TITLE: GCN CIRCULAR NUMBER: 6618 SUBJECT: SN 2007bg - off-axis GRB? DATE: 07/07/11 20:40:27 GMT FROM: Krzysztof Z. Stanek at CfA J. L. Prieto, K. Z. Stanek & J. F. Beacom (Ohio State) report: In a study of supernova hosts (Prieto, Stanek & Beacom 2007, arXiv:0707.0690v1 [astro-ph]), the recent broad-lined SN Ic 2007bg at z=0.034 (Quimby et al. 2007, CBET 927; IAUC 8834; Harutyunyan et al. 2007, CBET 948), was identified as a good candidate for an off-axis GRB. The supernova, discovered on April 16 2007 (CBET 927, IAUC 8834), is located at 1.6 arcsec North and 4.0 arcsec East of a source identified in the SDSS-DR6 catalog, SDSS J114925.74+514920.2, which has model magnitudes g=21.82 +/- 0.07, r=21.12 +/- 0.07 (uncorrected for Galactic extinction; Ag=0.08, Ar=0.06) and estimated photometric redshift between 0.3 and 0.4. There is a fainter source at ~2" from the position of the supernova clearly detected in the SDSS g-band image, and which is not identified in the SDSS-DR6 catalog. This fainter source is most likely the host galaxy of SN 2007bg (CBET 948). A 1x1 arcmin SDSS g-band image around the position of the supernova can be found here: http://www.astronomy.ohio-state.edu/~prieto/sn07bg_host.gif We used Sextractor to measure a difference of 1.7 mag in g-band between the likely host and SDSS J114925.74+514920.2. At the redshift of the supernova, z=0.034 (CBET 927), this makes the likely host an extremely low-luminosity galaxy with M_B ~ -12, one of the least-luminous supernova hosts ever observed. Such a low-luminosity host is certain to be very metal poor (~1/20 solar; Lee et al. 2006, ApJ, 647, 970L), and therefore this supernova is a very good candidate for association with an off-axis GRB (e.g., Stanek et al. 2006, AcA, 56, 333). We encourage follow-up observations to look for an off-axis GRB jet. This message may be cited.