Observing the Transient Pulsations of SMC X-1 with NuSTAR

Journal article


Publication Details

Author(s): Pike SN, Harrison FA, Bachetti M, Brumback MC, Furst FS, Madsen KK, Pottschmidt K, Tomsick JA, Wilms J
Journal: Astrophysical Journal
Publisher: IOP PUBLISHING LTD
Publication year: 2019
Volume: 875
Journal issue: 2
ISSN: 0004-637X
eISSN: 1538-4357


Abstract

We report on Nuclear Spectroscopic Telescope Array observations of transient pulsations in the neutron star X-ray binary SMC X-1. The transition from nonpulsing to pulsing states was not accompanied by a large change in flux. Instead, both pulsing and nonpulsing states were observed in a single observation during the low-flux super-orbital state. During the high state, we measure a pulse period of P = 0.70117(9) s at T-ref = 56145 MJD. Spectral analysis during nonpulsing and pulsing states reveals that the observations can be consistently modeled by an absorbed power law with a phenomenological cutoff resembling a Fermi-Dirac distribution, or by a partially obscured cutoff power law. The shapes of the underlying continua show little variability between epochs, while the covering fraction and column density vary between super-orbital states. The strength of pulsations also varies, leading us to infer that the absence and reemergence of pulsations are related to changing obscuration, such as by a warped accretion disk. SMC X-1 is accreting near or above its Eddington limit, reaching an unabsorbed X-ray luminosity of L-x (2-10 keV) approximate to 5 x 10(38) erg s(-1). This suggests that SMC X-1 may be a useful local analog to ultraluminous X-ray pulsars (ULXPs), which likewise exhibit strong variability in their pulsed fractions, as well as flux variability on similar timescales. In particular, the gradual pulse turn-on, which has been observed in M82 X-2, is similar to the behavior we observe in SMC X-1. Thus we propose that pulse fraction variability of ULXPs may also be due to variable obscuration.


FAU Authors / FAU Editors

Wilms, Jörn Prof. Dr.
Professur für Astronomie und Astrophysik


External institutions with authors

California Institute of Technology (Caltech)
Dartmouth College
European Space Astronomy Centre (ESAC)
INAF-Osservatorio Astronomico di Cagliari
University of California, Berkeley
University of Maryland, Baltimore County


How to cite

APA:
Pike, S.N., Harrison, F.A., Bachetti, M., Brumback, M.C., Furst, F.S., Madsen, K.K.,... Wilms, J. (2019). Observing the Transient Pulsations of SMC X-1 with NuSTAR. Astrophysical Journal, 875(2). https://dx.doi.org/10.3847/1538-4357/ab0f2b

MLA:
Pike, Sean N., et al. "Observing the Transient Pulsations of SMC X-1 with NuSTAR." Astrophysical Journal 875.2 (2019).

BibTeX: 

Last updated on 2019-03-06 at 18:08