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GCN Circular 447

Subject
GRB 991106, optical observations
Date
1999-11-12T21:55:16Z (25 years ago)
From
Paul Vreeswijk at U of Amsterdam <pmv@astro.uva.nl>
Javier Gorosabel, Univ of Amsterdam and LAEFF-INTA (Madrid)
 Evert Rol and Paul Vreeswijk, Univ of Amsterdam
 Alberto Castro-Tirado, LAEFF-INTA (Madrid) and IAA-CSIC (Granada)
 Antonio Aparicio, David Martinez Delgado, Sebastian L. Hidalgo, 
 Otilia de La Rosa, Instituto de Astrofisica de Canarias (IAC), 
 Marco Azzaro, Isaac Newton Group (ING),
 Katherine F. Gunn, University of Southampton, 
 Chryssa Kouveliotou (USRA/MSFC),
 Marco Feroci on behalf of the BeppoSAX team, IAS (Frascati)
 
 report:
 
 "We report on I band observations of the BeppoSAX WFC position of GRB
 991106 (Gandolfi et al., GCN 435), carried out on Nov 6.856-6.868 UT
 (roughly 9.6 hours after the burst) and on Nov 11.821-11.833 UT with
 the 2.5-m INT telescope at the Observatorio del Roque de los Muchachos
 at La Palma. On each of the two nights we used the Sloan I band filter
 and exposed for a total of 900s. The limiting magnitudes are I~23.5
 and I~23.7, respectively, for the first and second epoch.

 At R.A.= 22:24:27.85, decl.=+54:21:54.4 (J2000), we find a 5-sigma
 detection in our first epoch image (using a circular aperture with a
 radius equal to the FWHM). This position is ~2.2" away from the radio
 source reported by Frail et al (GCN 444). The detection is not present
 on the second epoch image.  We estimate the error in our astrometry to
 be about 1.5".  However, all the flux of the object is concentrated in
 2 or 3 pixels, while the FWHM is 4.3 pixels, so it does not appear to
 be an actual source.

 We checked for variability of all the objects we detected inside the
 WFC and NFI error circles (GCN 435 and 445, respectively). None of the
 sources brighter than I=22 vary by more than about 0.4 mag. For
 sources with I > 22 the large photometric errors do not allow us to
 discern any variability. In conclusion, no reliable candidates
 have been found. 

 We find that the two red objects reported by Stecklum et al. (GCN 446)
 are constant in brightness between our two epochs within the
 measurement errors. We measure the preliminary magnitudes I=19.8 +/-
 0.2 and I=20.1 +/- 0.2 for the objects located at R.A.= 22:24:32.4,
 decl.= +54:23:51 (J2000) and R.A.= 22:24:39.7, decl.= +54:21:46
 (J2000), respectively."

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