CaltechAUTHORS
Published April 1, 2020 | Version Accepted Version + Published
Journal Article Open

A NICER View of Spectral and Profile Evolution for Three X-Ray-emitting Millisecond Pulsars

Creators

  • 1. ROR icon Haverford College
  • 2. ROR icon North-West University
  • 3. ROR icon California Institute of Technology
  • 4. ROR icon United States Naval Research Laboratory
  • 5. ROR icon Columbia University
  • 6. ROR icon Research Institute in Astrophysics and Planetology
  • 7. ROR icon West Virginia University
  • 8. ROR icon National Radio Astronomy Observatory
  • 9. ROR icon Kyoto University

Abstract

We present two years of Neutron star Interior Composition Explorer (NICER) X-ray observations of three energetic rotation-powered millisecond pulsars (MSPs): PSRs B1937+21, B1821−24, and J0218+4232. We fit Gaussians and Lorentzians to the pulse profiles for different energy sub-bands of the soft X-ray regime to measure the energy dependence of pulse separation and width. We find that the separation between pulse components of PSR J0218+4232 decreases with increasing energy at >3σ confidence. The 95% upper limit on pulse separation evolution for PSRs B1937+21 and B1821−24 is less than 2 milliperiods per keV. Our phase-resolved spectral results provide updated constraints on the non-thermal X-ray emission of these three pulsars. The photon indices of the modeled X-ray emission spectra for each pulse component of PSR B1937+21 are inconsistent with each other at the 90% confidence level, suggesting different emission origins for each pulse. We find that the PSR B1821−24 and PSR J0218+4232 emission spectra are invariant with phase at the 90% confidence level. We describe the implications of our profile and spectral results in the context of equatorial current sheet emission models for these three MSPs with non-thermal, magnetospheric X-ray emission.

Additional Information

© 2020. The American Astronomical Society. Received 2019 November 1; revised 2020 January 27; accepted 2020 January 28; published 2020 April 7. This work was supported by NASA through the NICER mission and the Astrophysics Explorers Program. D.R., L.L., and Z.G. acknowledge support from the NANOGrav Physics Frontiers Center (NSF award No. 1430284) and from Haverford College through the Louis Green Fund. E.S. acknowledges support from the Marian E. Koshland Integrated Natural Sciences Center Summer Scholar fund at Haverford College. R.M.L. acknowledges the support of NASA through Hubble Fellowship Program grant HST-HF2-51440.001. The authors thank K. Kalapotharakos for his insight on interpretation of our results, and M. Corcoran for his assistance in generating the space-weather model background. We also thank J. Cammisa for his input on data acquisition and handling. This research has made use of NASA's Astrophysics Data System Bibliographic Services (ADS) and the arXiv. Software: HEAsoft (v6.26.1 Nasa High Energy Astrophysics Science Archive Research Center (Heasarc), 2014), PINT (https://github.com/nanograv/pint), XSELECT (v2.4), XSPEC (v12.1.0 Arnaud 1996), NICERSoft (https://github.com/paulray/NICERsoft). Facility: NICER. -

Attached Files

Published - Rowan_2020_ApJ_892_150.pdf

Accepted Version - 2001.11513.pdf

Files

2001.11513.pdf

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Additional details

Identifiers

Eprint ID
102457
Resolver ID
CaltechAUTHORS:20200409-115739757

Related works

Describes
https://arxiv.org/abs/2001.11513 (URL)

Funding

NSF
PHY-1430284
Haverford College
NASA Hubble Fellowship
HST-HF2-51440.001
NASA Einstein Fellowship

Dates

Created
2020-04-09
Created from EPrint's datestamp field
Updated
2021-11-16
Created from EPrint's last_modified field