavy element beyond iron in cosmic rays. With DAMPE's excellent charge resolution and broad energy range, a high-precision energy spectrum provides valuable insights into the acceleration sources of heavy nuclei and their propagation through the interstellar medium. In this analysis, we report the direct measurement of cosmic-ray nickel spectrum from 10 GeV/n to 2 TeV/n with nine years of flight data. The nickel spectrum is consistent with a single power law with spectral index -2.60 +/- 0.03 from 40 GeV/n to 1 TeV/n. This work provides an accurate measurement of differential flux of nickel with kinetic energy extending to TeV/n for the first time. △ Less

Submitted 12 December, 2025; originally announced December 2025.

Charge-dependent spectral softenings of primary cosmic-rays from proton to iron below the knee

Authors: DAMPE Collaboration, Francesca Alemanno, Qi An, Philipp Azzarello, Felicia-Carla-Tiziana Barbato, Paolo Bernardini, Xiao-Jun Bi, Hugo Valentin Boutin, Irene Cagnoli, Ming-Sheng Cai, Elisabetta Casilli, Jin Chang, Deng-Yi Chen, Jun-Ling Chen, Zhan-Fang Chen, Zi-Xuan Chen, Paul Coppin, Ming-Yang Cui, Tian-Shu Cui, Ivan De Mitri, Francesco de Palma, Adriano Di Giovanni, Tie-Kuang Dong, Zhen-Xing Dong, Giacinto Donvito , et al. (124 additional authors not shown)

Abstract: In most particle acceleration mechanisms, the maximum energy of the cosmic rays can achieve is charge dependent. However, the observational verification of such a fundamental relation is still lack due to the difficulty of measuring the spectra of individual particles from one (kind of) source(s) up to very high energies. This work reports direct measurements of the carbon, oxygen, and iron spectr… ▽ More In most particle acceleration mechanisms, the maximum energy of the cosmic rays can achieve is charge dependent. However, the observational verification of such a fundamental relation is still lack due to the difficulty of measuring the spectra of individual particles from one (kind of) source(s) up to very high energies. This work reports direct measurements of the carbon, oxygen, and iron spectra from ~ 20 gigavolts to ~ 100 teravolts (~ 60 teravolts for iron) with 9 years of on-orbit data collected by the Dark Matter Particle Explorer (DAMPE). Distinct spectral softenings have been directly detected in these spectra for the first time. Combined with the updated proton and helium spectra, the spectral softening appears universally at a rigidity of ~ 15 teravolts. A nuclei mass dependent softening is rejected at a confidence level of > 99.999%. Taking into account the correlated structures at similar energies in the large-scale anisotropies of cosmic rays, one of the most natural interpretations of the spectral structures is the presence of a nearby cosmic ray source. In this case, the softening energies correspond to the acceleration upper limits of such a source, forming the so-called Peters cycle of the spectra. The results thus offer observational verification of the long-standing prediction of the charge-dependent energy limit of cosmic ray acceleration. △ Less

Submitted 10 November, 2025; v1 submitted 7 November, 2025; originally announced November 2025.

Comments: This update corrects typos in the tables

A Star's Death by a Thousand Cuts: The Runaway Periodic Eruptions of AT2023uqm

Authors: Yibo Wang, Tingui Wang, Shifeng Huang, Jiazheng Zhu, Ning Jiang, Wenbin Lu, Rongfeng Shen, Shiyan Zhong, Dong Lai, Yi Yang, Xinwen Shu, Tianyu Xia, Di Luo, Jianwei Lyu, Thomas Brink, Alex Filippenko, Weikang Zheng, Minxuan Cai, Zelin Xu, Mingxin Wu, Xiaer Zhang, Weiyu Wu, Lulu Fan, Ji-an Jiang, Xu Kong , et al. (15 additional authors not shown)

Abstract: Stars on bound orbits around a supermassive black hole may undergo repeated partial tidal disruption events (rpTDEs), producing periodic flares. While several candidates have been suggested, definitive confirmation of these events remains elusive. We report the discovery of AT2023uqm, a nuclear transient that has exhibited at least five periodic optical flares, making it only the second confirmed… ▽ More Stars on bound orbits around a supermassive black hole may undergo repeated partial tidal disruption events (rpTDEs), producing periodic flares. While several candidates have been suggested, definitive confirmation of these events remains elusive. We report the discovery of AT2023uqm, a nuclear transient that has exhibited at least five periodic optical flares, making it only the second confirmed case of periodicity after ASASSN-14ko. Uniquely, the flares from AT2023uqm show a nearly exponential increase in energy--a "runaway" phenomenon signaling the star's progressive destruction. This behavior is consistent with rpTDEs of low-mass, main-sequence stars or evolved giant stars. Multiwavelength observations and spectroscopic analysis of the two most recent flares reinforce its interpretation as an rpTDE. Intriguingly, each flare displays a similar double-peaked structure, potentially originating from a double-peaked mass fallback rate or two discrete collisions per orbit. The extreme ratio of peak separation to orbital period draws attention to the possibility of a giant star being disrupted, which could be distinguished from a low-mass main-sequence star by its future mass-loss evolution. Our analysis demonstrates the power of rpTDEs to probe the properties of disrupted stars and the physical processes of tidal disruption, though it is currently limited by our knowledge of these events. AT2023uqm emerges as the most compelling rpTDE thus far, serving as a crucial framework for modeling and understanding these phenomena. △ Less

Submitted 30 October, 2025; v1 submitted 30 October, 2025; originally announced October 2025.

Comments: Submitted. Comments are welcome

Evidence of cosmic-ray acceleration up to sub-PeV energies in the supernova remnant IC 443

Authors: Zhen Cao, F. Aharonian, Y. X. Bai, Y. W. Bao, D. Bastieri, X. J. Bi, Y. J. Bi, W. Bian, A. V. Bukevich, C. M. Cai, W. Y. Cao, Zhe Cao, J. Chang, J. F. Chang, A. M. Chen, E. S. Chen, G. H. Chen, H. X. Chen, Liang Chen, Long Chen, M. J. Chen, M. L. Chen, Q. H. Chen, S. Chen, S. H. Chen , et al. (291 additional authors not shown)

Abstract: Supernova remnants (SNRs) have been considered as the primary contributors to cosmic rays (CRs) in our Galaxy. However, the maximum energy of particles that can be accelerated by shocks of SNRs is uncertain observationally and theoretically, and the role of contribution to CRs around PeV energies by SNRs is unclear. In this study, we present observations of high-energy $γ$-ray emission from the SN… ▽ More Supernova remnants (SNRs) have been considered as the primary contributors to cosmic rays (CRs) in our Galaxy. However, the maximum energy of particles that can be accelerated by shocks of SNRs is uncertain observationally and theoretically, and the role of contribution to CRs around PeV energies by SNRs is unclear. In this study, we present observations of high-energy $γ$-ray emission from the SNR IC 443 using the Large High Altitude Air Shower Observatory (LHAASO). The morphological analysis reveals a pointlike source whose location and spectrum are consistent with those of the Fermi-LAT-detected compact source with $π^0$-decay signature, and a more extended source which is consistent with a newly discovered source, previously unrecognized by Fermi-LAT. The spectrum of the point source can be described by a power-law function with an index of $\sim3.0$, extending beyond $\sim 30$ TeV without apparent cutoff. Assuming a hadronic origin of the $γ$-ray emission, the $95\%$ lower limit of accelerated protons reaches about 300 TeV. The extended source might be coincident with IC 443, SNR G189.6+3.3 or the putative pulsar wind nebula CXOU J061705.3+222127, and can be explained by either a hadronic or leptonic model. The LHAASO results provide compelling evidence that CR protons up to sub-PeV energies can be accelerated by the SNR. △ Less

Submitted 29 October, 2025; originally announced October 2025.

Investigation of hadronic cross sections of cosmic ray carbon and oxygen on BGO from 200 GeV to 10 TeV energy at the DAMPE experiment

Authors: F. Alemanno, Q. An, P. Azzarello, F. C. T. Barbato, P. Bernardini, X. J. Bi, H. Boutin, I. Cagnoli, M. S. Cai, E. Casilli, E. Catanzani, J. Chang, D. Y. Chen, J. L. Chen, Z. F. Chen, Z. X. Chen, P. Coppin, M. Y. Cui, T. S. Cui, Y. X. Cui, I. De Mitri, F. de Palma, A. Di Giovanni, T. K. Dong, Z. X. Dong , et al. (122 additional authors not shown)

Abstract: The Dark Matter Particle Explorer (DAMPE) has made significant progress in measuring the fluxes of cosmic rays. These new measurements are pivotal in advancing our understanding of the origins and propagation mechanisms of cosmic rays. The bismuth germanium oxide (BGO) calorimeter plays a crucial role in these measurements, particularly in the precise determination of cosmic ray fluxes. However, f… ▽ More The Dark Matter Particle Explorer (DAMPE) has made significant progress in measuring the fluxes of cosmic rays. These new measurements are pivotal in advancing our understanding of the origins and propagation mechanisms of cosmic rays. The bismuth germanium oxide (BGO) calorimeter plays a crucial role in these measurements, particularly in the precise determination of cosmic ray fluxes. However, for a calorimetric experiment like DAMPE, uncertainties in hadronic models persist as a major barrier in achieving more accurate measurements of fluxes of cosmic ray nuclei. This study centers on the measurement of the inelastic hadronic cross sections of carbon and oxygen nuclei interacting with BGO crystals target over an extensive energy range, spanning from 200 GeV to 10 TeV. For carbon nuclei interacting with the BGO target, the measurements of the cross sections have achieved a total relative uncertainty of less than 10% below 8 TeV for carbon, and below 3 TeV for oxygen. For oxygen nuclei, the same level of precision was attained below 3 TeV. Additionally, we compare the experimental results with Geant4 and FLUKA simulations to validate the accuracy and consistency of these simulation tools. Through comprehensive analysis of the inelastic hadronic interaction cross sections, this research provides validation for the hadronic interaction models used in DAMPE's cosmic-ray flux measurements. △ Less

Submitted 21 September, 2025; originally announced September 2025.

Einstein Probe Discovery of EP J182730.0-095633: A New Black Hole X-ray Binary Candidate in Faint Outburst?

Authors: Huaqing Cheng, Qingchang Zhao, L. Tao, H. Feng, F. Coti Zelati, H. W. Pan, A. L. Wang, Y. N. Wang, M. Y. Ge, A. Rau, A. Marino, L. Zhang, W. J. Zhang, F. Carotenuto, L. Ji, C. C. Jin, D. Y. Li, B. F. Liu, Y. Liu, E. L. Qiao, N. Rea, R. Soria, S. Wang, Z. Yan, W. Yuan , et al. (56 additional authors not shown)

Abstract: Black hole X-ray binaries (candidates) currently identified in our galaxy are mainly transient sources, with the majority discovered through the detection of their X-ray outbursts. Among these, only four were found during faint outbursts exhibiting peak X-ray luminosities $L_{\rm X}\lesssim10^{36}~{\rm erg~s^{-1}}$, likely due to the previous lack of sensitive, wide-field monitoring instruments in… ▽ More Black hole X-ray binaries (candidates) currently identified in our galaxy are mainly transient sources, with the majority discovered through the detection of their X-ray outbursts. Among these, only four were found during faint outbursts exhibiting peak X-ray luminosities $L_{\rm X}\lesssim10^{36}~{\rm erg~s^{-1}}$, likely due to the previous lack of sensitive, wide-field monitoring instruments in the X-ray band. In this Letter, we present the discovery of an intriguing X-ray transient, EP J182730.0-095633, via the Einstein Probe (EP) and subsequent multi-wavelength follow-up studies. This transient, located on the Galactic plane, experienced a faint and brief X-ray outburst lasting about 20 days. Its X-ray spectrum is non-thermal and consistent with a power-law model with a nearly constant photon index of $Γ\sim2$ throughout the outburst. A long-lasting millihertz quasi-periodic oscillation (QPO) signal was detected in its X-ray light curve, centered around a frequency of $\sim0.04$ Hz. A transient near-infrared source was identified as its counterpart, although no optical emission was detectable, likely due to significant extinction. A radio counterpart was also observed, displaying an inverted radio spectrum with $α\sim0.45$. The X-ray spectral and temporal characteristics, along with the multi-wavelength properties, indicate that the source is a faint low-mass X-ray binary, with the compact object likely being a black hole. This work demonstrates the potential of the EP in discovering new X-ray binaries by capturing faint-level X-ray outbursts. △ Less

Submitted 17 July, 2025; originally announced July 2025.

