Mirabal, NestorHalpern, J. P.An, D.Thorstensen, J. R.Terndrup, D. M.2020-09-082020-09-082006-05-08N. Mirabal et al., GRB 060218/SN 2006aj: A Gamma-Ray Burst and Prompt Supernova at z = 0.0335, ApJ 643 L99 (2006), doi: https://doi.org/10.1086/505177https://doi.org/10.1086/505177http://hdl.handle.net/11603/19604We report the imaging and spectroscopic localization of GRB 060218 to a low-metallicity dwarf starburst galaxy at z = 0.03345 ± 0.00006. In addition to making it the second nearest gamma-ray burst known, optical spectroscopy reveals the earliest detection of weak, supernova-like Si II near 5720 Å (~0.1c), starting 1.95 days after the burst trigger. UBVRI photometry obtained between 1 and 26 days postburst confirms the early rise of supernova light, and suggests a short time delay between the gamma-ray burst and the onset of SN 2006aj if the early appearance of a soft component in the X-ray spectrum is understood as a "shock breakout." Together, these results verify the long-hypothesized origin of soft gamma-ray bursts in the deaths of massive stars.5 pagesen-USThis item is likely protected under Title 17 of the U.S. Copyright Law. Unless on a Creative Commons license, for uses protected by Copyright Law, contact the copyright holder or the author.© 2006. The American Astronomical Society. All rights reservedText