NuSTAR and XMM-Newton observations of 1E1743.1-2843: indications of a neutron star LMXB nature of the compact object

TL;DR

This study uses NuSTAR and XMM-Newton observations to analyze the X-ray source 1E1743.1-2843, providing evidence that it is most likely a neutron star low-mass X-ray binary located beyond the Galactic Center.

Contribution

The paper presents the first combined NuSTAR and XMM-Newton spectral analysis of 1E1743.1-2843, strongly indicating its neutron star LMXB nature and ruling out alternative classifications.

Findings

Spectrum fits a black body model with kT~1.8 keV

Spectrum is thermally Comptonized by electrons at ~4.6 keV

Lack of pulsations and iron line disfavors HMXB interpretation

Abstract

We report on the results of NuSTAR and XMM-Newton observations of the persistent X-ray source 1E1743.1-2843, located in the Galactic Center region. The source was observed between September and October 2012 by NuSTAR and XMM-Newton, providing almost simultaneous observations in the hard and soft X-ray bands. The high X-ray luminosity points to the presence of an accreting compact object. We analyze the possibilities of this accreting compact object being either a neutron star (NS) or a black hole, and conclude that the joint XMM-Newton and NuSTAR spectrum from 0.3 to 40 $\mathrm{keV}$ fits to a black body spectrum with $kT\sim1.8~\mathrm{keV}$ emitted from a hot spot or an equatorial strip on a neutron star surface. This spectrum is thermally Comptonized by electrons with $kT_{e}\sim4.6~\mathrm{keV}$. Accepting this neutron star hypothesis, we probe the Low Mass (LMXB) or High Mass (HMXB) X-ray Binary nature of the source. While the lack of Type-I bursts can be explained in the LMXB scenario, the absence of pulsations in the 2 mHz - 49 Hz frequency range, the lack of eclipses and of an IR companion, and the lack of a $K_{\alpha}$ line from neutral or moderately ionized iron strongly disfavor interpreting this source as a HMXB. We therefore conclude that 1E1743.1-2843 is most likely a NS-LMXB located beyond the Galactic Center. There is weak statistical evidence for a soft X-ray excess possibly indicating thermal emission from an accretion disk. However, the disk normalization remains unconstrained due to the high hydrogen column density ($N_{H}\sim1.6\times10^{23}~\mathrm{cm^{-2}}$).