Comments: 22 pages, 5 figures (plus 3 in appendix), 3 tables in appendix. Accepted for publication in ApJ Letters

All-sky search for individual Primordial Black Hole bursts with LHAASO

Authors: Zhen Cao, F. Aharonian, Y. X. Bai, Y. W. Bao, D. Bastieri, X. J. Bi, Y. J. Bi, W. Bian, A. V. Bukevich, C. M. Cai, W. Y. Cao, Zhe Cao, J. Chang, J. F. Chang, A. M. Chen, E. S. Chen, G. H. Chen, H. X. Chen, Liang Chen, Long Chen, M. J. Chen, M. L. Chen, Q. H. Chen, S. Chen, S. H. Chen , et al. (293 additional authors not shown)

Abstract: Primordial Black Holes~(PBHs) are hypothetical black holes with a wide range of masses that formed in the early universe. As a result, they may play an important cosmological role and provide a unique probe of the early universe. A PBH with an initial mass of approximately $10^{15}$~g is expected to explode today in a final burst of Hawking radiation. In this work, we conduct an all-sky search for… ▽ More Primordial Black Holes~(PBHs) are hypothetical black holes with a wide range of masses that formed in the early universe. As a result, they may play an important cosmological role and provide a unique probe of the early universe. A PBH with an initial mass of approximately $10^{15}$~g is expected to explode today in a final burst of Hawking radiation. In this work, we conduct an all-sky search for individual PBH burst events using the data collected from March 2021 to July 2024 by the Water Cherenkov Detector Array of the Large High Altitude Air Shower Observatory (LHAASO). Three PBH burst durations, 10~s, 20~s, and 100~s, are searched, with no significant PBH bursts observed. The upper limit on the local PBH burst rate density is set to be as low as 181~pc$^{-3}$~yr$^{-1}$ at 99$\%$ confidence level, representing the most stringent limit achieved to date. △ Less

Submitted 2 November, 2025; v1 submitted 30 May, 2025; originally announced May 2025.

Comments: 8 pages, 2 figures

A Silicon Microstrip Detector for Power-Limited and Large Sensitive Area Applications

Authors: Dexing Miao, Zijun Xu, Zhiyu Xiang, Pingcheng Liu, Giovanni Ambrosi, Mattia Barbanera, Mengke Cai, Xudong Cai, Hsin-Yi Chou, Matteo Duranti, Valerio Formato, Maria Ionica, Yaozu Jiang, Liangchenglong Jin, Vladimir Koutsenko, Qinze Li, Cong Liu, Xingjian Lv, Alberto Oliva, Wenxi Peng, Rui Qiao, Gianluigi Silvestre, Zibing Wu, Xuhao Yuan, Hongyu Zhang , et al. (2 additional authors not shown)

Abstract: A silicon microstrip detector (SSD) has been developed to have state of the art spatial resolution and a large sensitive area under stringent power constraints. The design incorporates three floating strips with their bias resistors inserted between two aluminum readout strips. Beam test measurements with the single sensor confirmed that this configuration achieves a total detection efficiency of… ▽ More A silicon microstrip detector (SSD) has been developed to have state of the art spatial resolution and a large sensitive area under stringent power constraints. The design incorporates three floating strips with their bias resistors inserted between two aluminum readout strips. Beam test measurements with the single sensor confirmed that this configuration achieves a total detection efficiency of $99.8 \, \%$ and spatial resolution $7.6 \, \mathrm{μm}$ for MIPs. A double-$η$ algorithm was developed to optimize hit position reconstruction for this SSD. The design can be adapted for large area silicon detectors. △ Less

Submitted 28 May, 2025; originally announced May 2025.

Comments: 9 pages, 13 figures

Oort Cloud Formation and Evolution in Star Clusters

Authors: Justine C. Obidowski, Jeremy J. Webb, Simon Portegies Zwart, Maxwell X. Cai

Abstract: It is unknown if an Oort cloud reaches its maximum mass within its star's birth cluster or millions of years later. Complicating the Oort cloud evolution process is the fact that comets can be stripped from orbit due to perturbations from passing stars. We explore how a star's cluster escape time (t$_{ \rm esc}$) and the time its Oort cloud reaches maximum mass (t$_{ \rm max}$) affect the Oort clo… ▽ More It is unknown if an Oort cloud reaches its maximum mass within its star's birth cluster or millions of years later. Complicating the Oort cloud evolution process is the fact that comets can be stripped from orbit due to perturbations from passing stars. We explore how a star's cluster escape time (t$_{ \rm esc}$) and the time its Oort cloud reaches maximum mass (t$_{ \rm max}$) affect the Oort cloud's ability to survive via $N$-body simulations. In a 14 M$_\odot$/pc$^3$ cluster, we identify 50 stars of 1 M$_\odot$ with a range of t$_{ \rm esc}$ to host Oort clouds, each with 1000 comets at t$_{ \rm max}$. For each host, we consider Oort clouds that reach maximum mass 0, 50, and 250 Myr after the cluster's formation. Each Oort cloud's evolution is simulated in the cluster from t$_{ \rm max}$ to t$_{ \rm esc}$. Only a fraction of comets tend to remain in orbit, with this amount depending on t$_{ \rm max}$ and t$_{ \rm esc}$. We observe that 12%, 22%, and 32% of Oort clouds with a t$_{ \rm max}$ of 0, 50 and 250 Myr retain >50% of their comets at t$_{ \rm esc}$, respectively. We find that the fraction of comets stripped has the relationship, $\rm f=m\log_{10}(\frac{t_{ \rm esc}-t_{ \rm max}}{Myr})$ where m = 0.32$\pm$0.04, indicating that the longer the Oort cloud remains in the cluster, the more comets are stripped, with this fraction increasing logarithmically at approximately the same rate for each t$_{ \rm max}$. △ Less

Submitted 22 May, 2025; originally announced May 2025.

Comments: 14 pages, 7 figures, 1 table, accepted for publication in The Astrophysical Journal

First Identification and Precise Spectral Measurement of the Proton Component in the Cosmic-Ray `Knee'

Authors: The LHAASO Collaboration, Zhen Cao, F. Aharonian, Y. X. Bai, Y. W. Bao, D. Bastieri, X. J. Bi, Y. J. Bi, W. Bian, A. V. Bukevich, C. M. Cai, W. Y. Cao, Zhe Cao, J. Chang, J. F. Chang, A. M. Chen, E. S. Chen, G. H. Chen, H. X. Chen, Liang Chen, Long Chen, M. J. Chen, M. L. Chen, Q. H. Chen, S. Chen , et al. (292 additional authors not shown)

Abstract: We report the first high-purity identification of cosmic-ray (CR) protons and a precise measurement of their energy spectrum from 0.15 to 12 PeV using the Large High Altitude Air Shower Observatory (LHAASO). Abundant event statistics, combined with the simultaneous detection of electrons/photons, muons, and Cherenkov light in air showers, enable spectroscopic measurements with statistical and syst… ▽ More We report the first high-purity identification of cosmic-ray (CR) protons and a precise measurement of their energy spectrum from 0.15 to 12 PeV using the Large High Altitude Air Shower Observatory (LHAASO). Abundant event statistics, combined with the simultaneous detection of electrons/photons, muons, and Cherenkov light in air showers, enable spectroscopic measurements with statistical and systematic accuracy comparable to satellite data at lower energies. The proton spectrum shows significant hardening relative to low-energy extrapolations, culminating at 3 PeV, followed by sharp softening. This distinct spectral structure - closely aligned with the knee in the all-particle spectrum - points to the emergence of a new CR component at PeV energies, likely linked to the dozens of PeVatrons recently discovered by LHAASO, and offers crucial clues to the origin of Galactic cosmic rays. △ Less

Submitted 20 May, 2025; originally announced May 2025.

Measurement of separate electron and positron spectra from 10 GeV to 20GeV with the geomagnetic field on DAMPE

Authors: DAMPE Collaboration, F. Alemanno, Q. An, P. Azzarello, F. C. T. Barbato, P. Bernardini, X. J. Bi, H. Boutin, I. Cagnoli, M. S. Cai, E. Casilli, E. Catanzani, J. Chang, D. Y. Chen, J. L. Chen, Z. F. Chen, Z. X. Chen, P. Coppin, M. Y. Cui, T. S. Cui, Y. X. Cui, I. DeMitri, F. dePalma, A. DiGiovanni, T. K. Dong , et al. (127 additional authors not shown)

Abstract: The cosmic-ray (CR) electrons and positrons in space are of great significance for studying the origin and propagation of cosmic-rays. The satellite-borne experiment DArk Matter Particle Explorer (DAMPE) has been used to measure the separate electron and positron spectra, as well as the positron fraction. In this work, the Earth's magnetic field is used to distinguish CR electrons and positrons, a… ▽ More The cosmic-ray (CR) electrons and positrons in space are of great significance for studying the origin and propagation of cosmic-rays. The satellite-borne experiment DArk Matter Particle Explorer (DAMPE) has been used to measure the separate electron and positron spectra, as well as the positron fraction. In this work, the Earth's magnetic field is used to distinguish CR electrons and positrons, as the DAMPE detector does not carry an onboard magnet. The energy range for the measurements is from 10 to 20 GeV, being currently limited at high energy by the zenith pointing orientation of DAMPE. The results are consistent with previous measurements based on the magnetic spectrometer by AMS-02 and PAMELA, while the results of Fermi-LAT seem then to be systematically shifted to larger values. △ Less

Submitted 21 August, 2025; v1 submitted 9 May, 2025; originally announced May 2025.

Comments: Accepted for publication in Chinese Physics C

A pilot survey on globular clusters with the Wide Field Survey Telescope (WFST)

Authors: Zhen Wan, Lulu Fan, Xuzhi Li, Xu Kong, Tinggui Wang, Qingfeng Zhu, Ji-an Jiang, Minxuan Cai, Zelin Xu, Xianzhong Zheng, Jingquan Cheng, Feng Li, Ming Liang, Hao Liu, Wentao Luo, Jinlong Tang, Hairen Wang, Jian Wang, Yongquan Xue, Dazhi Yao, Hongfei Zhang, Wen Zhao

Abstract: We carry out an imaging survey of six globular clusters (GCs) with a limit magnitude to 22 mag at the 5 sigma level, down to the main sequence stars of the respective cluster, as one of the pilot observing program of the Wide Field Survey Telescope (WFST). This paper present the early results of this survey, where we investigate the tidal characters at the periphery of the clusters NGC 4147, NGC 5… ▽ More We carry out an imaging survey of six globular clusters (GCs) with a limit magnitude to 22 mag at the 5 sigma level, down to the main sequence stars of the respective cluster, as one of the pilot observing program of the Wide Field Survey Telescope (WFST). This paper present the early results of this survey, where we investigate the tidal characters at the periphery of the clusters NGC 4147, NGC 5024, NGC 5053, NGC 5272, NGC 5904 and NGC 6341. We present the estimated number density of cluster candidates and their spatial distribution. We confirm the presence of tidal arms in NGC 4147 and NGC 5904 and identify several intriguing potential tidal structures in NGC 4147, NGC 5024, NGC 5272, corroborated the elliptical morphology of the periphery of NGC 6341. WFST shows its ability to detect faint main-sequence stars of clusters beyond 15 kpc in helio-centric distance. Our findings underscore the WFST's capability for probing faint structural features in GCs, paving the way for future in-depth studies, especially for the search of the large scale tidal streams associated with the clusters with the future wide field survey. △ Less

Submitted 29 April, 2025; v1 submitted 7 March, 2025; originally announced March 2025.

Comments: 13 pages, 8 figures. accepted by MNRAS. Comments are welcome

Ultra-high-energy $γ$-ray emission associated with the tail of a bow-shock pulsar wind nebula

Authors: Zhen Cao, F. Aharonian, Y. X. Bai, Y. W. Bao, D. Bastieri, X. J. Bi, Y. J. Bi, W. Bian, A. V. Bukevich, C. M. Cai, W. Y. Cao, Zhe Cao, J. Chang, J. F. Chang, A. M. Chen, E. S. Chen, H. X. Chen, Liang Chen, Long Chen, M. J. Chen, M. L. Chen, Q. H. Chen, S. Chen, S. H. Chen, S. Z. Chen , et al. (274 additional authors not shown)

Abstract: In this study, we present a comprehensive analysis of an unidentified point-like ultra-high-energy (UHE) $γ$-ray source, designated as 1LHAASO J1740+0948u, situated in the vicinity of the middle-aged pulsar PSR J1740+1000. The detection significance reached 17.1$σ$ (9.4$σ$) above 25$\,$TeV (100$\,$TeV). The source energy spectrum extended up to 300$\,$TeV, which was well fitted by a log-parabola f… ▽ More In this study, we present a comprehensive analysis of an unidentified point-like ultra-high-energy (UHE) $γ$-ray source, designated as 1LHAASO J1740+0948u, situated in the vicinity of the middle-aged pulsar PSR J1740+1000. The detection significance reached 17.1$σ$ (9.4$σ$) above 25$\,$TeV (100$\,$TeV). The source energy spectrum extended up to 300$\,$TeV, which was well fitted by a log-parabola function with $N0 = (1.93\pm0.23) \times 10^{-16} \rm{TeV^{-1}\,cm^{-2}\,s^{-2}}$, $α= 2.14\pm0.27$, and $β= 1.20\pm0.41$ at E0 = 30$\,$TeV. The associated pulsar, PSR J1740+1000, resides at a high galactic latitude and powers a bow-shock pulsar wind nebula (BSPWN) with an extended X-ray tail. The best-fit position of the gamma-ray source appeared to be shifted by $0.2^{\circ}$ with respect to the pulsar position. As the (i) currently identified pulsar halos do not demonstrate such offsets, and (ii) centroid of the gamma-ray emission is approximately located at the extension of the X-ray tail, we speculate that the UHE $γ$-ray emission may originate from re-accelerated electron/positron pairs that are advected away in the bow-shock tail. △ Less

Submitted 24 February, 2025; v1 submitted 21 February, 2025; originally announced February 2025.

