Observations of a GX 301-2 Apastron Flare with the X-Calibur Hard X-Ray Polarimeter Supported by NICER, the Swift XRT and BAT, and Fermi GBM

Academic Article


  • Abstract The accretion-powered X-ray pulsar GX 301−2 was observed with the balloon-borne X-Calibur hard X-ray polarimeter during late 2018 December, with contiguous observations by the Neutron star Interior Composition Explorer Mission (NICER) X-ray telescope, the Swift X-ray Telescope and Burst Alert Telescope, and the Fermi Gamma-ray Burst Monitor spanning several months. The observations detected the pulsar in a rare apastron flaring state coinciding with a significant spin up of the pulsar discovered with the Fermi Gamma-ray Burst Monitor. The X-Calibur, NICER, and Swift observations reveal a pulse profile strongly dominated by one main peak, and the NICER and Swift data show strong variation of the profile from pulse to pulse. The X-Calibur observations constrain for the first time the linear polarization of the 15–35 keV emission from a highly magnetized accreting neutron star, indicating a polarization degree of % (90% confidence limit) averaged over all pulse phases. We discuss the spin up and the X-ray spectral and polarimetric results in the context of theoretical predictions. We conclude with a discussion of the scientific potential of future observations of highly magnetized neutron stars with the more sensitive follow-up mission XL-Calibur.
  • Authors

  • Abarr, Q
  • Baring, M
  • Beheshtipour, B
  • Beilicke, M
  • de Geronimo, G
  • Dowkontt, P
  • Errando, M
  • Guarino, V
  • Iyer, N
  • Kislat, Fabian
  • Kiss, M
  • Kitaguchi, T
  • Krawczynski, H
  • Lanzi, J
  • Li, S
  • Lisalda, L
  • Okajima, T
  • Pearce, M
  • Press, L
  • Rauch, B
  • Stuchlik, D
  • Takahashi, H
  • Tang, J
  • Uchida, N
  • West, A
  • Jenke, P
  • Krimm, H
  • Lien, A
  • Malacaria, C
  • Miller, JM
  • Wilson-Hodge, C
  • Status

    Publication Date

  • March 1, 2020
  • Has Subject Area


  • Bianchi cosmology
  • High mass x-ray binary stars
  • Neutron stars
  • Spectropolarimetry
  • X-ray astronomy
  • Digital Object Identifier (doi)

    Start Page

  • 70
  • End Page

  • 70
  • Volume

  • 891
  • Issue

  • 1