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An untriggered optical detection of GRB 130427A

ATel #5042; A. J. Drake, S. G. Djorgovski, A. A. Mahabal, M. J. Graham, R. Williams (Caltech); J. Prieto (Princeton); M. Catelan (PUC Chile); E. Christensen, S. M. Larson (LPL/ UA)
on 4 May 2013; 05:51 UT
Credential Certification: Andrew J. Drake (ajd@cacr.caltech.edu)

Subjects: Optical, Gamma-Ray Burst, Transient

During the course of the regular survey operations the Catalina Real-time Transient Survey (CRTS) automatically detected new optical source CSS130502:113233+274156 at RA=11:32:32.90, Dec=+27:41:56.5 (J2000). Based on four observations spanning the period May 02.191 to 02.211UT the transient was found to have V=19.6+/-0.2. A public alert for the transient detection was automatically sent to VOEventNet sources such as SkyAlert within minutes of observation. Subsequently, a clear match between CSS130502:113233+274156 and the recent luminous GRB 130427A (Palmer et al. 2013, GCN#14448, Elenin et al. 2013, GCN#14450) was discovered.

The untriggered optical detection of GRB 130427A by CRTS makes this one of the few GRBs that have been detected without prior knowledge of the event. Furthermore, this detection suggests that the increased cadence and coverage of the CRTS-II project, along with other future transient surveys, will strongly constrain the existence of GRB-related events such as orphan afterglows.

We wish to thank D. Bishop for bringing the correspondence between CSS130502:113233+274 and GRB 130427A to our attention.