[vsnet-grb-info 3846] GRB061002 - SDSS Pre-Burst Observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  5679
SUBJECT: GRB061002 - SDSS Pre-Burst Observations
DATE:    06/10/02 04:09:58 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), David
J. Schlegel (LBNL), J. Brinkmann (APO), Donald Q. Lamb
(Chicago), Donald P. Schneider (PSU), and Daniel E. Vanden
Berk (PSU) report:

The Sloan Digital Sky Survey (SDSS) imaged the field of
burst GRB061002 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/GRB061002

We supply FITS images in each of the 5 SDSS bands of a
8'x8' region centered on the GRB position (ra=220.346
(14:41:23.0), dec=48.7360 (48:44:09.6); BAT Trigger
231974), 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 GRB061002_sdss.calstar.dat, we report
photometry and astrometry of 226 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 GRB061002_sdss.objects_flux.dat and
GRB061002_sdss.objects_magnitudes.dat, we report photometry
of 371 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 GRB061002_sdss.objects_flux.dat
are in nanomaggies while the magnitudes listed in
GRB061002_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=0.223 mag, A_g=0.164 mag, A_r =
0.119 mag, A_i=0.090 mag, and A_z=0.064 mag.

There are currently no objects within 6 arcminutes of the
GRB position in the SDSS spectroscopic database.


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.

More detailed information pertaining to our SDSS GRB
releases can be found in our initial data release paper
(Cool et al. 2006, astro-ph/0601218).  See the SDSS DR4
documentation for more details: http://www.sdss.org/dr5.

These data have been reduced using a slightly different
pipeline than that used for SDSS public data releases.
We cannot guarantee that the values here will exactly match
those in the data release in which these data are included.
In particular, we expect the photometric calibrations to
differ by of order 0.01 mag.

This note may be cited, but please also cite the SDSS data
release paper, Adelman-McCarthy et al. (2006, ApJS, 162,
38), when using the data or referring to the technical
documentation.