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GCN Circular 4938

H4043, an unusual high-energy transient observed by HETE
2006-03-31T16:00:17Z (18 years ago)
Jean-Luc Atteia at Lab d Astrophys.,OMP,Toulouse <>
E. Fenimore, G. Ricker, J-L. Atteia, N. Kawai, D. Lamb, and S. Woosley,
on behalf of the HETE Science Team;

M. Arimoto, T. Donaghy, M. Galassi, C. Graziani, N. Ishikawa,
A. Kobayashi, J. Kotoku, M. Maetou, M. Matsuoka, Y. Nakagawa,
T. Sakamoto, R. Sato, T. Shimokawabe, Y. Shirasaki, S. Sugita,
M. Suzuki, T. Tamagawa, K. Tanaka, and A. Yoshida, on behalf of the

N. Butler, G. Crew, J. Doty, G. Prigozhin, R. Vanderspek,
J. Villasenor, J. G. Jernigan, A. Levine, G. Azzibrouck, J. Braga,
R. Manchanda, G. Pizzichini, and S. Gunasekera, on behalf of the HETE
Operations and HETE Optical-SXC Teams;

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


At 06:41:42 UTC on March 31, 2006 HETE-2 detected a long, bright
and soft event at the extreme edge of the WXM field of view.

Ground analysis yields an error box centered at (J2000):
(RA,DEC) (deg) = 233.444d  -15.235d (15h 33m 47s  -15d 14' 04")

with the following corners (J2000):
(RA,DEC) (deg) =   233.792   -15.396
(RA,DEC) (deg) =   233.081   -15.456
(RA,DEC) (deg) =   233.096   -15.072
(RA,DEC) (deg) =   233.806   -15.015

The error box area is 944 square arc minutes.

The time profile shows a rise time of ~10 seconds and a fall time
of >100s, with little obvious spectral evolution. Neither a power-law
nor a blackbody yields an acceptable spectral fit.

This event is unusual. It resembles an X-ray burst from a galactic binary,
yet its location at high galactic latitude, its long duration without the
expected spectral evolution from photospheric expansion, and the failure
of a blackbody spectral fit all argue against this interpretation.

On the other hand, it is unusually bright for an X-ray flash, and the
failure of a power law fit argues against this interpretation.

There is  a known x-ray source (1RXS J153521.7-150420) in the error box,
but this is not unlikely for a box this large.

A light-curve of the event is given at

We urge further observations of this unusual event at all wavelengths.

[GCN OPS NOTE(31mar06): Per author's request, the URL was corected; see 
GCN Circ 4939.]
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