Classification of AT2021afpi, a possible counterpart to IC211125A, as a classical nova

ATel #15069; Robert Stein (Caltech), Viraj Karambelkar (Caltech), Mansi M. Kasliwal (Caltech), Yashvi Sharma (Caltech), Kishalay De (MIT), Anna Franckowiak (RUB)
on 29 Nov 2021; 00:00 UT
Credential Certification: Robert Stein (rdstein@caltech.edu)

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AT2021afpi was a bright optical transient discovered by MASTER (ATEL #15067), and reported by them as a possible electromagnetic counterpart to high-energy neutrino IceCube-211125A (GCN #31126). We obtained a spectrum of AT2021afpi at 2021-11-28.203 UT with the IFU spectrograph SED machine on the 60-inch telescope at Palomar Observatory (Blagoradnova et al. 2018, Rigault et al. 2019).

The spectrum shows a hot blue continuum with strong Balmer lines at an apparent redshift of zero, confirming a galactic origin for AT2021afpi. It also exhibits HeI and HeII emission lines. The spectrum resembles that of V2860 Ori, a classical nova of subclass He/N (De et al. 2021). Given this, and the rapid 10 magnitude brightening, AT2021afpi is likely a young He nova.

Classical novae have been confirmed as gamma-ray sources (e.g Ackermann et al. 2014), with modelling suggesting that this emission may have a possible hadronic origin. Novae are thus considered possible neutrino sources (e.g Fang et al. 2020). However, we note that the accompanying neutrino emission has previously been mostly predicted to occur at GeV-TeV energies, while the neutrino IC211125A was reported with a higher estimated energy of 117 TeV.

Gamma-ray observations of this source, in particular measurements of any spectral cutoff, could help to constrain neutrino emission scenarios.

Our spectrum is also viewable on the Transient Name Server.

The SED Machine is based upon work supported by the National Science Foundation under Grant No. 1106171.