Comments: Corrected spelling errors in several author names

Journal ref: The Innovation (2025), 100802

Broadband $γ$-ray spectrum of supernova remnant Cassiopeia A

Authors: Zhen Cao, F. Aharonian, Y. X. Bai, Y. W. Bao, D. Bastieri, X. J. Bi, Y. J. Bi, W. Bian, A. V. Bukevich, C. M. Cai, W. Y. Cao, Zhe Cao, J. Chang, J. F. Chang, A. M. Chen, E. S. Chen, H. X. Chen, Liang Chen, Long Chen, M. J. Chen, M. L. Chen, Q. H. Chen, S. Chen, S. H. Chen, S. Z. Chen , et al. (293 additional authors not shown)

Abstract: The core-collapse supernova remnant (SNR) Cassiopeia A (Cas A) is one of the brightest galactic radio sources with an angular radius of $\sim$ 2.5 $\arcmin$. Although no extension of this source has been detected in the $γ$-ray band, using more than 1000 days of LHAASO data above $\sim 0.8$ TeV, we find that its spectrum is significantly softer than those obtained with Imaging Air Cherenkov Telesc… ▽ More The core-collapse supernova remnant (SNR) Cassiopeia A (Cas A) is one of the brightest galactic radio sources with an angular radius of $\sim$ 2.5 $\arcmin$. Although no extension of this source has been detected in the $γ$-ray band, using more than 1000 days of LHAASO data above $\sim 0.8$ TeV, we find that its spectrum is significantly softer than those obtained with Imaging Air Cherenkov Telescopes (IACTs) and its flux near $\sim 1$ TeV is about two times higher. In combination with analyses of more than 16 years of \textit{Fermi}-LAT data covering $0.1 \, \mathrm{GeV} - 1 \, \mathrm{TeV}$, we find that the spectrum above 30 GeV deviates significantly from a single power-law, and is best described by a smoothly broken power-law with a spectral index of $1.90 \pm 0.15_\mathrm{stat}$ ($3.41 \pm 0.19_\mathrm{stat}$) below (above) a break energy of $0.63 \pm 0.21_\mathrm{stat} \, \mathrm{TeV}$. Given differences in the angular resolution of LHAASO-WCDA and IACTs, TeV $γ$-ray emission detected with LHAASO may have a significant contribution from regions surrounding the SNR illuminated by particles accelerated earlier, which, however, are treated as background by IACTs. Detailed modelling can be used to constrain acceleration processes of TeV particles in the early stage of SNR evolution. △ Less

Submitted 7 February, 2025; originally announced February 2025.

A Heliocentric-orbiting Objects Processing System (HOPS) for the Wide Field Survey Telescope: Architecture, Processing Workflow, and Preliminary Results

Authors: Shao-Han Wang, Bing-Xue Fu, Jun-Qiang Lu, LuLu Fan, Min-Xuan Cai, Ze-Lin Xu, Xu Kong, Haibin Zhao, Bin Li, Ya-Ting Liu, Qing-feng Zhu, Xu Zhou, Zhen Wan, Jingquan Cheng, Ji-an Jiang, Feng Li, Ming Liang, Hao Liu, Wentao Luo, Zhen Lou, Hairen Wang, Jian Wang, Tinggui Wang, Yongquan Xue, Hongfei Zhang , et al. (1 additional authors not shown)

Abstract: Wide-field surveys have markedly enhanced the discovery and study of solar system objects (SSOs). The 2.5-meter Wide Field Survey Telescope (WFST) represents the foremost facility dedicated to optical time-domain surveys in the northern hemisphere. To fully exploit WFST's capabilities for SSO detection, we have developed a heliocentric-orbiting objects processing system (HOPS) tailored for identif… ▽ More Wide-field surveys have markedly enhanced the discovery and study of solar system objects (SSOs). The 2.5-meter Wide Field Survey Telescope (WFST) represents the foremost facility dedicated to optical time-domain surveys in the northern hemisphere. To fully exploit WFST's capabilities for SSO detection, we have developed a heliocentric-orbiting objects processing system (HOPS) tailored for identifying these objects. This system integrates HelioLinC3D, an algorithm well suited for the WFST survey cadence, characterized by revisiting the same sky field twice on the majority of nights. In this paper, we outline the architecture and processing flow of our SSO processing system. The application of the system to the WFST pilot survey data collected between March and May 2024 demonstrates exceptional performance in terms of both temporal efficiency and completeness. A total of 658,489 observations encompassing 38,520 known asteroids have been documented, and 241 newly discovered asteroids have been assigned provisional designations. In particular, 27% of these new discoveries were achieved using merely two observations per night on three nights. The preliminary results not only illuminate the effectiveness of integrating HelioLinC3D within the SSO processing system, but also emphasize the considerable potential contributions of WFST to the field of solar system science. △ Less

Submitted 29 January, 2025; originally announced January 2025.

Comments: 23 pages, 6 figures, submitted to AAS journal

The 2.5-meter Wide Field Survey Telescope Real-time Data Processing Pipeline I: From raw data to alert distribution

Authors: Minxuan Cai, Zelin Xu, Lulu Fan, Zhen Wan, Xu Kong, Weida Hu, Ji-an Jiang, Lei Hu, Qing-feng Zhu, Guoliang Li, Jie Lin, Min Fang, Yongquan Xue, Xianzhong Zhen, Tinggui Wang

Abstract: The Wide Field Survey Telescope (WFST) is a dedicated photometric surveying facility built jointly by the University of Science and Technology of China (USTC) and the Purple Mountain Observatory (PMO). Since many of its scientific objectives rely on near-real-time data for effective analysis, prompt processing of WFST images is of great significance. To meet this need, we adapted the Rubin Observa… ▽ More The Wide Field Survey Telescope (WFST) is a dedicated photometric surveying facility built jointly by the University of Science and Technology of China (USTC) and the Purple Mountain Observatory (PMO). Since many of its scientific objectives rely on near-real-time data for effective analysis, prompt processing of WFST images is of great significance. To meet this need, we adapted the Rubin Observatory Legacy Survey of Space and Time (LSST) science pipelines to handle the data collected by WFST. This paper presents the complete data processing workflow, from ingestion of raw images to the distribution of alerts, and details the primary data products generated by our pipeline. Researchers using data processed by this pipeline can refer to this document to fully understand the data processing procedures. △ Less

Submitted 24 January, 2025; originally announced January 2025.

Comments: 20 pages, 2 figures

Search Capability for Near-Earth Objects with the Wide Field Survey Telescope

Authors: Jun-Qiang Lu, Lu-Lu Fan, Min-Xuan Cai, Shao-Han Wang, Bing-Xue Fu, Xu Kong, Qing-Feng Zhu

Abstract: Wide Field Survey Telescope (WFST), with a powerful sky survey capability in the northern hemisphere, will play an important role in asteroid searching and monitoring. However, WFST is not a telescope dedicated to near-Earth asteroids (NEOs) searching. In order to improve the efficiency of finding NEOs on the premise of meeting the needs of other scientific research, we ran mock observations for W… ▽ More Wide Field Survey Telescope (WFST), with a powerful sky survey capability in the northern hemisphere, will play an important role in asteroid searching and monitoring. However, WFST is not a telescope dedicated to near-Earth asteroids (NEOs) searching. In order to improve the efficiency of finding NEOs on the premise of meeting the needs of other scientific research, we ran mock observations for WFST to study its search capability for NEOs. The NEO population model, the WFST detection model and site conditions are taken into account in our simulations. Based on the original scheduling scheme, we present two new schemes. Compared to the original scheme, the optimized scheme can improve the search capability of known and unknown NEOs by 100\% and 50\%. We also emphasized the importance of trailing loss and proposed an improved effective field of view model. In addition, it is predicted that adopting the clear-day ratio of 0.7 and the optimized scheme, during one year of regular survey, for NEOs with absolute magnitude from 17 to 25, WFST can provide tracklets for about 1800 NEOs if their orbits are known, and in the case of blind search, more than 600 NEOs can be found by WFST. The new schemes provide valuable reference and suggestions for the WFST's regular survey strategy. △ Less

Submitted 20 February, 2025; v1 submitted 21 January, 2025; originally announced January 2025.

Comments: Accepted for publication in PASP, 16 pages, 6 figures, 3 tables

Journal ref: PASP 137 (2025) 024401

Minute-cadence observations on Galactic plane with Wide Field Survey Telescope (WFST): Overview, methodology and early results

Authors: Jie Lin, Tinggui Wang, Minxuan Cai, Zhen Wan, Xuzhi Li, Lulu Fan, Qingfeng Zhu, Ji-an Jiang, Ning Jiang, Xu Kong, Zheyu Lin, Jiazheng Zhu, Zhengyan Liu, Jie Gao, Bin Li, Feng Li, Ming Liang, Hao Liu, Wei Liu, Wentao Luo, Jinlong Tang, Hairen Wang, Jian Wang, Yongquan Xue, Dazhi Yao , et al. (4 additional authors not shown)

Abstract: As the time-domain survey telescope of the highest survey power in the northern hemisphere currently, Wide Field Survey Telescope (WFST) is scheduled to hourly/daily/semi-weekly scan northern sky up to ~23 mag in four optical (ugri) bands. Unlike the observation cadences in the forthcoming regular survey missions, WFST performed "staring" observations toward Galactic plane in a cadence of… ▽ More As the time-domain survey telescope of the highest survey power in the northern hemisphere currently, Wide Field Survey Telescope (WFST) is scheduled to hourly/daily/semi-weekly scan northern sky up to ~23 mag in four optical (ugri) bands. Unlike the observation cadences in the forthcoming regular survey missions, WFST performed "staring" observations toward Galactic plane in a cadence of $\approx$1 minute for a total on-source time of about 13 hours, during the commissioning and pilot observation phases. Such an observation cadence is well applied in producing densely sampling light curves and hunting for stars exhibiting fast stellar variabilities. Here we introduce the primary methodologies in detecting variability, periodicity, and stellar flares among a half million sources from the minute-cadence observations, and present the WFST g-/r-band light curves generated from periodic variable stars and flaring stars. Benefit from high photometric precisions and deep detection limits of WFST, the observations have captured several rare variable stars, such as a variable hot white dwarf (WD) and an ellipsoidal WD binary candidate. By surveying the almost unexplored parameter spaces for variables, WFST will lead to new opportunities in discovering unique variable stars in the northern sky. △ Less

Submitted 16 March, 2025; v1 submitted 17 December, 2024; originally announced December 2024.

Comments: 20 pages, 12 figures, accepted by ApJS

Observation of a spectral hardening in cosmic ray boron spectrum with the DAMPE space mission

Authors: DAMPE Collaboration, F. Alemanno, C. Altomare, Q. An, P. Azzarello, F. C. T. Barbato, P. Bernardini, X. J. Bi, H. Boutin, I. Cagnoli, M. S. Cai, E. Casilli, E. Catanzani, J. Chang, D. Y. Chen, J. L. Chen, Z. F. Chen, Z. X. Chen, P. Coppin, M. Y. Cui, T. S. Cui, Y. X. Cui, I. De Mitri, F. de Palma, A. Di Giovanni , et al. (121 additional authors not shown)

Abstract: Secondary cosmic ray fluxes are important probes of the propagation and interaction of high-energy particles in the Galaxy. Recent measurements of primary and secondary cosmic ray nuclei have revealed unexpected spectral features that demand a deeper understanding. In this work we report the direct measurement of the cosmic ray boron spectrum from 10 GeV/n to 8 TeV/n with eight years of data colle… ▽ More Secondary cosmic ray fluxes are important probes of the propagation and interaction of high-energy particles in the Galaxy. Recent measurements of primary and secondary cosmic ray nuclei have revealed unexpected spectral features that demand a deeper understanding. In this work we report the direct measurement of the cosmic ray boron spectrum from 10 GeV/n to 8 TeV/n with eight years of data collected by the Dark Matter Particle Explorer (DAMPE) mission. The measured spectrum shows an evident hardening at $182\pm24$ GeV/n with a spectral power index of $γ_1 = 3.02 \pm 0.01$ before the break and an index change of $Δγ= 0.31 \pm 0.05$ after the break. A simple power law model is disfavored at a confidence level of 8$σ$. Compared with the hardenings measured in the DAMPE proton and helium spectra, the secondary boron spectrum hardens roughly twice as much as these primaries, which is consistent with a propagation related mechanism to interpret the spectral hardenings of cosmic rays observed at hundreds of GeV/n. △ Less

Submitted 18 December, 2024; v1 submitted 16 December, 2024; originally announced December 2024.

