Gamma-Ray Burst 920903B

This page is an addendum to the GCN Circular 6155 (D. Denisenko, O. Terekhov) published on 2007 Feb. 27 and the extended version of the paper submitted to Astronomy Letters (Pis'ma v Astronomicheskiy Zhurnal). It contains the color images and animations which cannot be inserted to the printed version of journal, but are essential for illustrating the discovery.

Abstract

As a result of the systematic search for the archival plates taken at the Palomar and Siding Spring observatories in the course of all sky survey, several cosmic gamma-ray bursts were selected whose error boxes were covered (entirely or in part) shortly after the event. Four suspect objects were found in the error box of bright GRB 920903B on the plate taken 16 days after the burst, one of them being consistent with IPN annulus. Two of these objects are probably variable stars, the other two - plate defects.

Comment: This page contains the data related to GRB 920903B. In order The article is divided in three parts. You can find the description of GRB afterglow search program, list of the events studied and the detailed analysis on GRB 920925C optical afterglow candidate at the separate pages:

GRB 920903B

There were two gamma-ray bursts detected on Sep. 3rd, 1992 by WATCH instrument (Sazonov et al., 1998). The brighter of them is the second one. The table below lists both bursts with their trigger time (UT), duration, fluences in 10-7 erg/cm2 in two energy bands and their ratio. The last column indicates the confirmation of bursts by the instruments on other spacecrafts (Ph - PHEBUS/Granat, U - Ulysses). 
--------------------------------------------------------
Burst    Trigger  Duration    Fluence      Hardn   Other
 name    h  m  s   T90, s  8-20 keV 20-60  ratio    S/C
--------------------------------------------------------
W920903  01 35 46  131.83   42.0   107.4    2.56    PhU
W920903b 23 29 01   23.80   61.5   171.3    2.78    PhU       
--------------------------------------------------------
Let us consider GRB 920903B in more detail.

WATCH detection

The light curve of GRB 920903B in two energy bands is given on the figure (top panel showing the counts per second in 8-20 keV range, bottom panel - 20-60 keV). Temporal resolution is 1 sec. Time is given in seconds since 23:29:01 UT.

The burst was localized by WATCH instrument to the circle centered at: 

R.A. = 301.54, Dec. = 22.59 deg (20h06m10s, +22o35'24", Epoch J2000.0)
with 3-sigma error radius 0.22 deg, or 0.30 deg including systematic error (Sazonov et al., 1998).

DSS plates coverage

WATCH error box falls inside the fields 527 and 595 of the 2nd Palomar Observatory Sky Survey (POSS-II). This area was covered by the Blue plates SJ01921 in June 1988 and SJ03405 in July 1990, Red plates SF04200 in September 1991 and SF04812 in September 1992 (see below), IR plates SN05844 in June 1994 and SN06295 in July 1995. POSS-I Red and Blue (O) plates were taken in July 1951, Quick-V plate - in August 1982.

Red Palomar plate SF04812 with 65-min exposure was taken on 1992 Sep. 20 between 03:19-04:24 UT (16.2 day after the burst). The WATCH position of GRB 920903B lies 2.90 deg from the plate center. We have downloaded the 15'x15' images from DSS Plate Finder.

Two sets of B, R and IR images of the field at different epochs allowed us to perform the color-combined blinking technique. Using IR plate as a Red channel, R plate - as Green and B plate as Blue, two color images were created which carry information on the variability inside the field in three photometric bands simultaneously. Blinking these images against each other makes easier to detect objects which are only present in Red plate of 1992 Sep. 20. These objects will stand out on the combined image with their green color. As a result, four suspect objects were found inside the WATCH error circle. They will be presented here later.

IPN error box

As noted above, GRB 920903B was also detected by the Ulysses spacecraft. That allowed to localize the burst to the box with an area of 29 square arcmin (Hurley et al., 2000). This is a 35 times reduction of WATCH error circle of 1018 square arcmin.

Intersection of the IPN annulus with the WATCH error circle is shown on the next figure. Half-width of annulus (3-sigma) is 0.007 deg, or 25'.

Links

Acknowledgements

This work has intensively used the Digitized Sky Survey produced at the Space Telescope Science Institute based on photographic data obtained at the Palomar Observatory with the help of California Institute of Technology and funds from NSF, NGS, Sloan Found., Samuel Oschin Found. and Eastman Kodak Corporation.
Page created: Feb. 27th, 2007 22:30+0300
Last updated: Feb. 27th, 2007 23:00+0300

Denis Denisenko denis@hea.iki.rssi.ru

To my GRB Page | To my Astronomy Page | To my Main Page