TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  1218
SUBJECT: GRB optical counterpart candidate in GCN 1217 is M dwarf
DATE:    02/01/20 21:33:19 GMT
FROM:    J.A.Tyson at Lucent  <tyson@silicon.div111.bell-labs.com>

Subject: GRB optical counterpart candidate in GCN 1217 is M dwarf


A. Clocchiatti (Catolica U., Chile), P.C. Boeshaar (Drew U.), J.A. Tyson, 
A.C. Becker, D. Wittman (Bell Labs, Lucent Technologies), and the 
Deep Lens Survey Team:

The possible GRB optical counterpart reported in GCN 1217 has the post
burst spectrum of a late M dwarf star. A follow-up spectrum and multi color
photometry taken on the Magellan telescope two days after the flare discovery
show a spectrum and colors corresponding to an dM4 dwarf star plus a fainter 
galaxy.  The composite V mag is ~19.4. The star is nearly centered on the galaxy. 
Coords J2000 galaxy: 10 48 56.14 -05 00 41.4, star: 10 48 56.12 -05 00 41.1.
The presence in the spectrum of TiO, CaOH (5530-60 A), and CaOH at
6385A plus B-V~1.7, V-R~1.3 are consistent with a dwarf M star of type dM4-4.5 
star with H_a + H_b seen in emission.  This type of star lies near the peak
of the disk stellar luminosity function. With an estimated Mv~12, this places 
the candidate star at a distance of approximately 300 pc and 200 pc above the
galactic plane, well within the scale height for disk population M dwarfs.
The ten minute optical burst reported in GCN 1217 was trans337 reported at
http://dls.bell-labs.com/transients.html