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ATEL # 1947; P. J. Brown (PSU), P. Milne (U of Arizona), and S. Immler (NASA/CRESST/GSFC), on behalf of the Swift satellite team
on 28 Feb 2009; 6:09 UT
Password Certification: Stefan Immler (email@example.com)
Subjects: Optical, Ultra-Violet, X-ray, Nova, Supernova
The Ultraviolet/Optical Telescope (UVOT) on board the Swift satellite started observing Supernova 2009aj in ESO 221-18 (CBET #1704) on 2009-02-27.63 UT. The following UVOT magnitudes were measured: v = 15.5±0.1 (320 s exposure time), b = 15.5±0.1 (160 s), u = 14.4±0.1 (160 s), uvw1 [181-321nm] = 14.4±0.1 (320 s), uvm2 [166-268nm] = 14.5±0.1 (869 s), uvw2 [112-264 nm] = 14.6±0.1 (640 s). These magnitudes are on the UVOT photometric system (Poole et al. 2008, MNRAS, 383, 627) which in the optical is close to Johnson UBV, and have not been corrected for extinction. The UV and UV-optical colors are very blue, similar to SNe 2005cs and 2006bp at their earliest epochs observed by Swift-UVOT (about 5 and 3 days after the inferred explosion date, respectively; Dessart et al. 2008, ApJ, 675, 644). So it is likely a young SN II, though rarer events like SN 2006jc and the shock breakout of GRB060218/SN 2006aj were similarly blue in UVOT (Brown et al. 2009, AJ, accepted, arXiv:0803.1265).
No X-ray source is detected at the position of the SN in the 3.9 ks Swift X-Ray Telescope (XRT) observation obtained simultaneously with the UVOT observations. The 3-sigma upper limit to the XRT net count rate is 3.7E-03 cts/s, corresponding to an unabsorbed (0.2-10 keV band) X-ray flux of <2.1E-13 erg/cm/cm/s and a luminosity of <9.0E40 erg/s for an adopted thermal plasma spectrum with a temperature of kT = 10 keV, a Galactic foreground column density of N_H = 1.23E+21 (Dickey & Lockman, 1990, ARAA, 28, 215) and a distance of ~60 Mpc (z=0.009618, NED).