GCN Circular 8685
Subject
Modification of Swift/UVOT response to bright GRBs
Date
2008-12-19T21:10:47Z (16 years ago)
From
Wayne Landsman at GSFC/SSAI <wayne.b.landsman@nasa.gov>
W. Landsman (GSFC), P. Kuin (MSSL), F. Marshall (GSFC), M. Page (MSSL),
P. Roming (PSU), N. Gehrels (GSFC) report on behalf of the Swift/UVOT team
The Swift/UVOT has modified its automated response to GRBs with a BAT
trigger rate larger than 100 cps. For these bright GRBs, a 50s UV
grism exposure is now inserted following the first 150s finding chart in
the white filter. Roughly half of all Swift GRBs are sufficiently
bright to trigger the use of the grism.
The UVOT grism covers the spectral range 1700 - 5500 A, and can provide
useful spectra for GRBs brighter than about V~13. Further details
are available in Kuin et al. (2008, astro-ph 0812/2943 ) who report
their analysis of the UVOT grism spectrum of GRB081203A.
The grism zero-order spectrum in the 50s exposure can provide photometry
for sources brighter than B-18. The zero-order spectrum includes
visible light and its brightness roughly correlates with Johnson B
magnitude, with a scatter of about 0.23 mag.