Low-luminosity Type II supernovae – III. SN 2018hwm, a faint event with an unusually long plateau

Reguitti, A.; Pumo, M. L.; Mazzali, Paolo A.; Pastorello, A.; Pignata, G.; Elias‐Rosa, N.; Prentice, S.; Reynolds, T.; Benetti, S.; Rodríguez, Ó.; Mattila, S.; Kuncarayakti, H.

doi:10.1093/mnras/staa3730

Cited by 22 publications

(24 citation statements)

References 103 publications

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“…Here we present analysis of the UV/optical light curve, sub-mm limits, optical and NIR spectroscopy, the spectral energy distribution, and X-rays to place ASASSN-20hx in context with other transients. While the long plateau phase of the light curve is reminiscent of Type IIP supernovae, the length of this phase is longer than even the most extreme of these SNe (e.g., Sanders et al 2015;Reguitti et al 2021). Additionally, the spectra are inconsistent with a SN II as they lack hydrogen features.…”

Section: Discussionmentioning

confidence: 99%

The Curious Case of ASASSN-20hx: A Slowly-Evolving, UV and X-ray Luminous, Ambiguous Nuclear Transient

Hinkle,

Holoien,

Shappee

et al. 2021

Preprint

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We present observations of ASASSN-20hx, a nearby ambiguous nuclear transient (ANT) discovered in NGC 6297 by the All-Sky Automated Survey for Supernovae (ASAS-SN). We observed ASASSN-20hx from −30 to 275 days relative to peak UV/optical emission using high-cadence, multi-wavelength spectroscopy and photometry. From Transiting Exoplanet Survey Satellite (TESS) data, we determine that the ANT began to brighten on 2020 June 23.3 with a linear rise in flux for at least the first week. ASASSN-20hx peaked in the UV/optical 29.5 days later on 2020 July 22.8 (MJD = 59052.8) at a bolometric luminosity of L = (3.15 ± 0.04) × 10 43 erg s −1 . The subsequent decline is slower than any TDE observed to date and consistent with many other ANTs. Compared to an archival X-ray detection, the X-ray luminosity of ASASSN-20hx increased by an order of magnitude to L x ∼ 1.5×10 42 erg s −1 and then slowly declined over time. The X-ray emission is well-fit by a power law with a photon index of Γ ∼ 2.3 − 2.6. Both the optical and near infrared spectra of ASASSN-20hx lack emission lines, unusual for any known class of nuclear transient. While ASASSN-20hx has some characteristics seen in both tidal disruption events (TDEs) and active galactic nuclei (AGNs), it cannot be definitively classified with current data.

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Section: Discussionmentioning

confidence: 99%

The Curious Case of ASASSN-20hx: A Slowly-Evolving, UV and X-ray Luminous, Ambiguous Nuclear Transient

Hinkle,

Holoien,

Shappee

et al. 2021

Preprint

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“…However, the large flux ratio between [Ca ] and [O ] seen in the late-time spectra suggests that the progenitor mass of SN 2018hfm is not as large as 27 M . Reguitti et al (2021) describe some observational similarities between low-energy SNe II and electron-capture SNe (ECSNe; Tominaga et al 2013;Moriya et al 2014), e.g., low explosion energy and little contribution of 56 Ni at late phase. ECSNe are believed to be the outcome of super-asymptotic giant branch (super-AGB) stars.…”

Section: Progenitor Scenario Of Sn 2018hfmmentioning

confidence: 96%

SN 2018hfm : A Low-Energy Type II Supernova with Prominent Signatures of Circumstellar Interaction and Dust Formation

Zhang,

Wang,

Sai

et al. 2021

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We present multiband optical photometric and spectroscopic observations of an unusual Type II supernova, SN 2018hfm, which exploded in the nearby (𝑑 ≈ 34.67 Mpc) dwarf galaxy PGC 1297331 with a very low star-formation rate (0.0270 M yr −1 ) and a subsolar metallicity environment (∼ 0.5 Z ). The 𝑉-band light curve of SN 2018hfm reaches a peak with value of −18.69 ± 0.64 mag, followed by a fast decline (4.42 ± 0.13 mag (100 d) −1 ). After about 50 days, it is found to experience a large flux drop (∼ 3.0 mag in 𝑉), and then enters into an unusually faint tail, which indicates a relatively small amount of 56 Ni synthesised during the explosion. From the bolometric light curve, SN 2018hfm is estimated to have low ejecta mass (∼ 1.3 M ) and low explosion energy (∼ 10 50 erg) compared with typical SNe II. The photospheric spectra of SN 2018hfm are similar to those of other SNe II, with P Cygni profiles of the Balmer series and metal lines, while at late phases the spectra are characterised by box-like profiles of H𝛼 emission, suggesting significant interaction between the SN ejecta and circumstellar matter. These box-like emission features are found to show increasing asymmetry with time, with the red-side component becoming gradually weaker, indicating that dust is continuously formed in the ejecta. Based on the dust-estimation tool , we find that the dust increases from ∼ 10 −6 M to 10 −4 -10 −3 M between +66.7 d and +389.4 d after explosion.

