Less noticeable shallow decay phase in early X-ray afterglows of GeV/TeV-detected gamma-ray bursts

Yamazaki, Ryo; Sato, Yuri; Sakamoto, T.; Serino, M.

doi:10.1093/mnras/staa1095

Cited by 11 publications

(8 citation statements)

References 76 publications

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“…Interestingly, a similar X-ray afterglow characteristic has been found for GeV-/TeV-detected GRBs(Yamazaki et al 2020). …”

supporting

confidence: 74%

Evidence of Photosphere Emission Origin for Gamma-Ray Burst Prompt Emission

Meng¹

2022

ApJS

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The physical origins of gamma-ray burst (GRB) prompt emission (photosphere or synchrotron) are still subject to debate, after more than five decades. Here, we find that many of the observed characteristics of 15 long GRBs, which have the highest prompt emission efficiency ϵ γ (ϵ γ ≳ 80%), strongly support photosphere (thermal) emission origin, in the following ways: (1) the relation between E p and E iso is almost E p ∝ ( E iso ) 1 / 4 and the dispersion is quite small; (2) the simple power-law shape of the X-ray afterglow light curves and the presence of significant reverse shock signals in the optical afterglow light curves; (3) the best fits using the cutoff power-law model for time-integrated spectra; and (4) the consistent efficiency from observations (with E iso/E k ) and the predictions from the photosphere emission model (with η/Γ). We then further investigate the characteristics of the long GRBs for two distinguished samples (ϵ γ ≳ 50% and ϵ γ ≲ 50%). It is found that the different distributions for E p and E iso, and the similar observed efficiency (from the X-ray afterglow) and theoretically predicted efficiency (from the prompt emission or the optical afterglow), follow the predictions of the photosphere emission model well. Also, based on the same efficiency, we derive an excellent correlation of Γ ∝ E iso 1 / 8 E p 1 / 2 / T 90 1 / 4 to estimate Γ. Finally, we show that different distributions for E p and E iso, and the consistent efficiency, exist for short GRBs. We also give a natural explanation of the extended emission (ϵ γ ≲ 50%) and the main pulse (ϵ γ ≳ 50%).

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“…Interestingly, a similar X-ray afterglow characteristic has been found for GeV-/TeV-detected GRBs(Yamazaki et al 2020). …”

supporting

confidence: 74%

Evidence of Photosphere Emission Origin for Gamma-Ray Burst Prompt Emission

Meng¹

2022

ApJS

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“…These arguments are consistent with earlier findings by Ref. 47 for 23 GRBs triggered by Swift -BAT and subsequently detected by Fermi -LAT 46 .…”

Section: Discussionsupporting

confidence: 93%

A wind environment and Lorentz factors of tens explain gamma-ray bursts X-ray plateau

et al. 2022

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Gamma-ray bursts (GRBs) are known to have the most relativistic jets, with initial Lorentz factors in the order of a few hundreds. Many GRBs display an early X-ray light-curve plateau, which was not theoretically expected and therefore puzzled the community for many years. Here, we show that this observed signal is naturally obtained within the classical GRB fireball model, provided that the initial Lorentz factor is rather a few tens, and the expansion occurs into a medium-low density wind. The range of Lorentz factors in GRB jets is thus much wider than previously thought and bridges an observational gap between mildly relativistic jets inferred in active galactic nuclei, to highly relativistic jets deduced in few extreme GRBs. Furthermore, long GRB progenitors are either not Wolf-Rayet stars, or the wind properties during the final stellar evolution phase are different than at earlier times. Our model has predictions that can be tested to verify or reject it in the future, such as lack of GeV emission, lack of strong thermal component and long (few seconds) variability during the prompt phase characterizing plateau bursts.

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“…The result without this flare show that the both slopes (−0.80 +0.03 −0.03 and −0.98 +0.06 −0.06 respectively with a break at 1.0 +0. 25 −0.16 × 10 4 s) are consistent with the expected slope (∼ −1.2) in a self-similar phase. This result is also consistent with a previous study in Ref.…”

Section: X-ray Data and Fitting Processessupporting

confidence: 87%

“…Slopes (−2.27 +0.07 −0.07 and −1.42 +0. 25 −0.30 with a break at 341 +31 −28 s) after these flares are very similar to the slopes found after the plateau phase. Therefore, either another flare might exist during this lack of the data or the plateau slope might be steeper with later break than T a,X defined here.…”

Section: X-ray Data and Fitting Processessupporting

confidence: 84%

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The X-ray plateau phase of gamma-ray burst originating from an expanding shell with a Lorentz factor of a few tens

Dereli-Bégué

Pe’er

Ryde

et al. 2021

Preprint

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Gamma-ray bursts (GRBs) are one of the most energetic explosions known in the Universe and are also known to have the most relativistic jets, with initial expansion Lorentz factors of $100< \Gamma_i <1000$ \cite{KP91, Fenimore+93, WL95, LS01, ZLB11, Zou+11, Racusin+11}. Many of these objects have a plateau in their early X-ray light curves (up to thousands of seconds) \cite{Nousek+06, OBrien+06, Zhang+06, Liang+07, Srinivasaragavan+20}. In this phase, the X-ray flux decreases much slower than theoretically expected \cite{MR93} which has puzzled the community for many years. Here, we show that the observed signal during this phase in both the X-ray and the optical bands is naturally obtained within the classical GRB “fireball” model, provided that (i) the initial Lorentz factor of the relativistically expanding jet is of the order of a few tens, rather than a few hundreds, as is often cited in the literature, and (ii) the expansion occurs into a medium-low density “wind” with density typically 3-4 orders of magnitude below the expectation from a Wolf-Rayet star \cite{CL99}. Within this framework, the end of the “plateau” phase (the beginning of the regular afterglow) marks the transition from the coasting phase to the self-similar expansion phase, which follows the scaling laws first derived by Blandford \& McKee.\cite{BM76}. This result therefore implies that the long GRB progenitors are either (i) not Wolf-Rayet stars, or (ii) the properties of the wind ejected by these stars prior to their final explosion are very different than the properties of the wind ejected at earlier times. This result shows that the range of Lorentz factors in GRB jets is much wider than previously thought, and bridges an observational ‘gap’ between mildly relativistic jets\cite{Ghisellini1993} inferred in active galactic nuclei, $\Gamma_i\lesssim 20$, to the much higher Lorentz factors, $\Gamma_i\lesssim 1000$ inferred in a few extreme GRBs\cite{Racusin+11}.

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Less noticeable shallow decay phase in early X-ray afterglows of GeV/TeV-detected gamma-ray bursts

Cited by 11 publications

References 76 publications

Evidence of Photosphere Emission Origin for Gamma-Ray Burst Prompt Emission

Evidence of Photosphere Emission Origin for Gamma-Ray Burst Prompt Emission

A wind environment and Lorentz factors of tens explain gamma-ray bursts X-ray plateau

The X-ray plateau phase of gamma-ray burst originating from an expanding shell with a Lorentz factor of a few tens

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