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Low-Frequency VLBI Network Using SKA-LOW
Authors:
Hideyuki Kobayashi,
Tomoaki Oyama,
Kazuma Fujita,
Syunsaku Suzuki,
Shintaro Yoshiura,
Hiroaki Misawa,
Fuminori Tsuchiya,
Kazuhiro Takefuji,
Kenta Fujisawa,
Kohtaro Niinuma,
Keitaro Takahashi,
Yashwant Gupta,
Bhal Chandra Joshi,
Vishwesh Marthi,
M. A. Krishnakumar,
Zhiqiang Shen,
Wu Jiang,
Yihua Yan,
Wei Wang,
Linjie Chen
Abstract:
We propose the development of a low-frequency Very Long Baseline Interferometry (VLBI) network operating in the 100-350 MHz range, incorporating the Square Kilometre Array Low (SKA-LOW). SKA-LOW is expected to achieve exceptionally high sensitivity within this frequency band. By integrating SKA-LOW with other high-sensitivity radio telescopes located across the Asia-Pacific region, the proposed ne…
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We propose the development of a low-frequency Very Long Baseline Interferometry (VLBI) network operating in the 100-350 MHz range, incorporating the Square Kilometre Array Low (SKA-LOW). SKA-LOW is expected to achieve exceptionally high sensitivity within this frequency band. By integrating SKA-LOW with other high-sensitivity radio telescopes located across the Asia-Pacific region, the proposed network is anticipated to deliver up to two orders of magnitude improvement in sensitivity compared to the existing VLBA. While several scientific themes utilizing low-frequency VLBI have already been proposed, we specifically advocate for astrometric studies employing existing VLBI stations to demonstrate the feasibility and scientific potential of this frequency regime. Furthermore, the combination of SKA-LOW with additional radio telescopes will enable high-fidelity imaging observations, significantly enhancing the quality and scope of low-frequency VLBI science.
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Submitted 16 July, 2026;
originally announced July 2026.
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VLBI-Enabled Localization of Continuous GW Sources
Authors:
Keitaro Takahashi,
Takuya Akahori,
Kenta Fujisawa,
Hiroshi Imai,
Hajime Kita,
Hideyuki Kobayashi,
Hiroaki Misawa,
Kotaro Niinuma,
Tomoaki Oyama,
Kazuhiro Takefuji,
Fuminori Tsuchiya
Abstract:
Pulsar timing arrays (PTAs) are opening the nanohertz gravitational-wave (GW) band by timing millisecond pulsars (MSPs) to target signals from supermassive black hole binaries (SMBHBs). Beyond evidence for a stochastic background, a central SKA-era objective is detecting individual continuous-wave (CW) sources. The scientific payoff hinges on localization: conventional PTA searches yield uncertain…
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Pulsar timing arrays (PTAs) are opening the nanohertz gravitational-wave (GW) band by timing millisecond pulsars (MSPs) to target signals from supermassive black hole binaries (SMBHBs). Beyond evidence for a stochastic background, a central SKA-era objective is detecting individual continuous-wave (CW) sources. The scientific payoff hinges on localization: conventional PTA searches yield uncertainties of tens-hundreds of deg$^2$, too large to identify a unique host, obtain a redshift, infer intrinsic masses, or pursue electromagnetic counterparts. This limitation is chiefly geometric: the CW response includes Earth and pulsar terms, and poorly known pulsar distances make the pulsar-term phase a free parameter that degrades triangulation. If distances to a few MSPs are known to better than a GW wavelength ($\sim$ 1 pc), these phases are fixed and localization improves by orders of magnitude. Simulations indicate that with sub-parsec distances for a handful of nearby MSPs, the uncertainty can shrink to $\sim 10^{-3}$ deg$^2$ (arcminute scale), enabling unique host association and multi-messenger follow-up. Achieving such distances requires $\sim$ 10 $μ$arcsec parallaxes for MSPs within a few hundred parsecs, a precision now approached with Very Long Baseline Interferometry (VLBI) and expected to become practical with phased-array SKA1-Mid operating as a sensitive VLBI element. SKA1's multi-beam, multi-calibrator astrometry will provide the independent distance priors needed for PTAs to localize nanohertz GW sources and measure SMBHB parameters and environments. We assess VLBI's role in PTA CW searches and propose a concrete SKA1-Mid observing strategy for nearby MSPs to deliver the required sub-parsec distances.
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Submitted 27 June, 2026;
originally announced June 2026.
