TITLE:   GCN CIRCULAR
NUMBER:  16891
SUBJECT: GRB141004A: NOT imaging and spectroscopy
DATE:    14/10/05 16:28:34 GMT
FROM:    Steve Schulze at U of Iceland  <sts30@hi.is>

S. Schulze (PUC, MAS), T. Kruehler (ESO Chile), D. Xu, J. P. U. Fynbo (DARK/NBI), N. R. Tanvir (U Leicester), P. Jakobsson (U. Iceland), S. Galleti (INAF-OAB) report on behalf a larger collaboration:

We observed the field of GRB 141004A (D'Elia et al. GCN 16878, Mereghetti et al. GCN 16879) with the 2.5-m Nordic Optical Telescope (NOT) equipped with ALFOSC. Observations started at 01:52:22 UT on October 5 (i.e., 2.52 hr after the burst). We obtained a 200-s image in the R band.

The afterglow reported in D'Elia et al. (GCN 16878) and Gorosabel et al. (GCN 16880) is clearly detected. It has an R-band magnitude of 20.6 mag (not corrected for foreground extinction), calibrated against several USNO stars. The mid-exposure time is 2.55 hr after the trigger. Compared to D’Elia et al (GCN 16881), the brightness of the afterglow did not decrease.

In addition, we obtained an optical spectrum, with a total exposure of 3 x 1800 s, using Grism #4 and covering the wavelength range 3750 - 9000 AA at a resolution of 17 AA. Observations started at 02:17:23 UT (i.e. 2.9 hr after the burst). The continuum is detected down to ~3750 AA. No absorption line is visible in the spectrum. A tentative emission line is detected at 5866.4 AA, which could be [OIII]-5007 at z=0.17 or [OII] at z=0.57. A higher S/N spectrum is needed to elucidate the nature of this feature.