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GRB 990316 (BATSE Trig. 7475)

GCN Circular

H.S. Park, L. Ott, R. Porrata (LLNL), G. Williams, D. Hartmann (Clemson Univ.) report on behalf of the LOTIS collaboration:

LOTIS obtained realtime images of GRB990316 (BATSE Trigger 7475). LOTIS started recording the first image 13.6 sec after the burst (on the rising edge of the GRB light curve). The first image was taken with a 30 s integration time, thus this image completely overlapped the remainder of the GRB gamma-ray emission which lasted a total of ~40 sec. The first image from one of our 4 cameras (each with 8.8 x 8.8 deg field of view) covers > 98% of the BATSE 3 sigma (0.3 deg statistical + 1.6 deg systematic) error circle. The GRB location is further constrained by an annulus derived from IPN data (GCN/IPN notice) that passes through the BATSE error circle in the image.

We searched for optical transients in this image by 1) comparing background images taken at later times and 2)comparing the stellar objects in the image with objects in the Guide Star Catalog and Digital Sky Survey images. We found one transient object at RA=147.54, DEC=-4.95 (J2000) near the edge of the IPN annulus with V~12.5 brightness. This object was seen only in the first image. No object is seen in the DSS image at this location. The second image was started after the gamma ray emission was over (at 55 sec after the start of the burst). We cannot rule out the possibility that this OT is a local effect rather than associated with the gamma ray burst. However, we encourage follow up observations at this location for possible afterglow observations.

Further analysis is in progress and associated data will be placed on our web page.

G RB 990316 (BATSE Trig. 7475) was detected by BATSE at 9:40:39.54 UT (1:40:39.54 PST). The burst had a duration of approximately 40 seconds. LOTIS received the 'Original' GCN coordinates of RA=156.08°, Dec=-9.42° at 9:40:45.4 UT. After a slew time of 7.7 seconds LOTIS began imaging at 9:40:53.1 UT, just 13.6 seconds after the burst began. The first image (30 s integration) was obtained simultaneous with the gamma-ray emission.

A n optical transient was found in the first LOTIS image inside the Huntsville 3-sigma BATSE error box and just slightly (49") outside the 3-sigma IPN annulus. The transient was found in only the first image and did not appear in any later image. After the IPN annulus refined the location of the burst the GCN circular above was disseminated to the community approximately 42 hours after the burst.

No fading optical or radio afterglow was found at the position (RA=147.54°, Dec=-4.95°) of the LOTIS transient.

Further analysis of this event is continuing.

T he plot below shows the gamma-ray light curve of GRB 990316. The shaded areas represent the times of the first three LOTIS images. These images covered most of the BATSE 3-sigma error circle and the IPN annulus.

LOTIS Response.
GRB 990316 Gamma-Ray Light Curve

LOTIS Coverage.
The two circles are the Huntsville 1-sigma and 3-sigma BATSE error circles. The annulus is the 3-sigma IPN annulus. The star indicates the position of the LOTIS OT.

GRB 990316 Coverage

LOTIS GRB 9903216 OT (Image Size - 2.0° x 2.0°).
The optical transient is in the center of the image and the 3-sigma IPN annulus extends from upper left to lower right. The image shown is the result of subtracting image ten from image one. This subtraction analysis produces a "3-D" image of constant sources while transient events appear in "2-D" as white or black objects. The LOTIS transient is 49" outside the annulus.


LOTIS GRB 9903216 OT Comparison (Image Size - 0.5° x 0.5°).
Composite of the first and second LOTIS images near the OT of GRB 990316. The difference in sensitivity is due to the different integration times of the first image (30 s) and second image (10 s).


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