Grb110721a: An Extreme Peak Energy and Signatures of the Photosphere

Axelsson, M.; Baldini, Luca; Barbiellini, G.; Baring, Matthew G.; Bellazzini, R.; Bregeon, J.; Brigida, M.; Bruel, Pascal; Buehler, R.; Caliandro, G. A.; Cameron, R. A.; Caraveo, P. A.; Cecchi, C.; Chaves, R. C. G.; Chekhtman, A.; Chiang, J.; Claus, R.; Conrad, J.; Cutini, S.; D’Ammando, F.; Palma, F. de; Dermer, C. D.; Silva, E. do Couto e; Drell, P. S.; Favuzzi, C.; Fegan, S. J.; Ferrara, E. C.; Focke, W. B.; Fukazawa, Yasushi; Fusco, P.; Gargano, F.; Gasparrini, D.; Gehrels, N.; Germani, S.; Giglietto, N.; Giroletti, M.; Godfrey, G.; Guiriec, S.; Hadasch, D.; Hanabata, Y.; Hayashida, M.; Hou, X.; Iyyani, Shabnam; Jackson, M. S.; Kocevski, D.; Kuss, M.; Larsson, Josefin; Larsson, Stefan; Longo, F.; Loparco, F.; Lundman, Christoffer; Mazziotta, M. N.; McEnery, J. E.; Mizuno, T.; Monzani, M. E.; Moretti, E.; Morselli, A.; Murgia, S.; Nuss, E.; Nymark, Tanja; Ohno, M.; Omodei, N.; Pesce-Rollins, M.; Piron, F.; Pivato, G.; Racusin, J. L.; Rainò, S.; Razzano, M.; Razzaque, S.; Reimer, A.; Roth, M.; Ryde, F.; Sánchez, David; Sgrò, C.; Siskind, E. J.; Spandre, G.; Spinelli, P.; Stamatikos, M.; Tibaldo, L.; Tinivella, M.; Usher, T.; Vandenbroucke, J.; Vasileiou, V.; Vianello, G.; Vitale, V.; Waite, A. P.; Winer, B. L.; Wood, K. S.; Burgess, J. Michael; Bhat, P. N.; Bissaldi, E.; Briggs, M. S.; Connaughton, V.; Fishman, G. J.; Fitzpatrick, G.; Foley, S.; Gruber, D.; Kippen, R. M.; Kouveliotou, C.; Jenke, P.; McBreen, S.; McGlynn, S.; Meegan, C.; Pačiesas, W. S.; Pelassa, V.; Preece, R.; Tierney, D.; Kienlin, A. von; Wilson-Hodge, C.; Xiong, S. L.; Pe’er, Asaf

doi:10.1088/2041-8205/757/2/l31

Cited by 168 publications

(141 citation statements)

References 34 publications

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“…Most importantly, the spectral shape of a photosphere, suffering dissipation below the photosphere, and a pure synchrotron emission spectrum can resemble each other to such a degree that the available γ-ray observations cannot clearly distinguish between them. In addition, the individual emission components can both be present in the observed spectrum, creating the possibility of misinterpreting the observations, if not all components are sought for (e.g., Ryde 2005;Axelsson et al 2012;Guiriec et al 2015). Finally, in addition to the prompt emission, an afterglow component is observed to coexist in some bursts (e.g., Fraija et al 2017;Ajello et al 2019a).…”

Section: Introductionmentioning

confidence: 99%

The Fraction of Gamma-Ray Bursts with an Observed Photospheric Emission Episode

Acuner

Ryde

Pe’er

et al. 2020

ApJ

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There is no complete description of the emission physics during the prompt phase in gamma-ray bursts. Spectral analyses, however, indicate that many spectra are narrower than what is expected for non-thermal emission models. Here, we reanalyse the sample of 37 bursts in Yu et al. (2019), by fitting the narrowest time-resolved spectrum in each burst. We perform model comparison between a photospheric and a synchrotron emission model based on Bayesian evidence. We choose to compare the shape of the narrowest expected spectra: emission from the photosphere in a non-dissipative flow and slow-cooled synchrotron emission from a narrow electron distribution. We find that the photospheric spectral shape is preferred by 54 ± 8% of the spectra (20/37), while 38 ± 8% of the spectra (14/37) prefer the synchrotron spectral shape; three spectra are inconclusive. We hence conclude that GRB spectra are indeed very narrow and that more than half of the bursts have a photospheric emission episode. We also find that a third of all analysed spectra, not only prefer, but are also compatible with a non-dissipative photosphere, confirming previous similar findings.Furthermore, we notice that the spectra, that prefer the photospheric model, all have a low-energy power-law indices α −0.5. This means that α is a good estimator of which model is preferred by the data.Finally, we argue that the spectra which statistically prefer the synchrotron model, could equally well be caused by subphotospheric dissipation. If that is the case, photospheric emission during the early, prompt phase would be even more dominant.

