1. 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
- Author
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Abarr, Q., Baring, M., Beheshtipour, B., Beilicke, M., deGeronimo, G., Dowkontt, P., Errando, M., Guarino, V., Iyer, N., Kislat, F., 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, J. M., and Wilson-Hodge, C.
- Subjects
Astrophysics - High Energy Astrophysical Phenomena ,High Energy Physics - Experiment - Abstract
The accretion-powered X-ray pulsar GX 301-2 was observed with the balloon-borne X-Calibur hard X-ray polarimeter during late December 2018, with contiguous observations by the 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 GBM. 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 (27+38-27)% (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., Comment: Accepted for publication in the Astrophysical Journal. 20 pages, 19 figures, 4 tables
- Published
- 2020
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