XMM-Newton observations of IGR J00291+5934: signs of a thermal spectral component during quiescence

TL;DR

This paper reports the first detection of a thermal spectral component in the quiescent emission of the accretion-powered millisecond pulsar IGR J00291+5934, indicating neutron star cooling and spin-up with minimal accreted mass.

Contribution

It provides the first evidence of a thermal component in the quiescent spectrum of an accretion-powered millisecond pulsar, enhancing understanding of neutron star cooling and accretion history.

Findings

Detection of a thermal component with temperatures ~64 eV and ~110 eV.

Presence of a dominant hard spectral component (>60% flux).

Neutron star can be spun up to millisecond periods with less than 0.2 solar masses accreted.

Abstract

We present X-ray observations of the transient accretion-powered millisecond pulsar IGR J00291+5934 during quiescence. IGR J00291+5934 is the first source among accretion powered millisecond pulsars to show signs of a thermal component in its quiescent spectrum. Fitting this component with a neutron star atmosphere or a black body model we obtain soft temperatures (~64 eV and ~110 eV, respectively). As in other sources of this class a hard spectral component is also present, comprising more than 60% of the unabsorbed 0.5-10 keV flux. Interpreting the soft component as cooling emission from the neutron star, we can conclude that the compact object can be spun up to milliscond periods by accreting only <0.2 solar masses.