Comments: 10 pages, 10 figures, submitted to PRL

Could the inter-band lag of active galactic nucleus vary randomly?

Authors: Zhen-Bo Su, Zhen-Yi Cai, Jun-Xian Wang, Tinggui Wang, Yongquan Xue, Min-Xuan Cai, Lulu Fan, Hengxiao Guo, Zhicheng He, Zizhao He, Xu-Fan Hu, Ji-an Jiang, Ning Jiang, Wen-Yong Kang, Lei Lei, Guilin Liu, Teng Liu, Zhengyan Liu, Zhenfeng Sheng, Mouyuan Sun, Wen Zhao

Abstract: The inter-band lags among the optical broad-band continua of active galactic nuclei (AGNs) have been intensively explored over the past decade. However, the nature of the lags remains under debate. Here utilizing two distinct scenarios for AGN variability, i.e., the thermal fluctuation of accretion disk and the reprocessing of both the accretion disk and clouds in the broad line region, we show th… ▽ More The inter-band lags among the optical broad-band continua of active galactic nuclei (AGNs) have been intensively explored over the past decade. However, the nature of the lags remains under debate. Here utilizing two distinct scenarios for AGN variability, i.e., the thermal fluctuation of accretion disk and the reprocessing of both the accretion disk and clouds in the broad line region, we show that, owing to the random nature of AGN variability, the inter-band lags of an individual AGN would vary from one campaign with a finite baseline to another. Specifically, the thermal fluctuation scenario implies larger variations in the lags than the reprocessing scenario. Moreover, the former predicts a positive correlation between the lag and variation amplitude, while the latter does not result in such a correlation. For both scenarios, averaging the lags of an individual AGN measured with repeated and non-overlapping campaigns would give rise to a stable lag, which is larger for a longer baseline and gets saturation for a sufficiently long baseline. However, obtaining the stable lag for an individual AGN is very time-consuming. Alternatively, it can be equivalently inferred by averaging the lags of a sample of AGNs with similar physical properties, thus can be properly compared with predictions of AGN models. In addition, discussed are several new observational tests suggested by our simulations as well as the role of the deep high-cadence surveys of the Wide Field Survey Telescope in enriching our knowledge of the lags. △ Less

Submitted 13 October, 2024; originally announced October 2024.

Comments: 16 pages, 10 figures. Accepted for publication in Astrophysical Journal, comments are welcome!

Ly$α$ imaging around the hyperluminous dust-obscured quasar W2246$-$0526 at $z=4.6$

Authors: Yibin Luo, Lulu Fan, Yongming Liang, Weida Hu, Junxian Wang, Zhen-ya Zheng, Zheyu Lin, Bojun Tao, Zesen Lin, Minxuan Cai, Mengqiu Huang, Zhen Wan, Yongling Tang

Abstract: Hot dust-obscured galaxies (Hot DOGs) are a population of hyperluminous, heavily obscured quasars discovered by the \emph{Wide-field Infrared Survey Explorer} (\emph{WISE}) all-sky survey at high redshift. Observations suggested the growth of these galaxies may be driven by mergers. Previous environmental studies have statistically shown Hot DOGs may reside in dense regions. Here we use the Very L… ▽ More Hot dust-obscured galaxies (Hot DOGs) are a population of hyperluminous, heavily obscured quasars discovered by the \emph{Wide-field Infrared Survey Explorer} (\emph{WISE}) all-sky survey at high redshift. Observations suggested the growth of these galaxies may be driven by mergers. Previous environmental studies have statistically shown Hot DOGs may reside in dense regions. Here we use the Very Large Telescope (VLT) narrowband and broadband imaging to search for Ly$α$ emitters (LAEs) in the 6.8' * 6.8' field of the Hot DOG W2246$-$0526 at $z=4.6$. W2246$-$0526 is the most distant Hot DOG. We find that there is an overdensity of LAEs in W2246$-$0526 field compared with the blank fields. This is the direct evidence that this most distant Hot DOG is in an overdense environment on the Mpc scale, and the result relates to the merger origin of Hot DOGs. △ Less

Submitted 23 July, 2024; originally announced July 2024.

Comments: 11 pages, 8 figures, Accepted for publication in The Astrophysical Journal

The Host Galaxy Fluxes of Active Galaxy Nuclei Are Generally Overestimated by the Flux Variation Gradient Method

Authors: Minxuan Cai, Zhen Wan, Zhenyi Cai, Lulu Fan, Junxian Wang

Abstract: In terms of the variable nature of normal active galaxy nuclei (AGN) and luminous quasars, a so-called flux variation gradient (FVG) method has been widely utilized to estimate the underlying non-variable host galaxy fluxes. The FVG method assumes an invariable AGN color, but this assumption has been questioned by the intrinsic color variation of quasars and local Seyfert galaxies. Here, using an… ▽ More In terms of the variable nature of normal active galaxy nuclei (AGN) and luminous quasars, a so-called flux variation gradient (FVG) method has been widely utilized to estimate the underlying non-variable host galaxy fluxes. The FVG method assumes an invariable AGN color, but this assumption has been questioned by the intrinsic color variation of quasars and local Seyfert galaxies. Here, using an up-to-date thermal fluctuation model to simulate multi-wavelength AGN variability, we theoretically demonstrate that the FVG method generally overestimates the host galaxy flux; that is, it is more significant for brighter AGN/quasars. Furthermore, we observationally confirm that the FVG method indeed overestimates the host galaxy flux by comparing it to that estimated through other independent methods. We thus caution that applying the FVG method should be performed carefully in the era of time-domain astronomy. △ Less

Submitted 3 July, 2024; originally announced July 2024.

Journal ref: Universe 2024, 10, 282

AT2023lli: A Tidal Disruption Event with Prominent Optical Early Bump and Delayed Episodic X-ray Emission

Authors: Shifeng Huang, Ning Jiang, Jiazheng Zhu, Yibo Wang, Tinggui Wang, Shan-Qin Wang, Wen-Pei Gan, En-Wei Liang, Yu-Jing Qin, Zheyu Lin, Lin-Na Xu, Min-Xuan Cai, Ji-An Jiang, Xu Kong, Jiaxun Li, Long Li, Jian-Guo Wang, Ze-Lin Xu, Yongquan Xue, Ye-Fei Yuan, Jingquan Cheng, Lulu Fan, Jie Gao, Lei Hu, Weida Hu , et al. (20 additional authors not shown)

Abstract: High-cadence, multiwavelength observations have continuously revealed the diversity of tidal disruption events (TDEs), thus greatly advancing our knowledge and understanding of TDEs. In this work, we conducted an intensive optical-UV and X-ray follow-up campaign of TDE AT2023lli, and found a remarkable month-long bump in its UV/optical light curve nearly two months prior to maximum brightness. The… ▽ More High-cadence, multiwavelength observations have continuously revealed the diversity of tidal disruption events (TDEs), thus greatly advancing our knowledge and understanding of TDEs. In this work, we conducted an intensive optical-UV and X-ray follow-up campaign of TDE AT2023lli, and found a remarkable month-long bump in its UV/optical light curve nearly two months prior to maximum brightness. The bump represents the longest separation time from the main peak among known TDEs to date. The main UV/optical outburst declines as $t^{-4.10}$, making it one of the fastest decaying optically selected TDEs. Furthermore, we detected sporadic X-ray emission 30 days after the UV/optical peak, accompanied by a reduction in the period of inactivity. It is proposed that the UV/optical bump could be caused by the self-intersection of the stream debris, whereas the primary peak is generated by the reprocessed emission of the accretion process. In addition, our results suggest that episodic X-ray radiation during the initial phase of decline may be due to the patched obscurer surrounding the accretion disk, a phenomenon associated with the inhomogeneous reprocessing process. The double TDE scenario, in which two stars are disrupted in sequence, is also a possible explanation for producing the observed early bump and main peak. We anticipate that the multicolor light curves of TDEs, especially in the very early stages, and the underlying physics can be better understood in the near future with the assistance of dedicated surveys such as the deep high-cadence survey of the 2.5-meter Wide Field Survey Telescope (WFST). △ Less

Submitted 26 March, 2024; v1 submitted 3 March, 2024; originally announced March 2024.

Comments: 14 pages, 8 figures,accepted for publication by ApJL

Hot Jupiter Formation in Dense Star Clusters

Authors: Leonard Benkendorff, Francesco Flammini Dotti, Katja Stock, Maxwell Xu Cai, Rainer Spurzem

Abstract: Hot Jupiters (HJ) are defined as Jupiter-mass exoplanets orbiting around their host star with an orbital period < 10 days. It is assumed that HJ do not form in-situ but ex-situ. Recent discoveries show that star clusters contribute to the formation of HJ. We present direct $N$-body simulations of planetary systems in star clusters and analyze the formation of HJ in them. We combine two direct $N$-… ▽ More Hot Jupiters (HJ) are defined as Jupiter-mass exoplanets orbiting around their host star with an orbital period < 10 days. It is assumed that HJ do not form in-situ but ex-situ. Recent discoveries show that star clusters contribute to the formation of HJ. We present direct $N$-body simulations of planetary systems in star clusters and analyze the formation of HJ in them. We combine two direct $N$-body codes: NBODY6++GPU for the dynamics of dense star clusters with 32 000 and 64 000 stellar members and LonelyPlanets used to follow 200 identical planetary systems around solar mass stars in those star clusters. We use different sets with 3, 4, or 5 planets and with the innermost planet at a semi-major axis of 5 au or 1 au and follow them for 100 Myr in our simulations. The results indicate that HJs are generated with high efficiency in dense star clusters if the innermost planet is already close to the host star at a semi-major axis of 1 au. If the innermost planet is initially beyond a semi-major axis of 5 au, the probability of a potential HJ ranges between $1.5-4.5$ percent. Very dense stellar neighborhoods tend to eject planets rather than forming HJs. A correlation between HJ formation and angular momentum deficit (AMD) is not witnessed. Young Hot Jupiters ($t_{\rm age} < 100$ Myrs) have only been found, in our simulations, in planetary systems with the innermost planet at a semi-major axis of 1 au. △ Less

Submitted 21 January, 2024; originally announced January 2024.

A hybrid approach for solving the gravitational N-body problem with Artificial Neural Networks

Authors: Veronica Saz Ulibarrena, Philipp Horn, Simon Portegies Zwart, Elena Sellentin, Barry Koren, Maxwell X. Cai

Abstract: Simulating the evolution of the gravitational N-body problem becomes extremely computationally expensive as N increases since the problem complexity scales quadratically with the number of bodies. We study the use of Artificial Neural Networks (ANNs) to replace expensive parts of the integration of planetary systems. Neural networks that include physical knowledge have grown in popularity in the l… ▽ More Simulating the evolution of the gravitational N-body problem becomes extremely computationally expensive as N increases since the problem complexity scales quadratically with the number of bodies. We study the use of Artificial Neural Networks (ANNs) to replace expensive parts of the integration of planetary systems. Neural networks that include physical knowledge have grown in popularity in the last few years, although few attempts have been made to use them to speed up the simulation of the motion of celestial bodies. We study the advantages and limitations of using Hamiltonian Neural Networks to replace computationally expensive parts of the numerical simulation. We compare the results of the numerical integration of a planetary system with asteroids with those obtained by a Hamiltonian Neural Network and a conventional Deep Neural Network, with special attention to understanding the challenges of this problem. Due to the non-linear nature of the gravitational equations of motion, errors in the integration propagate. To increase the robustness of a method that uses neural networks, we propose a hybrid integrator that evaluates the prediction of the network and replaces it with the numerical solution if considered inaccurate. Hamiltonian Neural Networks can make predictions that resemble the behavior of symplectic integrators but are challenging to train and in our case fail when the inputs differ ~7 orders of magnitude. In contrast, Deep Neural Networks are easy to train but fail to conserve energy, leading to fast divergence from the reference solution. The hybrid integrator designed to include the neural networks increases the reliability of the method and prevents large energy errors without increasing the computing cost significantly. For this problem, the use of neural networks results in faster simulations when the number of asteroids is >70. △ Less

Submitted 31 October, 2023; originally announced October 2023.

