A Fallback Accretion Model for the Unusual Type II-P Supernova iPTF14hls

Abstract

The Intermediate Palomar Transient Factory reported the discovery of an unusual type II-P supernova iPTF14hls. Instead of a ∼ 100-day plateau as observed for ordinary type II-P supernovae, the light curve of iPTF14hls has at least five distinct peaks, followed by a steep decline at ∼ 1000 days since discovery. Until 500 days since discovery, the effective temperature of iPTF14hls is roughly constant at 5000-6000 K. In this paper we propose that iPTF14hls is likely powered by intermittent fallback accretion. It is found that the light curve of iPTF14hls can be well fit by the usual t −5/3 accretion law until ∼ 1000 days post discovery when the light curve transitions to a steep decline. To account for this steep decline, we suggest a power-law density profile for the late accreted material, rather than the constant profile as appropriated for the t −5/3 accretion law. Detailed modeling indicates that the total fallback mass is ∼ 0.2M , with an ejecta mass M ej 21M . We find the third peak of the light curve cannot be well fit by the fallback model, indicating that there could be some extra rapid energy injection. We suggest that this extra energy injection may be a result of a magnetic outburst if the central object is a neutron star. These results indicate that the progenitor of iPTF14hls could be a massive red supergiant.

Emission peaks in the light curve of core collapse supernovae by late jets

“…We demonstrate our toy model for one specific set of parameters, which as we see in ection 4 might crudely fit the third peak (as defined in Wang et al 2018) in the light curve of iPTF14hls. First we recall that our derivation of equation (8) is for one jet, but in each jetlaunching episode there are two jets.…”

“…Several theoretical studies propose different scenarios to account for the properties of iPTF14hls, and in particular for its prolonged light curve, but none can fit all properties of iPTF14hls (e.g., Sollerman et al 2019;Woosley 2018). These scenarios include a pair instability supernova (e.g., Woosley 2018;Vigna-Gómez et al 2019), a magnetar, i.e., a rapidly rotating magnetic NS (e.g., Arcavi et al 2017;Dessart 2018;Woosley 2018), fallback accretion (e.g., Arcavi et al 2017;Wang et al 2018;Liu et al 2019), an interaction of the ejecta with a circumstellar matter (CSM; Andrews & Smith 2017;Milisavljevic & Margutti 2018), and a common envelope jets supernova scenario (CEJSN; e.g., Soker & Gilkis 2018).…”

“…Both the accretion fallback (Wang et al 2018) and the magnetar model deposit the energy at the center of the SN ejecta. We, on the other hand, deposit the energy further out in the ejecta and in a bipolar morphology rather than a spherical one.…”

“…These are the relative ejecta mass that is shocked by the jets, V (equation 6), and the half opening angle of each jet α j . Wang et al (2018) propose a scenario where intermittent fallback accretion of ≈ 0.2M explain the late peaks in the light curve of iPTF14hls. Their scenario has an explosion energy of 2.2 × 10 51 erg and an ejecta mass of about 21M .…”

“…We apply our toy model to the strongest peak in the light curve of the enigmatic type II-P SN iPTF14hls, i.e., the third peak that Wang et al (2018) had problems to fit. Wang et al (2018) suggest that this peak is due to a magnetic activity of the newly born NS, in contrast to the other peaks that they attribute to fallback accretion. We present the light curve from Wang et al (2018) in Fig.…”