TITLE: GCN GRB OBSERVATION REPORT NUMBER: 197 SUBJECT: Possible identification of SN1999E with GRB980910 DATE: 99/01/21 23:32:12 GMT FROM: David W. Hogg at Institute for Advanced Study 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.