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Diagnosing Long-Video Quantitative Reasoning in Multimodal LLMs via Enumeration and Counting
Authors:
Fumihiko Tsuchiya,
Taiki Miyanishi,
Shunsuke Yasuki,
Mahiro Ukai,
Nakamasa Inoue,
Shuhei Kurita,
Yusuke Iwasawa,
Yutaka Matsuo
Abstract:
Final-answer video QA can show whether a model predicts the right number, but not which instances it counted, when the supporting evidence occurs, or why it failed. We diagnose long-video quantitative reasoning in multimodal large language models (MLLMs) through three coupled abilities: enumerating query-relevant instances, temporally grounding supporting evidence, and aggregating the evidence int…
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Final-answer video QA can show whether a model predicts the right number, but not which instances it counted, when the supporting evidence occurs, or why it failed. We diagnose long-video quantitative reasoning in multimodal large language models (MLLMs) through three coupled abilities: enumerating query-relevant instances, temporally grounding supporting evidence, and aggregating the evidence into counts. To support this analysis, we build EC-Bench, an evidence-annotated evaluation suite with 152 untrimmed videos longer than 30 minutes, 1,699 open-ended queries across six reasoning categories, and human-verified evidence spans. We evaluate 22 open-source and proprietary MLLMs using timestamped visual frames and transcripts. The best average scores reach only 29.98% Enumeration F1 and 23.74% Counting accuracy, compared with human performance of 78.57% and 82.97%, respectively. Our analyses show that counting errors are rarely isolated arithmetic mistakes: Enumeration F1 is strongly associated with Counting accuracy, temporal grounding quality is associated with lower counting error, and Counting accuracy drops as supporting evidence becomes more distributed. These findings recast long-video counting as evidence retrieval, temporal grounding, deduplication, and aggregation across the video, rather than simple numerical prediction.
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Submitted 10 July, 2026; v1 submitted 31 March, 2026;
originally announced March 2026.
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Origin of the stellar Fe Kα line clarified with FUV and X-ray observations of a superflare on the RS Canum Venaticorum-type Star UX Arietis
Authors:
Shun Inoue,
Wataru Buz Iwakiri,
Tomoki Kimura,
Teruaki Enoto,
Yuta Notsu,
Hiroyuki Uchida,
Kenji Hamaguchi,
Shin Toriumi,
Atsushi Yamazaki,
Fuminori Tsuchiya,
Go Murakami,
Kazuo Yoshioka,
Zaven Arzoumanian,
Keith Gendreau
Abstract:
Fluorescence line diagnostics of the Fe Kα line at $\sim 6.4$ keV observed in both solar and stellar flares can constrain the latitude and size of the flare loop, even in the absence of imaging observations. However, they are hampered by the unresolved origin of stellar Fe Kα lines: i.e., it is unclear which of the two mechanisms-photoionization by hard X-ray photons or collisional ionization by n…
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Fluorescence line diagnostics of the Fe Kα line at $\sim 6.4$ keV observed in both solar and stellar flares can constrain the latitude and size of the flare loop, even in the absence of imaging observations. However, they are hampered by the unresolved origin of stellar Fe Kα lines: i.e., it is unclear which of the two mechanisms-photoionization by hard X-ray photons or collisional ionization by non-thermal electrons-is the dominant process. We present clear evidence for the photoionization origin based on simultaneous far ultraviolet (FUV) and soft X-ray observations of a superflare on the RS Canum Venaticorum-type Star UX Arietis with Extreme ultraviolet spetrosCope for ExosphEric Dynamic (EXCEED; 900$-$1480 Å) onboard Hisaki and Neutron Star Interior Composition Explorer (NICER; 0.2$-$12 keV). The flare started at 22:50 UT on 2018 November 15 and released $2 \times 10^{36}$ erg in the 900$-$1480 Å band and $3 \times 10^{36}$ erg in the 0.3$-$4 keV band. The FUV emission, a proxy for non-thermal activity, peaked approximately 1.4 hours before the soft X-rays. In contrast, the Fe Kα line, detected at a statistical significance of $5.3 σ$ with an equivalent width of $67^{+28}_{-20}$ eV, peaked simultaneously with the thermal X-ray maximum rather than the non-thermal FUV peak-strongly supporting the photoionization hypothesis. Radiative transfer calculations, combined with the observed Fe Kα line intensity, further support the photoionization scenario and demonstrate the potential of this line to provide the flare geometry.
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Submitted 10 December, 2025;
originally announced December 2025.
