GCN Circular 197

S. E. Thorsett (Princeton University) and David W. Hogg (Institute for
Advanced Study) report:

SN1999E is a bright (V=16) supernova discovered on Jan 15.276 (Perez
et al, IAUC 7089).  The supernova was not visible on 1998 Jul 29.046.
It is at redshift 0.025 (Filippenko et al, IAUC 7090), and is quite
luminous, with M_V<-19.4 (H_0 = 65 km s^-1 Mpc^-1, Jha et al, IAUC
7090).  The spectrum is similar to a spectrum of SN1997cy, the most
luminous supernova known (M_V<=-20.06), taken about 4 months after
discovery (Capellarro et al, IAUC 7091).  It is also similar in some
respects to the luminous SN1998bw (Filippenko et al, IAUC 7091).

SN1998bw has been identified with GRB980425 (e.g., Sadler et al, IAUC
6901).  SN1997cy has been associated with GRB970514 (Woosley et al,
ApJ, submitted, and http://xxx.lanl.gov/abs/astro-ph/?9806299).

In the five months between 1998 Jul 29 and 1999 Jan 15, BATSE observed
97 GRBs (Meegan et al,
http://www.batse.msfc.nasa.gov/data/grb/catalog/).  One of these, GRB
980910 (BATSE trigger 7077), is coincident with the position of
SN1999E, with a separation of 4.8 deg (the GRB position is uncertain
to 6.8 deg).  We note that this GRB occurred just over 4 months before
the SN discovery, in agreement with the rough SN age, and propose that
the GRB and SN may be associated.

It is difficult to estimate a meaningful a posteriori likelihood of a
chance coincidence.  The 97 GRBs have statistical error circles that
cover 6766 deg^2, or about 16 percent of the sky, giving a 1/6 chance
of accidental association.  However, only 31 GRBs fall between 3 and 5
months before the SN discovery. If further observations of the SN
lightcurve and spectrum allow a tighter constraint on the SN explosion
time, by comparison with the late-time properties of SN1998bw and
SN1997cy, confidence in the association could be greatly improved.
The existence of one very good SN-GRB identification (SN1998bw) and
now two weaker associations (SN1998cy and 1999E) strongly suggests
that a significant fraction of GRBs are caused by peculiar supernovae.