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ATEL # 2633; Peter J. Brown
on 25 May 2010; 1:53 UT
Password Certification: Peter J. Brown (email@example.com)
Subjects: Ultra-Violet, Nova, Supernova
Referred to by ATEL #: 2637, 2639, 2640, 2658, 2660
The Ultraviolet/Optical Telescope (UVOT) on board the Swift satellite started observing the possible Supernova 2010da in NGC 300 (CBET #2289) at 2010-05-24.7 UT. The following UVOT magnitudes were measured: v = 16.3±0.1 (157 s exposure time), b = 16.6±0.1 (157 s), u = 15.7±0.1 (157 s), uvw1 [181-321nm] = 16.0±0.1 (314 s), uvm2 [166-268nm] = 16.2±0.1 (2462 s), uvw2 [112-264 nm] = 16.4±0.1 (629 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. From these data, the spectral energy distribution appears to peak in the u band (central wavelength ~3465 Angstroms). Compared to SNe of different types, the blue colors are most similar to young SNe II (Brown et al. 2009, AJ, 137, 4517). As Khan et al. 2010 (ATEL#2632) suggest, the absolute magnitudes favor an LBV outburst. The blue UV-optical colors reported here show that the source is not heavily reddened, thus the absolute magnitudes are not faint because of dust extinction.