A Potential Cyclotron Resonant Scattering Feature in the ULX Pulsar NGC 300 ULX1 seen by NuSTAR and XMM-Newton

TL;DR

This study reports a potential cyclotron resonant scattering feature at 13 keV in the ULX pulsar NGC 300 ULX1, suggesting a neutron star magnetic field similar to Galactic X-ray pulsars, based on broadband spectroscopy data.

Contribution

It presents the first evidence of a cyclotron feature in NGC 300 ULX1, linking its magnetic field to known pulsars and comparing it with recent proton line discoveries in other ULXs.

Findings

Potential cyclotron feature at 13 keV detected

Magnetic field estimated at ~10^12 G

Implications for ULX pulsar magnetic properties

Abstract

Based on phase-resolved broadband spectroscopy using $XMM$-$Newton$ and $NuSTAR$, we report on a potential cyclotron resonant scattering feature at $E \sim 13$ keV in the pulsed spectrum of the recently discoverd ULX pulsar NGC 300 ULX1. If this interpretation is correct, the implied magnetic field of the central neutron star is $B \sim 10^{12}$ G (assuming scattering off electrons), similar to that estimated from the observed spin-up of the star, and also similar to known Galactic X-ray pulsars. We discuss the implications of this result for the connection between NGC 300 ULX1 and the other known ULX pulsars, particularly in light of the recent discovery of a likely proton Cyclotron line in another ULX, M51 ULX-8.