How Can The SN-GRB Time Delay Be Measured?

Abstract

The connection between SNe and GRBs, launched by SN 1998bw/GRB 980425 and clinched by SN 2003dh/GRB 030329 -- with the two GRBs differing by a factor of approximately 50000 in luminosity -- so far suggests a rough upper limit of ~ 1-2 days for the delay between SN and GRB. Only four SNe have had nonnegligible coverage in close coincidence with the initial explosion, near the UV shock breakout: two Type II, and two Type Ic, SN 1999ex and SN 1998bw. For the latter, only a hint of the minimum between the UV maximum and the radioactivity bump served to help constrain the interval between SN and GRB. Swift GRB alerts may provide the opportunity to study many SNe through the UV breakout phase: GRB 980425 "look alikes" -- apparently nearby, low-luminosity, soft-spectrum, long-lag GRBs -- accounted for half of BATSE bursts near threshold, and may dominate the Swift yield near threshold, since it has sensitivity to lower energies than did BATSE. The SN to GRB delay timescale should be better constrained by prompt UV/optical observations alerted by these bursts. Definitive delay measurements may be obtained if long-lag bursters are truly nearby: The SNe/GRBs could emit gravitational radiation detectable by LIGO-II if robust non-axisymmetric bar instabilities develop during core collapse, and/or neutrino emission may be detectable as suggested by Meszaros et al.