Synchrotron radiation from NGC 470 HLX1 - a hidden hyperluminous accreting neutron star?

TL;DR

This study analyzes the broadband spectrum of NGC 470 HLX1, exploring synchrotron radiation from a magnetized neutron star to understand its emission mechanisms and the nature of hyperluminous X-ray sources.

Contribution

It introduces a physically motivated synchrotron emission model for HLX sources and constrains particle acceleration parameters under super-Eddington accretion.

Findings

Detection of a blackbody-like component indicating a disk or outflow

Constraints on electron Lorentz factors in the neutron star magnetosphere

Synchrotron emission viability suggests neutron stars may power HLX sources

Abstract

We present the first broadband spectral analysis of NGC 470 HLX1, a hyperluminous X-ray source that exhibits significant flux variability over different epochs. We investigate the feasibility of synchrotron radiation with varying latitude from a magnetized neutron star to explain the source's spectra. Although the statistical quality of the data does not allow us to rule out simple phenomenological models, it is adequate to constrain the parameter space for this more physically motivated model. We also shed light on the particle acceleration mechanisms and maximum Lorentz factor of electrons within the neutron star magnetospheric plasma under super-Eddington accretion conditions. In our broadband spectral modeling, the detection of a blackbody-like component suggests the presence of a disk near the corotation radius or an outflow ejected from the disk. The viability of synchrotron emission in an HLX system offers new insights about the nature of these sources, motivating further sample studies to assess whether most of these sources are powered by accreting neutron stars.