GCN Circular 3332

Jason X. Prochaska (UCO/Lick Obs.), Sara Ellison (U. Victoria), 
R. J. Foley (UCB), J. S. Bloom (UCB), & H.-W. Chen (MIT) report on behalf 
of the GRAASP collaboration:

"We observed the afterglow of GRB 050502a for 3600s with HIRES on the KeckI     
telescope starting at UT 05:53:46 on May 02, 2005, 3.5 hours after the initial  
burst.  We obtained a low SNR, high resolution spectrum (R~40000).  We report  
a tentative redshift of z=3.793 based on the following lines of evidence:
 
1.  We detect a prominent flux discontinuity at 4400 Ang, blueward of which no  
flux is present.  We interpret the flux decrement at 4400 A as the Lyman 
limit absorption produced by the host of the GRB. 
 
2.  The flux blueward of ~5870 Ang is 'patchy', i.e. indicative of the Lya 
forest.  A broad absorption feature is present at 5820 Ang, which we 
interpret as the Lya absorption due to the ISM of the host galaxy.
 
3.  We identify a strong absorption feature at 6040 Ang, which is consistent
with SiII1260 at z=3.793.

Further analysis is underway.
 
This message can be cited."