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GRB 990308 (BATSE Trig. 7457)


GCN Circular

G. Williams, H. Park and R. Porrata report on behalf of the LOTIS collaboration:

LOTIS and Super-LOTIS obtained early time observations of the error box of GRB 990308 (BATSE Trig. 7457). This event was detected and localized by the XTE/All-Sky Monitor. LOTIS began imaging the area centered on the 'Original' GCN coordinates 12.6 s after the start of the burst. Five images (10 s integration) were obtained at these coordinates before the system received and responded to the 'Final' GCN coordinates. LOTIS began imaging the area centered on the 'Final' GCN coordinates 132.1 s after the start of the burst.

The first five LOTIS images covered a small portion of the XTE/ASM error box within but near the edge of the BATSE 3-sigma error circle. We matched all stellar objects in the error box with known Guide Star Catalogue objects. No transient sources brighter than m ~ 11.5 (no filter) were detected. Wispy high clouds reduced the system's limiting magnitude during this event.

LOTIS slewed to the more accurate 'Final' GCN coordinates 132.1 s after the start of the burst. The subsequent images covered the entire XTE/ASM error box within the BATSE 2-sigma error circle. We found a single anomalous constant source within the error box with a position which corresponds to the position of a V ~ 10.6 asteroid (Laetitia) at the time of the image. All other sources within the XTE/ASM error box correspond to known stars in the GSC. No fading or flaring objects brighter than m ~ 11.0 were found.

In addition, Super-LOTIS (60 cm reflector) began a raster scan around the 'LOCBURST' GCN coordinates 1700 s after the start of the burst. Four Super-LOTIS images (30 s integration; t=1694 s, 1809 s, 2620 s, 3923 s) covered most of the XTE/ASM error box within the BATSE 2-sigma error circle. No fading or flaring objects brighter than m ~ 14.0 (no filter) were detected in the Super-LOTIS images. Super-LOTIS is presently operating at a temporary site at LLNL utilizing an uncooled prototype CCD camera. Thin clouds and surrounding building lights prevented the system from reaching a deeper limiting magnitude.

Further details of the LOTIS timing and coverage as well as images are posted at:

http://hubcap.clemson.edu/~ggwilli/LOTIS/GRB990308.html

This message is citable.


O n the evening of March 7th - 8th LOTIS responded to 5 GCN Triggers:


BATSE Trigger 7456 - Original

BATSE Trigger 7457 - Original

BATSE Trigger 7457 - Final

BATSE Trigger 7457 - Locburst

BATSE Trigger 7457 - XTE/ASM

G RB 990308 (BATSE Trig. 7457) was detected by BATSE at 5:15:07.38 UT (9:15:07.38 PST). The burst had a duration of approximately 50 seconds. LOTIS received the 'Original' GCN coordinates of RA=174.35°, Dec=11.33° at 5:15:12.4 UT. After a slew time of 7.6 seconds LOTIS began imaging at 5:15:20.0 UT, just 12.6 seconds after the burst began. Five images (10 s integration) were obtained at this location.

A t 5:17:12.4 UT or approximately 125 seconds after the burst began LOTIS received the 'Final' GCN coordinates of RA=178.58°, Dec=5.91°. At 5:17:19.1 LOTIS began imaging the area of these more accurate coordinates. LOTIS obtained 40 images at this location. For the remainder of the evening LOTIS imaged the area centered on the 'Locburst' GCN coordinates of RA=185.82°, Dec=6.10°.

T he plot below shows the gamma-ray light curve of GRB 990308. The shaded/hatched areas show the times of the first five LOTIS images which covered a small portion of the XTE/ASM error box (see coverage plot below). The shaded area represents the time of the sixth LOTIS image. All subsequent images covered the entire XTE/ASM error box.

LOTIS Response.
GRB 990308 Gamma-Ray Light Curve

LOTIS Coverage 12.6 s - 110 s; five images.
Right Ascension increases to the right.

GRB 990308 Coverage

LOTIS Coverage 132 s - 1010 s; 40 images.
During the remainder of the evening LOTIS covered the entire XTE/ASM error box.

GRB 990308 Coverage

Portion of a LOTIS image (1.1° x 1.1°).
Right Ascension increases to the left.
The left image was obtained during the burst and the right image the following evening. The diagonal line through the left image is the center of the XTE/ASM error box which has a width of approximately 2.3' or less five LOTIS pixels (15 arcsec/pixel) on each side of the center line.

Asteroid Laetitia

Super-LOTIS responds to its first GCN Trigger!!

The four images shown from upper right to lower left were obtained at
t_burst + 1694 s, 1809 s, 2620 s, 3923 s respectively.
GRB 990308 Super-LOTIS Coverage


GRB 990308 Super-LOTIS Coverage




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