HETE Burst H1864

Burst H1864 summary

  • Trigger time is
    • UTC=20011130_061935
    • GRB=GRB011130+22775
  • Triggering instrument was WXM
  • Trigger timescale was 5.120 seconds
  • Trigger detected in 2-25 keV band

Evaluation

XRF 011130


GRB011130=XRF011130 (HETE Trigger #1864)

Contents:


Special note on Burst 1864:

HETE Trigger 1864 was detected as a long, soft "X-ray rich" event on 30 November 2001. The localization significance in the WXM was very high, but because the bright moon (only 2.5 hours from full) filled the field-of-view of the boresight star trackers, no real-time aspect was available. Attempts were made to calculate the spacecraft aspect on the ground 1-2 hours after the burst. Two methods were tried: one using stars detected by the "ACS" cameras, which point ~30 degrees off the earth-sun line, and one using the on-board sun sensors and magnetometers.

Ground calculation of spacecraft aspect using only stars detected by the ACS cameras is, in principle, possible, but it is not a routine procedure for HETE. As a result, attempts to derive the optical aspect in the early morning hours were not successful. However, because the trigger occurred while the spacecraft was in sunlight, it was possible to try to use the sun sensors and magnetometers to derive the aspect. This method of calculating aspect is done regularly, and typical errors measure a fraction of a degree. However, the magnetometer method relies on having significant magnetometer data at the current roll angle: unfortunately, this was not the case for H1864. In addition, there was a gap in the magnetometer data: as a result, the fit converged to an incorrect answer.

The solution derived ~4 hours after the burst, when used to calculate the coordinates of the Crab from its measured position in the WXM field-of-view, yielded an error of 0.4 degrees, entirely consistent with expectations. A localization calculated with this aspect solution was distributed in a GCN Notice (~5 hours after H1864) and GCN Circular(~6 hours after H1864); a second Notice, which was derived from the constraint in the angular separation of the burst source and the Crab in the WXM, was distributed about 8 hours after H1864.

Upon further review of the star camera data, it became clear that our estimate of the roll angle of the spacecraft was off by about four degrees. With this new constraint in hand, both methods of determining aspect converged on the correct solution. Calculation of the Crab coordinates from its WXM position yielded coordinates only 6 arcminutes from the Crab. A third GCN Notice was sent out about 10 hours after H1864 with the new burst coordinates which, unfortunately, differed by about four degrees from those in the first Notice.

We believe the coordinates distributed in third HETE_GND_ANALYSIS GCN Notice to be correct. WXM team members are currently working to reduce the estimated error in the WXM position: each better position will be distributed by GCN Notice. As a result of this chain of events, improved analysis software has been developed to reduce the time required and the possibility of error in calculating aspect near full moon.
GRB011130 = XRF011130: Chandra ACIS-I Observations

2nd Epoch Observations 20 February, from 10:02 UT - 14:30 UT (16 ksec)

Full 2nd Epoch Source Table

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 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, 
following up the 30 ksec observation performed 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

This message may be cited.

1st Epoch Observations 10 December, from 00:38 UT - 09:27 UT (30 ksec)

GRB011130 (=XRF011130): Further analysis of Chandra Target of 
Opportunity Observations

G. Monnelly, N. Butler, G. Ricker, P. Ford, R. Vanderspek (MIT); and
D. Lamb (U.Chicago)

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

write:

On 10 December, from 00:38 UT - 09:27 UT, the Chandra Observatory
targeted the field of the X-ray rich gamma-ray burst XRF011130 that
was previously localized by the HETE satellite (Ricker et al.,
GCN 1165). The revised error circle for XRF011130 (Ricker et al.
GCN 1178) fits completely within the field-of-view of the ACIS-I 
array on Chandra.  The observation duration was 30 ksec.

In Ricker et al. (GCN 1185), we reported the locations of the brightest 
10 X-ray sources localized in our Chandra observation.  In this Circular, 
we complete the list of detected sources by presenting all sources found 
in the entire ACIS detector area down to a limit of 10 detected counts, 
including the sources presented in GCN Circular #1185.  The information 
for sources outside the nominal 7.6' error region are presented in a 
separate table for clarity.  This analysis is based on wavedetect, 
whereas GCN #1185 was based on celldetect.  The results are similar: nine 
of the celldetect sources appear among the top ten wavedetect sources.

