HETE Burst H3862

Burst H3862 summary

  • Trigger time is
    • UTC=20050709_223636
    • GRB=GRB050709+81396
  • Triggering instrument was Fregate
  • Trigger timescale was 0.02 seconds
  • Trigger detected in 30-400 keV band


Evaluation GRB050709



GRB. Sharp spike followed by long, soft outburst.




Download ASCII table of Fregate Band A, B, C lightcurves here.


The color of trigger H3862, defined by the ratio of total counts in Fregate band C (30-400 keV) to band A (7-40 keV) vs. band B (7-80 keV) to band A, overlaid on a the color-color plot of all localized bursts detected to date. Note the separation of XRFs, XRRs, and GRBs.


The signal to noise in Fregate band C (30-400 keV) of trigger H3862 in relation to the S/N of band C of other localized HETE triggers. We find empirically that most XRFs are faint and soft: the fact that localized bursts require a minimum S/N in the 2-25 keV band means that the band C S/N should be low. We find a cutoff in the band C S/N of 6.5 delineates the XRF/non-XRF population with high reliability.


An automated fit of a cutoff power-law spectrum has been performed for H3862. The fit of the model to the data is shown below; the calculated values of Epeak and the burst fluence (25-100 keV) are:

	Epeak    = 93.50 keV
	Fluence  = 6.706e-07 erg/cm^2
	Duration = 0.500 seconds
	PseudoZ  = 2.096

CAUTION:

These results are computed by an automatic script. Please visually inspect the XSPEC summary plot to judge the quality of the results.

Please note that this value of Epeak results from a fit to FREGATE data (8-400 keV) only -- a more reliable joint fit to FREGATE and WXM data is not yet automated. As such, this Epeak estimate is likely to be biased high, especially for soft events, such as XRFs. In our experience, the inclusion of WXM data can lower the value of E_peak substantially. The above Epeak value should thus be viewed as a preliminary estimate. As better fits become available, the information will be posted here.

Click here for an explanation of the method.



Skymap for HETE trigger H3862


GCN 3653

GRB 050709: Refined Spectral and Temporal Properties

M. Boer, G. Ricker, J-L. Atteia, N. Kawai, D. Lamb, and S. Woosley, on
behalf of the HETE Science Team;

M. Arimoto, T. Donaghy, E. Fenimore, M. Galassi, C. Graziani,
J. Kotoku, M. Maetou, M. Matsuoka, Y. Nakagawa, T. Sakamoto, R. Sato,
Y. Shirasaki, M. Suzuki, T. Tamagawa, K. Tanaka, Y. Yamamoto,
and A. Yoshida, on behalf of the HETE WXM Team;

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

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

report:

We have performed a joint fit to the WXM and FREGATE spectral data
for GRB 050709, in order to refine the numbers initially reported in
GCN 3570 (Butler et al. 2005) for the short and long pulse components.

The short pulse is well-fit (chi2/DOF= 35.37/48) by a power-law times
exponential model with photon index alpha = -0.7 +/- 0.2 and nu-F_nu peak
energy Epeak = 83 +18/-12 keV.  The energy fluences of the short pulse
are

S_E(2-30 keV)   = (9.3 +/- 0.9) x 10^(-8) erg cm^-2 and 
S_E(30-400 keV) = (2.9 +/- 0.4) x 10^(-7) erg cm^-2. 

The X-ray to gamma-ray fluence ratio is thus 0.32.  The t90 duration of
the short pulse is 220 +/- 50 ms in the 2-25 keV energy band and 70 +/- 10
ms in the 30-400 keV band.  The t90 duration and Epeak of the short
pulse are consistent with those found for short/hard GRBs (see, e.g.,
Ghirlanda, Ghisellini, & Celotti 2004, A&A, 422, L55 for plots of the
short/hard GRB Epeak distribution).

The long pulse is well fit (chi2/DOF = 108.86/138) by a power-law model
with photon index beta = -2.2 +0.2/-0.4.  The energy fluences of the
long pulse are

S_E(2-30 keV)   = (7.1 +/- 1.5) x 10^(-7) erg cm^-2 and
S_E(30-400 keV) = (3.9 +4.1/-2.7) x 10^(-7) erg cm^-2. 

These spectral results are preliminary because there is a linear trend
in the background that affects the spectral analysis of the long pulse
and has not yet been taken into account.  The t90 of the long pulse is
130 +/- 7 s in the 2-25 keV energy band.

Using the redshift of z = 0.16 measured by Price et al. (2005; GCN 3605), 
the isotropic-equivalent energy of the short pulse in the 1-10,000 keV 
energy band in the rest frame of the source is

Eiso (short pulse) = (2.7 +1.1/-0.3) x 10^(49) erg,

using Omega_M=0.3, Omega_Lambda=0.7, and h=0.65.  The Eiso and Epeak 
values for the short pulse place it well off of the Amati et al. (2002;
A&A, 390, 81) relation for long duration GRBs.

Taking a time interval 0.060 s in the rest frame of the source
(corresponding to t90 = 0.07 s in the 30-400 keV energy band in the 
observer frame) and assuming the same cosmology and energy band as
used above for the Eiso determination, the luminosity of the short
pulse in the 1-10,000 keV energy band in the rest frame of the source 
is

Liso (short pulse) = (5.2 +/- 1.4) x 10^(50) erg s^-1.

Taking even this short time interval, the Liso and Epeak values for the
short pulse place it off the Yonetoku et al. (2004; ApJ, 609, 935)
correlation for long duration GRBs.


Link to Jochen Greiner's web page on GRB050709