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ATEL # 1412; S. Immler (NASA/CRESST/GSFC), and P. J. Brown (PSU), on behalf of the Swift satellite team
on 5 Mar 2008; 2:40 UT
Password Certification: Stefan Immler (firstname.lastname@example.org)
Subjects: Optical, Ultra-Violet, X-ray, Nova, Supernova
Swift Ultraviolet/Optical Telescope (UVOT) and X-Ray Telescope (XRT) observed the supernova (SN) in NGC 4490 (CBET #1280) on 2008-03-04.67 UT. The following UVOT magnitudes were measured: b = 17.0±0.2 (453 s), u = 16.7±0.2 (553 s), uvw1 [181-321nm] = 18.7±0.2 (1,153 s), and uvw2 [112-264 nm] > 19.5 (1,260 s; 3-sigma upper limit). These magnitudes are on the UVOT photometric system (see GCN Circ. 6614) which in the optical is close to the Johnson UBV. They have not been corrected for extinction.
A tentative X-ray source is detected in the 3.7 ks XRT image at the position of the SN within a 7 image pixel (18.9-arcsec) aperture centered on the SN, at a 3.3-sigma level of significance. The point-spread-function (PSF), dead-time, and vignetting corrected XRT net count rate is (4.4+/-1.4)E-03 cts/s, corresponding to an unabsorbed (0.2-10 keV band) X-ray flux of (2.2+/-0.7)E-13 erg/cm/cm/s and a luminosity of (1.7+/-0.5)E39 erg/s for an adopted thermal plasma spectrum with a temperature of kT = 10 keV, a Galactic foreground column density of N_H = 1.8E+20 (Dickey & Lockman, 1990, ARAA 28) and a distance of 8 Mpc (z=0.001885, NED; H_o = 71 km/s/Mpc, Omega_M = 1/3, Omega_L = 2/3). Inspection of the XRT raw image indicates that the X-ray source might be due to the high overall X-ray emission of the host galaxy and unresolved X-ray sources, although the results are not conclusive due to the large PSF of the XRT instrument (18-arcsec half-power diameter at 1.5 keV).
Observations in other wavelength regimes are encouraged.