TITLE: GCN CIRCULAR NUMBER: 7175 SUBJECT: XRB 080109/SN 2008D:PAIRITEL NIR observations and t_0 from Swift DATE: 08/01/13 03:42:47 GMT FROM: Maryam Modjaz at UC Berkeley M. Modjaz, J. S. Bloom, N. R. Butler, D. Starr (UC Berkeley), R. P. Kirshner, A. Friedman (Harvard/CfA) report on behalf of a larger collaboration: "From our analysis of the Swift XRT data we find an explosion time for the start of XRB 080109 (Berger & Soderberg, GCN 7159; Kong & Marcone, ATEL 1355) as viewed by Swift of: t_0 = 2008-01-09 13:32:49 UT (+/- 5 sec). We observed the field of SN 2007uy (Nakano et al. IAUC 8908; Blondin et al. CBET 1191) with the 1.3m PAIRITEL on Mt. Hopkins on 2008-01-09 08:45 UT, i.e. 4.5 hours before t_0. We started observing again on 2008-01-10 06:23:06 UT, i.e. 17 hours after the burst and for the following nights. The SN 2008D (Li & Filippenko, IAUC 1202; Soderberg et al., GCN 7165; Malesani et al., GCN 7169; Valenti et al., GCN 7171; Blondin et al., CBET 1205, see also GCN 7160-7168) associated with XRB 080109 is clearly detected in mosaic-stacks of each ~1100-sec integration time. From preliminary reductions of multi-epoch observations on Jan 11 and Jan 12, using ~15-20 2MASS stars in the field for the zeropoint, we derive the following error-weighted aperture magnitudes: Filter midtime (UTC) Magnitude MagError J 2008-01-11 8.4 16.63 0.13 H 2008-01-11 8.4 16.33 0.17 K_s 2008-01-11 8.3 16.11 0.18 J 2008-01-12 8.0 16.51 0.06 H 2008-01-12 7.9 16.15 0.14 K_s 2008-01-12 7.9 16.22 0.29 No strong variability is detected over those 2 nights but the source was clearly not visible at these magnitudes on Jan 9 UT. Further data reduction and observations are in progress. SN 2007uy was measured to be ~1 mag brighter in the J, H, K_s filters on Jan 11 and 12 UT." A comparison of the 9 Jan, 12 Jan and historical 2MASS imaging can be found at:" http://pairitel.org/2sne-fig4.tiff