Gamma Ray Burst 980703

RXTE has reported an 8 arcmin diameter error box for this burst. The burst is at high Galactic latitude and well placed for predawn optical followup from both hemispheres until about 980706, when moonlight will become a problem.

A 15 arcminute excerpt from the POSS plates is here in FITS format, gzipped Postscript format. The image is centered on the center of the error box, at RA=359.77, Dec=+8.56 (J2000.0). This translates to Galactic coordinates l=101.539, b=-52.124. Ecliptic coords are roughly (3.4,+7.5). The field is nice and uncrowded.

Also, here are Postscript finding charts of the HST Guide Stars in the same field. We have 15 arcminute and 23 arcminute sizes. These plots show several burst location constraints. The dashed line square box shows the location of the original RXTE 90% error region. The solid line diamond shows the location of the final (as of 980706) RXTE 90% error region. The "x"s mark the centers of the RXTE error boxes.
The empty circle with the dashed line is the first BeppoSAX NFI error circle, as reported in BeppoSAX GRB Mail n. 98/22. The empty circle with the solid line is the final BeppoSAX NFI error circle, as reported in BeppoSAX GRB Mail n. 98/23.
The solid line going from top right to bottom left of the image is the lower edge of the 3rd interplanetary network error annulus, as reported in GCN notice 125. The upper edge of the IPN annulus is outside the plotted field.
The filled circles are HST guide stars, with size indicating magnitude. Here is a text listing of the same stars to allow their easy identification for astrometry.

Observations at Kitt Peak

(See our GCN Circular for a citable form of this information.)

Ron Downes and Jennifer Christensen observed the error box of GRB 980703 in R band with the Kitt Peak National Observatory 0.9m telescope. Total integration time was 1 hour, beginning at 980704 09:51 UT. The field of view is 23 arcminutes, and so includes the entire RXTE and BeppoSAX error boxes for the gamma ray burst.

We compared our images with the digitized POSS II image of the field. No variable object consistent with a GRB afterglow and brighter than the detection limit of the POSS II plates was evident.

One moving source was detected, presumably a main belt asteroid (the ecliptic latitude of the field is about 7 degrees), which was travelling towards the east northeast at (very roughly) 27 arcseconds per hour. We estimate that this object was in the RXTE error box from about 0400 to 1600 UT, near the center of the RXTE error box around 1000 UT, and near the center of the BeppoSAX error circle (cf. BeppoSAX GRB Mail n. 98/22) around 1600 UT on 980704.

Our final image is linked below. You are welcome to use this data as a comparison epoch in counterpart searches. We request that you include Ron Downes, Jennifer Christensen, and James Rhoads as authors on any publications whose conclusions relied on this image. Here's the gzip compressed FITS image. Seeing was about 2 arcseconds. 1 ADU per second corresponds to R=21.69 based on comparison with a single standard star frame (Mark A). Airmass and color corrections have not been included but are expected to be small. Based on the RMS noise in the image and this photometric calibration, we estimate a 4 sigma limiting magnitude in a 4" diameter aperture of around R=23.0 to R=23.2.

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