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“…Kasen & Woosley (2009) derived scaling relations for the properties of SNe IIP, and conclude that the plateau duration is correlated with the explosion energy and the progenitor mass (where nickel in the ejecta tends to extend the plateau). However, given the low plateau luminosities of SN 2020cxd and SN 2018hwm these scaling relations would suggest a too low initial mass; this discrepancy was explained for SN 2018hwn by the extremely low explosion energy (Reguitti et al 2021) 20 .…”

Section: )mentioning

confidence: 99%

A low-energy explosion yields the underluminous Type IIP SN 2020cxd

Yang,

Sollerman,

Strotjohann

et al. 2021

Preprint

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Context. We present observations and analysis of SN 2020cxd, a low-luminosity (LL), long-lived Type IIP supernova (SN). This object was a clear outlier in the magnitude-limited SN sample recently presented by the Zwicky Transient Facility (ZTF) Bright Transient Survey. Aims. We demonstrate that SN 2020cxd is an additional member of the group of LL SNe, and discuss the rarity of LL SNe in the context of the ZTF survey, and how further studies of these faintest members of the core-collapse (CC) SN family might help understand the underlying initial mass function for stars that explode. Methods. We present optical light curves (LCs) from the ZTF in the gri bands and several epochs of ultra-violet data from the Neil Gehrels Swift Observatory as well as a sequence of optical spectra. We construct colour curves, a bolometric LC, compare ejectavelocity and black-body temperature evolutions for LL SNe, as well as for typical Type II SNe. Furthermore, we adopt a Monte Carlo code that fits semi-analytic models to the LC of SN 2020cxd, which allows the estimation of physical parameters. Using our late-time nebular spectra, we also compare against SN II spectral synthesis models from the literature to constrain the progenitor properties of SN 2020cxd.Results. The LCs of SN 2020cxd show great similarity with those of LL SNe IIP, in luminosity, timescale and colours. Also the spectral evolution of SN 2020cxd is that of a Type IIP SN. The spectra show prominent and narrow P-Cygni lines, indicating low expansion velocities. This is one of the faintest LL SNe observed, with an absolute plateau magnitude of M r = −14.5 mag, and also one with the longest plateau lengths, with a duration of 118 days. Finally, the velocities measured from the nebular emission lines are among the lowest ever seen in a SN, with intrinsic Full Width at Half Maximum of 478 km s −1 . The underluminous late-time exponential LC tail indicates that the mass of 56 Ni ejected during the explosion is much smaller than the average of normal SNe IIP, we estimate M56 Ni = 0.003 M . The Monte Carlo fitting of the bolometric LC suggests that the progenitor of SN 2020cxd had a radius of R 0 = 1.3 × 10 13 cm, kinetic energy of E kin = 4.3 × 10 50 erg, and ejecta mass M ej = 9.5 M . From the bolometric LC, we estimate the total radiated energy E rad = 1.52 × 10 48 erg. Using our late-time nebular spectra, we compare against SN II spectral synthesis models to constrain the progenitor Zero-age Main-sequence mass and found it likely to be 15 M . Conclusions. SN 2020cxd is a LL Type IIP SN. The inferred progenitor parameters and the features observed in the nebular spectrum favour a low-energy, Ni-poor, iron CC SN from a low mass (∼ 12 M ) red supergiant.

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Low-luminosity Type II supernovae – III. SN 2018hwm, a faint event with an unusually long plateau

Cited by 22 publications

References 103 publications

The Curious Case of ASASSN-20hx: A Slowly-Evolving, UV and X-ray Luminous, Ambiguous Nuclear Transient

The Curious Case of ASASSN-20hx: A Slowly-Evolving, UV and X-ray Luminous, Ambiguous Nuclear Transient

SN 2018hfm : A Low-Energy Type II Supernova with Prominent Signatures of Circumstellar Interaction and Dust Formation

A low-energy explosion yields the underluminous Type IIP SN 2020cxd

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