MG15 - Talk detail |
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Participant |
Zhang, Binbin | |||||||
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Institution |
Nanjing University - Xianlin Road - Nanjing - Jiangsu - China | |||||||
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Session |
GB4 |
Accepted |
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Time |
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Talk |
Oral abstract |
Title |
Transition from fireball to Poynting-flux-dominated outflow in the three-episode GRB 160625B | |||||
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Abstract |
The ejecta composition is an open question in gamma-ray bursts (GRB) physics. Some GRBs possess a quasi-thermal spectral component in the time-resolved spectral analysis, suggesting a hot fireball origin. Others show a featureless non-thermal spectrum known as the "Band" function, consistent with a synchrotron radiation origin and suggesting that the jet is Poynting-flux-dominated at the central engine and likely in the emission region as well. There are also bursts showing a sub-dominant thermal component and a dominant synchrotron component suggesting a likely hybrid jet composition. Here we report an extraordinarily bright GRB 160625B, simultaneously observed in gamma-rays and optical wavelengths, whose prompt emission consists of three isolated episodes separated by long quiescent intervals, with the durations of each "sub-burst" being ∼ 0.8 s, 35 s, and 212 s, respectively. Its high brightness (with isotropic peak luminosity Lp,iso∼4×1053 erg/s) allows us to conduct detailed time-resolved spectral analysis in each episode, from precursor to main burst and to extended emission. The spectral properties of the first two sub-bursts are distinctly different, allowing us to observe the transition from thermal to non-thermal radiation between well-separated emission episodes within a single GRB. Such a transition is a clear indication of the change of jet composition from a fireball to a Poynting-flux-dominated jet. |
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Pdf file |
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Session |
GB7 |
Accepted |
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Oral abstract |
Title |
A peculiar low-luminosity short gamma-ray burst from a double neutron star merger progenitor | |||||
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Abstract |
Double neutron star (DNS) merger events are promising candidates of short gamma-ray burst (sGRB) progenitors as well as high-frequency gravitational wave (GW) emitters. On August 17, 2017, such a coinciding event was detected by both the LIGO-Virgo gravitational wave detector network as GW170817 and Gamma-Ray Monitor on board NASA's Fermi Space Telescope as GRB 170817A. Here, we show that the fluence and spectral peak energy of this sGRB fall into the lower portion of the distributions of known sGRBs. Its peak isotropic luminosity is abnormally low. The estimated event rate density above this luminosity is at least 19 0-160+440 Gpc-3 yr-1, which is close to but still below the DNS merger event rate density. This event likely originates from a structured jet viewed from a large viewing angle. There are similar faint soft GRBs in the Fermi archival data, a small fraction of which might belong to this new population of nearby, low-luminosity sGRBs. |
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Pdf file |
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Session |
GB8 |
Accepted |
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Order |
Time |
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Talk |
Oral abstract |
Title |
Transition from Fireball to Poynting-flux-dominated Outflow in Three-Episode GRB 160625B | |||||
| Coauthors | ||||||||
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Abstract |
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Pdf file |
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