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GCN Circular 2655

Subject
GRB 040812: Second epoch CXO Observations
Event
GRB 040812
Date
2004-08-25T01:53:25Z (21 years ago)
From
Chryssa Kouveliotou at MSFC <chryssa.kouveliotou-1@nasa.gov>
S. Patel (USRA/NSSTC), C. Kouveliotou (NASA/MSFC,NSSTC), S. Mereghetti,
D. Gotz (IASF-Milano), N. Lund, J. Chenevez (Danish Space Research
Institute), P. Ubertini (IASF-Rome), A. Levan (U. Leicester), 
E. van den Heuvel (University of Amsterdam), K. Hurley (UCB), report on 
behalf of a larger Integral team:

We observed with Chandra/ACIS-S the error box of the Integral GRB 040812 
(Gotz et al. 2004, GCN 2640Loading...
 
 ) for a second time starting on 2004-08-22 9:55
UT, 
approximately 10 days after the trigger for 10 ks. We have compared the 
sources reported in our earlier GCN on the first CXO observation (Patel et 
al., 2004, GCN 2648Loading...
 
 ) with the second CXO image, applying a SNR>2 selection 
threshold. The results are shown in the Table below.

     No.       RA         Dec     Counts(1)* SNR Counts(2)  SNR  
      1  16 26 0.47 -44 41  22.6          9      2.8   --       --
      2  16 26 2.25 -44 43  49.4         57      6.9   38       5.4
      3  16 26 6.48 -44 43  20.8         10      2.9   10       2.7
      4  16 26 8.44 -44 41  25.2         33      5.0   33       5.2
      5  16 26 1.71 -44 43  27.9         --      ---   16       3.7

*0.5-8.0 keV band

All coordinates are given in J2000. 

We do not detect source #1 above SNR=2.0; a search in the corresponding
error 
region in the second epoch CXO image reveals 5 net counts at this location.
We 
conclude that there is no significant variation in that source within 
statistics. Source #2 decayed with an index of approximately 0.6 between the

two CXO observations; this source, thus, seems to be most likely the
candidate 
of the GRB 040812 afterglow, as also pointed out by Campana et al. 2004 
(GCN 2649Loading...
 
 ). Finally, a new source (#5) appeared within the IBIS error box; 
inspection of the first image reveals 3 net counts at this location, 
indicating a variable source.  

We detect two of the radio sources (#2 and #4) reported by Ishwara Chandra 
et al. 2004 (GCN # 2653) at the same flux level in both CXO observations.

We are grateful to the Chandra Science Data Center for processing the 
data rapidly and in particular to Harvey Tananbaum and Andrea Prestwich
for approving this DDT observation.