arXiv subjects

Min Zha

Publications and source records attributed to Min Zha.

6 recordsLinked to original sources

arXiv2026

FAST Discovery of $\mu$Jy Radio Pulsations from PSR J2238+5903, Providing a DM Distance Anchor for the Candidate TeV Halo 1LHAASO J2238+5900

We report the first detection of radio pulsations from PSR J2238+5903, a gamma-ray pulsar spatially coincident with the extended TeV source 1LHAASO J2238+5900. Our 3000 s FAST L-band observation reveals a weak periodic signal at the known Fermi-LAT spin period, with $P=162.76568$ ms and $\mathrm{DM}=247.5\pm3.0~\mathrm{pc~cm^{-3}}$. The signal is independently confirmed by both FFT-based and Fast Folding Algorithm searches. The radiometer equation gives a flux density of $S_{1250}\simeq3\,\mu$Jy, placing PSR J2238+5903 among the faintest radio-detected Fermi pulsars. Interpreting the DM with Galactic electron-density models gives $d_{\rm DM}=7.4\pm3.9$ kpc. At this distance, the LHAASO WCDA 39\% containment radius corresponds to a characteristic diameter of $\sim132$ pc, and the $>1$ TeV luminosity is $L_{\rm TeV}\simeq7.1\times10^{34}$ erg s$^{-1}$, about 8\% of the pulsar's spin-down power. The radio DM thus provides the first pulsar-specific distance constraint for assessing whether 1LHAASO J2238+5900 is a young relic-PWN / TeV-halo transition system.

astro-ph.HE↗

arXiv2024

Probing the nova shock physics with future gamma-ray observations of the upcoming outburst from T Coronae Borealis

Nova shocks behave like scaled-down supernova remnant shocks with a lifetime of only a few weeks or months, thereby providing a unique opportunity to study the dynamics of non-relativistic shocks as well as the shock acceleration physics. Recently, GeV and TeV gamma-ray emissions from an outburst of the recurrent nova RS Ophiuchi have been observed. The light curves of the gamma-ray emissions suggest that they arise from an external shock, which is formed as the nova ejecta interacts with the ambient medium. The shock is thought to transition from an adiabatic shock to a radiative one at later times, but no such later observations are available for RS Ophiuchi. The spectral evolution of the gamma-ray outburst of RS Ophiuchi was not well measured, and hence the related particle acceleration mechanisms are not well understood. T Coronae Borealis (T CrB) is another recurrent nova in Milky Way and its last outburst was nearly ten times optically brighter than RS Ophiuchi. Recently the optical light curve of T CrB displayed a state transition behavior before the eruption, and it has been predicted that T CrB will undergo an outburst in the near future. By performing a theoretical investigation, we find that Fermi-LAT could probably capture the transition of the shock from the adiabatic phase to the radiative phase at the GeV band if the ambient wind medium is dense with $A_{\star}\geq1$. Due to its higher brightness, we also find that imaging atmospheric Cherenkov telescopes such as MAGIC and VERITAS, and extensive air shower experiments such as LHAASO could detect the nova outburst and measure the gamma-ray spectrum in the very-high-energy ($>0.1\,{\rm TeV}$) band more precisely. This can be used to constrain the high-energy cutoff index in the accelerated proton spectrum and the acceleration efficiency, which will shed light on the particle acceleration physics in nova shocks.

astro-ph.HE↗

arXiv2022

A comparative study on different background estimation methods for extensive air shower arrays

Background estimation is essential when studying TeV gamma-ray astronomy for extensive air shower arrays. In this work, by applying four applying four different methods including equi-zenith angle method, surrounding window method, direct integration method, and time-swapping method, the number of the background events is calculated. Based on simulation samples, the statistical significance of the excess signal from different background estimation methods is determined. Following this, we discuss the limits and the applicability of the four methods under different conditions. Under the detector stability assumption with signal, the results from the above four methods are consistent at the 1 sigma level. In the no signal condition, when the acceptance of the detector changes with both space and time, the surrounding window method is most stable and hardly affected. In this acceptance assumption, we find that the background estimation in the direct integration and time-swapping methods are sensitive to the selection of time window, and the shorter time window can reduce the impact on the background estimation to some extent.

astro-ph.IM↗

arXiv2017

Study on single-channel signals of water Cherenkov detector array for the LHAASO

The Large High Altitude Air Shower Observatory (LHAASO) is planned to be built at Daocheng, Sichuan Province, China. The water Cherenkov detector array (WCDA), with an area of 78,000 m2 and capacity of 350,000 tons of purified water, is one of the major components of the LHAASO project. A 9-cell detector prototype array has been built at the Yangbajing site, Tibet, China to comprehensively understand the water Cherenkov technique and investigate the engineering issues of WCDA. In this paper, the rate and charge distribution of single-channel signals are evaluated using a full detail Monte Carlo simulation. The results are discussed and compared with the prototype array.

physics.ins-det↗

arXiv2017

A way to measure the water quality of the LHAASO-WCDA with cosmic muon signals

The Large High Altitude Air Shower Observatory (LHAASO) is to be built at Daocheng, Sichuan Province, China. As one of the major components of the LHAASO project, a Water Cherenkov Detector Array (WCDA), with an area of 78,000~$\rm m^{2}$, contains 350,000~tons of purified water. The water transparency and its stability are critical for successful long-term operation of this project. To gain full knowledge of the water Cherenkov technique and investigate the engineering issues, a 9-cell detector array has been built at the Yangbajing site, Tibet, China. With the help of the distribution of single cosmic muon signals, the monitoring and measurement of water transparency are studied. The results show that a precision of several percent can be obtained for the attenuation length measurement, which satisfies the requirements of the experiment. In the near future, this method could be applied to the LHAASO-WCDA project.

physics.ins-det↗

arXiv2002

Temporal and Spectral Properties of Gamma-Ray Flashes

The temporal and spectral properties of terrestrial gamma-ray flashes (TGFs) are studied. The delay of low energy photons relative to high energy ones in the gamma-ray variations of the TGFs with high signal to noise ratio has been revealed by an approach of correlation analysis in the time domain on different time scales. The temporal structures of the TGFs in high energy band are usually narrower than that in low energy band. The spectral hardness has a general trend of decreasing with time in a flash. The observed temporal and spectral characteristics give constraints and valuable hints on the flash production mechanism.

astro-ph↗