GCN Circular 2716

GRB040912(=H3557): Observations with the Chandra X-ray Observatory

N. Butler, P. Ford, G. Ricker, R. Vanderspek, J. Villasenor,
P. Csatorday (MIT); D.  Lamb (U. Chicago); and J.G. Jernigan (UCB), on 
behalf of a Chandra GRB ToO Team,

write:

On 15 September 2004, the Chandra Observatory targeted the field of 
GRB040912, an X-ray flash localized by the HETE satellite (=H3557; 
Butler et al, GCN 2701
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 ). The 20 ksec observation spanned the 
interval 21:57 UT on 15 September to 3:48 UT on 16 September, 3.32 - 3.57
days after the burst. The WXM error circle from Butler et al. was completely 
contained within the field-of-view of the Chandra ACIS-I array.

Within the WXM error region, we detect 22 sources with more than 6
source counts in the 0.5-8 keV band:

 #      Chandra Name           RA           DEC         Cts   HR
 1 CXOU J235631.0-005946    23 56 30.96  -0  59 46.1    55   -0.5
 2 CXOU J235700.0-010009    23 56 59.96  -1   0  9.7    40   -0.3
 3 CXOU J235712.2-005942    23 57 12.17  -0  59 42.1    33   -0.3
 4 CXOU J235642.9-005520    23 56 42.91  -0  55 20.4    32   -0.7
 5 CXOU J235645.7-005655    23 56 46.71  -0  56 54.9    32   -0.3
 6 CXOU J235707.6-005713    23 57  7.57  -0  57 12.6    31    0.8
 7 CXOU J235716.4-010109    23 57 16.37  -1   1  8.7    27   -0.2
 8 CXOU J235639.1-005556    23 56 39.10  -0  55 55.8    20    0.9
 9 CXOU J235651.2-005513    23 56 51.17  -0  55 12.5    17   -0.3
10 CXOU J235636.7-005431    23 56 36.74  -0  54 31.2    15   -0.6
11 CXOU J235711.1-005637    23 57 11.12  -0  56 37.1    12   -0.2
12 CXOU J235637.3-010160    23 56 37.26  -1   1 59.9    12   -0.6
13 CXOU J235656.4-005839    23 56 56.42  -0  58 39.2    11   -0.1
14 CXOU J235700.1-005713    23 57  0.09  -0  57 12.6    11   -1.0
15 CXOU J235659.8-005903    23 56 59.83  -0  59  2.8    10   -0.6
16 CXOU J235649.1-010344    23 56 49.07  -1   3 44.2     9    0.4
17 CXOU J235700.4-010018    23 57  0.36  -1   0 17.6     9   -0.7
18 CXOU J235646.4_005621    23 56 46.45  -0  56 21.4     8    1.1
19 CXOU J235647.0-010045    23 56 46.97  -1   0 45.1     8    0.0
20 CXOU J235648.8-010319    23 56 48.81  -1   3 18.6     8   -1.0
21 CXOU J235704.0-005859    23 57  4.03  -0  58 58.8     8   -0.2
22 CXOU J235707.2-010420    23 57  7.18  -1   4 19.6     7    0.4

We estimate a position uncertainty of 1.0" for the Chandra sources. 
Astrometry was performed using five stars from the USNO-A2 catalog.
The column labeled HR in the table above refers to the hardness
ratio ( Cts_2-8keV - Cts_0.5-2keV )/ Cts_0.5-8 keV.  This quantity is
typically in the range -0.5 to -0.1 for GRBs at high Galactic latitude
and attenuated by the Galactic absorption only.

An image of the Chandra data, with the detected sources overlaid, can
be found at http://space.mit.edu/HETE/Bursts/GRB040912.

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.