Circumstellar Interaction Models for the Bolometric Light Curve of Type I Superluminous SN 2017egm

Abstract

We explore simple semi-analytic fits to the bolometric light curve of Gaia17biu/SN 2017egm, the most nearby hydrogen-deficient superluminous supernova (SLSN I) yet discovered. SN 2017egm has a quasi-bolometric light curve that is uncharacteristic of other SLSN I by having a nearly linear rise to maximum and decline from peak, with a very sharp transition. Magnetar models have difficulty explaining the sharp peak and may tend to be too bright 20 d after maximum. Light curves powered only by radioactive decay of 56 Ni fail on similar grounds and because they demand greater nickel mass than ejecta mass. Simple models based on circumstellar interaction do have a sharp peak corresponding to the epoch when the forward shock breaks out of the optically-thick circumstellar medium or the reverse shock reaches the inside of the ejecta. We find that models based on circumstellar interaction with a constant-density shell provide an interesting fit to the bolometric light curve from 15 d before to 15 d after peak light of SN 2017egm and that both magnetar and radioactive decay models fail to fit the sharp peak. Future photometric observations should easily discriminate basic CSI models from basic magnetar models. The implications of a CSI model are briefly discussed.

The Type II superluminous SN 2008es at late times: near-infrared excess and circumstellar interaction

“…We apply a semi-analytical model of CSI by using the CSMRAD routine in the TigerFit package 3 . Similar to Chatzopoulos et al (2012), Chatzopoulos et al (2013), andWheeler et al (2017), this model implements CSI with a diffusion process, including forward/reverse shock interaction, and radioactive (i.e., 56 Ni and 56 Co) heating. Parameters in the model include the initial 56 Ni mass M Ni , explosion energy E SN , progenitor radius R p (which is equivalent to the inner radius of the CSM in this model), ejecta mass M ej , ejecta opacity κ ej , power-law index of the density profile of the inner ejecta d and of the outer ejecta n, power-law index of the density profile of the CSM s, CSM mass M CSM , mass-loss rate M, and CSM wind velocity v w .…”

A Systematic Study of Superluminous Supernova Light-curve Models Using Clustering

“…Finally, we estimate the fraction of CSM and MAG model SLSN LCs that have a concave-up shape during the rise to peak luminosity or, in other words, positive second derivative for t < t max . An example of an observed SLSN with concave-up LC during the rise is SN 2017egm (Wheeler et al 2017). Not a single MAG LCs is found to be concave-up during the rise.…”

“…In the latter case, we can use photometry alone to characterize the nature of SLSNe. Lastly, another LC shape property that will be interesting to constrain with future, high-cadence photometric follow-up of SLSNe would be the convexity (second derivative) of the bolometric LC during the rise to peak luminosity (Wheeler et al 2017). Given the low temporal resolution of the observed LC in our sample, we opt to not provide estimates of the percentages of concave-up and concave-down LCs, yet we briefly discuss the predictions for these parameters coming from semi-analytical models in the following section.…”

“…In addition, these semi-analytic models are numerically inexpensive to compute, allowing us to compute large grids of LC models throughout the associated, multi-dimensional parameter space. As such they remain a popular SN LC modeling tool with a few codes that have been made publicly available to compute them such as TigerFit (Wheeler et al 2017) and…”

“…We have adapted the TigerFit code (Chatzopoulos et al 2016;Wheeler et al 2017) to run grids of CSM and MAG models throughout a large parameter space in order to systematically study the statistical LC shape properties and determine their association with the observed SLSN sample presented in Section 2.…”