Spectral and Timing Analysis of the Accretion-powered Pulsar 4U 1626-67 Observed with Suzaku and NuSTAR

Iwakiri WB, Pottschmidt K, Falkner S, Hemphill PB, Furst F, Nishimura O, Schwarm FW, Wolff MT, Marcu-Cheatham DM, Chakrabarty D, Tomsick JA, Wilson-Hodge CA, Kühnel M, Terada Y, Enoto T, Wilms J (2019)

Publication Type: Journal article

Publication year: 2019

Journal

Book Volume: 878

Journal Issue: 2

DOI: 10.3847/1538-4357/ab1f87

Abstract

We present an analysis of the spectral shape and pulse profile of the accretion-powered pulsar 4U 1626-67 observed with Suzaku and Nuclear Spectroscopic Telescope Array (NuSTAR) during a spin-up state. The pulsar, which experienced a torque reversal to spin-up in 2008, has a spin period of similar to 7.7 s. Comparing the phase-averaged spectra obtained with Suzaku in 2010 and with NuSTAR in 2015, we find that the spectral shape changed between the two observations: the 3-10 keV flux increased by similar to 5%, while the 30-60 keV flux decreased significantly by similar to 35%. Phase-averaged and phase-resolved spectral analysis shows that the continuum spectrum observed by NuSTAR is well described by an empirical negative and positive power law times exponential continuum with an added broad Gaussian emission component around the spectral peak at similar to 20 keV. Taken together with the observed P. value obtained from the Fermi/gamma-ray burst monitor data, we conclude that the spectral change between the Suzaku and NuSTAR observations was likely caused by an increase in the accretion rate. We also report the possible detection of asymmetry in the profile of the fundamental cyclotron line. Furthermore, we present a study of the energy-resolved pulse profiles using a new relativistic ray tracing code, where we perform a simultaneous fit to the pulse profiles assuming a two-column geometry with a mixed pencil- and fan-beam emission pattern. The resulting pulse profile decompositions enable us to obtain geometrical parameters of accretion columns (inclination, azimuthal and polar angles) and a fiducial set of beam patterns. This information is important to validate the theoretical predictions from radiation transfer in a strong magnetic field.

Authors with CRIS profile

Involved external institutions

Chuo University / 中央大学 Japan (JP) University of Maryland, Baltimore County United States (USA) (US) Massachusetts Institute of Technology (MIT) United States (USA) (US) European Space Astronomy Centre (ESAC) Spain (ES) National Institute of Technology, Nagano College Japan (JP) U.S. Naval Research Laboratory United States (USA) (US) University of California, Berkeley United States (USA) (US) National Aeronautics and Space Administration (NASA) United States (USA) (US) Saitama University / 埼玉大学 Japan (JP) Kyoto University / 京都大学 Kyōto daigaku Japan (JP)

How to cite

APA:

Iwakiri, W.B., Pottschmidt, K., Falkner, S., Hemphill, P.B., Furst, F., Nishimura, O.,... Wilms, J. (2019). Spectral and Timing Analysis of the Accretion-powered Pulsar 4U 1626-67 Observed with Suzaku and NuSTAR. Astrophysical Journal, 878(2). https://dx.doi.org/10.3847/1538-4357/ab1f87

MLA:

Iwakiri, Wataru B., et al. "Spectral and Timing Analysis of the Accretion-powered Pulsar 4U 1626-67 Observed with Suzaku and NuSTAR." Astrophysical Journal 878.2 (2019).

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