GCN Circular 9137
Subject
GRB 090417A: Early-type nature of the putative host
Date
2009-04-17T17:35:29Z (15 years ago)
From
Josh Bloom at UC Berkeley <jbloom@astron.berkeley.edu>
J. S. Bloom (UC Berkeley), D. Fox (PSU), N. R. Tanvir, P. T. O'Brien
(U. Leicester), William Lee (UNAM), J. X. Prochaska (UCO/Lick) report:
We further note that the galaxy possibly associated (Fox GCN 9134)
with GRB 090417A (Mangano et al., GCN 9133) appears both visually and
spectrally to be of an early-type (smooth morphology, prominent Ca
H&K). In the 6df spectrum (O'Brien & Tanvir, GCN 9136), there is some
low-level H�� emission apparent suggesting some low-level star-
formation. However no other Balmer lines appear prominently detected
and there is no apparent [OIII] or [OII] as seen in the host galaxies
of essentially all long-soft GRB (LSB) hosts. Without a detailed
analysis, we classify this galaxy as a S0/lenticular or (more likely)
an elliptical. Given the connection of several other SHBs to
ellipticals at moderate redshift, we feel this identification can be
taken as weak observational support for a connection between this
galaxy and 090417A and further suggests that the burst was unlikely to
be due to an SGR flare-type event (O'Brien & Tanvir, GCN 9136). The
fact that the galaxy is at the edge of the BAT error circle does not
necessarily argue against it being the host: the offset from the
center of the circle, which amounts to ~320 kpc at this redshift, is
certainly within the range of plausible natal kicks of a compact
binary progenitor (~1 Gyr merger time for a 500 km/s kick).