Detection of a Spectral Break in the Extra Hard Component of GRB 090926A

By M. Ackermann, M. Ajello, K. Asano, M. Axelsson, L. Baldini, J. Ballet, G. Barbiellini, M. Baring, D. Bastieri, K. Bechtol and 189 more. 2011

176 citations recorded by the source corpus.

We report on the observation of the bright, long gamma-ray burst, GRB 090926A, by the Gamma-ray Burst Monitor and Large Area Telescope (LAT) instruments on board the Fermi Gamma-ray Space Telescope. GRB 090926A shares several features with other bright LAT bursts. In particular, it clearly shows a short spike in the light curve that is present in all detectors that see the burst, and this in turn suggests that there is a common region of emission across the entire Fermi energy range. In addition, while a separate high-energy power-law component has already been observed in other gamma-ray bursts, here we report for the first time the detection with good significance of a high-energy spectral break (or cutoff) in this power-law component around 1.4 GeV in the time-integrated spectrum. If the spectral break is caused by opacity to electron-positron pair production within the source, then this observation allows us to compute the bulk Lorentz factor for the outflow, rather than a lower limit.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/71a68e6700f91e61e75b44e37b43be125745e426

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In Astronomy and Astrophysics

1. Bing Zhang
2. A. Pe’er
3. Luciano Rezzolla
4. Y. Inoue
5. F. Ryde
6. J. Biteau
7. M. Meyer
8. D. Horns

In Nuclear and High Energy Physics

1. J. Biteau
2. Y. Inoue
3. Anna Franckowiak
4. D. Horns
5. M. Meyer
6. E. Orlando
7. C. Dermer
8. A. Reimer

Citations in the corpus

• 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…”
• THE FIRST FERMI-LAT GAMMA-RAY BURST CATALOG (2013, background): “In one case, Fermi observed a high-energy cutoff that required the addition of an exponential cutoff to the PL component in the spectral model (Ackermann et al. 2011), for a total of three components (Band, power law, and exponential cutoff).”
• THE MISSING LINK: MERGING NEUTRON STARS NATURALLY PRODUCE JET-LIKE STRUCTURES AND CAN POWER SHORT GAMMA-RAY BURSTS (2011, background): “However, a more realistic model (Granot et al. 2008) results in Γmin values lower by a factor of ∼ 3 (Ackermann et al. 2011).”
• THE FERMI GBM GAMMA-RAY BURST SPECTRAL CATALOG: FOUR YEARS OF DATA (2014, methodology): “Making use of the Castor statistics (Ackermann et al. 2011), we derive the best model for each GRB and present the distribution and characteristics of the model parameters.”
• Search for TeV Gamma-ray Emission from GRB 100621A, an extremely bright GRB in X-rays, with H.E.S.S (2014, background): “…is consistent with a Band function from keV to GeV energies, whereas other bursts show an additional hard power-law component at HE (e.g. GRB 090902B & 090510, Abdo et al. 2009a; Ackermann et al. 2010), which in some cases exhibits a spectral break (e.g. GRB 090926A, Ackermann et al. 2011).”