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GCN Circular 6170

Subject
GRB070306 - SDSS Pre-burst Observations
Date
2007-03-06T18:01:02Z (17 years ago)
From
Richard J. Cool at U.of AZ/Steward Obs <rcool@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 GRB070306
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/GRB070306

We supply FITS images in each of the 5 SDSS bands of a 8'x8' region  
centered
on the GRB position (ra=148.082 (09:52:19.7), dec=10.4710 (10:28:15.6);
Swift-BAT TRIGGER 263361), 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 GRB070306_sdss.calstar.dat, we report photometry and  
astrometry
of 266 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 GRB070306_sdss.objects_flux.dat and
GRB070306_sdss.objects_magnitudes.dat, we report photometry of 458
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 GRB070306_sdss.objects_flux.dat are in nanomaggies
while the magnitudes listed in GRB070306_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=0.148 mag, A_g=0.109 mag,  
A_r =
0.079 mag, A_i=0.060 mag, and A_z=0.042 mag.

The file GRB070306_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.

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.
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