The following table includes all sources above a limit of 10 detected
counts found within the HETE error circle (radius 7.6').  

  Chandra Source ID       RA         DEC      dRA(s) dDEC('') Cts SNR  
CXOU J030527.9+034657  3 5 27.70  3 46 56.46  0.057    1.18   128 56.6 
CXOU J030532.5+035140  3 5 32.32  3 51 39.79  0.057    1.18   105 49.6 
CXOU J030534.3+034958  3 5 34.08  3 49 58.35  0.057    1.18    37 18.8 
CXOU J030514.2+034854  3 5 14.03  3 48 53.56  0.057    1.19    32 15.4 
CXOU J030458.7+034702  3 4 58.46  3 47  2.31  0.067    1.28    31  8.0 
CXOU J030550.1+035009  3 5 49.88  3 50  8.80  0.058    1.20    28 11.5 
CXOU J030541.4+034808  3 5 41.25  3 48  7.26  0.057    1.19    23 11.5 
CXOU J030534.2+034208  3 5 34.07  3 42  8.24  0.062    1.33    22  7.0 
CXOU J030536.0+035303  3 5 35.83  3 53  2.99  0.058    1.19    20  9.7 
CXOU J030534.7+035147  3 5 34.68  3 51 47.96  0.057    1.19    18  8.8  

CXOU J030502.4+034522  3 5  2.44  3 45 22.41  0.071    1.30    18  5.8  
CXOU J030532.4+034301  3 5 32.44  3 43  1.87  0.062    1.29    17  6.0  
CXOU J030540.5+034936  3 5 40.45  3 49 36.96  0.057    1.19    15  7.8  
CXOU J030516.5+035229  3 5 16.48  3 52 29.34  0.059    1.19    14  7.3  
CXOU J030522.2+035354  3 5 22.21  3 53 54.43  0.059    1.19    14  7.1  
CXOU J030512.9+034936  3 5 12.75  3 49 36.22  0.057    1.19    12  6.5 
CXOU J030530.3+035224  3 5 30.31  3 52 24.48  0.057    1.18    11  6.0  
CXOU J030532.9+034927  3 5 32.86  3 49 27.94  0.057    1.19    11  6.0  
CXOU J030537.0+034406  3 5 37.04  3 44  6.95  0.059    1.25    10  4.6  
CXOU J030501.6+034613  3 5  1.65  3 46 13.94  0.061    1.24    10  3.9  

The following table includes all sources above a limit of 10 detected
counts found outside the HETE error circle (radius 7.6'), and within 10' 
of the HETE position.

  Chandra Source ID       RA         DEC      dRA(s) dDEC('') Cts SNR   
CXOU J030539.8+034148  3 5 39.79  3 41 48.82  0.060    1.23   132 26.0  
CXOU J030454.4+035149  3 4 54.39  3 51 49.41  0.066    1.25    52 11.7  
CXOU J030519.7+035711  3 5 19.67  3 57 11.99  0.062    1.21    50 14.8  
CXOU J030539.1+035652  3 5 39.09  3 56 52.21  0.063    1.21    42 12.4  
CXOU J030529.8+035711  3 5 29.79  3 57 11.93  0.063    1.21    36 12.3  
CXOU J030537.4+035744  3 5 37.41  3 57 44.79  0.065    1.22    32  8.5  
CXOU J030538.3+035825  3 5 38.28  3 58 25.95  0.067    1.26    24  7.4  
CXOU J030453.0+035144  3 4 53.04  3 51 44.28  0.070    1.25    16  5.3  
CXOU J030602.8+034737  3 6  2.77  3 47 37.64  0.074    1.39    16  4.8  
CXOU J030529.0+034115  3 5 29.02  3 41 15.90  0.065    1.38    11  4.0  

In the table, delta(RA), the uncertainty in RA, and delta(DEC),the
uncertainty in DEC, were established by summing the following in
quadrature for each coordinate: the error reported by wavdetect,
the error reported by the correlation code, and the error estimate
from the star reference catalog.

It is notable that during our Chandra observation there were no 
counts detected from within the error circle of the VLA radio source 
reported by Berger and Frail (GCN 1173).

The ACIS-I image of the error region of GRB011130
Click on image for the full source list and larger image!