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Swift/UVOT Observations of SN 2009dh

ATEL # 2109; Peter J. Brown on behalf of the Swift SN Team
on 5 Jul 2009; 5:29 UT
Password Certification: Peter J. Brown (

Subjects: Optical, Ultra-Violet, Nova, Supernova

The Ultraviolet/Optical Telescope (UVOT) on board the Swift satellite started observing supernova 2009hd in M66 (CBET #1867) on 2009-07-04.76 UT. The following UVOT magnitudes/3 sigma upper limits (including uncertainties in the host galaxy flux subtraction) were measured: v = 16.70.2 (79 s exposure time), b = 18.10.3 (152 s), u > 18.3 (157 s), uvw1 [181-321nm] > 18.5 (314 s), uvm2 [166-268nm] > 18.8 (1877 s), uvw2 [112-264 nm] > 18.6 (315 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 very red b-v color, lack of UV detections, and faint absolute magnitudes (using the Cepheid-based distance modulus of 29.9 from Freedman et al. 2001, ApJ, 553, 47) suggest a highly reddened event. Alternatively, M66 has already hosted at least one other "SN imposter" -- 1997bs (Van Dyk et al. 2000, PASP, 112, 1532).

We would like to express gratitude to the Swift Science Operations Team for the excellent and rapid execution of these observations.

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R. E. Rutledge , Editor
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