IDENTIFICATION AND PROPERTIES OF THE PHOTOSPHERIC EMISSION IN GRB090902B

By F. Ryde, M. Axelsson, B. Zhang, S. Mcglynn, A. Pe’er, C. Lundman, S. Larsson, M. Battelino, Binbin Zhang, E. Bissaldi and 12 more. 2009

192 citations recorded by the source corpus.

The Fermi Gamma-ray Space Telescope observed the bright and long GRB090902B, lying at a redshift of z = 1.822. Together the Large Area Telescope (LAT) and the Gamma-ray Burst Monitor (GBM) cover the spectral range from 8 keV to >300 GeV. Here we show that the prompt burst spectrum is consistent with emission from the jet photosphere combined with nonthermal emission described by a single power law with photon index −1.9. The photosphere gives rise to a strong quasi-blackbody spectrum which is somewhat broader than a single Planck function and has a characteristic temperature of ∼290 keV. We model the photospheric emission with a multicolor blackbody, and its shape indicates that the photospheric radius increases at higher latitudes. We derive the averaged photospheric radius Rph = (1.1 ± 0.3) × 1012 Y1/4 cm and the bulk Lorentz factor of the flow, which is found to vary by a factor of 2 and has a maximal value of Γ = 750 Y1/4. Here, Y is the ratio between the total fireball energy and the energy emitted in the gamma rays. We find that during the first quarter of the prompt phase the photospheric emission dominates, which explains the delayed onset of the observed flux in the LAT compared to the GBM. We interpret the broadband emission as synchrotron emission at R ∼ 4 × 1015 cm. Our analysis emphasizes the importance of having high temporal resolution when performing spectral analysis on gamma-ray bursts, since there is strong spectral evolution.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/763260fff90eff04a9951e117b7c2e429a9f950a

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Citations in the corpus

DETECTION OF GAMMA-RAY POLARIZATION IN PROMPT EMISSION OF GRB 100826A (2011, background): “The photospheric models include an idea that the emission below Ep is superposition of many quasi-thermal components with different temperature and/or Γ (e.g., Ryde et al. 2010; Toma et al. 2011).”
Collisional mechanism for gamma‐ray burst emission (2009, background): “The distinct source is visible in several GeV-emitting bursts (e.g. Abdoet al. 2009b; Ryde et al. 2010) and likely present in all of them, obscuring the behavior of the prompt Band spectrum at high energies (cf. the debate over GRB 080916C: Abdo et al. 2009a; Kumar & Barniol Duran 2009; Ghisellini…”
GRB110721A: AN EXTREME PEAK ENERGY AND SIGNATURES OF THE PHOTOSPHERE (2012, background): “…active in the prompt phase of gamma-ray bursts (GRBs) are still under debate, there is much evidence that the photosphere of the relativistic outflow plays an important role in the formation of the observed spectrum (e.g. Lazzati & Begelman 2010, Ryde et al. 2010, Guiriec et al. 2011, Vurm et el.”
THE INTERNAL-COLLISION-INDUCED MAGNETIC RECONNECTION AND TURBULENCE (ICMART) MODEL OF GAMMA-RAY BURSTS (2010, background): “For example, another LAT burst GRB 090902B shows a clear time-evolving blackbody component superposed on a non-thermal power law component (Ryde et al. 2010; Zhang et al. 2010), which is almost certainly the baryonic photosphere component.”
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.”
Detection of a Spectral Break in the Extra Hard Component of GRB 090926A (2011, methodology): “In the photospheric emission model of the Band component (e.g., Mészáros & Rees 2000), the extra component could be the IC of the photospheric emission by electrons in the dissipation region at large radius (Beloborodov 2009; Gao et al. 2009; Ryde et al. 2010).”
The physics of gamma-ray bursts & relativistic jets (2014, background): “In any case, the amplitude of the blackbody type — the prototype of which is GRB 090902B (Abdo et al., 2009b) — shows superposition of a thermal-like spectrum and a non-thermal power law spectrum extending both to low- and high-energy regimes (Ryde et al., 2010; Zhang et al., 2011).”
A COMPREHENSIVE ANALYSIS OF FERMI GAMMA-RAY BURST DATA. I. SPECTRAL COMPONENTS AND THE POSSIBLE PHYSICAL ORIGINS OF LAT/GBM GRBs (2010, methodology): “Ryde et al. (2010) found that the time-resolved spectra can be fit with a PL plus a multi-color blackbody model.”
The THESEUS space mission concept: science case, design and expected performances (2017, background): “It is worth noting that a number of recent studies have found evidence of a sub-dominant thermal emission in the prompt emission spectrum (Ryde et al., 2010; Guiriec et al., 2011; Basak & Rao, 2015).”
AFTERGLOW OBSERVATIONS OF FERMI LARGE AREA TELESCOPE GAMMA-RAY BURSTS AND THE EMERGING CLASS OF HYPER-ENERGETIC EVENTS (2010, background): “The calculations are further complicated if the spectrum is not a pure power law, as would be the case for thermal emission arising from the jet photosphere (Ryde et al. 2010).”
A theory of photospheric emission from relativistic, collimated outflows (2012, background): “The spectra are usually well fitted by the Band function, although more complex spectra has been observed (e.g. Ryde et al. 2010; Ackermann et al. 2011; Guiriec et al. 2011). c© 2012 RAS, MNRAS 000, 1–15 The average values of the low and high energy photon indices are α ≈ −1 and β ≈ −2.5…”
Transition from fireball to Poynting-flux-dominated outflow in the three-episode GRB 160625B (2016, methodology): “This is because: (1) the inference of jet composition mostly depends on the low-energy photon index in the sub-MeV range; (2) LAT data are available in only some sub-bursts and (3) for our fine-time slices (as small as 0.”