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Optical photon-counting observation of the Crab pulsar with Kanata telescope using prototype IMONY
Authors:
Takeshi Nakamori,
Kazuaki Hashiyama,
Rin Sato,
Masayoshi Shoji,
Anju Sato,
Eiji Ono,
Yuga Ouchi,
Tatsuya Nakaoka,
Koji S. Kawabata,
Toshio Terasawa,
Hiroaki Misawa,
Fuminori Tsuchiya,
Kazuhiro Takefuji,
Yasuhiro Murata,
Dai Takei,
Kazuki Ueno,
Hiroshi Akitaya
Abstract:
We have developed an optical photon-counting imaging system, IMONY, as an instrument for short-scale time-domain astronomy. In this study, we utilized a Geiger avalanche photodiode array with a $4\times 4$ pixel configuration, with each pixel measuring \SI{100}{\micro m}. We developed a dedicated analog frontend board and constructed a data acquisition system with an FPGA to time-stamp each photon…
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We have developed an optical photon-counting imaging system, IMONY, as an instrument for short-scale time-domain astronomy. In this study, we utilized a Geiger avalanche photodiode array with a $4\times 4$ pixel configuration, with each pixel measuring \SI{100}{\micro m}. We developed a dedicated analog frontend board and constructed a data acquisition system with an FPGA to time-stamp each photon with a time resolution of \SI{100}{\ns}. We mounted a prototype model of the system on the 1.5-m Kanata telescope, intending to observe the Crab pulsar and conduct joint observations with Iitate and Usuda radio telescopes in Japan. We successfully demonstrated that IMONY could image the Crab pulsar as an expected point source and acquire the well-known pulse shape. We found that the time lag between the optical and radio main pulses was $304\pm$\SI{35}{μs}, consistent with previous studies.
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Submitted 9 March, 2025;
originally announced March 2025.
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A Characteristic Signature of Magnetospheric Wave-Particle Interactions Found in the Turbulent E-region
Authors:
Magnus F Ivarsen,
Yukinaga Miyashita,
Jean-Pierre St-Maurice,
Glenn C Hussey,
Brian Pitzel,
Draven Galeschuk,
Saif Marei,
Richard B Horne,
Yoshiya Kasahara,
Shoya Matsuda,
Satoshi Kasahara,
Kunihiro Keika,
Yoshizumi Miyoshi,
Kazuhiro Yamamoto,
Atsuki Shinbori,
Devin R Huyghebaert,
Ayako Matsuoka,
Shoichiro Yokota,
Fuminori Tsuchiya
Abstract:
Plasma waves in the magnetosphere scatter electrons, causing them to precipitate into Earth's atmosphere, imparting their temporal characteristics to diffuse auroras. In a case study of conjugate radar and satellite observations, we demonstrate a close and unprecedented association between enhanced electrostatic cyclotron harmonic wave activity in the magnetosphere and the appearance of meter-scal…
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Plasma waves in the magnetosphere scatter electrons, causing them to precipitate into Earth's atmosphere, imparting their temporal characteristics to diffuse auroras. In a case study of conjugate radar and satellite observations, we demonstrate a close and unprecedented association between enhanced electrostatic cyclotron harmonic wave activity in the magnetosphere and the appearance of meter-scale plasma turbulence a few seconds later in the lower ionosphere on nearby magnetic field lines. Such direct structuring of the ionosphere carries implications for our understanding of space weather.
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Submitted 10 October, 2025; v1 submitted 7 January, 2025;
originally announced January 2025.
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Mass supply from Io to Jupiter's magnetosphere
Authors:
L. Roth,
A. Blöcker,
K. de Kleer,
D. Goldstein,
E. Lellouch,
J. Saur,
C. Schmidt,
D. F. Strobel,
C. Tao,
F. Tsuchiya,
V. Dols,
H. Huybrighs,
A. Mura,
J. R. Szalay,
S. V. Badman,
I. de Pater,
A. -C. Dott,
M. Kagitani,
L. Klaiber,
R. Koga,
A. McEwen,
Z. Milby,
K. D. Retherford,
S. Schlegel,
N. Thomas
, et al. (2 additional authors not shown)
Abstract:
Since the Voyager mission flybys in 1979, we have known the moon Io to be both volcanically active and the main source of plasma in the vast magnetosphere of Jupiter. Material lost from Io forms neutral clouds, the Io plasma torus and ultimately the extended plasma sheet. This material is supplied from Io's upper atmosphere and atmospheric loss is likely driven by plasma-interaction effects with p…
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Since the Voyager mission flybys in 1979, we have known the moon Io to be both volcanically active and the main source of plasma in the vast magnetosphere of Jupiter. Material lost from Io forms neutral clouds, the Io plasma torus and ultimately the extended plasma sheet. This material is supplied from Io's upper atmosphere and atmospheric loss is likely driven by plasma-interaction effects with possible contributions from thermal escape and photochemistry-driven escape. Direct volcanic escape is negligible. The supply of material to maintain the plasma torus has been estimated from various methods at roughly one ton per second. Most of the time the magnetospheric plasma environment of Io is stable on timescales from days to months. Similarly, Io's atmosphere was found to have a stable average density on the dayside, although it exhibits lateral and temporal variations. There is potential positive feedback in the Io torus supply: collisions of torus plasma with atmospheric neutrals are probably a significant loss process, which increases with torus density. The stability of the torus environment may be maintained by limiting mechanisms of either torus supply from Io or the loss from the torus by centrifugal interchange in the middle magnetosphere. Various observations suggest that occasionally the plasma torus undergoes major transient changes over a period of several weeks, apparently overcoming possible stabilizing mechanisms. Such events are commonly explained by some kind of change in volcanic activity that triggers a chain of reactions which modify the plasma torus state via a net change in supply of new mass. However, it remains unknown what kind of volcanic event (if any) can trigger events in torus and magnetosphere, whether Io's atmosphere undergoes a general change before or during such events, and what processes could enable such a change in the otherwise stable torus.
