GCN Circular 2347
Subject
XRF030723(=H2777): Chandra Fading X-ray Afterglow Confirmed
Event
Date
2003-08-07T01:27:59Z (23 years ago)
Edited On
2025-09-09T18:35:42Z (10 months ago)
From
George Ricker at MIT <grr@space.mit.edu>
Edited By
courey.elliott@gmail.com
XRF030723(=H2777): Chandra Fading X-ray Afterglow Confirmed
N. Butler, P. Ford, G. Ricker, R. Vanderspek, J. Villasenor (MIT); D.
Lamb (U. Chicago); G. Garmire (PSU); L. Piro (CNR); and J.G. Jernigan
(UCB), on behalf of a Chandra GRB ToO Team,
write:
On 4 August 2003, the Chandra Observatory targeted the field of
XRF030723, an X-ray flash localized by the HETE satellite (=H2777;
Prigozhin et al, GCN 2313). The duration of the observation was 85
ksec, and it was a followup to the 25 ksec observation reported by
Butler et al. in GCN 2328. The observation spanned the interval 4
August 22:22 UT to 5 August 22:27 UT, 12.66 to 13.67 days after the
burst. The SXC error circle from Prigozhin et al. was completely
contained within the field-of-view of the Chandra ACIS-S3 chip.
Within the SXC error circle, the three X-ray sources from GCN 2328
are detected. Only source #1 is observed to vary in flux at a
significance level of >1 sigma. We detect 74 counts in the 0.5-8.0
keV band, corresponding to a >7-sigma significance decrease (i.e.
factor of ~6) in flux since the first epoch observation. We are thus
extremely confident that source #1 is the X-ray counterpart to
XRF030723 and is the counterpart to the optical source discovered by
Fox et al. (GCN 2323).
If we jointly fit the counts from the first and second Chandra
epochs, we find that the data are well described by a power-law with
absorption fixed at the Galactic value in the source direction (chi^2
= 8.9 for 9 [12-3] degrees of freedom). The best fit photon number
index (for both epochs) is gamma = 1.9 +/- 0.3, which is a typical
value for the X-ray afterglows of long duration GRBs. Using this
model, we find that the first epoch flux is ( 2.2 +/- 0.3 ) x 10-14
erg cm-2 s-1 (0.5-8.0 keV band), while the second epoch flux is ( 3.5
+/- 0.5 ) x 10-15 erg cm-2 s-1 (0.5-8.0 keV band). The decrease in
flux between the two epochs can be described by a power-law with a
decay index of alpha= -1.0 +/- 0.1. This value of alpha is
consistent with the power-law decline reported in the optical by
Dullighan et al. (GCN 2336) for <~1.5 day after the GRB; however, the
index is considerably flatter than the index at t>1.5 days reported
by Dullighan et al. This flatter X-ray decay may possibly be related
to the rebrightening of the optical afterglow reported by Fynbo et
al. (GCN 2345).
We gratefully acknowledge the timely assistance of the observatory
staff at the Chandra Science Center in arranging for the acquisition
and preliminary processing of these data.
This message may be cited.