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Investigating the Evolution of Amati Parameters with Redshift

Research in Astronomy and Astrophysics 2024年第1期24卷 188-200页

作者： Meghendra Singh Darshan Singh Kanhaiya Lal Pandey Dinkar Verma Shashikant Gupta Delhi Metro Rail Corporation Limited New Delhi 110001India GD Goenka University Gurugram 122103India Department of Physics Mata Raj Kaur Institute of Engineering and TechnologyRewari 123401India Department of Physics School of Advanced SciencesVellore Institute of TechnologyVellore 632014India

gamma-ray bursts(GRBs) are among the brightest objects in the Universe and, hence, can be observed up to a very high redshift. Properly calibrated empirical correlations between intensity and spectral correlations of GRBs can be used to estimate the cosmological parameters. However, the possibility of the evolution of GRBs with redshift is a long-standing puzzle. In this work, we used 162 long-duration GRBs to determine whether GRBs below and above a certain redshift have different properties. The GRBs are split into two groups, and we fit the Amati relation for each group separately. Our findings demonstrate that estimations of the Amati parameters for the two groups are substantially dissimilar. We perform simulations to investigate whether the selection effects could cause the difference. Our analysis shows that the differences may be either intrinsic or due to systematic errors in the data, and the selection effects are not their true origin. However, in-depth analysis with a new data set comprised of 119 long GRBs shows that intrinsic scatter may partly be responsible for such effects.

关键词： Cosmology gamma rays:general (cosmology:)large-scale structure of universe galaxies:high-redshift

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The GeV emission of PSR B1259–63 during its last three periastron passages observed by Fermi-LAT

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Research in Astronomy and Astrophysics 2018年第12期18卷 89-94页

作者： Zhi Chang Shu Zhang Yu-Peng Chen Long Ji Ling-Da Kong Cong-Zhan Liu Key Laboratory of Particle Astrophysics Institute of High Energy PhysicsChinese Academy of SciencesBeijing 100049China Institut fur Astronomie und Astrophysik Kepler Center for Astro and Particle PhysicsEberhard Karls UniversitatSand 172076 TubingenGermany University of Chinese Academy of Sciences Beijing 100049China

PSR B1259–63 is a γ-ray emitting high mass X-ray binary system, in which the compact object is a millisecond pulsar.The system has an orbital period of 1236.7 d and shows peculiar γ-ray flares when the neutron star moves out of the stellar disk of the companion star.The γ-ray flare events were firstly discovered by using Fermi-LAT around the 2010 periastron passage, which was repeated for the 2014 and 2017 periastron passages.We analyze the Fermi-LAT data for all the three periastron passages and found that in each flare the energy spectrum can be represented well by a simple power law.The γ-ray light curves show that in 2010 and 2014 after each periastron there are two main flares,but in 2017 there are four flares including one precursor about 10 d after the periastron passage.The first main flares in 2010 and 2014 are located at around 35 d after the periastron passage, and the main flare in 2014 is delayed by roughly 1.7 d with respect to that in 2010.In the 2017 flare, the source shows a precursor about 10 d after the periastron passage, but the following two flares become weaker and lag behind those in 2010 by roughly 5 d.The strongest flares in 2017 occurred 58 d and 70 d after the periastron passage.These results challenge the previous models.

关键词： binaries:general pulsars:general gamma rays:general

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A diagnostic of the orbital spectrum of LS 5039 with Fermi-LAT

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Research in Astronomy and Astrophysics 2019年第12期19卷 281-286页

作者： Zhi Chang Shu Zhang Yu-Peng Chen Long Ji Ling-Da Kong Key Laboratory of Particle Astrophysics Institute of High Energy PhysicsChinese Academy of SciencesBejjing 100049China University of Chinese Academy of Sciences Beijing 100049China Institut fur Astronomie und Astrophysik Kepler Center for Astro and Particle PhysicsEberhard Karls UniversitatSand 172076 TibingenGermany

LS 5039 is a well-known γ-ray binary system which consists of an unknown compact object and a massive companion O star. It shows rather stable emissions at high energies over years and hence serves as an ideal laboratory to investigate the emission mechanism for such peculiar systems which emit prominent γ-rays. To this end, we take the orbital phase resolved energy spectrum as observed by Fermi-LAT over 10 years. We divide the orbit into four orbital phases, each with an orbital phase range of 0.25,centered at 0.00, 0.25, 0.50 and 0.75 respectively, where the phase 0.0 is the periastron and phase 0.5 is the apastron. The phases around 0.25 and 0.75 are symmetric and hence are supposed to have identical local acceleration environment. The spectral analysis shows that the Fermi-LAT spectra are largely different from these two symmetric orbital phases: the emission from orbital phase 0.25 turns out to be significantly stronger than that from 0.75. This result does not fit a scenario that γ-rays are Doppler boosted emission from bow shock tails if LS 5039 has a shock configuration similar to PSR B1259-63, and indicates that the inverse Compton scatterings between the shock accelerated plasma and the stellar particle environment is the underline procedure. We also find that the previous report for a disappearance of the orbital modulation at 3–20 GeV is due to the similar spectral turn-over energies of the different orbital phases. The spectral properties of periastron and apastron regions are addressed in the context of the measurements in phase regions around 0.25 and 0.75.

关键词： binaries:general gamma rays:general

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