[vsnet-grb-info 4363] GRB070224: Magellan Imaging Observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  6148
SUBJECT: GRB070224: Magellan Imaging Observations
DATE:    07/02/26 02:43:41 GMT
FROM:    Hsiao-Wen Chen at U Chicago  <hchen at oddjob.uchicago.edu>

H.-W. Chen (U Chicago), K. Glazebrook (Swinburne University), and J. S. 
Bloom (UC Berkeley) report on behalf of a larger collaboration:

"We continued imaging observations of the field around GRB 070224
(Racusin et al., GCN 6137), using MagIC on the Magellan Clay telescope.
The observations consisted of 5x300 sec dithered exposures in the i' band
and 6x600 sec dithered exposures in the z' band, starting at Feb 25.180 UT,
~ 8 hours after the initial Swift trigger.  The images were taken under
photometric conditions with a mean seeing of 0.5" in i' and 0.6" in z'.
Object photometry was calibrated using a Sloan Digital Sky Survey
photometric standard observed after the GRB field.  Combining the images
obtained using GMOS and MagIC, we measure photometry of the compact source
at RA(J2000)=11:56:06.6 and Dec(J2000)=-13:19:48.9 (Chen, Glazebrook, &
Bloom, GCN 6145; see also Thoene et al. GCN 6142, Mirabal et al. GCN
6146, Rol et al. GCN 6147) as the following:

   Filter         AB      UT(mid)         Camera

     i'    22.60 +/- 0.10  25.107          GMOS
     z'    22.40 +/- 0.20  25.135          GMOS
     i'    22.54 +/- 0.05  25.188         MagIC
     z'    22.56 +/- 0.05  25.221         MagIC

We therefore conclude that this is not a variable source.

The source at RA(J2000)=11:56:06.5 and Dec(J2000)=-13:19:49.9 that
appeared at low level in the first GMOS i'-band image (Chen,
Glazebrook, & Bloom GCN 6145) remains absent in the MagIC images."