Open questions in GRB physics

Zhang, Bing

doi:10.1016/j.crhy.2011.03.004

Cited by 121 publications

(95 citation statements)

References 353 publications

(551 reference statements)

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“…Gamma-ray bursts (GRBs) are highly energetic events that often are brighter than all other γ-ray objects visible on the sky combined, with an emission peak in the 200-500 keV region (for recent reviews, see Nakar 2007;Zhang 2011;Gehrels & Razzaque 2013;Berger 2014;Mészáros & Rees 2015). GRBs were detected by military satellites Vela in late 1960's.…”

Section: Introductionmentioning

confidence: 99%

Distinguishing short and longFermigamma-ray bursts

Tarnopolski

2015

Mon. Not. R. Astron. Soc.

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Two classes of gamma-ray bursts (GRBs), short and long, have been determined without any doubts, and are usually ascribed to different progenitors, yet these classes overlap for a variety of descriptive parameters. A subsample of 46 long and 22 short Fermi GRBs with estimated Hurst Exponents (HEs), complemented by minimum variability time-scales (MVTS) and durations (T 90 ) is used to perform a supervised Machine Learning (ML) and Monte Carlo (MC) simulation using a Support Vector Machine (SVM) algorithm. It is found that while T 90 itself performs very well in distinguishing short and long GRBs, the overall success ratio is higher when the training set is complemented by MVTS and HE. These results may allow to introduce a new (non-linear) parameter that might provide less ambiguous classification of GRBs.

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Section: Introductionmentioning

confidence: 99%

Distinguishing short and longFermigamma-ray bursts

Tarnopolski

2015

Mon. Not. R. Astron. Soc.

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“…The central engine of GRBs remains an open question (Zhang 2011). A hyper-accreting stellar-mass black hole (BH) or a millisecond magnetar (Usov 1992;Dai & Lu 1998;Zhang & Mészáros 2001;Metzger et al 2011) is usually invoked as possible GRB central engine.…”

Section: Introductionmentioning

confidence: 99%

Central Engine of Late-Time X-Ray Flares With Internal Origin

Hou

et al. 2016

ApJ

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This work focuses on a sample of seven extremely late-time X-ray flares with peak time t p > 10 4 s, among which two flares can be confirmed as the late-time activity of central engine. The main purpose is to investigate the mechanism of such late-time flares based on the internal origin assumption. In the hyper-accreting black hole (BH) scenario, we study the possibility of two well-known mechanisms as the central engine to power such X-ray flares, i.e., the neutrino-antineutrino annihilation and the Blandford-Znajek (BZ) process. Our results show that the annihilation luminosity is far below the observational data. Thus, the annihilation mechanism cannot account for such late-time flares. For the BZ process, if the role of outflows is taken into consideration, the inflow mass rate near the horizon will be quite low such that the magnetic field will probably be too weak to power the observed X-ray flares. We therefore argue that, for the late-time flares with internal origin, the central engine is unlikely to be associated with BHs. On the contrary, a fast rotating neutron star with strong bipolar magnetic fields may be responsible for such flares.

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“…Zhang (2011) proposed that more observational properties, namely redshift, fluence, flux, E peak of the υf υ spectrum and etc., should be taken into account together. Meanwhile, SGRBs usually have harder spectra than LGRBs (Kouveliotou et al 1993;Zhang & Choi 2008), the clustering phenomenon in the plane of duration versus harness ratio (T 90 vs HR) should also be useful to classify the GRBs.…”

Section: Introductionmentioning

confidence: 99%

Two dimensional classification of the Swift/BAT GRBs

Yang¹,

Zhang²,

Jiang³

2016

Astrophys Space Sci

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Using Gaussian Mixture Model and Expectation Maximization algorithm, we have performed a density estimation in the framework of T 90 versus hardness ratio for 296 Swift/BAT GRBs with known redshift. Here, Bayesian Information Criterion has been taken to compare different models. Our investigations show that two instead of three or more Gaussian components are favoured in both the observer and rest frames. Our key findings are consistent with some previous results.

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Open questions in GRB physics

Cited by 121 publications

References 353 publications

Distinguishing short and longFermigamma-ray bursts

Distinguishing short and longFermigamma-ray bursts

Central Engine of Late-Time X-Ray Flares With Internal Origin

Two dimensional classification of the Swift/BAT GRBs

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