TITLE: GCN CIRCULAR NUMBER: 7552 SUBJECT: GRB 080330 Swift-UVOT refined analysis DATE: 08/03/30 23:28:41 GMT FROM: Paul Kuin at MSSL N.P.M. Kuin (MSSL/UCL) and J.Mao (INAF) report on behalf of the Swift-UVOT team: The Swift/UVOT started observations of GRB 080330 (Mao et al, GCN Circ. 7537) with a settling exposure in the UVOT v-filter starting 2008-03-30 at 03:42:19 U, 63 seconds after the BAT trigger, and a finding chart exposure in the white filter starting 83 seconds after the trigger. During the subsequent exposure in the V filter, starting at 189 seconds after the trigger, the spacecraft lost lock and drifted. In the V image, a clear trail is visible that all the stars in the field follow. In other filters, there is no clear evidence of lost counts, except in one image in b. Those exposures are short, or have much background (white), which suggest that only a fraction of the counts is lost. The extraction of the magnitudes below relies on a 5¨ aperture around the source. No counts are visible due to the source outside the aperture in the images. However, these magnitudes should be regarded as upper limits until a more detailed reduction can be done. Based on some tests, the magnitude may be underestimated as much as 0.7 magnitudes. The v-filter data were extracted using an aperture closely matching the shape of the trail and were measured from the event data. There is an uncertainty in this approach as well, since it is not clear what part of the PSF is sampled. Therefore the V magnitudes can be over-or underestimated by 0.25 magnitudes. The observations start before a peak is reached. In the white filter, a peak is apparent at T+128 +/- 5 seconds. In the v filter data, two peaks may be present at T+ 438 and 1038 +/- 25s. It is unlikely that the satellite drift caused these variations because the aperture included the whole trail. The uvw1 magnitude has upper limits until quite late in the burst, and must rise between T+791 and T+1416s. This is an indication of achromatic evolution in this burst. Only an upper limit is found in the uvw2 and uvm2 filters, which is consistent with the reported redshift of 1.51 (Malesani, et al. GCN 7544, and Cucchiara et al. GCN 7547). Filter Tstart(s) Tstop(s) Exp(s) Mag Mag-error [systematic error] wh 83 183 98 18.2 0.06 [+0.7] v 189 588 399.8 18.5-17.2 0.3 [+/-0.25] (*) uvm2 594 1390 58.4 >18.55 (3 sigma UL) uvw1 619 638 19.5 >18.02 (3 sigma UL) u 644 664 19.4 17.14 0.16 [+0.7] b 669 678 9.6 18.9 0.6 [+0.7] wh 683 693 9.8 17.76 0.14 [+0.7] uvw2 698 870 38.9 >18.77 (3 sigma UL) uvw1 772 791 19.8 >18.04 (3 sigma UL) u 796 815 19.4 16.66 0.17 [+0.7] b 822 832 9.6 17.66 0.22 [+0.7] white 836 979 107.8 17.55 0.03 [+0.7] v 985 1384 400 18.0-17.2 0.3 [+/-0.25] (*) uvw1 1416 1436 19.4 17.7 0.3 [+0.7] b 1464 1483 19.8 18.14 0.22 [+0.7] white 1490 1499 9.6 17.91 0.15 [+0.7] (*) For the V magnitudes the range is given as seen in the event data. The values quoted above are not corrected for the expected Galactic extinction corresponding to a reddening of E_{B-V} = 0.02 mag in the direction of the burst (Schlegel et al. 1998).