TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4353 SUBJECT: GRB051215 - SDSS pre-burst observations DATE: 05/12/15 03:09:25 GMT FROM: Richard J. Cool at U.of AZ/Steward Obs Richard J. Cool (Arizona), Daniel J. Eisenstein (Arizona), David W. Hogg (NYU), and Michael R. Blanton (NYU) report on behalf of the Sloan Digital Sky Survey (SDSS) Collaboration: The Sloan Digital Sky Survey (SDSS) imaged the field of burst GRB051215 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/GRB051215 We supply FITS images in each of the 5 SDSS bands of a 8'x8' region centered on the GRB position (ra=163.139 (10:52:33.4), dec=38.6260 (38:37:33.6); GCN 4352), 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 GRB051215_sdss.calstar.dat, we report photometry and astrometry of 179 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 GRB051215_sdss.objects_flux.dat and GRB051215_sdss.objects_magnitudes.dat, we report photometry of 1240 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 GRB051215_sdss.objects_flux.dat are in nanomaggies while the magnitudes listed in GRB051215_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=0.081 mag, A_g=0.059 mag, A_r = 0.043 mag, A_i=0.033 mag, and A_z=0.023 mag. The file GRB051215_sdss.spectro.dat contains a list of the 8 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. Among the spectra, there are 4 galaxies at the same redshift z=0.145. Most likely, this is the redshift of the cluster noted in Ofek and Gal-Yam (GCN 4351). This value is somewhat higher than photometric redshift estimate of z=0.09 in Gal et al. (2003, AJ, 125, 2064), although there are also 2 galaxies near that redshift. 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 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, Abazajian et al. (AJ, 129, 1755, 2005), when using the data or referring to the technical documentation.