[vsnet-grb-info 2562] GRB051227: SDSS pre-burst observations

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  4399
SUBJECT: GRB051227: SDSS pre-burst observations
DATE:    05/12/27 21:36:11 GMT
FROM:    Richard J. Cool at U.of AZ/Steward Obs  <rcool at as.arizona.edu>

Richard J. Cool (Arizona), Daniel J. Eisenstein (Arizona), David
W. Hogg (NYU), Michael R. Blanton (NYU), J. Brinkmann (Apache
Point Observatory), Donald P. Schneider (PSU), and Daniel E. Vanden Berk
(PSU) report on behalf of the Sloan Digital Sky Survey (SDSS)
Collaboration:

The Sloan Digital Sky Survey (SDSS) imaged the field of burst
GRB051227 prior to the burst.  As these data should be useful
as a pre-burst comparison and for calibrating photometry, we are
supplying the images and photometry measurements for this GRB field
to the community.

Data from the SDSS, including 5 FITS images, 3 JPGS, and
3 files of photometry and astrometry, are being placed at
http://mizar.as.arizona.edu/~grb/public/GRB051227

We supply FITS images in each of the 5 SDSS bands of a 8'x8'
region centered on the GRB position (ra=125.270 (08:21:04.8),
dec=31.9290 (31:55:44.4); Swift-BAT TRIGGER 174738), as well as 3
gri color-composite JPGs (with different stretches). The units in
the FITS images are nanomaggies per pixel.  A pixel is 0.396 arcsec
on a side. A nanomaggie is a flux-density unit equal to 10^-9 of
a magnitude 0 source or, to the extent that SDSS is an AB system,
3.631e-6 Jy.  The FITS images have WCS astrometric information.

In the file GRB051227_sdss.calstar.dat, we report photometry
and astrometry of 825 bright stars (r<20.5) within 15' of the
burst location.  The magnitudes presented in this file are asinh
magnitudes as are standard in the SDSS (Lupton 1999, AJ, 118,
1406). Beware that some of these stars are not well-detected in
the u-band; use the errors and object flags to monitor data quality.

In the files GRB051227_sdss.objects_flux.dat and
GRB051227_sdss.objects_magnitudes.dat, we report photometry
of 2481 objects detected within 6' of the GRB position.
We have removed saturated objects and objects with model
magnitudes fainter than 23.0 in the r-band.  The fluxes listed
in GRB051227_sdss.objects_flux.dat are in nanomaggies while the
magnitudes listed in GRB051227_sdss.objects_magnitudes.dat are
asinh magnitudes.

All quantities reported are standard SDSS photometry, meaning that
they are very close to AB zeropoints and magnitudes are quoted
in asinh magnitudes.  Photometric zeropoints are known to about
2% rms.  None of the photometry is corrected for dust extinction.
The Schlegel, Finkbeiner, and Davis (1998) predictions for this
region are A_U=0.213 mag, A_g=0.157 mag, A_r = 0.114 mag, A_i=0.086
mag, and A_z=0.061 mag.

The file GRB051227_sdss.spectro.dat contains a list of the 4 objects
with SDSS spectroscopy within 6 arcminutes of the GRB position.
In addition to the redshift and 1-sigma error for each object,
this file also lists the object spectroscopic classification.

SDSS astrometry is generally better than 0.1 arcsecond per
coordinate.  Users requiring high precision astrometry should take
note that the SDSS astrometric system can differ from other systems
such as those used in other notices; we have not checked the offsets
in this region.

See the SDSS DR4 documentation for more details:
http://www.sdss.org/dr4