HETE- 2 OBSERVATIONS OF THE EXTREMELY

SOFT X-RAY FLASH XRF 020903

Liang Jau-shianInstitute of Physics, NTHU

Introduction The Vela satellites

• The discovery of GRB was published in the year 1973.

IPN (Interplanetary Network)

• 1980s• Helios 2, Pioneer Venus Orbiter, Intern

ational Sun-Earth Explorer, Venera 11, Venera 12, the Earth orbiter Prognoz 7

The Compton Gamma-Ray Observatory

• April 1991• The Burst and Transient Source Exper

iment (BATSE) (10keV ~ MeV)

Observational properties

• GRB light curves

Durations

Classes of Bursts

duration/fluence/spectrum• Long/bright/soft bursts (59%)• Short/faint/hard bursts (23%)• Intermediate (2-5 s)/intermediate/soft

busts (18%)

GRB energy spectra

• Range: 1keV-18GeV

The Band function

),exp()100

()(0E

E

keV

EAENE

,)100

)(exp(100

)( 0

keV

E

keV

EA

breakEEE 0)(

breakEEE 0)(

1~

)2( 0

EEpeak Epeak is the energy of the peak ofSpectrum.

F

XRF

• no gamma ray counterpart• The XRF spectra are also well

described by the Band function.

• X-ray rich GRB : Epeak < 50keV• XRF : Epeak at a few keV

XRF 020903

Observations• HETE-2• the French Gamma Telescope (

FREGATE) • the wide-field X-ray monitor (WXM) • the soft X-ray cameras (SXC)

French Gamma Telescope

Wide Field X-ray Monitor

Soft X-ray Camera

Temporal properties

• Two peaks: 2-5 and 5-10 keV• No significant flux above 10 keV• The duration of the burst is longer in t

he lower energy band. this trend is similar to long bright G

RBs.

Spectrum

The constrained Band function method

Result:• Best-fit value Epeak = 2.7 keV• 1.1 keV < Epeak < 3.6keV with 68% prob

ability• Epeak < 5.0 keV with 99.7% probability

Discussion• XRF 020903 is an XRF and not a type I X-ray b

urst• 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 S7-30 and S30-400 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.

Thank you