GCN Circular 2782
Subject
GRB041006: Optical photometry and spectroscopy at TNG
Date
2004-10-07T17:55:28Z (20 years ago)
From
Angelo Antonelli at Obs. Astro. di Roma <angelo@coma.mporzio.astro.it>
D. Fugazza, F. Fiore, S. Covino, L.A. Antonelli, P. D'Avanzo, F. Cocchia,
D. Malesani, E. Pian, L. Stella (on behalf of the Italian CIBO collaboration);
V. Lorenzi and G. Tessicini (INAF-TNG), report:
"We observed the optical afterglow (Da Costa, Noel & Price, GCN 2765;
Maeno et al. GCN 2772) of the X-ray rich GRB 041006 (Galassi et al.,
GCN 2770) with the Italian 3.6m telescope TNG at the Canary Islands.
Both photometric and spectroscopic observations were carried out using
DOLORES under good observing conditions (seeing of ~1").
From two R-band images (2x120 s), we obtain the following magnitude on
Oct 7.07 UT (0.557 days after the GRB):
R = 20.76 +- 0.04.
This value is based on a calibration with Landolt standard stars.
We list below magnitudes we obtain for the two stars close to the
optical transient:
star RA Dec R mag err
- ---------------------------------------------------------
U0900_00213234 00:54:47.045 +01:14:05.60 17.75 +- 0.04
U0900_00213423 00:54:50.131 +01:12:10.33 18.90 +- 0.04
Note as the above magnitudes are fainter than those given by USNO,
by about 0.4 mag. This may indicate a non photometric night, or
that the USNO catalog is not particularly accurate in this region
of the sky.
Starting on Oct 7.10 UT, a low resolution (R ~ 1000) spectrum of the
transient was also obtained. Observations consisted of three exposures,
for a total exposure time of 1 hour, and cover the full spectral range
3800-8000 A. The observed spectrum has a relatively low signal-to-noise
and does not show any strong obvious emission line. The most prominent
absorption feature is at 4800 A. If this feature is identified with the
blend of the MgII lambda2803,2796 doublet, a redshift of z=0.712 is
implied. If this is the case, the MgI lambda2852, FeII lambda2382,2374
and FeII lambda2344 transitions might coincide with other absorption
features in the spectrum, although each single line is not statistically
significant.
At the estimated redshift the isotropic-equivalent gamma-ray energy of
the burst is E = 1.5x10^52 erg (2-400 keV), adopting the fluence reported
by Galassi et al. (GCN 2770),
We are particularly grateful to the TNG staff for their remarkable
support to these observations."
This message is citeable.
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