GCN Circular 9444
Subject
Strong radio emission from SN 2007bg one year after the explosion - detection of spreading, off-axis GRB jet?
Date
2009-05-30T14:22:52Z (16 years ago)
From
Krzysztof Z. Stanek at Ohio State U <kstanek@astronomy.ohio-state.edu>
J. L. Prieto, L. C. Watson & K. Z. Stanek (Ohio State University)
In their study of supernova hosts using SDSS data (Prieto, Stanek & Beacom
2008, ApJ, 673, 999), the broad-lined SN Ic 2007bg at z=0.034 (Quimby et
al. 2007, CBET 927; Harutyunyan et al. 2007, CBET 948; Soderberg & Immler
2007, ATEL 1142), was identified as a good candidate for an off-axis GRB.
The likely host of SN 2007bg is an extremely low-luminosity galaxy with
M_B ~ -12, one of the least-luminous supernova hosts of any kind ever
observed. Since such a low-luminosity host is almost certain to be very
metal poor (~1/20 solar; e.g., Lee et al. 2006, ApJ, 647, 970), this
broad-line SN Ic supernova is a very good candidate for association with
an off-axis GRB (e.g., Stanek et al. 2006, AcA, 56, 333). Given that,
Prieto, Stanek & Beacom (2007, GCN 6618) encouraged follow-up observations
of SN 2007bg to look for an off-axis GRB jet.
Following up on their suggestion, we have analyzed some of the publicly
available radio data obtained at the VLA at several epochs in several
bands (Proposal #AS0887; PI A. Soderberg), and have detected a very strong
radio source at the position of SN 2007bg:
UT | days after SN disc. | nu (GHz) | flux (mJy) | error (mJy) | Luminosity density (erg/s/Hz)
Apr. 19.2, 2007 3.1 8.46 0.15 0.04 3.6e27
Aug. 18.9, 2007 124.7 8.46 0.58 0.04 1.4e28
Feb. 25.2, 2008 315.0 8.46 1.77 0.10 4.4e28
This makes SN 2007bg one of the strongest radio supernovae ever observed,
in fact >4 times more luminous at approx. 1 year after explosion compared
with SN 2003L (Soderberg et al. 2005, ApJ, 621, 908) and SN 2003bg
(Soderberg et al. 2006, ApJ, 651, 1005), which were among the most
luminous SN Ib/c observed in radio, see more details and figures at
http://www.astronomy.ohio-state.edu/~prieto/sn2007bg/
In fact, such strong radio emission a year after the explosion makes SN
2007bg an even better candidate for an off-axis GRB (e.g., Paczynski 2001,
AcA, 51, 1), given that the only other broad-line SNe Ic ever observed in
low metallicity enviroments have been associated with GRBs (Stanek et al.
2006, AcA, 56, 333; Modjaz et al. 2008, AJ, 135, 1136).
Further follow-up observations at all wavelengths are greatly
encouraged.