Comments: Accepted for publication in the Journal of Computational Physics

The Lobster Eye Imager for Astronomy Onboard the SATech-01 Satellite

Authors: Z. X. Ling, X. J. Sun, C. Zhang, S. L. Sun, G. Jin, S. N. Zhang, X. F. Zhang, J. B. Chang, F. S. Chen, Y. F. Chen, Z. W. Cheng, W. Fu, Y. X. Han, H. Li, J. F. Li, Y. Li, Z. D. Li, P. R. Liu, Y. H. Lv, X. H. Ma, Y. J. Tang, C. B. Wang, R. J. Xie, Y. L. Xue, A. L. Yan , et al. (101 additional authors not shown)

Abstract: The Lobster Eye Imager for Astronomy (LEIA), a pathfinder of the Wide-field X-ray Telescope of the Einstein Probe (EP) mission, was successfully launched onboard the SATech-01 satellite of the Chinese Academy of Sciences on 27 July 2022. In this paper, we introduce the design and on-ground test results of the LEIA instrument. Using state-of-the-art Micro-Pore Optics (MPO), a wide field-of-view (Fo… ▽ More The Lobster Eye Imager for Astronomy (LEIA), a pathfinder of the Wide-field X-ray Telescope of the Einstein Probe (EP) mission, was successfully launched onboard the SATech-01 satellite of the Chinese Academy of Sciences on 27 July 2022. In this paper, we introduce the design and on-ground test results of the LEIA instrument. Using state-of-the-art Micro-Pore Optics (MPO), a wide field-of-view (FoV) of 346 square degrees (18.6 degrees * 18.6 degrees) of the X-ray imager is realized. An optical assembly composed of 36 MPO chips is used to focus incident X-ray photons, and four large-format complementary metal-oxide semiconductor (CMOS) sensors, each of 6 cm * 6 cm, are used as the focal plane detectors. The instrument has an angular resolution of 4 - 8 arcmin (in FWHM) for the central focal spot of the point spread function, and an effective area of 2 - 3 cm2 at 1 keV in essentially all the directions within the field of view. The detection passband is 0.5 - 4 keV in the soft X-rays and the sensitivity is 2 - 3 * 10-11 erg s-1 cm-2 (about 1 mini-Crab) at 1,000 second observation. The total weight of LEIA is 56 kg and the power is 85 W. The satellite, with a design lifetime of 2 years, operates in a Sun-synchronous orbit of 500 km with an orbital period of 95 minutes. LEIA is paving the way for future missions by verifying in flight the technologies of both novel focusing imaging optics and CMOS sensors for X-ray observation, and by optimizing the working setups of the instrumental parameters. In addition, LEIA is able to carry out scientific observations to find new transients and to monitor known sources in the soft X-ray band, albeit limited useful observing time available. △ Less

Submitted 24 May, 2023; originally announced May 2023.

Comments: Accepted by RAA

Measurement of the cosmic p+He energy spectrum from 50 GeV to 0.5 PeV with the DAMPE space mission

Authors: DAMPE Collaboration, F. Alemanno, C. Altomare, Q. An, P. Azzarello, F. C. T. Barbato, P. Bernardini, X. J. Bi, I. Cagnoli, M. S. Cai, E. Casilli, E. Catanzani, J. Chang, D. Y. Chen, J. L. Chen, Z. F. Chen, P. Coppin, M. Y. Cui, T. S. Cui, Y. X. Cui, H. T. Dai, A. De Benedittis, I. De Mitri, F. de Palma, M. Deliyergiyev , et al. (130 additional authors not shown)

Abstract: Recent observations of the light component of the cosmic-ray spectrum have revealed unexpected features that motivate further and more precise measurements up to the highest energies. The Dark Matter Particle Explorer is a satellite-based cosmic-ray experiment that has been operational since December 2015, continuously collecting data on high-energy cosmic particles with very good statistics, ener… ▽ More Recent observations of the light component of the cosmic-ray spectrum have revealed unexpected features that motivate further and more precise measurements up to the highest energies. The Dark Matter Particle Explorer is a satellite-based cosmic-ray experiment that has been operational since December 2015, continuously collecting data on high-energy cosmic particles with very good statistics, energy resolution, and particle identification capabilities. In this work, the latest measurements of the energy spectrum of proton+helium in the energy range from 46 GeV to 464 TeV are presented. Among the most distinctive features of the spectrum, a spectral hardening at 600 GeV has been observed, along with a softening at 29 TeV measured with a 6.6σ significance. Moreover, the detector features and the analysis approach allowed for the extension of the spectral measurement up to the sub-PeV region. Even if with small statistical significance due to the low number of events, data suggest a new spectral hardening at about 150 TeV. △ Less

Submitted 14 August, 2024; v1 submitted 31 March, 2023; originally announced April 2023.

Comments: Published on PRD

First wide field-of-view X-ray observations by a lobster eye focusing telescope in orbit

Authors: C. Zhang, Z. X. Ling, X. J. Sun, S. L. Sun, Y. Liu, Z. D. Li, Y. L. Xue, Y. F. Chen, Y. F. Dai, Z. Q. Jia, H. Y. Liu, X. F. Zhang, Y. H. Zhang, S. N. Zhang, F. S. Chen, Z. W. Cheng, W. Fu, Y. X. Han, H. Li, J. F. Li, Y. Li, P. R. Liu, X. H. Ma, Y. J. Tang, C. B. Wang , et al. (53 additional authors not shown)

Abstract: As a novel X-ray focusing technology, lobster eye micro-pore optics (MPO) feature both a wide observing field of view and true imaging capability, promising sky monitoring with significantly improved sensitivity and spatial resolution in soft X-rays. Since first proposed by Angel (1979), the optics have been extensively studied, developed and trialed over the past decades. In this Letter, we repor… ▽ More As a novel X-ray focusing technology, lobster eye micro-pore optics (MPO) feature both a wide observing field of view and true imaging capability, promising sky monitoring with significantly improved sensitivity and spatial resolution in soft X-rays. Since first proposed by Angel (1979), the optics have been extensively studied, developed and trialed over the past decades. In this Letter, we report on the first-light results from a flight experiment of the Lobster Eye Imager for Astronomy ($LEIA$), a pathfinder of the wide-field X-ray telescope of the Einstein Probe mission. The piggyback imager, launched in July 2022, has a mostly un-vignetted field of view of $18.6^\circ \times 18.6^\circ $. Its spatial resolution is in the range of 4$-$7 arcmin in FWHM and the focal spot effective area is 2$-$3 cm$^2$, both showing only mild fluctuations across the field of view. We present images of the Galactic center region, Sco X-1 and the diffuse Cygnus Loop nebular taken in snapshot observations over 0.5$-$4 keV. These are truly wide-field X-ray images of celestial bodies observed, for the first time, by a focusing imaging telescope. Initial analyses of the in-flight data show excellent agreement between the observed images and the on-ground calibration and simulations. The instrument and its characterization are briefly described, as well as the flight experiment. The results provide a solid basis for the development of the present and proposed wide-field X-ray missions using lobster eye MPO. △ Less

Submitted 17 November, 2022; originally announced November 2022.

Comments: 11 pages, 4 figures. Accepted for publication in Astrophysical Journal Letter

Search for relativistic fractionally charged particles in space

Authors: DAMPE Collaboration, F. Alemanno, C. Altomare, Q. An, P. Azzarello, F. C. T. Barbato, P. Bernardini, X. J. Bi, M. S. Cai, E. Casilli, E. Catanzani, J. Chang, D. Y. Chen, J. L. Chen, Z. F. Chen, M. Y. Cui, T. S. Cui, Y. X. Cui, H. T. Dai, A. De-Benedittis, I. De Mitri, F. de Palma, M. Deliyergiyev, A. Di Giovanni, M. Di Santo , et al. (126 additional authors not shown)

Abstract: More than a century after the performance of the oil drop experiment, the possible existence of fractionally charged particles FCP still remains unsettled. The search for FCPs is crucial for some extensions of the Standard Model in particle physics. Most of the previously conducted searches for FCPs in cosmic rays were based on experiments underground or at high altitudes. However, there have been… ▽ More More than a century after the performance of the oil drop experiment, the possible existence of fractionally charged particles FCP still remains unsettled. The search for FCPs is crucial for some extensions of the Standard Model in particle physics. Most of the previously conducted searches for FCPs in cosmic rays were based on experiments underground or at high altitudes. However, there have been few searches for FCPs in cosmic rays carried out in orbit other than AMS-01 flown by a space shuttle and BESS by a balloon at the top of the atmosphere. In this study, we conduct an FCP search in space based on on-orbit data obtained using the DArk Matter Particle Explorer (DAMPE) satellite over a period of five years. Unlike underground experiments, which require an FCP energy of the order of hundreds of GeV, our FCP search starts at only a few GeV. An upper limit of $6.2\times 10^{-10}~~\mathrm{cm^{-2}sr^{-1} s^{-1}}$ is obtained for the flux. Our results demonstrate that DAMPE exhibits higher sensitivity than experiments of similar types by three orders of magnitude that more stringently restricts the conditions for the existence of FCP in primary cosmic rays. △ Less

Submitted 9 September, 2022; originally announced September 2022.

Comments: 19 pages, 6 figures, accepted by PRD

Report number: 106, 063026

Journal ref: Physical Review D 106.6 (2022): 063026

Birth cluster simulations of planetary systems with multiple super-Earths: initial conditions for white dwarf pollution drivers

Authors: Katja Stock, Dimitri Veras, Maxwell X. Cai, Rainer Spurzem, Simon Portegies Zwart

Abstract: Previous investigations have revealed that eccentric super-Earths represent a class of planets which are particularly effective at transporting minor bodies towards white dwarfs and subsequently polluting their atmospheres with observable chemical signatures. However, the lack of discoveries of these planets beyond a few astronomical units from their host stars prompts a better understanding of th… ▽ More Previous investigations have revealed that eccentric super-Earths represent a class of planets which are particularly effective at transporting minor bodies towards white dwarfs and subsequently polluting their atmospheres with observable chemical signatures. However, the lack of discoveries of these planets beyond a few astronomical units from their host stars prompts a better understanding of their orbital architectures from their nascent birth cluster. Here, we perform stellar cluster simulations of 3-planet and 7-planet systems containing super-Earths on initially circular, coplanar orbits. We adopt the typical stellar masses of main-sequence progenitors of white dwarfs ($1.5\,\mathrm{M}_{\odot}$-$2.5\,\mathrm{M}_{\odot}$) as host stars and include 8,000 main-sequence stars following a Kroupa initial mass function in our clusters. Our results reveal that about 30 per cent of the simulated planets generate eccentricities of at least 0.1 by the time of cluster dissolution, which would aid white dwarf pollution. We provide our output parameters to the community for potential use as initial conditions for subsequent evolution simulations. △ Less

Submitted 2 March, 2022; originally announced March 2022.

Comments: 16 pages, 18 figures, accepted for publication in MNRAS

Search for gamma-ray spectral lines with the DArk Matter Particle Explorer

Authors: Francesca Alemanno, Qi An, Philipp Azzarello, Felicia Carla Tiziana Barbato, Paolo Bernardini, Xiao-Jun Bi, Ming-Sheng Cai, Elisabetta Casilli, Enrico Catanzani, Jin Chang, Deng-Yi Chen, Jun-Ling Chen, Zhan-Fang Chen, Ming-Yang Cui, Tian-Shu Cui, Yu-Xing Cui, Hao-Ting Dai, Antonio De Benedittis, Ivan De Mitri, Francesco de Palma, Maksym Deliyergiyev, Margherita Di Santo, Qi Ding, Tie-Kuang Dong, Zhen-Xing Dong , et al. (121 additional authors not shown)

Abstract: The DArk Matter Particle Explorer (DAMPE) is well suitable for searching for monochromatic and sharp $γ$-ray structures in the GeV$-$TeV range thanks to its unprecedented high energy resolution. In this work, we search for $γ$-ray line structures using five years of DAMPE data. To improve the sensitivity, we develop two types of dedicated data sets (including the BgoOnly data which is the first ti… ▽ More The DArk Matter Particle Explorer (DAMPE) is well suitable for searching for monochromatic and sharp $γ$-ray structures in the GeV$-$TeV range thanks to its unprecedented high energy resolution. In this work, we search for $γ$-ray line structures using five years of DAMPE data. To improve the sensitivity, we develop two types of dedicated data sets (including the BgoOnly data which is the first time to be used in the data analysis for the calorimeter-based gamma-ray observatories) and adopt the signal-to-noise ratio optimized regions of interest (ROIs) for different DM density profiles. No line signals or candidates are found between 10 and 300 GeV in the Galaxy. The constraints on the velocity-averaged cross section for $χχ\to γγ$ and the decay lifetime for $χ\to γν$, both at 95% confidence level, have been calculated and the systematic uncertainties have been taken into account. Comparing to the previous Fermi-LAT results, though DAMPE has an acceptance smaller by a factor of $\sim 10$, similar constraints on the DM parameters are achieved and below 100 GeV the lower limits on the decay lifetime are even stronger by a factor of a few. Our results demonstrate the potential of high-energy-resolution observations on dark matter detection. △ Less

Submitted 6 December, 2022; v1 submitted 16 December, 2021; originally announced December 2021.

