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

Iwakiri, Wataru B. and Pottschmidt, Katja and Falkner, Sebastian and Hemphill, Paul B. and Fürst, Felix and Nishimura, Osamu and Schwarm, Fritz-Walter and Wolff, Michael T. and Marcu-Cheatham, Diana M. and Chakrabarty, Deepto and Tomsick, John A. and Wilson-Hodge, Colleen A. and Bissinger Kühnel, Matthias and Terada, Yukikatsu and Enoto, Teruaki and Wilms, Jörn (2019) Spectral and Timing Analysis of the Accretion-powered Pulsar 4U 1626–67 Observed with Suzaku and NuSTAR. Astrophysical Journal, 878 (2). Art. No. 121. ISSN 1538-4357. https://resolver.caltech.edu/CaltechAUTHORS:20190620-093003303

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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 ~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 ~5%, while the 30–60 keV flux decreased significantly by ~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 ~20 keV. Taken together with the observed Ṗ 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.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.3847/1538-4357/ab1f87DOIArticle
https://arxiv.org/abs/1905.05356arXivDiscussion Paper
ORCID:
AuthorORCID
Iwakiri, Wataru B.0000-0002-0207-9010
Pottschmidt, Katja0000-0002-4656-6881
Falkner, Sebastian0000-0001-5209-991X
Hemphill, Paul B.0000-0002-1676-6954
Fürst, Felix0000-0003-0388-0560
Wolff, Michael T.0000-0002-4013-5650
Marcu-Cheatham, Diana M.0000-0001-8061-611X
Chakrabarty, Deepto0000-0001-8804-8946
Tomsick, John A.0000-0001-5506-9855
Wilson-Hodge, Colleen A.0000-0002-8585-0084
Bissinger Kühnel, Matthias0000-0002-8709-8236
Terada, Yukikatsu0000-0002-2359-1857
Enoto, Teruaki0000-0003-1244-3100
Wilms, Jörn0000-0003-2065-5410
Additional Information:© 2019. The American Astronomical Society. Received 2017 November 1; revised 2019 April 29; accepted 2019 May 5; published 2019 June 20. The authors appreciate very much the many constructive comments from the anonymous referee. This work is based on data from the NuSTAR mission, a project led by the California Institute of Technology, managed by the Jet Propulsion Laboratory, and funded by the National Aeronautics and Space Administration. We thank the NuSTAR Operations, Software and Calibration teams for support with the execution and analysis of these observations. This research has made use of the NuSTAR Data Analysis Software (NuSTARDAS) jointly developed by the ASI Science Data Center (ASDC, Italy) and the California Institute of Technology (USA). We also thank the Suzaku, Fermi/GBM and MAXI team members for their dedicated support in satellite operations and calibration. This work has been partially funded by the Deutsche Forschungsgemeinschaft under the DFG grant No. WI 1860/11-1. It uses ISIS functions (ISISscripts) provided by the ECAP/Remeis observatory and MIT (http://www.sternwarte.uni-erlangen.de/isis/). The figures in this work have been produced with the S-Lang module slxfig. K.P. acknowledges support by NASA's NuSTAR Cycle 1 Guest Observer grant No. NNX15AV17G. M.T.W. is supported by the Chief of Naval Research. W.I. is supported by the Special Postdoctoral Researchers Program in RIKEN and JSPS KAKENHI grant No. 16K17717.
Group:NuSTAR
Funders:
Funding AgencyGrant Number
NASA/JPL/CaltechUNSPECIFIED
Deutsche Forschungsgemeinschaft (DFG)WI 1860/11-1
NASANNX15AV17G
Chief of Naval ResearchUNSPECIFIED
Japan Society for the Promotion of Science (JSPS)16K17717
Subject Keywords:magnetic fields; pulsars: individual (4U 1626–67) ; X-rays: binaries
Issue or Number:2
Record Number:CaltechAUTHORS:20190620-093003303
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20190620-093003303
Official Citation:Wataru B. Iwakiri et al 2019 ApJ 878 121
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:96582
Collection:CaltechAUTHORS
Deposited By: George Porter
Deposited On:20 Jun 2019 19:47
Last Modified:03 Oct 2019 21:23

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