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The performance of the TA$\times$4 surface detector array: 4.3 years of the first-half expansion
Authors:
Telescope Array Collaboration,
R. U. Abbasi,
T. Abu-Zayyad,
M. Allen,
J. W. Belz,
D. R. Bergman,
F. Bradfield,
I. Buckland,
W. Campbell,
B. G. Cheon,
K. Endo,
A. Fedynitch,
T. Fujii,
K. Fujisue,
K. Fujita,
M. Fukushima,
G. Furlich,
A. Gálvez Ureña,
Z. Gerber,
N. Globus,
T. Hanaoka,
W. Hanlon,
N. Hayashida,
H. He,
K. Hibino
, et al. (105 additional authors not shown)
Abstract:
The Telescope Array (TA) experiment aims to reveal the origin of ultra-high-energy cosmic rays (UHECRs) by observing air showers using surface detectors (SDs), which spread over an area of approximately 700 km$^2$, and fluorescence detectors (FDs) viewing the skies above the SD array. The TA experiment has been observing UHECRs since 2008, and has reported an indication of clustering in the arriva…
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The Telescope Array (TA) experiment aims to reveal the origin of ultra-high-energy cosmic rays (UHECRs) by observing air showers using surface detectors (SDs), which spread over an area of approximately 700 km$^2$, and fluorescence detectors (FDs) viewing the skies above the SD array. The TA experiment has been observing UHECRs since 2008, and has reported an indication of clustering in the arrival directions of cosmic-ray events with energy greater than 57 EeV. To improve the exposure for anisotropy studies of UHECRs, the TA$\times$4 upgrade was designed to expand the observational area by approximately 2,000 km$^2$ with 500 additional SDs. Half of the planned upgrade, consisting of 257 SDs, was completed, and the newly installed array began operation in 2019. In addition to the expanded SD array, two FD stations were constructed for the TA$\times$4 experiment. In this paper, we present a study of the performance of the expanded SD array, including the energy resolution, angular resolution, and effective aperture, over the first 4.3 years of data acquisition. While the effective aperture varied initially due to changing detector states, it has stabilized since June 2023 with more than 90% operational SDs. Furthermore, a new inter-tower trigger system was implemented to connect six new communication towers to form two geographically separated arrays, increasing the effective aperture. The time variation of this effective aperture, the resulting total exposure of approximately 3,500 km$^2$ sr yr, and a comparison with the original TA SD array are presented to demonstrate the performance of the expanded array.
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Submitted 23 August, 2026; v1 submitted 26 June, 2026;
originally announced June 2026.
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Relativistic Jets and Winds in Radio-Identified Supermassive Black Hole Binary Candidates
Authors:
Andrew G. Sullivan,
Roger D. Blandford,
Anna Synani,
Philipe V. de la Parra,
Noémie Globus,
Mitchell C. Begelman,
Anthony C. S. Readhead
Abstract:
Supermassive black hole binary systems (SMBHBs) are thought to emit the recently discovered nHz gravitational wave background; however, not a single individual nHz source has been confirmed to date. Long-term radio-monitoring at the Owens Valley Radio Observatory has revealed two potential SMBHB candidates: blazars PKS 2131-021 and PKS J0805-0111. These sources show periodic flux density variation…
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Supermassive black hole binary systems (SMBHBs) are thought to emit the recently discovered nHz gravitational wave background; however, not a single individual nHz source has been confirmed to date. Long-term radio-monitoring at the Owens Valley Radio Observatory has revealed two potential SMBHB candidates: blazars PKS 2131-021 and PKS J0805-0111. These sources show periodic flux density variations across the electromagnetic spectrum, signaling the presence of a good clock. To explain the emission, we propose a generalizable jet model, where a mildly relativistic wind creates an outward-moving helical channel, along which the ultra-relativistic jet propagates. The observed flux variation from the jet is mostly due to aberration. The emission at lower frequency arises at larger radius and its variation is consequently delayed, as observed. Our model reproduces the main observable features of both sources and can be applied to other sources as they are discovered. We make predictions for radio polarization, direct imaging, and emission line variation, which can be tested with forthcoming observations. Our results motivate future numerical simulations of jetted SMBHB systems and have implications for the fueling, structure, and evolution of blazar jets.
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Submitted 25 November, 2025; v1 submitted 2 October, 2025;
originally announced October 2025.
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First High-speed Video Camera Observations of a Lightning Flash Associated with a Downward Terrestrial Gamma-ray Flash
Authors:
R. U. Abbasi,
M. M. F. Saba,
J. W. Belz,
P. R. Krehbiel,
W. Rison,
N. Kieu,
D. R. da Silva,
Dan Rodeheffer,
M. A. Stanley,
J. Remington,
J. Mazich,
R. LeVon,
K. Smout,
A. Petrizze,
T. Abu-Zayyad,
M. Allen,
Y. Arai,
R. Arimura,
E. Barcikowski,
D. R. Bergman,
S. A. Blake,
I. Buckland,
B. G. Cheon,
M. Chikawa,
T. Fujii
, et al. (127 additional authors not shown)
Abstract:
In this paper, we present the first high-speed video observation of a cloud-to-ground lightning flash and its associated downward-directed Terrestrial Gamma-ray Flash (TGF). The optical emission of the event was observed by a high-speed video camera running at 40,000 frames per second in conjunction with the Telescope Array Surface Detector, Lightning Mapping Array, interferometer, electric-field…
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In this paper, we present the first high-speed video observation of a cloud-to-ground lightning flash and its associated downward-directed Terrestrial Gamma-ray Flash (TGF). The optical emission of the event was observed by a high-speed video camera running at 40,000 frames per second in conjunction with the Telescope Array Surface Detector, Lightning Mapping Array, interferometer, electric-field fast antenna, and the National Lightning Detection Network. The cloud-to-ground flash associated with the observed TGF was formed by a fast downward leader followed by a very intense return stroke peak current of -154 kA. The TGF occurred while the downward leader was below cloud base, and even when it was halfway in its propagation to ground. The suite of gamma-ray and lightning instruments, timing resolution, and source proximity offer us detailed information and therefore a unique look at the TGF phenomena.
