NICER Detection of Thermal X-ray Pulsations from the Massive Millisecond Pulsars PSR J0740+6620 and PSR J1614-2230

TL;DR

This paper reports the first detection of thermal X-ray pulsations from two massive millisecond pulsars, PSR J0740+6620 and PSR J1614-2230, using NICER, revealing their surface emission characteristics and phase relationships with radio signals.

Contribution

It presents the first NICER detection of X-ray pulsations from these two massive neutron stars, providing new insights into their surface emission and pulsation profiles.

Findings

PSR J0740+6620 shows a double-peaked X-ray profile.

PSR J1614-2230 exhibits a single broad X-ray peak.

Both pulsars display thermal X-ray spectra indicative of surface emission.

Abstract

We report the detection of X-ray pulsations from the rotation-powered millisecond-period pulsars PSR J0740+6620 and PSR J1614-2230, two of the most massive neutron stars known, using observations with the Neutron Star Interior Composition Explorer (NICER). We also analyze X-ray Multi-Mirror Mission (XMM-Newton) data for both pulsars to obtain their time-averaged fluxes and study their respective X-ray fields. PSR J0740+6620 exhibits a broad double-peaked profile with a separation of ~0.4 in phase. PSR J1614-2230, on the other hand, has a broad single-peak profile. The broad modulations with soft X-ray spectra of both pulsars are indicative of thermal radiation from one or more small regions of the stellar surface. We show the NICER detections of X-ray pulsations for both pulsars and also discuss the phase relationship to their radio pulsations. In the case of PSR J0740+6620, this paper documents the data reduction performed to obtain the pulsation detection and prepare for pulse profile modeling analysis.