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Submitted 14 January, 2025; v1 submitted 20 March, 2024;
originally announced March 2024.
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Constraints on Europa's water group torus from HST/COS observations
Authors:
Lorenz Roth,
H. Todd Smith,
Kazuo Yoshioka,
Tracy M. Becker,
Aljona Blöcker,
Nathaniel J. Cunningham,
Nickolay Ivchenko,
Kurt D. Retherford,
Joachim Saur,
Michael Velez,
Fuminori Tsuchiya
Abstract:
In-situ plasma measurements as well as remote mapping of energetic neutral atoms around Jupiter provide indirect evidence that an enhancement of neutral gas is present near the orbit of the moon Europa. Simulations suggest that such a neutral gas torus can be sustained by escape from Europa's atmosphere and consists primarily of molecular hydrogen, but the neutral gas torus has not yet been measur…
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In-situ plasma measurements as well as remote mapping of energetic neutral atoms around Jupiter provide indirect evidence that an enhancement of neutral gas is present near the orbit of the moon Europa. Simulations suggest that such a neutral gas torus can be sustained by escape from Europa's atmosphere and consists primarily of molecular hydrogen, but the neutral gas torus has not yet been measured directly through emissions or in-situ. Here we present observations by the Cosmic Origins Spectrograph of the Hubble Space Telescope (HST/COS) from 2020 and 2021, which scanned the equatorial plane between 8 and 10 planetary radii west of Jupiter. No neutral gas emissions are detected. We derive upper limits on the emissions and compare these to modelled emissions from electron impact and resonant scattering using a Europa torus Monte Carlo model for the neutral gases. The comparison supports the previous findings that the torus is dilute and primarily consists of molecular hydrogen. A detection of sulfur ion emissions radially inward of the Europa orbit is consistent with emissions from the extended Io torus and with sulfur ion fractional abundances as previously detected.
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Submitted 18 April, 2023;
originally announced April 2023.
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Revealing the dynamics of magnetosphere, atmosphere, and interior of solar system objects with the Square Kilometre Array
Authors:
Tomoki Kimura,
Yuka Fujii,
Hajime Kita,
Fuminori Tsuchiya,
Hideo Sagawa,
the SKA-Japan Planetary Science Team
Abstract:
Bodies such as planets, moons, and asteroids in our solar system are the brightest objects in the low-frequency radio astronomy at $\lesssim$ 10 GHz. The low-frequency radio emissions from our solar system bodies exhibit various observed characteristics in the spectrum, polarization, periodicity, and flux. The observed characteristics are essential probes for explorations of the bodies' magnetosph…
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Bodies such as planets, moons, and asteroids in our solar system are the brightest objects in the low-frequency radio astronomy at $\lesssim$ 10 GHz. The low-frequency radio emissions from our solar system bodies exhibit various observed characteristics in the spectrum, polarization, periodicity, and flux. The observed characteristics are essential probes for explorations of the bodies' magnetosphere, atmosphere, surface, and even their interior. Generation and propagation theories of the radio emissions associate the characteristics with fundamental physics embedded in the environments: e.g., auroral electron acceleration, betatron acceleration, and atmospheric momentum transfer. Here we review previous studies on the low-frequency radio emissions from our solar system bodies to unveil some outstanding key questions on the dynamics and evolution of the bodies. To address the key questions by the future observations with the Square Kilometre Array (SKA), we made feasibility studies for detection and imaging of the radio emissions. Possible extensions of the solar system observations with SKA to the exoplanets are also proposed in the summary.
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Submitted 13 March, 2023;
originally announced March 2023.