Comments: 14 pages, 8 figures. Update the content to keep up with the published version

Journal ref: Science Bulletin, Volume 67, Issue 7, 15 April 2022, Pages 679-684

Neural Symplectic Integrator with Hamiltonian Inductive Bias for the Gravitational $N$-body Problem

Authors: Maxwell X. Cai, Simon Portegies Zwart, Damian Podareanu

Abstract: The gravitational $N$-body problem, which is fundamentally important in astrophysics to predict the motion of $N$ celestial bodies under the mutual gravity of each other, is usually solved numerically because there is no known general analytical solution for $N>2$. Can an $N$-body problem be solved accurately by a neural network (NN)? Can a NN observe long-term conservation of energy and orbital a… ▽ More The gravitational $N$-body problem, which is fundamentally important in astrophysics to predict the motion of $N$ celestial bodies under the mutual gravity of each other, is usually solved numerically because there is no known general analytical solution for $N>2$. Can an $N$-body problem be solved accurately by a neural network (NN)? Can a NN observe long-term conservation of energy and orbital angular momentum? Inspired by Wistom & Holman (1991)'s symplectic map, we present a neural $N$-body integrator for splitting the Hamiltonian into a two-body part, solvable analytically, and an interaction part that we approximate with a NN. Our neural symplectic $N$-body code integrates a general three-body system for $10^{5}$ steps without diverting from the ground truth dynamics obtained from a traditional $N$-body integrator. Moreover, it exhibits good inductive bias by successfully predicting the evolution of $N$-body systems that are no part of the training set. △ Less

Submitted 28 November, 2021; originally announced November 2021.

Comments: 7 pages, 2 figures, accepted for publication at the NeurIPS 2021 workshop "Machine Learning and the Physical Sciences"

Fast and Credible Likelihood-Free Cosmology with Truncated Marginal Neural Ratio Estimation

Authors: Alex Cole, Benjamin Kurt Miller, Samuel J. Witte, Maxwell X. Cai, Meiert W. Grootes, Francesco Nattino, Christoph Weniger

Abstract: Sampling-based inference techniques are central to modern cosmological data analysis; these methods, however, scale poorly with dimensionality and typically require approximate or intractable likelihoods. In this paper we describe how Truncated Marginal Neural Ratio Estimation (TMNRE) (a new approach in so-called simulation-based inference) naturally evades these issues, improving the $(i)$ effici… ▽ More Sampling-based inference techniques are central to modern cosmological data analysis; these methods, however, scale poorly with dimensionality and typically require approximate or intractable likelihoods. In this paper we describe how Truncated Marginal Neural Ratio Estimation (TMNRE) (a new approach in so-called simulation-based inference) naturally evades these issues, improving the $(i)$ efficiency, $(ii)$ scalability, and $(iii)$ trustworthiness of the inferred posteriors. Using measurements of the Cosmic Microwave Background (CMB), we show that TMNRE can achieve converged posteriors using orders of magnitude fewer simulator calls than conventional Markov Chain Monte Carlo (MCMC) methods. Remarkably, the required number of samples is effectively independent of the number of nuisance parameters. In addition, a property called \emph{local amortization} allows the performance of rigorous statistical consistency checks that are not accessible to sampling-based methods. TMNRE promises to become a powerful tool for cosmological data analysis, particularly in the context of extended cosmologies, where the timescale required for conventional sampling-based inference methods to converge can greatly exceed that of simple cosmological models such as $Λ$CDM. To perform these computations, we use an implementation of TMNRE via the open-source code \texttt{swyft}. △ Less

Submitted 8 November, 2022; v1 submitted 15 November, 2021; originally announced November 2021.

Comments: v2: accepted journal version. v1: 37 pages, 13 figures. \texttt{swyft} is available at https://github.com/undark-lab/swyft, and demonstration code for cosmological examples is available at https://github.com/acole1221/swyft-CMB

Observations of Forbush Decreases of cosmic ray electrons and positrons with the Dark Matter Particle Explorer

Authors: Francesca Alemanno, Qi An, Philipp Azzarello, Felicia Carla Tiziana Barbato, Paolo Bernardini, XiaoJun Bi, MingSheng Cai, Elisabetta Casilli, Enrico Catanzani, Jin Chang, DengYi Chen, JunLing Chen, ZhanFang Chen, MingYang Cui, TianShu Cui, YuXing Cui, HaoTing Dai, Antonio De Benedittis, Ivan De Mitri, Francesco de Palma, Maksym Deliyergiyev, Margherita Di Santo, Qi Ding, TieKuang Dong, ZhenXing Dong , et al. (124 additional authors not shown)

Abstract: The Forbush Decrease (FD) represents the rapid decrease of the intensities of charged particles accompanied with the coronal mass ejections (CMEs) or high-speed streams from coronal holes. It has been mainly explored with ground-based neutron monitors network which indirectly measure the integrated intensities of all species of cosmic rays by counting secondary neutrons produced from interaction b… ▽ More The Forbush Decrease (FD) represents the rapid decrease of the intensities of charged particles accompanied with the coronal mass ejections (CMEs) or high-speed streams from coronal holes. It has been mainly explored with ground-based neutron monitors network which indirectly measure the integrated intensities of all species of cosmic rays by counting secondary neutrons produced from interaction between atmosphere atoms and cosmic rays. The space-based experiments can resolve the species of particles but the energy ranges are limited by the relative small acceptances except for the most abundant particles like protons and helium. Therefore, the FD of cosmic ray electrons and positrons have just been investigated by the PAMELA experiment in the low energy range ($<5$ GeV) with limited statistics. In this paper, we study the FD event occurred in September, 2017, with the electron and positron data recorded by the Dark Matter Particle Explorer. The evolution of the FDs from 2 GeV to 20 GeV with a time resolution of 6 hours are given. We observe two solar energetic particle events in the time profile of the intensity of cosmic rays, the earlier and weak one has not been shown in the neutron monitor data. Furthermore, both the amplitude and recovery time of fluxes of electrons and positrons show clear energy-dependence, which is important in probing the disturbances of the interplanetary environment by the coronal mass ejections. △ Less

Submitted 30 September, 2021; originally announced October 2021.

Comments: This article is dedicated to the 72nd anniversary of People's Republic of China

Oort cloud Ecology II: The chronology of the formation of the Oort cloud

Authors: Simon Portegies Zwart, Santiago Torres, Maxwell X. Cai, Anthony Brown

Abstract: We present a chronology of the formation and early evolution of the Oort cloud by simulations. These simulations start with the Solar System being born with planets and asteroids in a stellar cluster orbiting the Galactic center. Upon ejection from its birth environment, we continue to follow the evolution of the Solar System while it navigates the Galaxy as an isolated planetary system. We conclu… ▽ More We present a chronology of the formation and early evolution of the Oort cloud by simulations. These simulations start with the Solar System being born with planets and asteroids in a stellar cluster orbiting the Galactic center. Upon ejection from its birth environment, we continue to follow the evolution of the Solar System while it navigates the Galaxy as an isolated planetary system. We conclude that the range in semi-major axis between 100au and several 10$^3$\,au still bears the signatures of the Sun being born in a 1000MSun/pc$^3$ star cluster, and that most of the outer Oort cloud formed after the Solar System was ejected. The ejection of the Solar System, we argue, happened between 20Myr and 50Myr after its birth. Trailing and leading trails of asteroids and comets along the Sun's orbit in the Galactic potential are the by-product of the formation of the Oort cloud. These arms are composed of material that became unbound from the Solar System when the Oort cloud formed. Today, the bulk of the material in the Oort cloud ($\sim 70$\%) originates from the region in the circumstellar disk that was located between $\sim 15$\,au and $\sim 35$\,au, near the current location of the ice giants and the Centaur family of asteroids. According to our simulations, this population is eradicated if the ice-giant planets are born in orbital resonance. Planet migration or chaotic orbital reorganization occurring while the Solar System is still a cluster member is, according to our model, inconsistent with the presence of the Oort cloud. About half the inner Oort cloud, between 100 and $10^4$\,au, and a quarter of the material in the outer Oort cloud, $\apgt 10^4$\,au, could be non-native to the Solar System but was captured from free-floating debris in the cluster or from the circumstellar disk of other stars in the birth cluster. △ Less

Submitted 11 June, 2021; v1 submitted 26 May, 2021; originally announced May 2021.

Comments: Corrected proofs for publication in A&A

Journal ref: A&A 652, A144 (2021)

Measurement of the cosmic ray helium energy spectrum from 70 GeV to 80 TeV with the DAMPE space mission

Authors: F. Alemanno, Q. An, P. Azzarello, F. C. T. Barbato, P. Bernardini, X. J. Bi, M. S. Cai, E. Catanzani, J. Chang, D. Y. Chen, J. L. Chen, Z. F. Chen, M. Y. Cui, T. S. Cui, Y. X. Cui, H. T. Dai, A. D'Amone, A. De Benedittis, I. De Mitri, F. de Palma, M. Deliyergiyev, M. Di Santo, T. K. Dong, Z. X. Dong, G. Donvito , et al. (120 additional authors not shown)

Abstract: The measurement of the energy spectrum of cosmic ray helium nuclei from 70 GeV to 80 TeV using 4.5 years of data recorded by the DArk Matter Particle Explorer (DAMPE) is reported in this work. A hardening of the spectrum is observed at an energy of about 1.3 TeV, similar to previous observations. In addition, a spectral softening at about 34 TeV is revealed for the first time with large statistics… ▽ More The measurement of the energy spectrum of cosmic ray helium nuclei from 70 GeV to 80 TeV using 4.5 years of data recorded by the DArk Matter Particle Explorer (DAMPE) is reported in this work. A hardening of the spectrum is observed at an energy of about 1.3 TeV, similar to previous observations. In addition, a spectral softening at about 34 TeV is revealed for the first time with large statistics and well controlled systematic uncertainties, with an overall significance of $4.3σ$. The DAMPE spectral measurements of both cosmic protons and helium nuclei suggest a particle charge dependent softening energy, although with current uncertainties a dependence on the number of nucleons cannot be ruled out. △ Less

Submitted 21 May, 2021; v1 submitted 19 May, 2021; originally announced May 2021.

Comments: 11 pages, 13 figures, published in Phys. Rev. Lett. Add one more digit for first three columns in Table S2

Journal ref: Phys. Rev. Lett. 126, 201102 (2021)

Inside-Out Planet Formation: VI. Oligarchic Coagulation of Planetesimals from a Pebble Ring?

Authors: Maxwell X. Cai, Jonathan C. Tan, Simon Portegies Zwart

Abstract: Inside-Out Planet Formation (IOPF) is a theory addressing the origin of Systems of Tightly-Packed Inner Planets (STIPs) via {\it in situ} formation and growth of the planets. It predicts that a pebble ring is established at the pressure maximum associated with the dead zone inner boundary (DZIB) with an inner disk magnetorotational instability (MRI)-active region. Using direct $N$-body simulations… ▽ More Inside-Out Planet Formation (IOPF) is a theory addressing the origin of Systems of Tightly-Packed Inner Planets (STIPs) via {\it in situ} formation and growth of the planets. It predicts that a pebble ring is established at the pressure maximum associated with the dead zone inner boundary (DZIB) with an inner disk magnetorotational instability (MRI)-active region. Using direct $N$-body simulations, we study the collisional evolution of planetesimals formed from such a pebble ring, in particular examining whether a single dominant planet emerges. We consider a variety of models, including some in which the planetesimals are continuing to grow via pebble accretion. We find that the planetesimal ring undergoes oligarchic evolution, and typically turns into 2 or 3 surviving oligarchs on nearly coplanar and circular orbits, independent of the explored initial conditions or form of pebble accretion. The most massive oligarchs typically consist of about $70\%$ of the total mass, with the building-up process typically finishing within $\sim 10^5$ years. However, a relatively massive secondary planet always remains with $\sim30-65\%$ of the mass of the primary. Such secondary planets have properties that are inconsistent with the observed properties of the innermost pairs of planets in STIPs. Thus, for IOPF to be a viable theory for STIP formation, it needs to be shown how oligarchic growth of a relatively massive secondary from the initial pebble ring can be avoided. We discuss some potential additional physical processes that should be included in the modeling and explored as next steps. △ Less

Submitted 13 December, 2021; v1 submitted 7 April, 2021; originally announced April 2021.

