arXiv subjects

K. Hashiyama

Publications and source records attributed to K. Hashiyama.

3 recordsLinked to original sources

arXiv2025

Development of an imager with high time resolution optical photon counter

Astrophysical transient phenomena on sub-millisecond timescales, such as fast radio bursts and giant radio pulses from the Crab pulsar, have been primarily observed in radio wavebands. To investigate their origins, a photon detector with high sensitivity and high time resolution is required also in other wavelengths. Recently, we developed the Imager of MPPC-based Optical photoN counter from Yamagata (IMONY), an observation system utilizing a Geiger-mode avalanche photodiode (GAPD) as a sensor. The sensor consists of 64 pixels, each comprising a GAPD and a quenching resistor, with pixel sizes of 75, 100, 150, and 200\,$\mu$m. Each pixel signal is read out independently, enabling single-photon detection. After successfully observing the Crab pulsar using two Japanese telescopes, we upgraded the readout boards to achieve a more compact and stable system. The new system incorporates an analog application-specific integrated circuit (ASIC) developed at KEK for multi-purpose fast readout for silicon photomultipliers. This ASIC features a fast transimpedance amplifier and a comparator, independently processing 16 channels. A Global Navigation Satellite System receiver and a Field Programmable Gate Array (FPGA) provide timestamps for each detected photon with a resolution of 100 ns. The FPGA transmits the acquired data to a PC via Ethernet. This paper presents the details of the new system and the results of its initial evaluation.

astro-ph.IM↗

arXiv2023

Characterization of SiPM and development of test bench modules for the next-generation cameras for Large-Sized Telescopes for Cherenkov Telescope Array

The recent improvements in the performance of the silicon photomultipliers (SiPMs) made them attractive options as photo sensors of imaging atmospheric Cherenkov telescopes (IACTs). In fact, they are already adopted in some IACTs such as FACT and the Small-Sized Telescopes of the Cherenkov Telescope Array (CTA). However, the application to the Large-Sized Telescopes (LSTs) of CTA requires additional studies. As the pixel size of LSTs is larger than the nominal size of SiPMs, the signal from multiple sensors must be summed up. Also, the high detection efficiency of the night sky background (NSB) photons may degrade the telescope performance. To overcome this, the pulse width must be as small as 3 ns and the detection efficiency for NSB photons must be suppressed as much as possible. Heat generation and gain stabilization are also issues. We studied different types of SiPMs from Hamamatsu photonics and characterized them for the LST application, addressing the previous points. Also, to prove the SiPM performance in LST, we are developing a SiPM module which can be installed in the exisiting LST camera. Here we present the results of this evaluation and the status of the test bench module development.

astro-ph.IM↗

arXiv2022

Multi-wavelength study of the galactic PeVatron candidate LHAASO J2108+5157

LHAASO J2108+5157 is one of the few known unidentified Ultra-High-Energy (UHE) gamma-ray sources with no Very-High-Energy (VHE) counterpart, recently discovered by the LHAASO collaboration. We observed LHAASO J2108+5157 in the X-ray band with XMM-Newton in 2021 for a total of 3.8 hours and at TeV energies with the Large-Sized Telescope prototype (LST-1), yielding 49 hours of good quality data. In addition, we analyzed 12 years of Fermi-LAT data, to better constrain emission of its High-Energy (HE) counterpart 4FGL J2108.0+5155. We found an excess (3.7 sigma) in the LST-1 data at energies E > 3 TeV. Further analysis in the whole LST-1 energy range assuming a point-like source, resulted in a hint (2.2 sigma) of hard emission which can be described with a single power law with photon index Gamma = 1.6 +- 0.2 between 0.3 - 100 TeV. We did not find any significant extended emission which could be related to a Supernova Remnant (SNR) or Pulsar Wind Nebula (PWN) in the XMM-Newton data, which puts strong constraints on possible synchrotron emission of relativistic electrons. The LST-1 and LHAASO observations can be explained as inverse Compton-dominated leptonic emission of relativistic electrons with a cutoff energy of $100^{+70}_{-30}$ TeV. The low magnetic field in the source imposed by the X-ray upper limits on synchrotron emission is compatible with a hypothesis of a PWN or a TeV halo. The lack of a pulsar in the neighborhood of the UHE source is a challenge to the PWN/TeV-halo scenario. The UHE gamma rays can also be explained as $\pi^0$ decay-dominated hadronic emission due to interaction of relativistic protons with one of the two known molecular clouds in the direction of the source. The hard spectrum in the LST-1 band is compatible with protons escaping a shock around a middle-aged SNR because of their high low-energy cut-off.

astro-ph.HE↗