Spectroscopic and Photometric classification of the transient ASAS-SN 20om = AT 2020aapw = PNV J00401974+4049360 as a nova in M31

ATel #14204; Kenta Taguchi, Naoto Kojiguchi, Keisuke Isogai (Kyoto University)
on 21 Nov 2020; 00:31 UT
Credential Certification: Keisuke Isogai (isogai@kusastro.kyoto-u.ac.jp)

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We report on a spectrum of the transient AT 2020aapw associated with M31. We obtained the spectrum on 2020-11-20.76 UT by using a fiber-fed integral field spectrograph (KOOLS-IFU; Matsubayashi et al. 2019) mounted on the 3.8-m telescope Seimei at Okayama Observatory of Kyoto University.

Our spectrum shows broad Balmer emission lines (FWHM of Hα ∼ 100 Å). The peak of the emission part of Hα emission is around 6550 Å, which is consistent with the blue-shift of M31 (∼300 km/s).

Both Hα and Hβ lines have apparent blue-shifted components. However, we cannot conclude that these lines have P Cygni profiles, because it may come from the noise and/or our normalization. No other remarkable lines are there. These features are consistent with the spectrum by Claudio Balcon, which was obtained on 2020-11-20.80 UT and was reported to Transient Name Server (TNS). A nova prefers all of these features, namely broad emission lines and possible P Cygni profiles.

We also performed multicolor photometry in 2020-11-20.63-64 UT by using Kyoto University 40-cm telescope. According to our quick look, this object was B ∼ 17.1, V ∼ 16.3, Rc ∼ 15.7, Ic ∼ 15.3 then.

As reported to TNS, this object was discovered by ASAS-SN at 16.6 mag on 2020-11-20.40 UT. Also, as reported to CBAT, this object was discovered independently by XOSS at 16.7 mag on 2020-11-20.54 UT. After those discovery reports, this object was found to be at 18.4 mag on 2020-11-19.83 by GOTO and fainter than 18 mag on 2020-11-19.60 by XOSS, as is reported to TNS. There is no optical counterpart down to 22.0 mag in Pan-STARRS g.

Compared to other discovery reports, our photometry is brighter, that means this object may be still on the rise. Moreover, this transient is brighter than usual novae in M31. So, more follow up observations are encouraged!

Our Spectrum