TY - JOUR

T1 - AT 2017be - a new member of the class of intermediate-luminosity red transients

AU - Cai, Y.-Z.

AU - Pastorello, A.

AU - Fraser, M.

AU - Botticella, M. T.

AU - Gall, C.

AU - Arcavi, I.

AU - Benetti, S.

AU - Cappellaro, E.

AU - Elias-Rosa, N.

AU - Harmanen, J.

AU - Hosseinzadeh, G.

AU - Howell, D. A.

AU - Isern, J.

AU - Kangas, T.

AU - Kankare, E.

AU - Kuncarayakti, H.

AU - Lundqvist, P.

AU - Mattila, S.

AU - McCully, C.

AU - Reynolds, T. M.

AU - Somero, A.

AU - Stritzinger, M. D.

AU - Terreran, G.

PY - 2018/11/1

Y1 - 2018/11/1

N2 - We report the results of our spectrophotometric monitoring campaign for AT 2017be in NGC 2537. Its light curve reveals a fast rise to an optical maximum, followed by a plateau lasting about 30 d, and finally a fast decline. Its absolute peak magnitude (Mr ≃ -12 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 light-curve peaks at ˜2 × 1040 erg s-1, and the late-time photometry allows us to constrain an ejected 56Ni mass of ˜8 × 10-4 M⊙. The spectra of AT 2017 be show minor evolution over the observational period, a relatively blue continuum showing at early phases, which becomes redder with time. A prominent H α emission line always dominates over other Balmer lines. Weak Fe II features, Ca II H&K, and the Ca II NIR triplet are also visible, while P-Cygni absorption troughs are found in a high-resolution spectrum. In addition, the [Ca II] λλ7291, 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 superasymptotic giant branch star, still embedded in a thick dusty envelope.

AB - We report the results of our spectrophotometric monitoring campaign for AT 2017be in NGC 2537. Its light curve reveals a fast rise to an optical maximum, followed by a plateau lasting about 30 d, and finally a fast decline. Its absolute peak magnitude (Mr ≃ -12 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 light-curve peaks at ˜2 × 1040 erg s-1, and the late-time photometry allows us to constrain an ejected 56Ni mass of ˜8 × 10-4 M⊙. The spectra of AT 2017 be show minor evolution over the observational period, a relatively blue continuum showing at early phases, which becomes redder with time. A prominent H α emission line always dominates over other Balmer lines. Weak Fe II features, Ca II H&K, and the Ca II NIR triplet are also visible, while P-Cygni absorption troughs are found in a high-resolution spectrum. In addition, the [Ca II] λλ7291, 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 superasymptotic giant branch star, still embedded in a thick dusty envelope.

KW - stars: AGB and post-AGB

KW - stars: mass-loss

KW - supernovae: general

KW - galaxies: individual: NGC 2537

KW - supernovae: individual: AT 2017be

U2 - 10.1093/mnras/sty2070

DO - 10.1093/mnras/sty2070

M3 - Journal article

VL - 480

SP - 3424

EP - 3445

JO - Royal Astronomical Society. Monthly Notices

JF - Royal Astronomical Society. Monthly Notices

SN - 0035-8711

IS - 3

ER -