title: The optical afterglow of the short gamma-ray burst GRB 050709.
abstract: It has long been known that there are two classes of gamma-ray bursts (GRBs), mainly distinguished by their durations. The breakthrough in our understanding of long-duration GRBs (those lasting more than approximately 2 s), which ultimately linked them with energetic type Ic supernovae, came from the discovery of their long-lived X-ray and optical 'afterglows', when precise and rapid localizations of the sources could finally be obtained. X-ray localizations have recently become available for short (duration <2 s) GRBs, which have evaded optical detection for more than 30 years. Here we report the first discovery of transient optical emission (R-band magnitude approximately 23) associated with a short burst: GRB 050709. The optical afterglow was localized with subarcsecond accuracy, and lies in the outskirts of a blue dwarf galaxy. The optical and X-ray afterglow properties 34 h after the GRB are reminiscent of the afterglows of long GRBs, which are attributable to synchrotron emission from ultrarelativistic ejecta. We did not, however, detect a supernova, as found in most nearby long GRB afterglows, which suggests a different origin for the short GRBs.
authors.affiliation: Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej, DK-2100 Copenhagen Ø, Denmark. jens@astro.ku.dk
authors.forename: Jens
authors.initials: J
authors.lastname: Hjorth
authors.forename: Darach
authors.initials: D
authors.lastname: Watson
authors.forename: Johan P U
authors.initials: JP
authors.lastname: Fynbo
authors.forename: Paul A
authors.initials: PA
authors.lastname: Price
authors.forename: Brian L
authors.initials: BL
authors.lastname: Jensen
authors.forename: Uffe G
authors.initials: UG
authors.lastname: Jørgensen
authors.forename: Daniel
authors.initials: D
authors.lastname: Kubas
authors.forename: Javier
authors.initials: J
authors.lastname: Gorosabel
authors.forename: Páll
authors.initials: P
authors.lastname: Jakobsson
authors.forename: Jesper
authors.initials: J
authors.lastname: Sollerman
authors.forename: Kristian
authors.initials: K
authors.lastname: Pedersen
authors.forename: Chryssa
authors.initials: C
authors.lastname: Kouveliotou