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Compton Echoes from Gamma‐Ray Bursts

Madau, Piero and Blandford, Roger D. and Rees, Martin J. (2000) Compton Echoes from Gamma‐Ray Bursts. Astrophysical Journal, 541 (2). pp. 712-719. ISSN 0004-637X. doi:10.1086/309463.

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Recent observations of γ-ray bursts (GRBs) have provided growing evidence for collimated outflows and emission and strengthened the connection between GRBs and supernovae. If massive stars are the progenitors of GRBs, the hard photon pulse will propagate in the preburst, dense environment. Circumstellar material will Compton scatter the prompt GRB radiation and give rise to a reflection echo. We calculate luminosities, spectra, and light curves of such Compton echoes in a variety of emission geometries and ambient gas distributions and show that the delayed hard X-ray flash from a pulse propagating into a red supergiant wind could be detectable by Swift out to z ~ 0.2. Independently of the γ-ray spectrum of the prompt burst, reflection echoes will typically show a high-energy cutoff between m_ec^2/2 and m_ec^2 because of Compton downscattering. At fixed burst energy per steradian, the luminosity of the reflected echo is proportional to the beaming solid angle, Ω_b, of the prompt pulse, while the number of bright echoes detectable in the sky above a fixed limiting flux increases as Ω_b^(1/2), i.e., it is smaller in the case of more collimated jets. The lack of an X-ray echo at about 1 month delay from the explosion poses severe constraints on the possible existence of a lateral GRB jet in SN 1987A. The late r-band afterglow observed in GRB 990123 is fainter than the optical echo expected in a dense red supergiant environment from an isotropic prompt optical flash. Significant MeV delayed emission may be produced through the bulk Compton (or Compton drag) effect resulting from the interaction of the decelerating fireball with the scattered X-ray radiation.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Blandford, Roger D.0000-0002-1854-5506
Additional Information:© 2000 The American Astronomical Society. Received 1999 December 14; accepted 2000 April 25. We have benefited from many useful discussions with G. Ghisellini, D. Helfand, E. Ramirez-Ruiz, and C. Thompson. Support for this work was provided by the NSF through grant PHY94-07194 (P. M. and R. D. B.), by NASA through grant 5-2837 and the Beverly and Raymond Sackler Foundation (R. D. B.), and by the Royal Society (M. J. R.).
Funding AgencyGrant Number
Raymond and Beverly Sackler FoundationUNSPECIFIED
Subject Keywords:gamma rays : bursts - gamma rays : theory - supernovae: general - X-rays: general
Issue or Number:2
Record Number:CaltechAUTHORS:20190604-083813923
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Official Citation:Piero Madau et al 2000 ApJ 541 712
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:96101
Deposited By: Tony Diaz
Deposited On:04 Jun 2019 18:20
Last Modified:16 Nov 2021 17:18

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