The Cooling Behavior of Thermal Pulses in Gamma-Ray Bursts

By F. Ryde. 2004

196 citations recorded by the source corpus.

We discuss gamma-ray bursts (GRBs) that have very hard spectra, consistent with blackbody radiation. Several emission components are expected, on the basis of theoretical considerations, to be visible in the gamma-ray band, mainly nonthermal emission from cooling, relativistic electrons and thermal emission from a wind photosphere. We find that the pulses we study are consistent with a thermal blackbody radiation throughout their duration and that the temperature kT can be well described by a broken power law as a function of time, with an initially constant temperature or weak decay (~100 keV). After the break, most cases are consistent with a decay with index -. A few of the pulses have a weak nonthermal component overlaying the thermal one and are better fitted with a combination of a thermal and a nonthermal component. We further demonstrate that such a two-component model can explain the whole time evolution of other bursts that are found to be thermal only initially and later become nonthermal. The relative strengths between the two components vary with time, and this is suggested, among other things, to account for the change in the modeled low-energy power-law slope that is often observed in GRBs. The secondary, nonthermal components are consistent with optically thin synchrotron emission in the cooling regime. We interpret the observations within a model of an optically thick shell (fireball) that expands adiabatically. The slow, or absent, temperature decrease is in the acceleration phase, during which the bulk Lorentz factor increases, and the faster temperature decay is reached as the flow saturates and starts to coast with a constant speed. We also discuss a Poynting-flux model, in which the saturation radius is reached close to the photosphere. Even though these observations cannot tell these models apart, the latter has several attractive advantages. The GLAST satellite will be able to clarify and further test the physical setting of similar thermal pulses.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/cc71152ee7546fb52aae786e9a1257c310a5274e

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In Astronomy and Astrophysics

1. Bing Zhang
2. E. Berger
3. Pawan Kumar
4. A. Pe’er
5. B. Metzger
6. P. Mészáros
7. F. Ryde
8. D. Giannios

Citations in the corpus

• Is Thermal Emission in Gamma-Ray Bursts Ubiquitous? (2005, background): “Figure 2 also shows that the temperature of the black body, for this burst, exhibits a similar evolution like the purely quasi-thermal bursts discussed by Ryde (2004), with a distinct break in the cooling curve.”
• The physics of gamma-ray bursts & relativistic jets (2014, background): “In the pre-Fermi era, it was suggested (Ryde, 2004; Ryde and Pe’er, 2009) that the observed prompt GRB spectrum is the superposition of a thermal (blackbody) component and a non-thermal (power law) component.”
• A New Method of Determining the Initial Size and Lorentz Factor of Gamma-Ray Burst Fireballs Using a Thermal Emission Component (2007, methodology): “…increasing evidence has appeared that, during the first stages of the prompt emission of long duration gamma-ray bursts (GRBs), a thermal component accompanies the underlying non-thermal emission [Ryde (2004, 2005); Campana et al. (2006); see also Ghirlanda et al. (2003); Kaneko et al. (2003)].”
• Temporal Evolution of Thermal Emission from Relativistically Expanding Plasma (2008, background): “As was shown by Ryde (2004, 2005), after ∼ 1−3 s the temperature of the thermal component decreases as a power law in time, T ob.”
• AFTERGLOW OBSERVATIONS OF FERMI LARGE AREA TELESCOPE GAMMA-RAY BURSTS AND THE EMERGING CLASS OF HYPER-ENERGETIC EVENTS (2010, background): “…is still not entirely understood; possible explanations include a hadronic origin [either proton synchrotron radiation (Razzaque et al. 2009) or photohadronic interactions (Asano et al. 2009)] or thermal emission from the jet photosphere (Mészáros & Rees 2000; Ryde 2004; Ryde et al. 2010).”
• The Observable Effects of a Photospheric Component on GRB and XRF Prompt Emission Spectrum (2005, background): “Here, we overcome this problem by assuming that the thermal component seen in many bursts (e.g., Ryde 2004), and presumably exist in all of them at early times, is advected from the core.”
• Prompt emission spectra from the photosphere of a GRB (2006, background): “Quasi-thermal emission has been observed in a fraction of GRBs (Ryde 2004; 2005) and they may be a result of low σ0 (i.e. high baryon loading).”
• DETECTION OF A THERMAL SPECTRAL COMPONENT IN THE PROMPT EMISSION OF GRB 100724B (2010, background): “Observationally, Ghirlanda et al. (2003), Ryde (2004, 2005), and Ryde et al. (2010) argued that a photospheric component is present in CGRO BATSE data.”
• IDENTIFICATION AND PROPERTIES OF THE PHOTOSPHERIC EMISSION IN GRB090902B (2009, background): “Several spectra haveα ∼ +0.3, which are among the hardest GRB spectra ever measured (Ryde 2004; Kaneko et al. 2006).”
• QUASI-BLACKBODY COMPONENT AND RADIATIVE EFFICIENCY OF THE PROMPT EMISSION OF GAMMA-RAY BURSTS (2008, methodology): “This is consistent with the findings in the works by Ryde (2004, 2005).”
• GRB110721A: AN EXTREME PEAK ENERGY AND SIGNATURES OF THE PHOTOSPHERE (2012, methodology): “The evolution of kT seen here is similar to what was observed by BATSE over individual GRB pulses where a thermal emission component was identified (Ryde 2004).”
• Reconciling observed gamma-ray burst prompt spectra with synchrotron radiation? (2010, background): “The scenario proposed in this paper can never produce low-energy slopesα steeper than−2/3, whereas such slopes are measured in a non negligible fraction of GRB spectra (Ryde 2004; Ghirlanda et al. 2003).”
• Dissipative Photosphere Models of Gamma-Ray Bursts and X-Ray Flashes (2004, unknown): “, by Ryde ( 2004 ) .”