Comments: 15 pages, 10 figures, accepted for publication in MNRAS

Energy Partition in Four Confined Circular-Ribbon Flares

Authors: Z. M. Cai, Q. M. Zhang, Z. J. Ning, Y. N. Su, H. S. Ji

Abstract: In this study, we investigated the energy partition of four confined circular-ribbon flares (CRFs) near the solar disk center, which are observed simultaneously by SDO, GOES, and RHESSI. We calculated different energy components, including the radiative outputs in 1$-$8, 1$-$70, and 70$-$370 Å, total radiative loss, peak thermal energy derived from GOES and RHESSI, nonthermal energy in flare-accel… ▽ More In this study, we investigated the energy partition of four confined circular-ribbon flares (CRFs) near the solar disk center, which are observed simultaneously by SDO, GOES, and RHESSI. We calculated different energy components, including the radiative outputs in 1$-$8, 1$-$70, and 70$-$370 Å, total radiative loss, peak thermal energy derived from GOES and RHESSI, nonthermal energy in flare-accelerated electrons, and magnetic free energy before flares. It is found that the energy components increase systematically with the flare class, indicating that more energies are involved in larger flares. The magnetic free energies are larger than the nonthermal energies and radiative outputs of flares, which is consistent with the magnetic nature of flares. The ratio $\frac{E_{nth}}{E_{mag}}$ of the four flares, being 0.70$-$0.76, is considerably higher than that of eruptive flares. Hence, this ratio may serve as an important factor that discriminates confined and eruptive flares. The nonthermal energies are sufficient to provide the heating requirements including the peak thermal energy and radiative loss. Our findings impose constraint on theoretical models of confined CRFs and have potential implication for the space weather forecast. △ Less

Submitted 19 February, 2021; originally announced February 2021.

Comments: 20 pages, 14 figures, accepted for publication in Solar Physics, comments are welcome

Mapping Diffuse Emission in Lyman UV band

Authors: Li Ji, Zheng Lou, Jinlong Zhang, Keqiang Qiu, Shuangying Li, Wei Sun, Shuping Yan, Shuinai Zhang, Yuan Qian, Sen Wang, Klaus Werner, Taotao Fang, Tinggui Wang, Jürgen Barnstedt, Sebastian Buntrock, Mingsheng Cai, Wen Chen, Lauro Conti, Lei Deng, Sebastian Diebold, Shaojun Fu, Jianhua Guo, Lars Hanke, Yilin Hong, Christoph Kalkuhl , et al. (16 additional authors not shown)

Abstract: The CAFE (Census of warm-hot intergalactic medium, Accretion, and Feedback Explorer) and LyRIC (Lyman UV Radiation from Interstellar medium and Circum-galactic medium) have been proposed to the space agencies in China respectively. CAFE was first proposed in 2015 as a joint scientific CAS-ESA small space mission. LyRIC was proposed in 2019 as an independent external payload operating on the Chines… ▽ More The CAFE (Census of warm-hot intergalactic medium, Accretion, and Feedback Explorer) and LyRIC (Lyman UV Radiation from Interstellar medium and Circum-galactic medium) have been proposed to the space agencies in China respectively. CAFE was first proposed in 2015 as a joint scientific CAS-ESA small space mission. LyRIC was proposed in 2019 as an independent external payload operating on the Chinese Space Station. Both missions are dedicated to mapping the Lyman UV emission (ionized oxygen (O VI) resonance lines at 103.2 and 103.8 nm, and Lyman series) for the diffuse sources in our Galaxy and the circum-galactic mediums of the nearby galaxies. We present the primary science objectives, mission concepts, the enabling technologies, as well as the current status. △ Less

Submitted 15 December, 2020; v1 submitted 14 December, 2020; originally announced December 2020.

Comments: 9 pages, 6 figures, SPIE Astronomical Telescopes + Instrumentation 2020 conference Paper No. 11444-4

DeepGalaxy: Deducing the Properties of Galaxy Mergers from Images Using Deep Neural Networks

Authors: Maxwell X. Cai, Jeroen Bédorf, Vikram A. Saletore, Valeriu Codreanu, Damian Podareanu, Adel Chaibi, Penny X. Qian

Abstract: Galaxy mergers, the dynamical process during which two galaxies collide, are among the most spectacular phenomena in the Universe. During this process, the two colliding galaxies are tidally disrupted, producing significant visual features that evolve as a function of time. These visual features contain valuable clues for deducing the physical properties of the galaxy mergers. In this work, we pro… ▽ More Galaxy mergers, the dynamical process during which two galaxies collide, are among the most spectacular phenomena in the Universe. During this process, the two colliding galaxies are tidally disrupted, producing significant visual features that evolve as a function of time. These visual features contain valuable clues for deducing the physical properties of the galaxy mergers. In this work, we propose DeepGalaxy, a visual analysis framework trained to predict the physical properties of galaxy mergers based on their morphology. Based on an encoder-decoder architecture, DeepGalaxy encodes the input images to a compressed latent space $z$, and determines the similarity of images according to the latent-space distance. DeepGalaxy consists of a fully convolutional autoencoder (FCAE) which generates activation maps at its 3D latent-space, and a variational autoencoder (VAE) which compresses the activation maps into a 1D vector, and a classifier that generates labels from the activation maps. The backbone of the FCAE can be fully customized according to the complexity of the images. DeepGalaxy demonstrates excellent scaling performance on parallel machines. On the Endeavour supercomputer, the scaling efficiency exceeds 0.93 when trained on 128 workers, and it maintains above 0.73 when trained with 512 workers. Without having to carry out expensive numerical simulations, DeepGalaxy makes inferences of the physical properties of galaxy mergers directly from images, and thereby achieves a speedup factor of $\sim 10^5$. △ Less

Submitted 22 October, 2020; originally announced October 2020.

Comments: 7 pages, 7 figures. Accepted for publication at the 2020 IEEE/ACM Fifth Workshop on Deep Learning on Supercomputers (DLS)

On the survival of resonant and non-resonant planetary systems in star clusters

Authors: Katja Stock, Maxwell X. Cai, Rainer Spurzem, M. B. N. Kouwenhoven, Simon Portegies Zwart

Abstract: Despite the discovery of thousands of exoplanets in recent years, the number of known exoplanets in star clusters remains tiny. This may be a consequence of close stellar encounters perturbing the dynamical evolution of planetary systems in these clusters. Here, we present the results from direct $N$-body simulations of multiplanetary systems embedded in star clusters containing… ▽ More Despite the discovery of thousands of exoplanets in recent years, the number of known exoplanets in star clusters remains tiny. This may be a consequence of close stellar encounters perturbing the dynamical evolution of planetary systems in these clusters. Here, we present the results from direct $N$-body simulations of multiplanetary systems embedded in star clusters containing $N = 8k, 16k, 32k$, and $64k$ stars. The planetary systems, which consist of the four Solar system giant planets Jupiter, Saturn, Uranus, and Neptune, are initialized in different orbital configurations, to study the effect of the system architecture on the dynamical evolution of the entire planetary system, and on the escape rate of the individual planets. We find that the current orbital parameters of the Solar system giants (with initially circular orbits, as well as with present-day eccentricities) and a slightly more compact configuration, have a high resilience against stellar perturbations. A configuration with initial mean-motion resonances of 3:2, 3:2, and 5:4 between the planets, which is inspired by the Nice model, and for which the two outermost planets are usually ejected within the first $10^5$ yr, is in many cases stabilized due to the removal of the resonances by external stellar perturbation and by the rapid ejection of at least one planet. Assigning all planets the same mass of 1 Jovian mass almost equalizes the survival fractions. Our simulations reproduce the broad diversity amongst observed exoplanet systems. We find not only many very wide and/or eccentric orbits, but also a significant number of (stable) retrograde orbits. △ Less

Submitted 22 July, 2020; originally announced July 2020.

Comments: 21 pages, 21 figures, accepted by MNRAS

Linking the formation and fate of exo-Kuiper belts within solar system analogues

Authors: Dimitri Veras, Katja Reichert, Francesco Flammini Dotti, Maxwell X. Cai, Alexander J. Mustill, Andrew Shannon, Catriona H. McDonald, Simon Portegies Zwart, M. B. N. Kouwenhoven, Rainer Spurzem

Abstract: Escalating observations of exo-minor planets and their destroyed remnants both passing through the solar system and within white dwarf planetary systems motivate an understanding of the orbital history and fate of exo-Kuiper belts and planetesimal discs. Here we explore how the structure of a 40-1000 au annulus of planetesimals orbiting inside of a solar system analogue that is itself initially em… ▽ More Escalating observations of exo-minor planets and their destroyed remnants both passing through the solar system and within white dwarf planetary systems motivate an understanding of the orbital history and fate of exo-Kuiper belts and planetesimal discs. Here we explore how the structure of a 40-1000 au annulus of planetesimals orbiting inside of a solar system analogue that is itself initially embedded within a stellar cluster environment varies as the star evolves through all of its stellar phases. We attempt this computationally challenging link in four parts: (1) by performing stellar cluster simulations lasting 100 Myr, (2) by making assumptions about the subsequent quiescent 11 Gyr main-sequence evolution, (3) by performing simulations throughout the giant branch phases of evolution, and (4) by making assumptions about the belt's evolution during the white dwarf phase. Throughout these stages, we estimate the planetesimals' gravitational responses to analogues of the four solar system giant planets, as well as to collisional grinding, Galactic tides, stellar flybys, and stellar radiation. We find that the imprint of stellar cluster dynamics on the architecture of $\gtrsim 100$ km-sized exo-Kuiper belt planetesimals is retained throughout all phases of stellar evolution unless violent gravitational instabilities are triggered either (1) amongst the giant planets, or (2) due to a close ($\ll 10^3$ au) stellar flyby. In the absence of these instabilities, these minor planets simply double their semimajor axis while retaining their primordial post-cluster eccentricity and inclination distributions, with implications for the free-floating planetesimal population and metal-polluted white dwarfs. △ Less

Submitted 19 February, 2020; originally announced February 2020.

Comments: Accepted for publication in MNRAS

Measurement of the cosmic-ray proton spectrum from 40 GeV to 100 TeV with the DAMPE satellite

Authors: Q. An, R. Asfandiyarov, P. Azzarello, P. Bernardini, X. J. Bi, M. S. Cai, J. Chang, D. Y. Chen, H. F. Chen, J. L. Chen, W. Chen, M. Y. Cui, T. S. Cui, H. T. Dai, A. D'Amone, A. De Benedittis, I. De Mitri, M. Di Santo, M. Ding, T. K. Dong, Y. F. Dong, Z. X. Dong, G. Donvito, D. Droz, J. L. Duan , et al. (129 additional authors not shown)

Abstract: The precise measurement of the spectrum of protons, the most abundant component of the cosmic radiation, is necessary to understand the source and acceleration of cosmic rays in the Milky Way. This work reports the measurement of the cosmic ray proton fluxes with kinetic energies from 40 GeV to 100 TeV, with two and a half years of data recorded by the DArk Matter Particle Explorer (DAMPE). This i… ▽ More The precise measurement of the spectrum of protons, the most abundant component of the cosmic radiation, is necessary to understand the source and acceleration of cosmic rays in the Milky Way. This work reports the measurement of the cosmic ray proton fluxes with kinetic energies from 40 GeV to 100 TeV, with two and a half years of data recorded by the DArk Matter Particle Explorer (DAMPE). This is the first time an experiment directly measures the cosmic ray protons up to ~100 TeV with a high statistics. The measured spectrum confirms the spectral hardening found by previous experiments and reveals a softening at ~13.6 TeV, with the spectral index changing from ~2.60 to ~2.85. Our result suggests the existence of a new spectral feature of cosmic rays at energies lower than the so-called knee, and sheds new light on the origin of Galactic cosmic rays. △ Less

Submitted 30 September, 2019; v1 submitted 27 September, 2019; originally announced September 2019.

Comments: 37 pages, 5 figures, published in Science Advances

Journal ref: Science Advances, Vol. 5, no. 9, eaax3793 (2019)

Planetary systems in a star cluster I: the Solar system scenario

Authors: Francesco Flammini Dotti, M. B. N. Kouwenhoven, Maxwell Xu Cai, Rainer Spurzem

Abstract: Young stars are mostly found in dense stellar environments, and even our own Solar system may have formed in a star cluster. Here, we numerically explore the evolution of planetary systems similar to our own Solar system in star clusters. We investigate the evolution of planetary systems in star clusters. Most stellar encounters are tidal, hyperbolic, and adiabatic. A small fraction of the planeta… ▽ More Young stars are mostly found in dense stellar environments, and even our own Solar system may have formed in a star cluster. Here, we numerically explore the evolution of planetary systems similar to our own Solar system in star clusters. We investigate the evolution of planetary systems in star clusters. Most stellar encounters are tidal, hyperbolic, and adiabatic. A small fraction of the planetary systems escape from the star cluster within 50 Myr; those with low escape speeds often remain intact during and after the escape process. While most planetary systems inside the star cluster remain intact, a subset is strongly perturbed during the first 50 Myr. Over the course of time, 0.3 % - 5.3 % of the planets escape, sometimes up to tens of millions of years after a stellar encounter occurred. Survival rates are highest for Jupiter, while Uranus and Neptune have the highest escape rates. Unless directly affected by a stellar encounter itself, Jupiter frequently serves as a barrier that protects the terrestrial planets from perturbations in the outer planetary system. In low-density environments, Jupiter provides protection from perturbations in the outer planetary system, while in high-density environments, direct perturbations of Jupiter by neighbouring stars is disruptive to habitable-zone planets. The diversity amongst planetary systems that is present in the star clusters at 50 Myr, and amongst the escaping planetary systems, is high, which contributes to explaining the high diversity of observed exoplanet systems in star clusters and in the Galactic field △ Less

Submitted 21 August, 2019; originally announced August 2019.

