TITLE: GCN CIRCULAR NUMBER: 6486 SUBJECT: GRB 070419A, deep LBT photometry and possible supernova detection DATE: 07/06/04 18:36:29 GMT FROM: Peter Garnavich at U of Notre Dame J. Hill (LBTO/UAz), P. Garnavich (Notre Dame), O. Kuhn (LBTO/UAz), N. Bouche, P. Buschkamp (MPE), X. Fan, (U Ariz), X. Dai, J. Prieto, K. Z. Stanek (Ohio State), P. Milne, J. Bechtold (U Ariz), R. M. Wagner (LBTO/OSU), J. Rhoads (Ariz State) report: The Large Binocular Telescope (LBT) continued to image the position of the GRB 070419A afterglow (Stamatikos et al, GCN 6302; Chornock et al. GCN 6304; Garnavich et al. GCN 6406) with the LBC-blue CCD camera (http//lbc.mporzio.astro.it) and 8.4-m SX mirror. Data were obtained 2007 May 10.18 (UT) and May 20.22 (UT) which are 20.8 and 30.8 days after the burst. Using the calibration assumed by Garnavich et al. (GCN 6406), we estimate the brightness of the source at the position of the afterglow using point-spread-function fitting photometry as follows: UT Date Age (days) Exposures Seeing r mag Error ----------------------------------------------------------- Apr 23.15 3.7 10x200s 1.2" 24.75 0.18 (GCN 6406) May 10.18 20.8 25x200s 0.96" 25.29 0.05 May 20.22 30.8 15x200s 0.73" 25.71 0.13 The decay between 4 days (LBT observation from GCN 6406) and 20 days after the burst is very slow and corresponds to a power-law index of 0.3. This could indicate host galaxy contamination, but the images remain unresolved. Extrapolating the decline to 30 days post-burst predicts the afterglow should be 30% brighter than the actual observed magnitude. This increased fading rate is inconsistent with a host galaxy dominating the flux and suggests light from a GRB progenitor supernova may be powering the late-time light curve. The Sloan-r filter has an effective wavelength of 623 nm which maps to a rest-frame UV wavelength near 316 nm at a redshift of 0.97 (Cenko et al. GCN 6322). The U-band light curve of SN 1998bw peaked 13 to 15 days after GRB 980425 (Galama et al. 1998, Nature, 395, 670) and possibly earlier at short wavelengths. Some supernovae associated with GRB such as SN 2001dh/011121 (Garnavich et al. 2003, ApJ, 582, 924) and 2006aj/060218 (Modjaz et al. 2006, ApJ, 645, 21) have peaked earlier than SN 1998bw, so the decay seen at 16 rest-frame days is consistent with a supernova interpretation. Extrapolating the spectrum of SN 1998bw near maximum (Patat et al. 2001, ApJ, 555, 900) out to UV wavelengths, we estimate a peak brightness of R=25.4 when viewed at z=0.97, which is also consistent with the LBT observations. A plot of the light curve can be found at: http://www.nd.edu/~pgarnavi/grb070419a/grb070419a_lc.jpg The LBT is an international collaboration among institutions in the United States, Italy and Germany. The LBT Corporation partners are: * The University of Arizona on behalf of the Arizona university system * Istituto Nazionale di Astrofisica, Italy * LBT Beteiligungsgesellschaft, Germany, representing the Max Planck Society, the Astrophysical Institute Potsdam, and Heidelberg University * The Ohio State University * The Research Corporation, on behalf of The University of Notre Dame, University of Minnesota and University of Virginia This message may be cited