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GCN Circular 2797

Subject
Search for SN light in XRF 040912 with MEGACAM
Date
2004-10-12T15:18:08Z (20 years ago)
From
Jean-Luc Atteia at Lab d Astrophys.,OMP,Toulouse <atteia@ast.obs-mip.fr>
G. Stratta (OMP), F. Malacrino (OMP), M. Boer (OHP), A. Klotz (OMP), J-L Atteia (OMP), P. Martin (CFHT), C. Veillet (CFHT), J-C Cuillandre (CFHT) and Lisa Wells (CFHT) communicate:

We observed the HETE WXM error region of XRF 040912 (Butler et al. GCN 2701)  with the wide-field imager MegaCam (36 2048 x 4612 pixel CCDs, 1 square degree FOV), mounted on the 3.6-m CFH Telescope.

Two exposures with integration time of 860s each, in the i' band have been performed consecutively starting on October 5.4197 UT (T_grb+22.8 days). 

We looked for a possible SN emission for the 22 X-ray sources detected with Chandra 
(Butler et al., GCN Circ=2716).  The observation results follow:        

	First exposure (T)            Second exposure (T+15min)
------  ---------------------------   --------------------------
CXO      Distance to      i-band      Distance to      i-band 
source   X-ray position   mag         X-ray position   mag  
        (")                          (")                  
------  ---------------------------   -------------------------- 
#1 *    1.5            20.60           -               - 
#2      1.6            22.25           1.5             22.26 
#3      1.4            20.17           1.5             20.20 
#4       -             -               -               - 
#5      1.4            21.21           1.5             21.00 
#6      1.5            18.96           1.3             18.99 
#7      1.0            21.82           1.1             21.61 
#8      1.8            23.02           1.3             23.09 
#9      -              -               -               - 
#10     3.2            20.74           2.1             20.66 
#11     1.0            21.68           0.9             22.44 
#12     -              -               -               - 
#13 *   -              -               0.5             22.21 
#14     1.2            21.84           1.6             21.39 
#15     1.6            22.79           -               - 
#16     -              -               -               - 
#17     -              -               -               - 
#18     0.7            21.35           0.6             20.86 
#19     -              -               -               -      
#20     -              -               -               -             
#21     -              -               -               -      
#22     -              -               -               -     -------------------------------------------------------------------- 
* Source was at the CCD line separation and was missed in one image
--------------------------------------------------------------------

We did not consider sources at distances greater than 2.5" from the 
X-ray source position. 
Our conclusions from these observations are:

1- If source #4 is the afterglow of XRF 040912 (as suggested in GCN 2731), we do not observed any SN emission down to i=23.2+/0.2 mag at 22.8 days after the burst event.

2- Source #13, which has been considered as the tentative afterglow of XRF 040912 (GCN 2728) does not appear to vary from the second Magellan observation. 

We note that source #6 is coincident with an underlying galaxy with i'=19 mag, it has a decaying behavior in X-rays (Butler et al. GCN=2716) and shows the highest V-i' color index (V-i'=2.05, V magnitude reported by Gorosabel et al., GCN 2724), requiring a very red galaxy, or a rebrightning.  
This resemble the case of XRF 040701 (Barraud et al. GCN 2620) for which the potentially associated Chandra source (Fox et al. GCN 2626) was coincident with a z=0.2146 emission-line galaxy (Kelson et al. GCN 2631) with lower limit R~17.9 mag that possibly prevented the observation of a delayed SN emission, assuming a SN fainter than SN 1998bw and more similar to SN2002ap or SN1994I (Pian et al. GCN 2638). 
Further observations of source #6 are welcome.

A comparison of the two CFHT images that show the nearest objects to the
Chandra sources detected in the i' band, can be found at
http://www.cfht.hawaii.edu/~grb/XRF040912.html
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