[vsnet-grb-info 4891] SN 2007bg - off-axis GRB?

[GCN Circulars]

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  <kstanek at cfa.harvard.edu>

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.

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