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Multi-frequency radio observations of the radio-loud magnetar XTE J1810-197
Authors:
Sujin Eie,
Toshio Terasawa,
Takuya Akahori,
Tomoaki Oyama,
Tomoya Hirota,
Yoshinori Yonekura,
Teruaki Enoto,
Mamoru Sekido,
Kazuhiro Takefuji,
Hiroaki Misawa,
Fuminori Tsuchiya,
Shota Kisaka,
Takahiro Aoki,
Mareki Honma
Abstract:
We report on the multi-frequency multi-epoch radio observations of the magnetar, XTE J1810-197, which exhibited a radio outburst from December 2018 after its 10-year quiescent period. We performed quasi-simultaneous observations with VERA (22 GHz), Hitachi (6.9 GHz and 8.4 GHz), Kashima (2.3 GHz), and Iitate (0.3 GHz) radio telescopes located in Japan to trace the variability of the magnetar radio…
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We report on the multi-frequency multi-epoch radio observations of the magnetar, XTE J1810-197, which exhibited a radio outburst from December 2018 after its 10-year quiescent period. We performed quasi-simultaneous observations with VERA (22 GHz), Hitachi (6.9 GHz and 8.4 GHz), Kashima (2.3 GHz), and Iitate (0.3 GHz) radio telescopes located in Japan to trace the variability of the magnetar radio pulsations during the observing period from 13 December 2018 to 12 June 2019. The pulse width goes narrower as the observing frequency goes higher, analogous to the general profile narrowing behavior of ordinary pulsars. When assuming a simple power law in the range of 2.3 GHz and 8.7 GHz, the radio spectrum of the magnetar goes steeper with the average spectral index $ \langle α\rangle \approx -0.85$ for the first four months. The wide-band radio spectra inferred from our observations and the literature suggest that XTE J1810-197 would have a double-peaked spectrum with a valley point in 22 - 150 GHz, where the first spectral peak infers a gigahertz-peaked spectrum (GPS) feature with a peak at a few GHz. The GPS and the high-frequency peak have been identified in the spectra of other radio-loud magnetars, thus they may be intrinsic features that can give a new insight to understand various emission mechanisms and surrounding environments of radio magnetars. Our study emphasizes the importance of simultaneous long-term broad-band observations toward radio-loud magnetars to capture the puzzling spectral features and establish a link to other types of neutron stars.
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Submitted 24 September, 2021;
originally announced September 2021.
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Enhanced X-ray Emission Coinciding with Giant Radio Pulses from the Crab Pulsar
Authors:
Teruaki Enoto,
Toshio Terasawa,
Shota Kisaka,
Chin-Ping Hu,
Sebastien Guillot,
Natalia Lewandowska,
Christian Malacaria,
Paul S. Ray,
Wynn C. G. Ho,
Alice K. Harding,
Takashi Okajima,
Zaven Arzoumanian,
Keith C. Gendreau,
Zorawar Wadiasingh,
Craig B. Markwardt,
Yang Soong,
Steve Kenyon,
Slavko Bogdanov,
Walid A. Majid,
Tolga Güver,
Gaurava K. Jaisawal,
Rick Foster,
Yasuhiro Murata,
Hiroshi Takeuchi,
Kazuhiro Takefuji
, et al. (12 additional authors not shown)
Abstract:
Giant radio pulses (GRPs) are sporadic bursts emitted by some pulsars, lasting a few microseconds. GRPs are hundreds to thousands of times brighter than regular pulses from these sources. The only GRP-associated emission outside radio wavelengths is from the Crab Pulsar, where optical emission is enhanced by a few percent during GRPs. We observed the Crab Pulsar simultaneously at X-ray and radio w…
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Giant radio pulses (GRPs) are sporadic bursts emitted by some pulsars, lasting a few microseconds. GRPs are hundreds to thousands of times brighter than regular pulses from these sources. The only GRP-associated emission outside radio wavelengths is from the Crab Pulsar, where optical emission is enhanced by a few percent during GRPs. We observed the Crab Pulsar simultaneously at X-ray and radio wavelengths, finding enhancement of the X-ray emission by $3.8\pm0.7\%$ (a 5.4$σ$ detection) coinciding with GRPs. This implies that the total emitted energy from GRPs is tens to hundreds of times higher than previously known. We discuss the implications for the pulsar emission mechanism and extragalactic fast radio bursts.
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Submitted 7 April, 2021;
originally announced April 2021.
