[vsnet-grb-info 7581] GRB 090417A: Early-type nature of the putative host

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  9137
SUBJECT: GRB 090417A: Early-type nature of the putative host
DATE:    09/04/17 17:35:29 GMT
FROM:    Josh Bloom at UC Berkeley  <jbloom at 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 Hα 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).