[vsnet-grb-info 4768] GRB070612 - SDSS Pre-Burst Observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  6510
SUBJECT: GRB070612 - SDSS Pre-Burst Observations
DATE:    07/06/12 03:34:29 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 GRB070612
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/GRB070612

We supply FITS images in each of the 5 SDSS bands of a 8'x8' region
centered on the GRB position (ra=121.385 (08:05:32.4), dec=37.2660
(37:15:57.6); GCN 6509), 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 GRB070612_sdss.calstar.dat, we report photometry and
astrometry of 396 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 GRB070612_sdss.objects_flux.dat and
GRB070612_sdss.objects_magnitudes.dat, we report photometry of 1013
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 GRB070612_sdss.objects_flux.dat are in nanomaggies
while the magnitudes listed in GRB070612_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=0.281
mag, A_g=0.207 mag, A_r = 0.150 mag, A_i=0.114 mag, and A_z=0.081 mag.

The file GRB070612_sdss.spectro.dat contains a list of the 2 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.

More detailed information pertaining to our SDSS GRB releases can be
found in our initial data release paper (Cool et al. 2006, PASP 118, 733).
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.