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An attempt to detect transient changes in Io's SO2 and NaCl atmosphere
Authors:
L. Roth,
J. Boissier,
A. Moullet,
A. Sanchez-Monge,
K. de Kleer,
M. Yoneda,
R. Hikida,
H. Kita,
F. Tsuchiya,
A. Blcker,
G. R. Gladstone,
D. Grodent,
N. Ivchenko,
E. Lellouch,
K. Retherford,
J. Saur,
P. Schilke D. Strobel,
S. Thorwirth
Abstract:
Io's atmosphere is predominately SO2 sustained by a combination of volcanic outgassing and sublimation. The loss from the atmosphere is the main mass source for Jupiter's large magnetosphere. Previous studies attributed various transient phenomena in Io's environment and Jupiter's magnetosphere to a sudden change in the mass loss from the atmosphere supposedly triggered by a change in volcanic act…
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Io's atmosphere is predominately SO2 sustained by a combination of volcanic outgassing and sublimation. The loss from the atmosphere is the main mass source for Jupiter's large magnetosphere. Previous studies attributed various transient phenomena in Io's environment and Jupiter's magnetosphere to a sudden change in the mass loss from the atmosphere supposedly triggered by a change in volcanic activity. Since the gas in volcanic plumes does not escape directly, such causal correlation would require a transient volcano-induced change in atmospheric abundance, which has never been observed so far. Here we report four observations of atmospheric SO2 and NaCl obtained with the IRAM NOEMA interferometer. These observations are compared to measurements of volcanic hot spots and Io's neutral and plasma environment. We find a stable NaCl column density in Io's atmosphere. The SO2 column density derived for December 2016 is about 30% lower compared to the period of March to April 2017. This increase in SO2 from December 2016 to March 2017 might be related to increasing volcanic activity observed at several sites in spring 2017, but the stability of the volcanic trace gas NaCl and resulting decrease in NaCl/SO2 ratio do not support this interpretation. Observed dimmings in both the sulfur ion torus and Na neutral cloud suggest rather a decrease in mass loading in the period of increasing SO2 abundance. The dimming Na brightness and stable atmospheric NaCl furthermore dispute an earlier suggested positive correlation of the sodium cloud and the hot spot activity at Loki Patara, which considerably increased in this period. The environment of Io overall appears to be in a quiescent state, preventing further conclusions. Only Jupiter's aurora morphology underwent several short-term changes, which are apparently unrelated to Io's quiescent environment or the relatively stable atmosphere.
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Submitted 17 June, 2020;
originally announced June 2020.
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Hitomi X-ray studies of Giant Radio Pulses from the Crab pulsar
Authors:
Hitomi Collaboration,
Felix Aharonian,
Hiroki Akamatsu,
Fumie Akimoto,
Steven W. Allen,
Lorella Angelini,
Marc Audard,
Hisamitsu Awaki,
Magnus Axelsson,
Aya Bamba,
Marshall W. Bautz,
Roger Blandford,
Laura W. Brenneman,
Gregory V. Brown,
Esra Bulbul,
Edward M. Cackett,
Maria Chernyakova,
Meng P. Chiao,
Paolo S. Coppi,
Elisa Costantini,
Jelle de Plaa,
Cor P. de Vries,
Jan-Willem den Herder,
Chris Done,
Tadayasu Dotani
, et al. (179 additional authors not shown)
Abstract:
To search for giant X-ray pulses correlated with the giant radio pulses (GRPs) from the Crab pulsar, we performed a simultaneous observation of the Crab pulsar with the X-ray satellite Hitomi in the 2 -- 300 keV band and the Kashima NICT radio observatory in the 1.4 -- 1.7 GHz band with a net exposure of about 2 ks on 25 March 2016, just before the loss of the Hitomi mission.The timing performance…
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To search for giant X-ray pulses correlated with the giant radio pulses (GRPs) from the Crab pulsar, we performed a simultaneous observation of the Crab pulsar with the X-ray satellite Hitomi in the 2 -- 300 keV band and the Kashima NICT radio observatory in the 1.4 -- 1.7 GHz band with a net exposure of about 2 ks on 25 March 2016, just before the loss of the Hitomi mission.The timing performance of the Hitomi instruments was confirmed to meet the timing requirement and about 1,000 and 100 GRPs were simultaneously observed at the main and inter-pulse phases, respectively, and we found no apparent correlation between the giant radio pulses and the X-ray emission in either the main or inter-pulse phases.All variations are within the 2 sigma fluctuations of the X-ray fluxes at the pulse peaks, and the 3 sigma upper limits of variations of main- or inter- pulse GRPs are 22\% or 80\% of the peak flux in a 0.20 phase width, respectively, in the 2 -- 300 keV band.The values become 25\% or 110\% for main or inter-pulse GRPs, respectively, when the phase width is restricted into the 0.03 phase.Among the upper limits from the Hitomi satellite, those in the 4.5-10 keV and the 70-300 keV are obtained for the first time, and those in other bands are consistent with previous reports.Numerically, the upper limits of main- and inter-pulse GRPs in the 0.20 phase width are about (2.4 and 9.3) $\times 10^{-11}$ erg cm$^{-2}$, respectively. No significant variability in pulse profiles implies that the GRPs originated from a local place within the magnetosphere and the number of photon-emitting particles temporally increases.However, the results do not statistically rule out variations correlated with the GRPs, because the possible X-ray enhancement may appear due to a $>0.02$\% brightening of the pulse-peak flux under such conditions.
