The Optical Afterglow of GRB971214: Further Evidence for a Varied Population

We present an R-band lightcurve of an optical transient which is likely to be associated with the gamma-ray burst event GRB971214. Our first measurement took place 17 hours after the gamma-ray event. The brightness decayed with a power-law exponent α = −1.380 ± 0.013, which is significantly faster than the other two optically identified bursts, GRB970228 and GRB970508 which had exponents of α = −1.10 ± 0.04 (Galama et al. 1997) and α = −1.141 ± 0.014 (Galama et al. 1998) respectively. The transient decayed monotonically during the first four days following the gamma-ray event in contrast with the optical transient associated with GRB970508 which increased in brightness, peaking two days after the burst, before settling to a power-law decay. This event provides clear observational evidence that the optical afterglows of gamma-ray bursts are not universal. The differences are plausibly intrinsic but could also be due to varying source redshifts. Subject headings: gamma rays: bursts Department of Astronomy, Box 351580, University of Washington, Seattle, WA 98195; [email protected]; [email protected] Department of Astronomy and Astrophysics, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637; [email protected]; [email protected] Apache Point Observatory, 2001 Apache Point Rd., Sunspot NM 88349; [email protected] Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK; [email protected] Princeton University Observatory, Peyton Hall, Princeton, NJ 08544; [email protected] Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, MD 21218; [email protected]