1. HETE- 2 OBSERVATIONS OF THE EXTREMELY SOFT X-RAY FLASH XRF 020903 Liang Jau-shian Institute of Physics, NTHU

2. Introduction The Vela satellites The discovery of GRB was published in the year 1973.

3. IPN (Interplanetary Network) 1980s Helios 2, Pioneer Venus Orbiter, International Sun-Earth Explorer, Venera 11, Venera 12, the Earth orbiter Prognoz 7

4. The Compton Gamma-Ray Observatory April 1991 The Burst and Transient Source Experiment (BATSE) (10keV ~ MeV)

6. Observational properties GRB light curves

7. Durations

8. Classes of Bursts duration/fluence/spectrum Long/bright/soft bursts (59%) Short/faint/hard bursts (23%) Intermediate (2-5 s)/intermediate/soft busts (18%)

9. GRB energy spectra Range: 1keV-18GeV

10. The Band function E peak is the energy of the peak of Spectrum.

12. XRF no gamma ray counterpart The XRF spectra are also well described by the Band function.

13. X-ray rich GRB : E peak < 50keV XRF : E peak at a few keV

14. XRF 020903 Observations HETE-2 the French Gamma Telescope (FREGATE)FREGATE the wide-field X-ray monitor (WXM)WXM the soft X-ray cameras (SXC)SXC

15. French Gamma Telescope

16. Wide Field X-ray Monitor

17. Soft X-ray Camera

19. Temporal properties Two peaks: 2-5 and 5-10 keV No significant flux above 10 keV The duration of the burst is longer in the lower energy band.  this trend is similar to long bright GRBs.

22. Spectrum

26. The constrained Band function method Result: Best-fit value E peak = 2.7 keV 1.1 keV < E peak < 3.6keV with 68% probability E peak < 5.0 keV with 99.7% probability

29. Discussion XRF 020903 is an XRF and not a type I X-ray burst The observes spectrum of XRF 020903 were not the redshifted spectrum of a typical GRB. The properties of XRF 020903 are consistent with the relation between S 7-30 and S 30-400 found by Barraud et al.(2003) Figures 6-8 provide evidence that XRFs, X-ray rich GRBs, and GRBs from a continuum and are therefore the same phenomenon.

33. Thank you