XMM-Newton discovery of a possible cyclotron emission feature from the SFXT IGR J18483-0311

TL;DR

This paper reports the possible detection of a cyclotron emission feature in the X-ray spectrum of the SFXT IGR J18483-0311, suggesting a neutron star magnetic field of about 3x10^11 G, which could be the first such detection in an SFXT.

Contribution

It presents the first potential detection of a cyclotron emission line in an SFXT, indicating a neutron star magnetic field and advancing understanding of these transient sources.

Findings

Detection of a 3.3 keV emission feature in the spectrum.

Possible first harmonic hint of the cyclotron line.

Implication of a neutron star magnetic field around 3x10^11 G.

Abstract

We report the results from an archival XMM-Newton observation of the Supergiant Fast X-ray Transient (SFXT) IGR J18483-0311 during its apastron passage. The measured 0.5--10 keV luminosity state (1.3$\times10^{33}$ erg s$^{-1}$) is the lowest ever reported in the literature, it is best fitted by an absorbed black body model yielding parameters consistent with previous measurements. In addition, we find evidence of an emission line feature at $\sim$3.3 keV in the 0.5--10 keV EPIC-pn source spectrum. We show that its physical explanation in terms of atomic emission line appears unlikely and conversely we attempt to ascribe it to an electron cyclotron emission line which would implies a neutron star magnetic field of the order of $\sim3\times10^{11}$ G. A possible hint of the first harmonic is also found. If firmly confirmed by future longer X-ray observations, this would be the first detection ever of a cyclotron feature in the X-ray spectrum of a SFXT, with important implications on theoretical models.