Identification and Properties of the Photospheric Emission in Grb090902b

Ryde, F.; Axelsson, M.; Zhang, Bingbing; McGlynn, S.; Pe’er, Asaf; Lundman, Christoffer; Larsson, Stefan; Battelino, Milan; Bissaldi, E.; Bregeon, J.; Briggs, M. S.; Chiang, J.; Palma, F. de; Guiriec, S.; Larsson, Josefin; Longo, F.; McBreen, S.; Omodei, N.; Petrosian, V.; Preece, R.; Horst, A. J. van der

doi:10.1088/2041-8205/709/2/l172

Cited by 267 publications

(394 citation statements)

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“…If an additional blackbody is observed, the temperature of the photosphere can be deduced (Rees & Mészáros 2005) whereas an underlying power-law can provide constraints on emission mechanisms (e.g. Asano et al 2009;Ryde et al 2010) and the extragalactic background light (EBL, Ackermann et al 2011). An overview of the observational and physical interpretations of the results from the Fermi era are presented by Bhat & Guiriec (2011).…”

Section: Introductionmentioning

confidence: 99%

Anomalies in low-energy gamma-ray burst spectra with theFermiGamma-ray Burst Monitor

Tierney

McBreen

Preece

et al. 2013

A&A

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Context. A Band function has become the standard spectral function used to describe the prompt emission spectra of gamma-ray bursts (GRBs). However, deviations from this function have previously been observed in GRBs detected by BATSE and in individual GRBs from the Fermi era. Aims. We present a systematic and rigorous search for spectral deviations from a Band function at low energies in a sample of the first two years of high fluence, long bursts detected by the Fermi Gamma-ray Burst Monitor (GBM). The sample contains 45 bursts with a fluence greater than 2 × 10 −5 erg/cm 2 (10−1000 keV).Methods. An extrapolated fit method is used to search for low-energy spectral anomalies, whereby a Band function is fit above a variable low-energy threshold and then the best fit function is extrapolated to lower energy data. Deviations are quantified by examining residuals derived from the extrapolated function and the data and their significance is determined via comprehensive simulations which account for the instrument response. This method was employed for both time-integrated burst spectra and time-resolved bins defined by a signal-to-noise ratio of 25σ and 50σ. Results. Significant deviations are evident in 3 bursts (GRB 081215A, GRB 090424 and GRB 090902B) in the time-integrated sample (∼7%) and 5 bursts (GRB 090323, GRB 090424, GRB 090820, GRB 090902B and GRB 090926A) in the time-resolved sample (∼11%). Conclusions. The advantage of the systematic, blind search analysis is that it can demonstrate the requirement for an additional spectral component without any prior knowledge of the nature of that extra component. Deviations are found in a large fraction of high fluence GRBs; fainter GRBs may not have sufficient statistics for deviations to be found using this method.

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Section: Introductionmentioning

confidence: 99%

Anomalies in low-energy gamma-ray burst spectra with theFermiGamma-ray Burst Monitor

Tierney

McBreen

Preece

et al. 2013

A&A

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“…Finally, if the PE dominates the prompt emission as in GRB090902B 9 (Ryde et al 2010), several constraints can also be obtained:…”

Section: Case 3: Pe the Prompt Emissionmentioning

confidence: 99%

The Anatomy of a Long Gamma-Ray Burst: A Simple Classification Scheme for the Emission Mechanism(s)

Bégué

Burgess

2016

ApJ

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Ultra-relativistic motion and efficient conversion of kinetic energy to radiation are required by gamma-ray burst (GRB) observations, yet they are difficult to simultaneously achieve. Three leading mechanisms have been proposed to explain the observed emission emanating from GRB outflows: radiation from either relativistic internal or external shocks, or thermal emission from a photosphere. Previous works were dedicated to independently treating these three mechanisms and arguing for a sole, unique origin of the prompt emission of GRBs. In contrast, herein, we first explain why all three models are valid mechanisms and that a contribution from each of them is expected in the prompt phase. Additionally, we show that a single parameter, the dimensionless entropy of the GRB outflow, determines which mechanism contributes the most to the emission. More specifically, internal shocks dominate for low values of the dimensionless entropy, external shocks for intermediate values, and finally, photospheric emission for large values. We present a unified framework for the emission mechanisms of GRBs with easily testable predictions for each process.

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“…It was observed by both Fermi gamma-ray burst monitor (GBM) and Large Area Telescope (LAT) for a T 90 = 22 s, the time during which 90% of the emission was observed. Here, we perform the time-resolved spectral analysis of the burst using HEASARC's spectral analysis software package XSPEC 8 (Arnaud 1996), for the same time binning that was adopted in the analysis previously performed in Ryde et al (2010Ryde et al ( , 2011. The spectral analysis is done for the pulse height analyzer (PHA) data of the GBM detectors, sodium iodide NaI 0,1, bismuth gallium oxide BGO 0,1 and the reprocessed pass 7 data from LAT front and back detectors (P7V6_Transient class event; Atwood et al 2009).…”

Section: Grb 090902b: Transparency At the Accelerating Phasementioning

confidence: 99%

“…In Ryde et al (2010), the first epoch is fitted using a multicolor black body and a power law. However, the second epoch of the burst shows a broader spectral component.…”

Section: Grb 090902b: Transparency At the Accelerating Phasementioning

confidence: 99%

Transparency Parameters From Relativistically Expanding Outflows

Bégué

Iyyani

2014

ApJ

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In many gamma-ray bursts a distinct blackbody spectral component is present, which is attributed to the emission from the photosphere of a relativistically expanding plasma. The properties of this component (temperature and flux) can be linked to the properties of the outflow and have been presented in the case where there is no subphotospheric dissipation and the photosphere is in coasting phase. First, we present the derivation of the properties of the outflow for finite winds, including when the photosphere is in the accelerating phase. Second, we study the effect of localized sub-photospheric dissipation on the estimation of the parameters. Finally, we apply our results to GRB 090902B. We find that during the first epoch of this burst the photosphere is most likely to be in the accelerating phase, leading to smaller values of the Lorentz factor than the ones previously estimated. For the second epoch, we find that the photosphere is likely to be in the coasting phase.

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Identification and Properties of the Photospheric Emission in Grb090902b

Cited by 267 publications

References 35 publications

Anomalies in low-energy gamma-ray burst spectra with theFermiGamma-ray Burst Monitor

Anomalies in low-energy gamma-ray burst spectra with theFermiGamma-ray Burst Monitor

The Anatomy of a Long Gamma-Ray Burst: A Simple Classification Scheme for the Emission Mechanism(s)

Transparency Parameters From Relativistically Expanding Outflows

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