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Submitted 7 August, 2017; v1 submitted 27 July, 2017;
originally announced July 2017.
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Polarization Characteristics of Zebra Patterns in Type IV Solar Radio Bursts
Authors:
Kazutaka Kaneda,
H. Misawa,
K. Iwai,
F. Tsuchiya,
T. Obara,
Y. Katoh,
S. Masuda
Abstract:
The polarization characteristics of zebra patterns (ZPs) in type IV solar bursts were studied. We analyzed 21 ZP events observed by the Assembly of Metric-band Aperture Telescope and Real-time Analysis System between 2010 and 2015 and identified the following characteristics: a degree of circular polarization (DCP) in the range of 0%-70%, a temporal delay of 0-70 ms between the two circularly pola…
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The polarization characteristics of zebra patterns (ZPs) in type IV solar bursts were studied. We analyzed 21 ZP events observed by the Assembly of Metric-band Aperture Telescope and Real-time Analysis System between 2010 and 2015 and identified the following characteristics: a degree of circular polarization (DCP) in the range of 0%-70%, a temporal delay of 0-70 ms between the two circularly polarized components (i.e., the right- and left-handed components), and dominant ordinary-mode emission in about 81% of the events. For most events, the relation between the dominant and delayed components could be interpreted in the framework of fundamental plasma emission and depolarization during propagation, though the values of DCP and delay were distributed across wide ranges. Furthermore, it was found that the DCP and delay were positively correlated (rank correlation coefficient R = 0.62). As a possible interpretation of this relationship, we considered a model based on depolarization due to reflections at sharp density boundaries assuming fundamental plasma emission. The model calculations of depolarization including multiple reflections and group delay during propagation in the inhomogeneous corona showed that the DCP and delay decreased as the number of reflections increased, which is consistent with the observational results. The dispersive polarization characteristics could be explained by the different numbers of reflections causing depolarization.
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Submitted 3 July, 2017;
originally announced July 2017.
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Wide-Band Spectra of Giant Radio Pulses from the Crab Pulsar
Authors:
Ryo Mikami,
Katsuaki Asano,
Shuta J. Tanaka,
Shota Kisaka,
Mamoru Sekido,
Kazuhiro Takefuji,
Hiroshi Takeuchi,
Hiroaki Misawa,
Fuminori Tsuchiya,
Hajime Kita,
Yoshinori Yonekura,
Toshio Terasawa
Abstract:
We present the results of the simultaneous observation of the giant radio pulses (GRPs) from the Crab pulsar at 0.3, 1.6, 2.2, 6.7, and 8.4 GHz with four telescopes in Japan. We obtain 3194 and 272 GRPs occurring at the main pulse and the interpulse phases, respectively. A few GRPs detected at both 0.3 and 8.4 GHz are the most wide-band samples ever reported. In the frequency range from 0.3 to 2.2…
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We present the results of the simultaneous observation of the giant radio pulses (GRPs) from the Crab pulsar at 0.3, 1.6, 2.2, 6.7, and 8.4 GHz with four telescopes in Japan. We obtain 3194 and 272 GRPs occurring at the main pulse and the interpulse phases, respectively. A few GRPs detected at both 0.3 and 8.4 GHz are the most wide-band samples ever reported. In the frequency range from 0.3 to 2.2 GHz, we find that about 70\% or more of the GRP spectra are consistent with single power laws and the spectral indices of them are distributed from $-4$ to $-1$. We also find that a significant number of GRPs have such a hard spectral index (approximately $-1$) that the fluence at 0.3 GHz is below the detection limit ("dim-hard" GRPs). Stacking light curves of such dim-hard GRPs at 0.3 GHz, we detect consistent enhancement compared to the off-GRP light curve. Our samples show apparent correlations between the fluences and the spectral hardness, which indicates that more energetic GRPs tend to show softer spectra. Our comprehensive studies on the GRP spectra are useful materials to verify the GRP model of fast radio bursts in future observations.
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Submitted 10 November, 2016; v1 submitted 27 August, 2016;
originally announced August 2016.
