Diffusive photospheres in gamma-ray bursts

Vereshchagin, Gregory; Siutsou, I. A.

doi:10.1093/mnras/staa868

“…Indeed, based on spectral analysis, a quasi-thermal component has been found in several Swift GRBs (Ryde 2004(Ryde , 2005Ryde & Pe'er 2009) and Fermi GRBs (Guiriec et al 2011;Axelsson et al 2012;Ghirlanda et al 2013;Guiriec et al 2013;Larsson et al 2015;Tang et al 2021;Deng et al 2022;Wang et al 2022;Zhao et al 2022), especially GRB 090902B (Abdo et al 2009;Ryde et al 2010;Zhang 2011). But whether the typically observed Band function (a smoothly joint broken power law; Band et al 1993) or a cutoff power law (CPL) can be explained by the photosphere emission-namely, by the photospheric emission model-remains unknown (e.g., Abramowicz et al 1991;Thompson 1994;Mészáros & Rees 2000;Rees & Mészáros 2005;Pe'er & Ryde 2011;Fan et al 2012;Lazzati et al 2013;Ruffini et al 2013;Bégué & Pe'er 2015;Gao et al 2015;Pe'er et al 2015;Ryde et al 2017;Acuner & Ryde 2018;Hou et al 2018;Meng et al 2018;Li 2019aLi , 2019bMeng et al 2019;Acuner et al 2020;Dereli-Bégué et al 2020;Li 2020;Vereshchagin & Siutsou 2020;…”

Section: Introductionmentioning

confidence: 99%

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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“…Indeed, based on the spectral analysis, a quasi-thermal component has been found in several Swift GRBs (Ryde 2004(Ryde , 2005Ryde & Pe'er 2009) and Fermi GRBs (Guiriec et al 2011(Guiriec et al , 2013Axelsson et al 2012;Ghirlanda et al 2013;Larsson et al 2015), especially in GRB 090902B (Abdo et al 2009;Ryde et al 2010;Zhang 2011). But whether the typical observed Band function (smoothly joint broken power law) (Band et al 1993) or cutoff power law can be explained by the photosphere emission, namely the photospheric emission model, remains unknown (e.g., Abramowicz et al 1991;Thompson 1994;Mészáros & Rees 2000;Rees & Mészáros 2005;Pe'er & Ryde 2011;Fan et al 2012;Lazzati et al 2013;Ruffini et al 2013;Gao et al 2015;Bégué & Pe'er 2015;Pe'er et al 2015;Ryde et al 2017;Acuner & Ryde 2018;Hou et al 2018;Meng et al 2018Meng et al , 2019Meng et al , 2022Li 2019aLi ,c, 2020Acuner et al 2020;Dereli-Bégué et al 2020;Vereshchagin & Siutsou 2020;Wang et al 2020;Parsotan & Lazzati 2022;Song & Meng 2022). If this scenario is true, the quasi-thermal spectrum should be broadened.…”

Section: Introductionmentioning

confidence: 99%

Evidences of the Photosphere Emission Origin for the Gamma-ray Burst Prompt Emission

Meng¹

2022

Preprint

0

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The physical origin of gamma-ray burst (GRB) prompt emission is still subject to debate after five decades (photosphere or synchrotron). Here, firstly we find that many observed characteristics of 15 long GRBs, which have the highest prompt emission efficiency γ ( γ 80%), strongly support the photosphere (thermal) emission origin: (1) The relation between E p and E iso is almost, and the dispersion is quite small. (2) The simple power-law shape of the X-ray afterglow light curves and the significant reverse shock signals in the optical afterglow light curves. (3) Best-fitted by the cutoff power-law model for the time-integrated spectrum. (4) The consistent efficiency from observation (with E iso /E k ) and the prediction of photosphere emission model (with η/Γ). Then, we further investigate the characteristics of the long GRBs for two distinguished samples ( γ 50% and 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) well follow the prediction of photosphere emission model. Also, based on the same efficiency, we derive an excellent correlation of Γ ∝ E 1/8 iso E 1/2 p /(T 90 ) 1/4 to estimate Γ. Finally, the different distributions for E p and E iso , and the consistent efficiency exist for the short GRBs. Besides, we give a natural explanation of the extended emission ( γ 50%) and the main pulse ( γ 50%).

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“…The reader interested in the derivation in other regimes relevant for GRBs is refered toBégué & Iyyani (2014);Vereshchagin & Siutsou (2020) andZhang et al (2021).…”

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confidence: 99%

Is magnetically dominated outflow required to explain GRBs?

Vereshchagin,

Li,

Bégué

2022

Preprint

0

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The composition of relativistic outflows producing gamma-ray bursts is a long standing open question. One of the main arguments in favor of magnetically dominated outflows is the absence of photospheric component in their broadband time resolved spectra, with such notable example as GRB 080916C. Here, we perform a time-resolved analysis of this burst and confirm the previous detection of an additional spectral component. We show that this subdominant component is consistent with the photosphere of ultrarelativistic baryonic outflow, deep in the coasting regime. We argue that, contrary to previous statements, the magnetic dominance of the outflow is not required for the interpretation of this GRB. Moreover, simultaneous detection of high energy emission in its prompt phase requires departure from a one-zone emission model.

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Diffusive photospheres in gamma-ray bursts

Cited by 6 publications

References 49 publications

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

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

Evidences of the Photosphere Emission Origin for the Gamma-ray Burst Prompt Emission

Is magnetically dominated outflow required to explain GRBs?

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