We present a search for extragalactic fast blue optical transients (FBOTs) during Phase I of the Zwicky Transient Facility (ZTF). We identify 38 candidates with durations above half-maximum light 1 day <
We present the discovery and extensive follow-up of a remarkable fast-evolving optical transient, AT 2022aedm, detected by the Asteroid Terrestrial impact Last Alert Survey (ATLAS). In the ATLAS
- NSF-PAR ID:
- 10452095
- Author(s) / Creator(s):
- ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; more »
- Publisher / Repository:
- DOI PREFIX: 10.3847
- Date Published:
- Journal Name:
- The Astrophysical Journal Letters
- Volume:
- 954
- Issue:
- 1
- ISSN:
- 2041-8205
- Format(s):
- Medium: X Size: Article No. L28
- Size(s):
- ["Article No. L28"]
- Sponsoring Org:
- National Science Foundation
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Abstract t 1/2< 12 days, of which 28 have blue (g −r ≲ −0.2 mag) colors at peak light. Of the 38 transients (28 FBOTs), 19 (13) can be spectroscopically classified as core-collapse supernovae (SNe): 11 (8) H- or He-rich (Type II/IIb/Ib) SNe, 6 (4) interacting (Type IIn/Ibn) SNe, and 2 (1) H&He-poor (Type Ic/Ic-BL) SNe. Two FBOTs (published previously) had predominantly featureless spectra and luminous radio emission: AT2018lug (The Koala) and AT2020xnd (The Camel). Seven (five) did not have a definitive classification: AT 2020bdh showed tentative broad Hα in emission, and AT 2020bot showed unidentified broad features and was 10 kpc offset from the center of an early-type galaxy. Ten (eight) have no spectroscopic observations or redshift measurements. We present multiwavelength (radio, millimeter, and/or X-ray) observations for five FBOTs (three Type Ibn, one Type IIn/Ibn, one Type IIb). Additionally, we search radio-survey (VLA and ASKAP) data to set limits on the presence of radio emission for 24 of the transients. All X-ray and radio observations resulted in nondetections; we rule out AT2018cow-like X-ray and radio behavior for five FBOTs and more luminous emission (such as that seen in the Camel) for four additional FBOTs. We conclude that exotic transients similar to AT2018cow, the Koala, and the Camel represent a rare subset of FBOTs and use ZTF’s SN classification experiments to measure the rate to be at most 0.1% of the local core-collapse SN rate. -
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Abstract We present observations of a peculiar hydrogen- and helium-poor stripped-envelope (SE) supernova (SN) 2020wnt, primarily in the optical and near-infrared (near-IR). Its peak absolute bolometric magnitude of −20.9 mag (
L bol, peak= (6.8 ± 0.3) × 1043erg s−1) and a rise time of 69 days are reminiscent of hydrogen-poor superluminous SNe (SLSNe I), luminous transients potentially powered by spinning-down magnetars. Before the main peak, there is a brief peak lasting <10 days post explosion, likely caused by interaction with circumstellar medium (CSM) ejected ∼years before the SN explosion. The optical spectra near peak lack a hot continuum and Oii absorptions, which are signs of heating from a central engine; they quantitatively resemble those of radioactivity-powered hydrogen/helium-poor Type Ic SESNe. At ∼1 yr after peak, nebular spectra reveal a blue pseudo-continuum and narrow Oi recombination lines associated with magnetar heating. Radio observations rule out strong CSM interactions as the dominant energy source at +266 days post peak. Near-IR observations at +200–300 days reveal carbon monoxide and dust formation, which causes a dramatic optical light-curve dip. Pair-instability explosion models predict slow light curve and spectral features incompatible with observations. SN 2020wnt is best explained as a magnetar-powered core-collapse explosion of a 28M ⊙pre-SN star. The explosion kinetic energy is significantly larger than the magnetar energy at peak, effectively concealing the magnetar-heated inner ejecta until well after peak. SN 2020wnt falls into a continuum between normal SNe Ic and SLSNe I, and demonstrates that optical spectra at peak alone cannot rule out the presence of a central engine. -
