ASAS observations of SN 2011dh in M51

J. L. Prieto (Carnegie Observatories), D. M. Szczygiel (Ohio State University), G. Pojmanski (Warsaw University Observatory), J. F. Beacom (Ohio State)

We report V-band observations of the type II supernova 2011dh (CBET #2736, ATEL #3398, #3399, #3400, #3401, #3402, #3405, #3406, #3411, #3413, #3414, #3420, #3428, #3431) in M51 obtained between May 28.4 and June 13.4 (UT) with the 10-cm All Sky Automated Survey North (ASAS-N; Pojmanski et al. 2002, AcA, 52, 397; Pigulski et al. 2009, AcA, 59, 33) telescope in Haleakala, Hawaii (see this mosaic with ASAS images). We estimate the magnitudes of SN 2011dh using image subtraction with a template made from the combination of several images obtained during April 2011. The magnitudes of the supernova are calibrated using magnitudes of non-variable stars in the field obtained by the ASAS automatic pipeline. We confirm the continuing brightening reported by Arcavi et al. 2011 (ATEL #3413). In ASAS data, we see a brightening of 0.9 mag between June 6.3 and June 13.4 in V-band (~0.13 mag/day). We also report 3-sigma upper limits on the magnitudes of SN 2011dh from May 28.4 and May 30.5 (V > 15.5 mag), 3.5 and 1.4 days before the time of discovery (CBET #2736), respectively. The ASAS magnitudes and upper limits are listed below in Table 1. Unfortunately, ASAS did not obtain observations of SN 2011dh in the critical time window between May 31 and June 5, mainly due to weather.

The upper limits from ASAS and the early bright magnitude of g=13.18 mag in June 1.69 reported by Arcavi et al., show that SN 2011dh brightened by >2.3 mag in ~2 days after the explosion. These observations and the further fast decline between June 1.69 and June 3.85 reported by Arcavi et al. are consistent with the initial peak in the light curve of the type IIb SN 1993J (Richmond et al. 1994, ApJ, 107, 1022; Li et al. 2011, MNRAS, 412, 1441). However, the duration of the initial peak seems to be significantly shorter than in the case of SN 1993J. We show a figure with the light curve here.

Table 1. ASAS V-band observations of SN 2011dh

 UT Date         HJD            V (mag)   
May  28.41   2455709.9117   > 15.5
May  30.48   2455711.9827   > 15.5
June 06.29   2455718.7932   14.30 +/- 0.11
June 07.47   2455719.9679   14.07 +/- 0.12
June 09.35   2455721.8490   14.16 +/- 0.15
June 11.38   2455723.8842   13.57 +/- 0.07
June 13.39   2455725.8948   13.41 +/- 0.07





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