GCN Circular 2322

GRB030725 (=H2779): A Bright GRB Localized by the HETE WXM and SXC

Y. Shirasaki, T. Tamagawa, M. Suzuki, C. Graziani, T. Donaghy, M.
Matsuoka, K. Torii, T. Sakamoto, A. Yoshida, E. Fenimore, M. Galassi,
Y. Nakagawa, R. Satoh, Y. Urata, T. Yamazaki and Y. Yamamoto, on
behalf of the HETE WXM Team;

G. Ricker, J-L. Atteia, N. Kawai, D. Lamb, and S. Woosley
on behalf of the HETE Science Team;

G. Prigozhin, N. Butler, G. Crew, J. Doty, A. Dullighan, R.
Vanderspek, J. Villasenor, T. Cline, J. G. Jernigan, A. Levine, F.
Martel, E. Morgan, G. Monnelly, G. Azzibrouck, J. Braga, R.
Manchanda, and G. Pizzichini, on behalf of the HETE Operations and
HETE Optical-SXC Teams;

C. Barraud, M. Boer, J-F Olive, J-P Dezalay, and K. Hurley on behalf 
of the HETE
FREGATE Team;

write:

At 11:46:24.82 UTC (42384.82 s UT) on 25 July 2003, the HETE FREGATE 
and WXM instruments detected  GRB030725 (=H2779), a bright, 
double-peaked long GRB located at high galactic latitude (b = 37 
degrees).

The burst triggered Fregate in the 5-120 keV energy band. A GCN burst 
alert was issued 2.6 m later. Because the source was located at the 
extreme edge of the FOV of the WXM Y counter, no flight localization 
was derived. Ground analysis of the WXM data provided a localization 
that was reported in a GCN Notice at 13:19:34 UT. The WXM 
localization can be expressed as a 90% confidence error region that 
is centered at:

WXM Center-ground:   RA= 20h 33m 34s,  Dec= -50d 45' 30"  (J2000)

The WXM error region is unusually elongated because of the very low 
exposure of the Y detector. The four corners of the WXM error region 
are located at J2000 coordinates:

WXM_CORNER1:    	RA= 20h 33m 53.3s, Dec= -51d 00' 04"
WXM_CORNER2:    	RA= 20h 33m 15.3s, Dec= -50d 59' 02"
WXM_CORNER3:    	RA= 20h 33m 15.1s, Dec= -50d 30' 58"
WXM_CORNER4:    	RA=	20h 33m 52.8s, Dec= -50d 31' 59"

Ground analysis of the SXC data provided a better localization that 
was disseminated as a GCN notice at 16:07:46 UT. The SXC localization 
can be expressed as a 90% confidence error region that is centered at:

SXC Center-Ground:   RA= 20h 33m 47s , Dec= -50d 45' 49"  (J2000)

The SXC X camera detected the burst, but the SXC Y camera did not. We 
were able to use the WXM Y localization to constrain the SXC error 
region in the Y direction. The four corners of the SXC error region 
are located at J2000 coordinates:

SXC_CORNER1:    RA= 20h 33m 36.5s, Dec= -50d 59' 35"
SXC_CORNER2:    RA= 20h 33m 57.3s, Dec= -51d 00' 11"
SXC_CORNER3:    RA= 20h 33m 56.6s, Dec= -50d 32' 06"
SXC_CORNER4:    RA= 20h 33m 35.7s, Dec= -50d 31' 30"

H2779 was comprised by two FRED-like* peaks, separated by ~160s. The 
duration of the first peak was ~40s, while that of the second peak 
was ~10s. A total of 25000 counts were detected in the 7-30 keV 
energy band during the ~180s interval encompassing both peaks, 
corresponding to a fluence of ~5 x 10-6 ergs cm-2. The peak flux 
was >2 x 10-7 ergs cm-2 s-1 (ie >5 x Crab flux) in the same energy 
band. [* FRED = Fast rise, exponential decay]

In the 30-400 keV band, the fluence was ~2 x 10-5 ergs cm-2, which is 
~4 times the fluence in the 7-30 keV band. Thus, H2779 appears to be 
a "classical" long hard burst.

A light curve and finding chart for GRB030725 is provided at the following URL:

http://space.mit.edu/HETE/Bursts/GRB030725

This message may be cited.