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Very Long Baseline Interferometry Experiment on Giant Radio Pulses of Crab Pulsar toward Fast Radio Burst Detection
Authors:
K. Takefuji,
T. Terasawa,
T. Kondo,
R. Mikami,
H. Takeuchi,
H. Misawa,
F. Tsuchiya,
H. Kita,
M. Sekido
Abstract:
We report on a very long baseline interferometry (VLBI) experiment on giant radio pulses (GPs) from the Crab pulsar in the radio 1.4 to 1.7 GHz range to demonstrate a VLBI technique for searching for fast radio bursts (FRBs). We carried out the experiment on 26 July 2014 using the Kashima 34 m and Usuda 64 m radio telescopes of the Japanese VLBI Network (JVN) with a baseline of about 200 km. Durin…
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We report on a very long baseline interferometry (VLBI) experiment on giant radio pulses (GPs) from the Crab pulsar in the radio 1.4 to 1.7 GHz range to demonstrate a VLBI technique for searching for fast radio bursts (FRBs). We carried out the experiment on 26 July 2014 using the Kashima 34 m and Usuda 64 m radio telescopes of the Japanese VLBI Network (JVN) with a baseline of about 200 km. During the approximately 1 h observation, we could detect 35 GPs by high-time-resolution VLBI. Moreover, we determined the dispersion measure (DM) to be 56.7585 +/- 0.0025 on the basis of the mean DM of the 35 GPs detected by VLBI. We confirmed that the sensitivity of a detection of GPs using our technique is superior to that of a single-dish mode detection using the same telescope.
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Submitted 23 May, 2016;
originally announced May 2016.
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Frequency Dependence of Polarization of Zebra Pattern in Type-IV Solar Radio Bursts
Authors:
Kazutaka Kaneda,
Hiroaki Misawa,
Kazumasa Iwai,
Fuminori Tsuchiya,
Takahiro Obara
Abstract:
We investigated the polarization characteristics of a zebra pattern (ZP) in a type-IV solar radio burst observed with AMATERAS on 2011 June 21 for the purpose of evaluating the generation processes of ZP. Analyzing highly resolved spectral and polarization data revealed the frequency dependence of the degree of circular polarization and the delay between two polarized components for the first time…
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We investigated the polarization characteristics of a zebra pattern (ZP) in a type-IV solar radio burst observed with AMATERAS on 2011 June 21 for the purpose of evaluating the generation processes of ZP. Analyzing highly resolved spectral and polarization data revealed the frequency dependence of the degree of circular polarization and the delay between two polarized components for the first time. The degree of circular polarization was 50-70 percent right-handed and it varied little as a function of frequency. Cross-correlation analysis determined that the left-handed circularly polarized component was delayed by 50-70 ms relative to the right-handed component over the entire frequency range of the ZP and this delay increased with the frequency. We examined the obtained polarization characteristics by using pre-existing ZP models and concluded that the ZP was generated by the double plasma resonance process. Our results suggest that the ZP emission was originally generated in a completely polarized state in the O-mode and was partly converted into the X-mode near the source. Subsequently, the difference between the group velocities of the O-mode and X-mode caused the temporal delay.
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Submitted 11 August, 2015;
originally announced August 2015.
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Spectral Structures and Their Generation Mechanisms for Solar Radio Type-I Bursts
Authors:
Kazumasa Iwai,
Yoshizumi Miyoshi,
Satoshi Masuda,
Fuminori Tsuchiya,
Akira Morioka,
Hiroaki Misawa
Abstract:
The fine spectral structures of solar radio type-I bursts were observed by the solar radio telescope AMATERAS. The spectral characteristics, such as the peak flux, duration, and bandwidth, of the individual burst elements were satisfactorily detected by the highly resolved spectral data of AMATEAS with the burst detection algorithm that is improved in this study. The peak flux of the type-I bursts…
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The fine spectral structures of solar radio type-I bursts were observed by the solar radio telescope AMATERAS. The spectral characteristics, such as the peak flux, duration, and bandwidth, of the individual burst elements were satisfactorily detected by the highly resolved spectral data of AMATEAS with the burst detection algorithm that is improved in this study. The peak flux of the type-I bursts followed a power-law distribution with a spectral index of 2.9-3.3, whereas their duration and bandwidth were distributed more exponentially. There were almost no correlations between the peak flux, duration, and bandwidth. That means there were no similarity shapes in the burst spectral structures. We defined the growth rate of a burst as the ratio between its peak flux and duration. There was a strong correlation between the growth rate and peak flux. These results suggest that the free energy of type-I bursts that is originally generated by non-thermal electrons is modulated in the subsequent stages of the generation of non-thermal electrons, such as plasma wave generation, radio wave emissions, and propagation. The variation of the time scale of the growth rate is significantly larger than that of the coronal environments. These results can be explained by the situation that the source region may have the inhomogeneity of an ambient plasma environment, such as the boundary of open and closed field lines, and the superposition of entire emitted bursts was observed by the spectrometer.
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Submitted 4 May, 2014;
originally announced May 2014.