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GCN Circular 10041

Subject
GRB091018: Swift/UVOT observations
Date
2009-10-19T04:12:08Z (15 years ago)
From
Wayne Landsman at GSFC/SSAI <wayne.b.landsman@nasa.gov>
W.B. Landsman (NASA/GSFC) and M. Stamatikos (OSU/NASA/GSFC) report on  
behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 091018  
69s after the BAT trigger (Stamatikos et al., GCN 10034).    The  
afterglow is well-detected in all seven UVOT filters at the position 
reported by Stamatikos et al.     The initial magnitudes are as follows:

Filter    T_start(s) Exp(s)      Mag
white         69    147     14.57 � 0.012
white        860    147     16.48 � 0.018

u            281    246     15.07 � 0.017
u           6911    197     18.04 � 0.08

v            610     19     16.4 � 0.14
b            536     19     16.4 � 0.08
uvw1         660     20     15.9 � 0.12
uvm2         635     20     15.7 � 0.16
uvw2         586     20     16.1 � 0.15

The detection in the uvw2 filter indicates a redshift less than z = 1.1, 
consistent with the value of z= 0.971 reported by the Magellan group ( 
Chen et al., GCN 10038).

The values quoted above are not corrected for the Galactic extinction  
due to the reddening of E(B-V) = 0.029 in the direction of the burst  
(Schlegel  et al. 1998). The photometry is on the UVOT photometric 
system described in Poole et al. (2008, MNRAS, 383, 627).
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