Swift identification of dark gamma-ray bursts

P. Jakobsson*, J. Hjorth, J. P.U. Fynbo, D. Watson, K. Pedersen, G. Björnsson, J. Gorosabel

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

197 Citations (Scopus)


We present an optical flux versus X-ray flux diagram for all known gamma-ray bursts (GRBs) for which an X-ray afterglow has been detected. We propose an operational definition of dark bursts as those bursts that are optically subluminous with respect to the fireball model, i.e., that have an optical-to-X-ray spectral index βox < 0.5. Out of a sample of 52 GRBs, we identify five dark bursts. The definition and diagram serve as a simple and quick diagnostic tool for identifying dark GRBs based on limited information, particularly useful for early and objective identification of dark GRBs observed with the Swift satellite.

Original languageEnglish
Pages (from-to)L21-L24
JournalAstrophysical Journal
Issue number1 II
Publication statusPublished - 10 Dec 2004

Bibliographical note

Funding Information:
We thank J. Bloom, C. Kouveliotou, D. Lazzati, E. Rol, and R. Wijers for discussions on dark GRBs over the years. We thank the anonymous referee for a critical reading and useful comments on this Letter. P. J. and G. B. gratefully acknowledge support from a special grant from the Icelandic Research Council. K. P. acknowledges support from the Carlsberg foundation and from the Instrument Center for Danish Astrophysics. This work was supported by the Danish Natural Science Research Council. The authors acknowledge benefits from collaboration within the EU FP5 Research Training Network “Gamma-Ray Bursts: An Enigma and a Tool.”

Other keywords

  • Dust, extinction
  • Galaxies: high-redshift
  • Gamma rays: bursts


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