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GRB 000313

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  612
SUBJECT: GRB 000313 - optical transient in the BATSE error box
DATE:    00/03/15 03:40:19 GMT
FROM:    Alberto Castro-Tirado at LAEFF-INTA  <ajct@laeff.esa.es> Alberto Castro-Tirado, LAEFF-INTA (Madrid) and IAA-CSIC (Granada) Jan Soldan and Rene Hudec, ASU (Ondrejov) Petr Pata and Martin Bernas, CVUT-FEL (Prague) Javier Gorosabel, DSRI (Copenhagen) Jose Maria Castro Ceron, ROA (San Fernando) Tomas Mateo Sanguino, INTA-CEDEA (Huelva) Antonio de Ugarte, UCM (Madrid) Jose Angel Berna, UA (Alicante) on behalf of the BOOTES-1 Team: Arne Henden, USRA/USNO (Flagstaff) ;
F. Vrba, B. Canzian, H. Harris, USNO (Flagstaff) ; Xavier Delfosse, IAC (Tenerife) ; and Scott Barthelmy, NASA-GSFC (Greenbelt) report:

"We have obtained several images centred at the BATSE ORIGINAL error box for the rather faint burst GRB 000313 (BATSE trigger 8035) with the wide-field CCD of BOOTES-1 on Mar 13.8868 UT (4-min after the GRB, 5-min exposure time in the I-band) and with the narrow-field CCD attached to the 0.3-m telescope on Mar 14.0847 UT (4.8-h after the event, 10-min exposure time, no filter). Limiting magnitudes of the images are about 13 and 18 respectively. The first frame reveals a bright new source of about 10th mag when comparing with the following images obtained starting 55-min later. This point-like object, with the same PSF than other field stars, is not detected in the rest of BOOTES-1 images taken during the night. The position of this optical transient is AR(2000) = 13h50m07.9s, Dec(2000) =+31 16 49  (+/- 3"). Unfortunately no more frames were obtained at the same position in the time interval 9-min < T < 55-min due to a mosaizing around the field. Further images were acquired at the 1.0-m Jacobus Kapteyn Telescope on March 14.169-14.200 UT (BVRI bands) and at the 1.3-m and 1.55-m USNO telescopes on March 14.216-14.261 UT (R- and I-bands) but no object is detected within the OT error box down to a limiting magnitude of I = 21. Although we cannot exclude at this moment that this object could be due to a satellite glint or to an airplane flash, multiwavelength observations (specially radio and deep optical) are encouraged in order to see whether this could be the optical afterglow to GRB 000313. The images are posted at http://www.laeff.esa.es/~ajct/GRBs/GRB000313".

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Here is an example of what all of the wide-field quick-response GRB systems run into almost constantly.  A burst occurred Monday, and a 50mm lens / CCD system in Spain (BOOTES) imaged an 11x16 degree field centered on the coarse BATSE error box within a few minutes after the burst. Out of the thousand or so objects on the frame, there was one that was absent from any previous survey -- at tenth magnitude! A subsequent snapshot an hour later showed nothing at the same position.  Clear-cut case, right?

  Unfortunately, these wide-field cameras have correspondingly big pixels (38 arcsec/pixel in this case), and the fwhm (measure of the star diameter) is essentially one pixel.  This means a cosmic radiation event and a star look almost identical.  There are satellite glints, airplane lights, internal reflections from bright stars in the field, even head-on meteors.  LOTIS and ROTSE also suffer from false detections (a dozen or more per field). It is always a tough call as to whether to publish such an isolated event and take the heat from the community if it proves false, or to ignore it and possibly miss an unusual burst.

  However, this is a good method for amateurs to go after *every* burst (about once/day), since the error box on most bursts is about 16x16 degrees, which fits nicely on a CCD with a 35mm camera telephoto lens.  If you can image within the first minute or so, an optical afterglow may be as bright as 8th or 9th magnitude and easily detectable with such a system.  The tricks are to be able to locate a single such event out of the thousand objects you will detect, and then to continue imaging so that you can confirm the object is present on more than one frame and is fading.

  This is a cheap way to use that old CCD camera that you are replacing.

Arne

I checked pretty thoroughly before making my 'first amateur' statement, but obviously overlooked Warren Offutt's IAUC 7098.  Sorry folks (and sorry Warren!).

  As Janet mentioned, what Bill Aquino and the Buffalo Astronomical Society have shown is that with *very* modest equipment and perseverance, these afterglows can be imaged. They are within the range of almost any amateur system for the first day or so.  This means it is only a matter of time before an amateur becomes the first to discover an afterglow.

Arne

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TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  613
SUBJECT: GRB000313, Radio observations
DATE:    00/03/15 15:36:37 GMT
FROM:    Edo Berger at Caltech  <ejb@astro.caltech.edu> E. Berger (Caltech) and D. A. Frail (NRAO) report on behalf of a larger collaboration:

"Beginning on March 15.57 UT we used the VLA to observe a field centered at the position of the optical transient reported by Castro-Tirado, et al (GCN 612).  There are no radio sources brighter than a 3-sigma level of 205 microJy at 8.46 GHz within a radius of 20" from the location of the optical transient.  Further observations are planned."

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