HETE FOV

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High Energy Transient Explorer 2 (HETE-2) reports the coordinates of Gamma-ray burst (GRB) more quickly and accurately than that we have ever had. X-ray detectors of HETE-2 determine the GRB position with an accuracy of 10 arcmin (10 arcsec for the best case) on board, and report them to the world within 10 sec via the internet. By combining the HETE-2 GRB alerts with follow-up observations, we can study GRBs from just after the burst where the most informative phase of the GRBs. The wide-field X-ray monitor (WXM), which has a field of view of 60deg x 60deg, is the key instrument for the HETE-2 localization. It is important to study the performance of the WXM in orbit for reporting the GRB position with good accuracy.

GRB detection by HETE : GRB010213

HETE Burst Alert Network

When a GRB is detected by HETE, a summary of the collected data send to the series of 12 burst

alert stations distributed around the equator in 10 sec after the burst. These data is forwarded to

MIT and distributed to the ground observers via GRB Coordinate Network (GCN).

In-orbit Performance of the Wide-field X-ray Monitoron board the High Energy Transient Explorer 2

N. Kawai, A. Yoshida, T. Tamagawa (RIKEN), M. Matsuoka, Y. Shirasaki (NASDA)M. Yamauchi (Miyazaki Univ.), E.E. Fenimore, and M. Galassi (LANL)

on behalf of the HETE-2 science mission team

In-orbit WXM calibration with the Crab nebula

Palau burstalert station

Singapore primarystation and a 1.8mparabolic antenna

X counters Y counters

Cross section perpendicular to Crab drift direction

3 m

in

Tim

e

Launched at 4:45pm October 9, 2000 (JST) WXM light curve30sec

Fundamental(29.83 Hz:P=33.52 ms)

Data: Dec. 22, 2000 256 seconds duration

Pulse Profile(2 cycles are shown)

Power spectrum density

GRB010213

HETE orbit and the burst alert stations

A red circle shows the coveragearea of a burst alert station. RIKEN provides Singapore primary / burst alert station andPalau one.

• Imaging ~10” • Spectroscopy

WXM

SXC

FREGATE

BoresightCamera

Attitude ControlCamera

2 - 25 keV

6 - 400 keV

0.5 - 14 keV

39"/pix.

88"/pix.• Spectroscopy• Trigger

• Imaging ~10’ • Spectroscopy

12.6x12.6 deg

2

5.5x5.5 deg

2

TOP VIEW

weight 124 kghight 89 cmwidth 66 cm

altitude 590-630 km equatorial orbitpointing to anti-solar direction

WXM : 1D proportional counters + coded-masks

Coded-mask image as a function of time

Energy spectrum

We measured Crab position with WXM at

a few hundred points distributed in its field

of view. The data were compare to the

positions measured by the optical cameras

which provide more accurate position

information than WXM.

The high galactic latitude of the source, well away from the Galactic Bulge, and the shape of its lightcurve 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 catalog search of the WXM error circle 　 revealedno correspondence with known globular sources, cataclysmic variables, low mass X-ray binaries, or flare stars.

We issued the HETE’s first GCN report (GCN #934) on February 13. The coordinates of the burst are derived from combining data from the WXM and Boresighted Optical Cameras. The statistical error radius in the WXM localizationis 3.5 arcmin (95%CL). In addition, we have an unresolved systematic error of a fraction of degree, and it will beimproved.