Synchrotron Radiation as the Source of Gamma-Ray Burst Spectra

By N. Lloyd, V. Petrosian. 2000

149 citations recorded by the source corpus.

We investigate synchrotron emission models as the source of gamma-ray burst (GRB) spectra. We show that including the possibility for synchrotron self-absorption, a "smooth cutoff" to the electron energy distribution, and an anisotropic distribution for the electron pitch angles produces a whole range of low-energy spectral behavior. In addition, we show that the procedure of spectral fitting to GRB data over a finite bandwidth can introduce a spurious correlation between spectral parameters—in particular, the value of the peak of the νFν spectrum, Ep, and the low-energy photon spectral index α (the lower Ep is, the lower [softer] the fitted value of α will be). From this correlation and knowledge of the Ep distribution, we show how to derive the expected distribution of α. We show that optically thin synchrotron models with an isotropic electron pitch angle distribution can explain the distribution of α below α = - . This agreement is achieved if we relax the unrealistic assumption of the presence of a sharp low-energy cutoff in the spectrum of accelerated electrons and allow for a more gradual break. We show that this low-energy portion of the electron spectrum can be at most flat. We also show that optically thin synchrotron models with an anisotropic electron pitch angle distribution can explain all bursts with - ≲ α ≲ 0. The very few bursts with low-energy spectral indices that fall above α = 0 may be due to the presence of a synchrotron self-absorption frequency entering the lower end of the BATSE window. Our results also predict a particular relationship between α and Ep during the temporal evolution of a GRB. We give examples of spectral evolution in GRBs and discuss how its behavior is consistent with the above models.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/2f68ea4ee3f53fb3dd91eaad91f8cef35c921d7e

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In Astronomy and Astrophysics

Citations in the corpus

Extremely hard GRB spectra prune down the forest of emission models (2002, background): “Lloyd & Petrosian (2000) propose a scenario in which electrons have a small pitch angle distribution (SPD in Fig.”
Gamma-Ray Bursts in the Swift Era (2007, unknown): “…prom t emission models, see e.g., Mészáros et al. (1994), Thompson (1994), Daigne & Mochkovitch (1998), Pilla & Loeb (1998), Medvedev & Loeb (1999), Lloyd & Petrosian (2000), Ghisellini et al. (2000),Panaitescu & Mészáros (2000), Medvedev (2000), Mészáros & Rees (2000), Spruit et al. (2001),…”
On the Hubble Constant Tension in the SNe Ia Pantheon Sample (2021, methodology): “…choice of this function g(z) is standard for characterizing the evolution of many astrophysical sources, and it is widely used for GRBs and quasars (Lloyd & Petrosian 2000; Singal et al. 2011, 2013; Dainotti et al. 2013b, 2015, 2016, 2017b, 2020; Petrosian et al. 2015; Dainotti & Del Vecchio 2017).”
Reconciling observed gamma-ray burst prompt spectra with synchrotron radiation? (2010, background): “…of the spectrum around the peak energy and the limited spectral energy range sampled by the instruments; 3. as discussed by Preece et al. (1998) and Lloyd & Petrosian (2000) for the BATSE spectra, the data don’t always approach the GRB spectral low energy power law within the instrument energy…”
Short-hard gamma-ray bursts (2007, background): “…leading to jitter radiation instead of synchrotron (Medvedev, 2000), effects of synchrotron self absorption or anisotropic electron pitching angles (Lloyd & Petrosian, 2000; Granot, Piran & Sari , 2000), Upscatter of optical selfabsorbed photons by inverse Compton (Panaitescu & Mészáros, 2000)…”