Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userLess noticeable shallow decay phase in early X-ray afterglows of GeV/TeV-detected gamma-ray bursts
70
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
The nature of the shallow decay phase in the X-ray afterglow of the gamma-ray burst (GRB) is not yet clarified. We analyze the data of early X-ray afterglows of 26 GRBs triggered by Burst Alert Telescope onboard Neil Gehrels Swift Observatory and subsequently detected by Fermi Large Area Telescope (LAT) and/or Imaging Atmospheric Cherenkov Telescopes. It is found that 9 events (including 2 out of 3 very-high-energy gamma-ray events) have no shallow decay phase and that their X-ray afterglow light curves are well described by single power-law model except for the jet break at later epoch. The rest are fitted by double power-law model and have a break in the early epoch (around ks), however, 8 events (including a very-high-energy gamma-ray event) have the pre-break decay index larger than 0.7. We also analyze the data of well-sampled X-ray afterglows of GRBs without LAT detection, and compare their decay properties with those of high-energy and very-high-energy gamma-ray events. It is found that for the GeV/TeV bursts, the fraction of events whose X-ray afterglows are described by single power-law is significantly larger than those for non GeV/TeV GRBs. Even if the GeV/TeV GRBs have shallow decay phase, their decay slope tends to be steeper than non GeV/TeV bursts, that is, they have less noticeable shallow decay phase in the early X-ray afterglow. A possible interpretation along with the energy injection model is briefly discussed.
rate research
Read More
We present a set of seventeen Gamma-Ray Bursts (GRBs) with known redshifts and X-ray afterglow emission. We apply cosmological corrections in order to compare their fluxes normalized at a redshift of 1. Two classes of GRB can be defined using their X-ray afterglow light curves. We show that the brightest afterglows seem to decay faster than the dimer ones. We also point out evidences for a possible flux limit of the X-ray afterglow depending on the time elapsed since the burst. We try to interpret these observations in the framework of the canonical fireball model of GRB afterglow emission.
The origin of the X-ray afterglows of gamma-ray bursts has regularly been debated. We fit both the fireball-shock and millisecond-magnetar models of gamma-ray bursts to the X-ray data of GRB 130603B and 140903A. We use Bayesian model selection to answer the question of which model best explains the data. This is dependent on the maximum allowed non-rotating neutron star mass $M_{textrm{TOV}}$, which depends solely on the unknown nuclear equation of state. We show that the data for GRB140903A favours the millisecond-magnetar model for all possible equations of state, while the data for GRB130603B favours the millisecond-magnetar model if $M_{textrm{TOV}} gtrsim 2.3 M_{odot}$. If $M_{textrm{TOV}} lesssim 2.3 M_{odot}$, the data for GRB130603B supports the fireball-shock model. We discuss implications of this result in regards to the nuclear equation of state and the prospect of gravitational-wave emission from newly-born millisecond magnetars.
I will review the constraints set by X-ray measurements of afterglows on several issues of GRB, with particular regard to the fireball model, the environment, the progenitor and dark GRB.
Recent analytical and numerical work argue that successful relativistic Fermi acceleration requires a weak magnetization of the unshocked plasma, all the more so at high Lorentz factors. The present paper tests this conclusion by computing the afterglow of a gamma-ray burst outflow propagating in a magnetized stellar wind using ab initio principles regarding the microphysics of relativistic Fermi acceleration. It is shown that in magnetized environments, one expects a drop-out in the X-ray band on sub-day scales as the synchrotron emission of the shock heated electrons exits the frequency band. At later times, Fermi acceleration becomes operative when the blast Lorentz factor drops below a certain critical value, leading to the recovery of the standard afterglow light curve. Interestingly, the observed drop-out bears resemblance with the fast decay found in gamma-ray bursts early X-ray afterglows.
Strong spectral softening has been revealed in the late X-ray afterglows of some gamma-ray bursts (GRBs). The scenario of X-ray scattering around circum-burst dusty medium has been supported by previous works due to its overall successful prediction of both the temporal and spectral evolution of some X-ray afterglows. To further investigate the observed feature of spectral softening, we now systematically search the X-ray afterglows detected by X-Ray Telescope (XRT) of Swift and collect twelve GRBs with significant late-time spectral softening. We find that dust scattering could be the dominant radiative mechanism for these X-ray afterglows regarding their temporal and spectral features. For some well observed bursts with high-quality data, their time-resolved spectra could be well produced within the scattering scenario by taking into account the X-ray absorption from circum-burst medium. We also find that during spectral softening the power-law index in the high energy end of the spectra does not vary much. The spectral softening is mainly manifested by the spectral peak energy continually moving to the soft end.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