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Section: Introductionmentioning

confidence: 99%

The Fraction of Gamma-Ray Bursts with an Observed Photospheric Emission Episode

Acuner

Ryde

Pe’er

et al. 2020

ApJ

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“…Photospheric emission, which is inherently present in the fireball model, was thus invoked to resolve some of these issues. Studies conducted by Ryde 2005;Ryde & Pe'er 2009, Ryde et al 2010Guiriec et al 2011;Axelsson et al 2012, Iyyani et al 2013, Iyyani et al 2015and Acuner et al 2019 found that many GRBs were best modelled using a combination of thermal (blackbody function) and non-thermal (power law, Band function (Band et al 1993) or synchrotron) spectral functions. These detections also supported the idea that within the picture of classical fireball model, the thermal emission from the photosphere can be either subdominant or sometimes dominant depending on how much adiabatic cooling the outflow has undergone in the coasting phase before it reaches the photosphere.…”

Section: Introductionmentioning

confidence: 99%

Spectropolarimetric analysis of prompt emission of GRB 160325A: jet with evolving environment of internal shocks

Sharma

Iyyani

Bhattacharya

et al. 2020

Monthly Notices of the Royal Astronomical Society

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GRB 160325A is the only bright burst detected by AstroSat CZT Imager in its primary field of view to date. In this work, we present the spectral and polarimetric analysis of the prompt emission of the burst using AstroSat, Fermi and Niel Gehrels Swift observations. The prompt emission consists of two distinct emission episodes separated by a few seconds of quiescent/ mild activity period. The first emission episode shows a thermal component as well as a low polarisation fraction of PF < 37 % at 1.5 σ confidence level. On the other hand, the second emission episode shows a non-thermal spectrum and is found to be highly polarised with PF > 43 % at 1.5σ confidence level. We also study the afterglow properties of the jet using Swift/XRT data. The observed jet break suggests that the jet is pointed towards the observer and has an opening angle of 1.2 • for an assumed redshift, z = 2. With composite modelling of polarisation, spectrum of the prompt emission and the afterglow, we infer that the first episode of emission originates from the photosphere with localised dissipation happening below it, and the second from the optically thin region above the photosphere. The photospheric emission is generated mainly by inverse Compton scattering, whereas the emission in the optically thin region is produced by the synchrotron process. The low radiation efficiency of the burst suggests that the outflow remains baryonic dominated throughout the burst duration with only a subdominant Poynting flux component, and the kinetic energy of the jet is likely dissipated via internal shocks which evolves from an optically thick to optically thin environment within the jet.

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“…This was later confirmed. 4,12,14,[24][25][26]28,35 Multiple spectral breaks in GRB spectra had been claimed even earlier. For instance, using data from the PHEBUS experiment, Barat et al (1998) found that, apart from the typical spectral break at ∼ 300 keV an additional break exists at around 1-2 MeV.…”

Section: 38mentioning

confidence: 99%

“…4,14,18,28,41,43,44,50,53 Later, in Ryde (2005) it was shown that a large fraction of bursts could be fitted by a Planck function in addition to a power law, over the limited energy range of BATSE (20-1800 keV). 49,50 Varying amplitudes of these two components then lead to a broad variation of spectral shapes.…”

mentioning

confidence: 99%

Appearances of the jet photosphere in GRB spectra

Acuner¹,

Ryde²

2017

The Fourteenth Marcel Grossmann Meeting

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There are several strong arguments for considering photospheric emission in GRBs. Here, we describe the two main appearances of the photospheric emission that are currently discussed. In the multi-component models the photosphere only contributes to a part of the spectrum, while the main part is due to optically-thin synchrotron emission. In the photospheric emission models the whole emission spectrum is from the photosphere: The emission spectrum has been altered due to subphotospheric dissipation and/or off-axis emission. In many cases, though, it is difficult to distinguish between these models on a purely statistical ground. Therefore, more detailed predictions from different physical scenarios should be tested on the observations.

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Grb110721a: An Extreme Peak Energy and Signatures of the Photosphere

Cited by 168 publications

References 34 publications

The Fraction of Gamma-Ray Bursts with an Observed Photospheric Emission Episode

The Fraction of Gamma-Ray Bursts with an Observed Photospheric Emission Episode

Spectropolarimetric analysis of prompt emission of GRB 160325A: jet with evolving environment of internal shocks

Appearances of the jet photosphere in GRB spectra

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