G. Ricker, D. Lamb, and S. Woosley on behalf of the HETE Science Team;
R. Vanderspek, G. Crew, J. Doty, G. Monnelly, J. Villasenor; N. Butler, T. Cline, J.G. Jernigan, A. Levine, F. Martel, G. Pizzichini, and G. Prigozhin, on behalf of the HETE Operations and HETE Optical-SXC Teams;
N. Kawai, M. Matsuoka, Y. Shirasaki, T. Tamagawa, A. Yoshida, E. Fenimore, M. Galassi, and C. Graziani, on behalf of the HETE WXM Team;
J-L Atteia, M. Boer, J-F Olive, J-P Dezalay, and K. Hurley on behalf of the HETE FREGATE Team;
On 13 February 2001 at 12:35:35 UTC, a soft spectrum, high energy transient at high galactic latitude was detected and localized by HETE. Both the WXM and the FREGATE instruments detected the event. Although the WXM and FREGATE cover extremely broad energy bands (WXM: 2-25 keV; FREGATE: 6-500 keV), the burst event was only detectable in the 2-18 keV band by WXM, and in the 6-10 keV band by FREGATE. Because of the unusual spectrum of the transient, neither instrument triggered.
The preliminary coordinates of the burst are RA= 10h 31m 36s, Dec= +5d 30' 39" (J2000), derived from combining data from the WXM and Boresighted Optical Cameras. The statistical error radius in the WXM localization is 3.5 arcmin (95% confidence) In addition, we estimate a systematic error radius at present of 30 arcmin about this location. The spacecraft aspect was known to an accuracy of +/- 30 arcsec (95% confidence) from the optical cameras, and will be improved.
The burst exhibited a double-peaked structure and lasted about 30 seconds. The incident flux measured with the WXM (2-18 keV) at the first peak is about 0.7 Crab, and at the second peak is about 2.4 Crab. The spectrum in the 2-18 keV range was harder than that of the Crab nebula at the first peak, and softer than that of the Crab at the second peak. The peak flux seen with FREGATE (6-10 keV) was ~2 Crab. Assuming a Crab-like spectrum, the peak energy flux was ~1.5 E-8 erg/cm2/sec in the 6-10 keV range.
The high galactic latitude of the source, well away from the Galactic Bulge, and the shape of its light curve suggest that it is a gamma-ray burst with a very unusual spectrum, perhaps similar to those reported for "X-ray rich" GRBs by Heise et al (2001) from BeppoSAX observations. Conceivably, it could instead be a nearby X-ray burst source. A preliminary catalog search of the WXM error circle revealed no correspondence with known globular sources, cataclysmic variables, low mass X-ray binaries, or flare stars.
Follow-up observations of this unusual transient are encouraged.
Additional information on the 13 February high energy transient (including light curves, the WXM error box and results from the preliminary catalog searches), as well as the HETE mission, is available at:
HETE=High Energy Transient Explorer
FREGATE=French Gamma Ray Telescope
WXM=Wide Field X-ray Monitor
SXC=Soft X-ray Camera
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This page may be updated frequently.
|Light curve for the WXM instrument.|
|IRAS F10289+0547||G||10 31 33.94||+05 32 01.4|
|Zel 1029+056||Rad||10 32 21||+05 24.9|
|PMN J1031+0543||Rad||10 31 24.3||+05 43 02|
|HD 91085||*||10 31 00.79||+05 20 28.8|
|HD 91234||*||10 32 06.39||+05 14 48.7|
|HD 91235||*||10 32 10.88||+05 12 15.0|
|BPM 86854||*||10 33 03.3||+05 35 58|
|HD 90993||*||10 30 22.33||+05 43 36.3|
|GSC 00259-01186||*||10 32 26.67||+05 50 34.3|
|** HEI 762||**||10 30.0||+05 43|
|PGC 31052||G||10 31 28.6||+05 01 26|
Last modified: February 14, 2001