Comments: 20 pages, 46 figures, accepted for pubblication on Monthly Notices of the Royal Astronomical Society on date 13 August 2019

The on-orbit calibration of DArk Matter Particle Explorer

Authors: G. Ambrosi, Q. An, R. Asfandiyarov, P. Azzarello, P. Bernardini, M. S. Cai, M. Caragiulo, J. Chang, D. Y. Chen, H. F. Chen, J. L. Chen, W. Chen, M. Y. Cui, T. S. Cui, H. T. Dai, A. D'Amone, A. De Benedittis, I. De Mitri, M. Ding, M. Di Santo, J. N. Dong, T. K. Dong, Y. F. Dong, Z. X. Dong, D. Droz , et al. (133 additional authors not shown)

Abstract: The DArk Matter Particle Explorer (DAMPE), a satellite-based cosmic ray and gamma-ray detector, was launched on December 17, 2015, and began its on-orbit operation on December 24, 2015. In this work we document the on-orbit calibration procedures used by DAMPE and report the calibration results of the Plastic Scintillator strip Detector (PSD), the Silicon-Tungsten tracKer-converter (STK), the BGO… ▽ More The DArk Matter Particle Explorer (DAMPE), a satellite-based cosmic ray and gamma-ray detector, was launched on December 17, 2015, and began its on-orbit operation on December 24, 2015. In this work we document the on-orbit calibration procedures used by DAMPE and report the calibration results of the Plastic Scintillator strip Detector (PSD), the Silicon-Tungsten tracKer-converter (STK), the BGO imaging calorimeter (BGO), and the Neutron Detector (NUD). The results are obtained using Galactic cosmic rays, bright known GeV gamma-ray sources, and charge injection into the front-end electronics of each sub-detector. The determination of the boundary of the South Atlantic Anomaly (SAA), the measurement of the live time, and the alignments of the detectors are also introduced. The calibration results demonstrate the stability of the detectors in almost two years of the on-orbit operation. △ Less

Submitted 3 July, 2019; originally announced July 2019.

Journal ref: Astroparticle Physics, Volume 106, p. 18-34 (2019)

Galactic Tide and Local Stellar Perturbations on the Oort Cloud: Creation of Interstellar Comets

Authors: Santiago Torres, Maxwell X. Cai, A. G. A. Brown, S. Portegies Zwart

Abstract: Comets in the Oort cloud evolve under the influence of internal and external perturbations, such as giant planets, stellar passages, and the galactic tidal field. We aim to study the dynamical evolution of the comets in the Oort cloud, accounting for external perturbations (passing stars and the galactic tide). We first construct an analytical model of stellar encounters. We find that individual p… ▽ More Comets in the Oort cloud evolve under the influence of internal and external perturbations, such as giant planets, stellar passages, and the galactic tidal field. We aim to study the dynamical evolution of the comets in the Oort cloud, accounting for external perturbations (passing stars and the galactic tide). We first construct an analytical model of stellar encounters. We find that individual perturbations do not modify the dynamics of the comets in the cloud unless very close (< 0.5pc) encounters occur. Using proper motions, parallaxes, and radial velocities from Gaia DR2, we construct an astrometric catalogue of 14,659 stars that are within 50pc from the Sun. For all these stars we calculate the time and the closest distance to the Sun. We find that the cumulative effect of relatively distant ($\leq1$ pc) passing stars can perturb the comets in the Oort cloud. Finally, we study the dynamical evolution of the comets in the Oort cloud under the influence of multiple stellar encounters within 2.5pc from the Sun and the galactic tidal field over $\pm10$Myr. We considered two models for the Oort cloud, compact (a $\leq$0.25 pc) and extended (a$ \leq0.5$ pc). We find that the cumulative effect of stellar encounters is the major perturber of the Oort cloud for a compact configuration while for the extended, the galactic tide is the major perturber. In both cases, the effect of passing stars and the galactic tide raises the semi-major axis of $\sim1.1$\% of the comets at the edge of the cloud up to interstellar regions ($a >0.5$pc). This leads to the creation of transitional interstellar comets, which might become interstellar objects due to external perturbations. This raises the question about the existence of a cloud of objects in the interstellar space which might overlap with our Oort cloud if we consider that other planetary systems face similar processes for the ejection of comets. △ Less

Submitted 15 August, 2019; v1 submitted 25 June, 2019; originally announced June 2019.

Comments: 13 pages, 13 figures, accepted for publication in Astronomy & Astrophysics

Journal ref: A&A 629, A139 (2019)

Planets In Young Massive Clusters: On the survivability of planets in young massive clusters and its implication of planet orbital architectures in globular clusters

Authors: Maxwell Xu Cai, S. Portegies Zwart, M. B. N. Kouwenhoven, Rainer Spurzem

Abstract: As of August 2019, among the more than 4000 confirmed exoplanets, only one has been detected in a globular cluster (GC) M4. The scarce of exoplanet detections motivates us to employ direct $N$-body simulations to investigate the dynamical stability of planets in young massive clusters (YMCs), which are potentially the progenitors of GCs. In an $N=128{\rm k}$ cluster of virial radius 1.7 pc (compar… ▽ More As of August 2019, among the more than 4000 confirmed exoplanets, only one has been detected in a globular cluster (GC) M4. The scarce of exoplanet detections motivates us to employ direct $N$-body simulations to investigate the dynamical stability of planets in young massive clusters (YMCs), which are potentially the progenitors of GCs. In an $N=128{\rm k}$ cluster of virial radius 1.7 pc (comparable to Westerlund-1), our simulations show that most wide-orbit planets ($a\geq 20$~au) will be ejected within a timescale of 10 Myr. Interestingly, more than $70\%$ of planets with $a<5$~au survive in the 100 Myr simulations. Ignoring planet-planet scattering and tidal damping, the survivability at $t$ Myr as a function of initial semi-major axis $a_0$ in au in such a YMC can be described as $f_{\rm surv}(a_0, t)=-0.33 \log_{10}(a_0) \left(1 - e^{-0.0482t} \right) + 1$. Upon ejection, about $28.8\%$ of free-floating planets (FFPs) have sufficient speeds to escape from the host cluster at a crossing timescale. The other FFPs will remain bound to the cluster potential, but the subsequent dynamical evolution of the stellar system can result in the delayed ejection of FFPs from the host cluster. Although a full investigation of planet population in GCs requires extending the simulations to multi-Gyr, our results suggest that wide-orbit planets and free-floating planets are unlikely to be found in GCs. △ Less

Submitted 9 September, 2019; v1 submitted 6 March, 2019; originally announced March 2019.

Comments: 12 pages, 11 figures, 1 table, accepted by MNRAS

Tropical and Extratropical General Circulation with a Meridional Reversed Temperature Gradient as Expected in a High Obliquity Planet

Authors: Wanying Kang, Ming Cai, Eli Tziperman

Abstract: Planets with high obliquity receive more radiation in the polar regions than at low latitudes, and thus, assuming an ocean-covered surface with sufficiently high heat capacity, their meridional temperature gradient was shown to be reversed for the entire year. The objective of this work is to investigate the drastically different general circulation of such planets, with an emphasis on the tropica… ▽ More Planets with high obliquity receive more radiation in the polar regions than at low latitudes, and thus, assuming an ocean-covered surface with sufficiently high heat capacity, their meridional temperature gradient was shown to be reversed for the entire year. The objective of this work is to investigate the drastically different general circulation of such planets, with an emphasis on the tropical Hadley circulation and the mid-latitude baroclinic eddy structure. We use a 3D dry dynamic core model, accompanied by an eddy-free configuration and a generalized 2D Eady model. When the meridional temperature gradient $T_y$ is reversed, the Hadley cell remains in the same direction, because the surface wind pattern and hence the associated meridional Ekman transport are not changed, as required by the baroclinic eddy momentum transport. The Hadley cell under reversed $T_y$ also becomes much shallower and weaker, even when the magnitude of the gradient is the same as in the normal case. The shallowness is due to the bottom-heavy structure of the baroclinic eddies in the reverse case, and the weakness is due to the weak wave activity. We propose a new mechanism to explain the mid-latitude eddy structure for both cases, and verify it using the generalized Eady model. With seasonal variations included, the annual mean circulation resembles that under perpetual annual mean setup. Approaching the solstices, a strong cross-equator Hadley cell forms in both cases, and about 2/3 of the Hadley circulation is driven by eddies, as shown by eddy-free simulations and using a decomposition of the Hadley cell. △ Less

Submitted 18 February, 2019; originally announced February 2019.

Survivability of planetary systems in young and dense star clusters

Authors: Arjen van Elteren, Simon Portegies Zwart, Inti Pelupessy, Maxwell Cai, Steve McMillan

Abstract: We perform a simulation using the Astrophysical Multipurpose Software Environment of the Orion Trapezium star cluster in which the evolution of the stars and the dynamics of planetary systems are taken into account. The initial conditions from earlier simulations were selected in which the size and mass distributions of the observed circumstellar disks in this cluster are satisfactorily reproduced… ▽ More We perform a simulation using the Astrophysical Multipurpose Software Environment of the Orion Trapezium star cluster in which the evolution of the stars and the dynamics of planetary systems are taken into account. The initial conditions from earlier simulations were selected in which the size and mass distributions of the observed circumstellar disks in this cluster are satisfactorily reproduced. Four, five, or size planets per star were introduced in orbit around the 500 solar-like stars with a maximum orbital separation of 400au. Our study focuses on the production of free-floating planets. A total of 357 become unbound from a total of 2522 planets in the initial conditions of the simulation. Of these, 281 leave the cluster within the crossing timescale of the star cluster; the others remain bound to the cluster as free-floating intra-cluster planets. Five of these free-floating intra-cluster planets are captured at a later time by another star. The two main mechanisms by which planets are lost from their host star, ejection upon a strong encounter with another star or internal planetary scattering, drive the evaporation independent of planet mass of orbital separation at birth. The effect of small perturbations due to slow changes in the cluster potential are important for the evolution of planetary systems. In addition, the probability of a star to lose a planet is independent of the planet mass and independent of its initial orbital separation. As a consequence, the mass distribution of free-floating planets indistinguishable from the mass distribution of planets bound to their host star. △ Less

Submitted 11 March, 2019; v1 submitted 12 February, 2019; originally announced February 2019.

Comments: A&A in press

Journal ref: A&A 624, A120 (2019)

Planetary Systems in Star Clusters: the dynamical evolution and survival

Authors: Francesco Flammini Dotti, Maxwell Xu Cai, Rainer Spurzem, M. B. N. Kouwenhoven

Abstract: Most stars, perhaps even all stars, form in crowded stellar environments. Such star forming regions typically dissolve within ten million years, while others remain bound as stellar groupings for hundreds of millions to billions of years, and then become the open clusters or globular clusters that are present in our Milky Way galaxy today. A large fraction of stars in the Galaxy hosts planetary co… ▽ More Most stars, perhaps even all stars, form in crowded stellar environments. Such star forming regions typically dissolve within ten million years, while others remain bound as stellar groupings for hundreds of millions to billions of years, and then become the open clusters or globular clusters that are present in our Milky Way galaxy today. A large fraction of stars in the Galaxy hosts planetary companions. To understand the origin and dynamical evolution of such exoplanet systems, it is necessary to carefully study the effect of their environments. Here, we combine theoretical estimates with state-of-the-art numerical simulations of evolving planetary systems similar to our own solar system in different star cluster environments. We combine the REBOUND planetary system evolution code, and the NBODY6++GPU star cluster evolution code, integrated in the AMUSE multi-physics environment. With our study we can constrain the effect of external perturbations of different environments on the planets and debris structures of a wide variety of planetary systems, which may play a key role for the habitability of exoplanets in the Universe. △ Less

Submitted 30 November, 2018; originally announced November 2018.

Comments: 2 pages, 2 figures, Proceedings for Symposia IAU 345 "Origins: from the Protosun to the First Steps of Life" at the XXX general assembly in Vienna