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Submitted 9 August, 2023; v1 submitted 10 May, 2022;
originally announced May 2022.
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Observation of Variations in Cosmic Ray Single Count Rates During Thunderstorms and Implications for Large-Scale Electric Field Changes
Authors:
R. U. Abbasi,
T. Abu-Zayyad,
M. Allen,
Y. Arai,
R. Arimura,
E. Barcikowski,
J. W. Belz,
D. R. Bergman,
S. A. Blake,
I. Buckland,
R. Cady,
B. G. Cheon,
J. Chiba,
M. Chikawa,
T. Fujii,
K. Fujisue,
K. Fujita,
R. Fujiwara,
M. Fukushima,
R. Fukushima,
G. Furlich,
N. Globus,
R. Gonzalez,
W. Hanlon,
M. Hayashi
, et al. (140 additional authors not shown)
Abstract:
We present the first observation by the Telescope Array Surface Detector (TASD) of the effect of thunderstorms on the development of cosmic ray single count rate intensity over a 700 km$^{2}$ area. Observations of variations in the secondary low-energy cosmic ray counting rate, using the TASD, allow us to study the electric field inside thunderstorms, on a large scale, as it progresses on top of t…
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We present the first observation by the Telescope Array Surface Detector (TASD) of the effect of thunderstorms on the development of cosmic ray single count rate intensity over a 700 km$^{2}$ area. Observations of variations in the secondary low-energy cosmic ray counting rate, using the TASD, allow us to study the electric field inside thunderstorms, on a large scale, as it progresses on top of the 700 km$^{2}$ detector, without dealing with the limitation of narrow exposure in time and space using balloons and aircraft detectors. In this work, variations in the cosmic ray intensity (single count rate) using the TASD, were studied and found to be on average at the $\sim(0.5-1)\%$ and up to 2\% level. These observations were found to be both in excess and in deficit. They were also found to be correlated with lightning in addition to thunderstorms. These variations lasted for tens of minutes; their footprint on the ground ranged from 6 to 24 km in diameter and moved in the same direction as the thunderstorm. With the use of simple electric field models inside the cloud and between cloud to ground, the observed variations in the cosmic ray single count rate were recreated using CORSIKA simulations. Depending on the electric field model used and the direction of the electric field in that model, the electric field magnitude that reproduces the observed low-energy cosmic ray single count rate variations was found to be approximately between 0.2-0.4 GV. This in turn allows us to get a reasonable insight on the electric field and its effect on cosmic ray air showers inside thunderstorms.
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Submitted 18 November, 2021;
originally announced November 2021.
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Polarized muons and the origin of biological homochirality
Authors:
Noemie Globus,
Roger D. Blandford,
Anatoli Fedynitch
Abstract:
While biologists have not yet reached a consensus on the definition of life, homochirality - the specific molecular handedness of biomolecules - is a phenomenon only produced by life. The unraveling of its origin requires interdisciplinary research, by exploring fundamental physics, chemistry, astrophysics and biology. Here, we consider the origin of biological homochirality in the context of astr…
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While biologists have not yet reached a consensus on the definition of life, homochirality - the specific molecular handedness of biomolecules - is a phenomenon only produced by life. The unraveling of its origin requires interdisciplinary research, by exploring fundamental physics, chemistry, astrophysics and biology. Here, we consider the origin of biological homochirality in the context of astrophysics and particle physics. The weak force, one of the fundamental forces operating in nature, is parity-violating. On Earth, at ground level, most of our cosmic radiation dose comes from polarized muons formed in a decay involving the weak force. We discuss how the magnetic polarization is transmitted in cosmic showers within several different environments which are prime targets in the search for the origin of life. We consider how this polarization could have induced a biological preference for one type of chirality over the other, and discuss the implications for the search of life in other worlds.
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Submitted 16 September, 2021;
originally announced October 2021.
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Cosmic Rays and the Chiral Puzzle of Life
Authors:
Noemie Globus,
Roger D. Blandford
Abstract:
Living organisms exhibit consistent homochirality. It is argued that the specific, binary choice made is not an accident but is a consequence of parity violation in the weak interaction expressed by cosmic irradiation. The secondary muons and pairs are spin- and magnetic moment- polarized and may introduce a small, net chiral preference when they interact electromagnetically or quantum mechanicall…
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Living organisms exhibit consistent homochirality. It is argued that the specific, binary choice made is not an accident but is a consequence of parity violation in the weak interaction expressed by cosmic irradiation. The secondary muons and pairs are spin- and magnetic moment- polarized and may introduce a small, net chiral preference when they interact electromagnetically or quantum mechanically with molecules that have made the transition to self-replication. Although this preference is likely to be very small, it may suffice to give a chirally-dominant outcome after billions of replications, especially if combined with chirally-unbiased conflict between the two choices. Examples of mechanisms that can manifest the three essential steps of polarization, preference and domination are presented and some variations and possible implications are discussed.
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Submitted 30 October, 2019;
originally announced November 2019.