[vsnet-grb-info 100] GRB011130 (XRF011130) Second Epoch Chandra Observations

[GCN Circulars <gcncirc@lheawww.gsfc.nasa.gov>]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  1272
SUBJECT: GRB011130 (XRF011130) Second Epoch Chandra Observations
DATE:    02/03/15 03:33:31 GMT
FROM:    George Ricker at MIT  <grr@space.mit.edu>

GRB011130 (=XRF011130): Results of a Second Epoch Observation with 
the Chandra X-ray Observatory

N. Butler, G. Monnelly, G. Ricker, J. Doty, P. Ford, R. Vanderspek, 
G. Crew, A. Dullighan (MIT); D. Lamb (U.Chicago); and P. Plucinsky 
(CFA)

on behalf of the Chandra GRB ToO Team and the HETE Science Team

write:

On 20 February, from 10:02 UT - 14:30 UT, the Chandra Observatory 
targeted the field of the X-ray rich gamma-ray burst XRF011130, 
localized by the HETE satellite (Ricker et al., GCN1165)  This was a 
16 ksec observation with ACIS-I, following up the 30 ksec observation 
performed with ACIS-I on 10 December (Ricker et al., GCN 1185).

Of the 20 brightest sources reported in GCN 1190 (Monnelly et al.), 
none were observed to fade in a manner that is consistent with the 
power-law behavior that is characteristic of gamma-ray burst 
afterglows.  (A power law index of -1.3 implies a fade by a factor 
~15, between our 1st and 2nd epoch observations.)  Corrected for 
exposure, the largest fade for any of the sources in the list was by 
a factor of 3.  We note that our brightest epoch 1 source (CXOU 
J030527.9+034657), which appears to be associated with a 20th 
magnitude galaxy (Mirabal & Halpern, GCN 1187), faded by a factor of 
approximately 2.

Beyond the top 20 brightest, we note that our 24th and 27th brightest 
1st epoch sources (see partial table below) faded to levels 
consistent with the background.  We estimate a 50% probability for 
chance fading to the background in one or more of our 24 brightest 
sources; we estimate a 75% probability for chance fading to the 
background in one or more of our 27 brightest sources.

Chandra Name               RA          DEC     E1C  E1B  <E2C>  E2C  E2B
CXOU J030515.1+034457  3 5 15.12  3 44 57.02   8.1  2.9   4.0  -0.7  0.7
CXOU J030527.8+035548  3 5 27.81  3 55 48.09  13.8  4.2   6.5  -1.3  4.3

Here E1C denotes the epoch 1 net counts for the source, E1B the epoch 
1 background counts estimate, <E2C> the expected epoch 2 net number 
of counts based on epoch 1, E2C the observed net counts in epoch 2, 
and E2B the epoch 2 background counts estimate.  A complete table in 
this form, containing all of our 1st epoch sources, can be found at:

http://space.mit.edu/HETE/Bursts/GRB011130/epoch2_table.html

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