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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