Hard X-ray Observations of the Hydrogen-poor Superluminous Supernova SN 2018hti with NuSTAR

TL;DR

This study used NuSTAR to observe the hydrogen-poor superluminous supernova SN 2018hti, aiming to detect X-ray emission from a potential magnetar engine, but found no flux, constraining the magnetar's contribution to the supernova's luminosity.

Contribution

First X-ray observational constraints on SN 2018hti's magnetar engine using NuSTAR, providing limits on its X-ray luminosity and energy contribution.

Findings

No X-ray flux detected at the supernova's position.

Upper limit constrains magnetar's X-ray contribution to less than 36%.

Results inform models of superluminous supernova energy sources.

Abstract

Some Hydrogen-poor superluminous supernovae are likely powered by a magnetar central engine, making their luminosity larger than common supernovae. Although a significant amount of X-ray flux is expected from the spin down of the magnetar, direct observational evidence is still to be found, giving rise to the "missing energy" problem. Here we present NuSTAR observations of nearby SN 2018hti 2.4y (rest frame) after its optical peak. We expect that, by this time, the ejecta have become optically thin for photons more energetic than about 15keV. No flux is detected at the position of the supernova down to $F_{\rm{10-30keV}} = 9.0\times 10^{-14}$ erg cm$^{-2}$ s$^{-1}$, or an upper limit of $7.9 \times 10^{41}$ erg s$^{-1}$ at a distance of 271Mpc. This constrains the fraction of bolometric luminosity from the putative spinning down magnetar to be $f_{\rm X} \lesssim 36$% in the 10-30keV range in a conservative case, $f_{\rm X} \lesssim 11$% in an optimistic case.