Bright, Months-long Stellar Outbursts Announce the Explosion of Interaction-powered Supernovae

Abstract

Interaction-powered supernovae (SNe) explode within an optically thick circumstellar medium (CSM) that could be ejected during eruptive events. To identify and characterize such pre-explosion outbursts, we produce forcedphotometry light curves for 196 interacting SNe, mostly of Type IIn, detected by the Zwicky Transient Facility between early 2018 and 2020 June. Extensive tests demonstrate that we only expect a few false detections among the 70,000 analyzed pre-explosion images after applying quality cuts and bias corrections. We detect precursor eruptions prior to 18 Type IIn SNe and prior to the Type Ibn SN 2019uo. Precursors become brighter and more frequent in the last months before the SN and month-long outbursts brighter than magnitude −13 occur prior to 25% (5-69%, 95% confidence range) of all Type IIn SNe within the final three months before the explosion. With radiative energies of up to 10 49 erg, precursors could eject ∼1 M e of material. Nevertheless, SNe with detected precursors are not significantly more luminous than other SNe IIn, and the characteristic narrow hydrogen lines in their spectra typically originate from earlier, undetected mass-loss events. The long precursor durations require ongoing energy injection, and they could, for example, be powered by interaction or by a continuum-driven wind. Instabilities during the neon-and oxygen-burning phases are predicted to launch precursors in the final years to months before the explosion; however, the brightest precursor is 100 times more energetic than anticipated.

AT 2018lqh and the Nature of the Emerging Population of Day-scale Duration Optical Transients

“…The second is that the event is powered, at early times, by ejecta moving into low-mass (10 −2 M e ) CSM at a distance of about 10 14 -10 15 cm from the progenitor, while at late times, it must be powered by a different mechanism, such as shock cooling or collisionless shocks from CSM interaction. The existence of such low-mass CSM around SN progenitors is consistent with the finding that a large fraction of Type IIn SNe have precursors (outbursts) prior to their explosion (e.g., Ofek et al 2014b;Strotjohann et al 2021), and that a fraction of core-collapse SNe show evidence of a confined CSM (e.g., Yaron et al 2017;Bruch et al 2021). However, in the context of AT 2018lqh, the possible absence of intermediate-width emission lines from the CSM is puzzling (but still, this scenario cannot ruled out).…”

A WC/WO star exploding within an expanding carbon–oxygen–neon nebula

“…https://wis-tns.weizmann.ac.il/object/2019hgp) on June 10, 2019 38 and was allocated the name AT 2019hgp. Forced photometry analysis performed at the SN location using custom methodology 39 recovered prediscovery signal in stacked r-band images obtained during the night prior to discovery (Extended Data Fig. 6).…”

“…//starlink.eao.hawaii.edu/starlink/2015ADownload). We performed aperture photometry using a custom tool 112 39 we can rule out eruptions brighter than an absolute magnitude of -15.5 in the g or r band during 20%…”

A systematic reclassification of Type IIn supernovae

“…This is consistent with Ofek et al (2014), who find that mass-loss events which cause brightening are common in SN IIn progenitors; they are seen in around half of a sample of SNe IIn observed by PTF. Furthermore, Strotjohann et al (2021) find that month-long precursor events brighter than an absolute magnitude of −13 were found in ∼ 25% of a sample of 131 SNe IIn from ZTF within the three months prior to the SN explosion.…”