Abstract We present observations of SN 2021csp, the second example of a newly identified type of supernova (SN) hallmarked by strong, narrow, P Cygni carbon features at early times (Type Icn). The SN appears as a fast and luminous blue transient at early times, reaching a peak absolute magnitude of −20 within 3 days due to strong interaction between fast SN ejecta ( v ≈ 30,000 km s −1 ) and a massive, dense, fast-moving C/O wind shed by the WC-like progenitor months before explosion. The narrow-line features disappear from the spectrum 10–20 days after explosion and are replaced by a blue continuum dominated by broad Fe features, reminiscent of Type Ibn and IIn supernovae and indicative of weaker interaction with more extended H/He-poor material. The transient then abruptly fades ∼60 days post-explosion when interaction ceases. Deep limits at later phases suggest minimal heavy-element nucleosynthesis, a low ejecta mass, or both, and imply an origin distinct from that of classical Type Ic SNe. We place SN 2021csp in context with other fast-evolving interacting transients, and discuss various progenitor scenarios: an ultrastripped progenitor star, a pulsational pair-instability eruption, or a jet-driven fallback SN from a Wolf–Rayet (W-R) star. The fallback scenario would naturally explain the similarity between these events and radio-loud fast transients, and suggests a picture in which most stars massive enough to undergo a W-R phase collapse directly to black holes at the end of their lives.more » « less
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Abstract If the envelope of a massive star is not entirely removed during common envelope (CE) interaction with an orbiting compact (e.g., black hole (BH) or neutron star (NS)) companion, the residual bound material eventually cools, forming a centrifugally supported disk around the binary containing the stripped He core. We present a time-dependent height-integrated model for the long-term evolution of post-CE circumbinary disks (CBDs), accounting for mass and angular momentum exchange with the binary, irradiation heating by the He core, and photoevaporation wind mass loss. A large fraction of the CBD’s mass is accreted prior to its outwards viscous spreading and wind dispersal on a timescale of ∼104–105yr, driving significant orbital migration, even for disks containing ∼10% of the original envelope mass. Insofar that the CBD lifetime is comparable to the thermal (and, potentially, nuclear) timescale of the He core, over which a second mass-transfer episode onto the companion can occur, the presence of the CBD could impact the stability of this key phase. Disruption of the core by the BH/NS would result in a jetted energetic explosion into the dense gaseous CBD (≲1015cm) and its wind (≳1016cm), consistent with the environments of luminous fast blue optical transients like AT2018cow. Evolved He cores that undergo core collapse still embedded in their CBD could generate Type Ibn/Icn supernovae. Thousands of dusty wind-shrouded massive-star CBDs may be detectable as extragalactic luminous infrared sources with the Roman Space Telescope; synchrotron radio nebulae powered by the CBD-fed BH/NS may accompany these systems.
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Abstract A growing number of core-collapse supernovae (SNe) that show evidence for interaction with dense circumstellar medium (CSM) are accompanied by “precursor” optical emission rising weeks to months prior to the explosion. The precursor luminosities greatly exceed the Eddington limit of the progenitor star, implying that they are accompanied by substantial mass loss. Here, we present a semi-analytic model for SN precursor light curves, which we apply to constrain the properties and mechanisms of the pre-explosion mass loss. We explore two limiting mass-loss scenarios: (1) an “eruption” arising from shock breakout following impulsive energy deposition below the stellar surface; and (2) a steady “wind,” due to sustained heating of the progenitor envelope. The eruption model, which resembles a scaled-down version of Type IIP SNe, can explain the luminosities and timescales of well-sampled precursors, for ejecta masses ∼ 0.1–1
M ⊙and velocities ∼ 100–1000 km s−1. By contrast, the steady wind scenario cannot explain the highest precursor luminosities ≳ 1041erg s−1, under the constraint that the total ejecta mass does not exceed the entire progenitor mass (though the less luminous SN 2020tlf precursor can be explained by a mass-loss rate ∼ 1M ⊙yr−1). However, shock interaction between the wind and pre-existing (earlier ejected) CSM may boost its radiative efficiency and mitigate this constraint. In both the eruption and wind scenarios, the precursor ejecta forms compact (≲1015cm) optically thick CSM at the time of core collapse; though only directly observable via rapid post-explosion spectroscopy (≲ a few days before being overtaken by the SN ejecta), this material can boost the SN luminosity via shock interaction.
