Can a bright and energetic X-ray pulsar be hiding amid the debris of SN 1987A?

TL;DR

This study assesses the current observational limits on detecting a neutron star in SN 1987A, suggesting that a typical young neutron star could still be hidden within the remnant despite the lack of direct evidence.

Contribution

The paper provides updated constraints on the X-ray luminosity of a potential neutron star in SN 1987A based on recent Chandra data and discusses the possibility of its obscuration by surrounding matter.

Findings

Limits on X-ray luminosity are around (1-5)×10^{35} erg s^{-1}.

A brighter X-ray source cannot be excluded due to possible absorption.

A typical young neutron star could still be hidden inside SN 1987A.

Abstract

The mass of the stellar precursor of supernova (SN) 1987A and the burst of neutrinos observed at the moment of the explosion are consistent with the core-collapse formation of a neutron star. However, no compelling evidence for the presence in SN 1987A of a compact object of any kind has been found yet in any band of the electromagnetic spectrum, prompting questions on whether the neutron star survived and, if it did, on its properties. Starting from the analysis of recent Chandra observations, here we appraise the current observational situation. We derived limits on the X-ray luminosity of a compact object with a nonthermal, Crab-pulsar-like spectrum of the order of $\approx$$(1$-$5)\times10^{35}$ erg s$^{-1}$, corresponding to limits on the rotational energy loss of a possible X-ray pulsar in SN 1987A of $\approx$$(0.5$-$1.5)\times10^{38}$ erg s$^{-1}$. However, a much brighter X-ray source cannot be excluded if, as is likely, it is enshrouded in a cloud of absorbing matter with metallicity similar to that expected in the outer layers of a massive star towards the end of its life. We found that other limits obtained from various arguments and observations in other energy ranges either are unbinding or allow a similar maximum luminosity of the order of $\approx$$10^{35}$ erg s$^{-1}$. We conclude that while a pulsar alike the one in the Crab Nebula in both luminosity and spectrum is hardly compatible with the observations, there is ample space for an `ordinary' X-ray-emitting young neutron star, born with normal initial spin period, temperature and magnetic field, to be hiding inside the evolving remnant of SN 1987A.