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NASA Swift: GRB060526 - SDSS Pre-burst Observations

Status Report From: Goddard Space Flight Center
Posted: Friday, May 26, 2006

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TITLE: GCN GRB OBSERVATION REPORT
NUMBER: 5164
SUBJECT: GRB060526 - SDSS Pre-burst Observations
DATE: 06/05/26 17:43:57 GMT
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 GRB060526 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/GRB060526

We supply FITS images in each of the 5 SDSS bands of a 8'x8' region centered on the GRB position (ra=232.827 (15:31:18.4), dec=0.286400 (00:17:11.0); GCN 5162), 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 GRB060526_sdss.calstar.dat, we report photometry and astrometry of 753 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 GRB060526_sdss.objects_flux.dat and GRB060526_sdss.objects_magnitudes.dat, we report photometry of 1467 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 GRB060526_sdss.objects_flux.dat are in nanomaggies while the magnitudes listed in GRB060526_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=0.337 mag, A_g=0.248 mag, A_r = 0.180 mag, A_i=0.136 mag, and A_z=0.097 mag.

The file GRB060526_sdss.spectro.dat contains a list of the 5 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, astro-ph/0601218). See the SDSS DR4 documentation for more details: http://www.sdss.org/dr4.

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, in press, astro-ph/0507711), when using the data or referring to the technical documentation.

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