AT 2017be - a new member of the class of Intermediate-Luminosity Red Transients

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    Y-Z Cai, A. Pastorello, M. Fraser, M. T. Botticella,
  • C. Gall
  • I. Arcavi, S. Benetti, E. Cappellaro, N. Elias-Rosa, J. Harmanen, G. Hosseinzadeh, D. A. Howell, J. Isern, T. Kangas, E. Kankare, H. Kuncarayakti, P. Lundqvist, S. Mattila, C. McCully, T. M. Reynolds, A. Somero,
  • M. D. Stritzinger
  • G. Terreran
We report the results of our spectrophotometric monitoring campaign for AT~2017be in NGC~2537. Its lightcurve reveals a fast rise to an optical maximum, followed by a plateau lasting about 30 days, and finally a fast decline. Its absolute peak magnitude ($M_{r}$ $\simeq$ $-$12 $\rm{mag}$) is fainter than that of core-collapse supernovae, and is consistent with those of supernova impostors and other Intermediate-Luminosity Optical Transients. The quasi-bolometric lightcurve peaks at $\sim$ 2 $\times$ 10$^{40}$ erg s$^{-1}$, and the late-time photometry allows us to constrain an ejected $^{56}$Ni mass of $\sim$ 8 $\times$ 10$^{-4}$\msun. The spectra of AT~2017be show minor evolution over the observational period, a relatively blue continuum showing at early phases, which becomes redder with time. A prominent H$\alpha$ emission line always dominates over other Balmer lines. Weak Fe {\sc ii} features, Ca~{\sc ii} H$\&$K and the Ca {\sc ii} NIR triplet are also visible, while P-Cygni absorption troughs are found in a high resolution spectrum. In addition, the [Ca~{\sc ii}] $\lambda$7291,7324 doublet is visible in all spectra. This feature is typical of Intermediate-Luminosity Red Transients (ILRTs), similar to SN~2008S. The relatively shallow archival Spitzer data are not particularly constraining. On the other hand, a non-detection in deeper near-infrared HST images disfavours a massive Luminous Blue Variable eruption as the origin for AT~2017be. As has been suggested for other ILRTs, we propose that AT~2017be is a candidate for a weak electron-capture supernova explosion of a super-asymptotic giant branch star, still embedded in a thick dusty envelope.
TidsskriftMonthly Notices of the Royal Astronomical Society
StatusUdgivet - 31 jul. 2018

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