GRB 990308

On behalf of the Konus team, David Palmer writes:

Konus has detected two series of short spike bursts (typically shorter
than the 64 ms sampling time) on 1999 March 7 & 8.  One such series
begins on 990307 at Seconds of Day (SOD) 62019.5, with subsequent bursts
at +12, +20, +57 (double spike), +72, and +87 (positive flux in 4
consecutive 64 ms samples) seconds later.  The fine time resolution
sampling ends at +100 seconds.  The spikes at +20 and +87 seconds each
exceed 200 counts per sample.

The second series begins at 990308 SOD 11094.5, with a complex burst,
with subsequent peaks at +2, +6, +21 and +28 seconds.

The initial burst of the second series corresponds to BATSE #7456
(990308_11093), which has a final estimated position of (RA, dec) =
(24.8,+67.8) degrees J2000. This is just barely above the horizon as
seen by BATSE at that time, and subsequent spikes may have been blocked
by Earth occultation.

BATSE #7460 (990308_71254) has a final position of (RA,Dec)=(39.8,+71.6)
or 6 degrees away from the final BATSE #7456 position.  This is
consistent with the measurement accuracy, and improbable for two
independent bursts on the same day at better than the 95% level, with
the usual caveats about post-prior probabilities.  The mean location is
8 degrees from the Galactic plane.

All of these properties are consistent with a proposed source
identification as a previously-unknown SGR.

Observations of this sky location with other high-energy instruments are
requested.

            David Palmer
                  palmer@lheamail.gsfc.nasa.gov
           USA    (301) 286-2739  Voice  
           USA    (301) 286-1684  Fax

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 
preliminary 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.

David Palmer, on behalf of the Konus team, writes:

More complete data from Konus suggests that the spikes in GRB light curves
on 990307 and 990308 reported in GCN #271
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  are instrumental in origin.

In addition, the pulses were absent in data from other spacecraft, including Ulysses (K. Hurley, priv. comm.), RXTE (F. Marshall, priv. comm.) and BATSE (Woods et al.  GCN 273
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 ).

We therefore retract our suggestion that these observations are of a new
Soft Gamma Repeater.


            David Palmer
                  palmer@lheamail.gsfc.nasa.gov
           USA    (301) 286-2739  Voice  
           USA    (301) 286-1684  Fax

D. A. Smith, A. Levine, and R. Remillard (MIT), on behalf of the
RXTE/ASM team at MIT and NASA/GSFC, K. Hurley (UCB), on behalf of the
Ulysses GRB team, and S. Barthelmy (NASA/GSFC) report:

GRB 990308 was detected by the All-Sky Monitor on RXTE during a 90-s
observation that began at MJD 51245.218333 (03/08/99 05:14:24 UTC).
This burst was also observed by BATSE (Trigger #7457), and the BATSE
trigger time was 05:15:07 UTC.  At this time, SSC 3 of the ASM (the
camera aligned with the rotation axis of the ASM assembly) observed an
interval of enhanced count rates that lasted until the end of the
observation.  The light curve of the event was highly variable, with a
mean 1.5-12 keV flux of about 400 mCrab.  SSC 3 has lost the use of
four of its eight resistive anodes over its the three years of
operation, but we could still localize this GRB with the remaining
anodes to a 10 deg by 6.6 arcmin error box (full-width at 90%
confidence, including estimates of both statistical and systematic
effects), centered at R.A. = 182.761832, Decl. = +4.282319 (J2000) and
rotated 51.2 deg east from north.

GRB 990308 was also detected, very weakly, by Ulysses, and it was
therefore possible to obtain an IPN annulus by triangulation of burst
arrival times at Ulysses and BATSE.  This annulus is centered at
R.A. = 154.0761 degrees, Decl. = -9.6383 degrees, with a radius of
35.583 degrees, and a 3 sigma half-width of 0.399 degrees.  This
annulus is based on preliminary data, but we do not expect it to
improve much, if at all.

The IPN annulus and the ASM error box cross each other, yielding a
joint error box 48 arcmin by 6.6 arcmin.  The corners of this box lie
within the BATSE LOCBURST error circle, and their celestial
coordinates are:

R.A.(J2000)  Decl. (J2000)
186.142867     +6.921870
186.091377     +7.021754
185.502582     +6.412172
185.451355     +6.512323

This position was still in the FOV of SSC 3 after its 6-deg rotation,
and examination of the instrument response at the center of the joint
error box yields a ~4-sigma detection of a ~50 mCrab flux (1.5-12
keV), averaged over the next 90-s ASM observation (56-146 s after the
burst trigger).  This is an average of less than 2 c/s in the
time-series data during this observation, which shows an average total
count rate of 27 c/s, so it is not possible to directly measure the
burst behavior on any shorter time-scales.  By the second observation
after the burst (t=152-242 s), the average flux had fallen below 30
mCrab (3-sigma upper limit). 

Figures showing localizations of GRB 990308, as well as the time-
series data from the first ASM observation, can be seen on the WWW at

http://xte.mit.edu/grb/trig7457.24/web_trig7457_24.html

This report may be cited.

Stephen Holland, Johan Fynbo, Bjarne Thomsen (University of Aarhus),
Michael Andersen (University of Oulu),
Gunnlaugur Bjornsson (University of Iceland),
Jens Hjorth (University of Copenhagen),
Andreas Jaunsen (University of Oslo),
Priya Natarajan (University of Cambridge, & Yale), and
Nial Tanvir (University of Hertfordshire)

     We have obtained 7842 seconds of STIS images with the 50CCD
(clear) aperture of the sky where the optical afterglow associated
with GRB 990308 was detected.  This data was taken as part of the
Survey of the Host Galaxies of Gamma-Ray Bursts (Holland et al. GCN
698
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 ) approximately 468 days after the burst occurred.  Combined images
are now available at
"http://www.ifa.au.dk/~hst/grb_hosts/data/index.html".

     We estimate that the uncertainty in the location of the optical
afterglow in our drizzled STIS image is approximately 1.2 arcsec,
mostly due to the uncertainty in transferring the Schaefer et
al. (1999, ApJL, 524, L103) coordinates for the afterglow to the STIS
image.  We do not detect any objects within this error circle, and
estimate that our five-sigma limiting magnitude is V ~ 28.5.  There
are two faint, extended sources located 1.448 arcseconds (1.2 sigma)
and 2.228 arcseconds (1.9 sigma) west of Schaefer et al. (1999)'s
position for the optical afterglow.  Some properties of these objects
are given below.

Object    X       Y       magnitude      FWHM(")  Ellipticity
  1    1081.77  909.91   26.9 +/- 0.1     0.10       0.09
  2    1086.91  879.21   27.0 +/- 0.1     0.11       0.36

The X and Y values are the pixel coordinates on our drizzled image and
the magnitude is the STIS 50CCD (clear) AB magnitude measured in an
aperture with a diameter of 0.75 arcsec.  The resolution limit of the
image is ~0.084 arcseconds.  There are no other objects within
approximately six arcseconds of the Schaefer et al. (1999) position
for the optical afterglow, so it is possible that one of these objects
is the host galaxy for GRB 990308.  A GIF image of the error circle,
and the two extended objects, is available at
"http://www.ifa.au.dk/~hst/grb_hosts/data/grb990308cd.gif".