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Measurements of Cyclotron Features and Pulse Periods in the High-Mass X-Ray Binaries 4U 1538-522 and 4U 1907+09 with the International Gamma-Ray Astrophysics LaboratoryWe present a spectral and timing analysis of International Gamma-Ray Astrophysics Laboratory (INTEGRAL) observations of two high-mass X-ray binaries, 4U 1538−522 and 4U 1907+09. Our timing measurements for 4U 1538−522 find the pulse period to have exhibited a spin-up trend until approximately 2009, after which there is evidence for a torque reversal, with the source beginning to spin down to the most recently measured period of 525.407 plus or minus 0.001 seconds. The most recent INTEGRAL observations of 4U 1907+09 are not found to yield statistically significant pulse periods due to the significantly lower flux from the source compared with 4U 1538−522. A spectral model consisting of a power-law continuum with an exponential cutoff and modified by two cyclotron resonance scattering features is found to fit both sources well, with the cyclotron scattering features detected at approximately 22 and approximately 49 kiloelectronvolts for 4U 1538−522 and at approximately 18 and approximately 36 kiloelectronvolts for 4U 1907+09. The spectral parameters of 4U 1538−522 are generally not found to vary significantly with flux and there is little to no variation across the torque reversal. Examining our results in conjunction with previous work, we find no evidence for a correlation between cyclotron line energy and luminosity for 4U 1538−522. 4U 1907+09 shows evidence for a positive correlation between cyclotron line energy and luminosity, which would make it the fourth, and lowest luminosity, cyclotron line source to exhibit this relationship.
Document ID
20160005793
Acquisition Source
Goddard Space Flight Center
Document Type
Reprint (Version printed in journal)
Authors
Hemphill, Paul B.
(California Univ. San Diego, CA, United States)
Rothschild, Richard E.
(California Univ. San Diego, CA, United States)
Caballero, Isabel
(Saclay Research Centre Gif-sur-Yvette, France)
Pottschmidt, Katja
(Maryland Univ. Baltimore County Baltimore, MD, United States)
Kuhnel, Matthias
(Erlangen-Nuernberg Univ. Bamberg, Germany)
Furst, Felix
(California Inst. of Tech. Pasadena, CA, United States)
Wilms, Jorn
(Erlangen-Nuernberg Univ. Bamberg, Germany)
Date Acquired
May 4, 2016
Publication Date
October 17, 2013
Publication Information
Publication: The Astrophysical Journal
Publisher: The American Astronomical Society.
Volume: 777
Issue: 1
Subject Category
Astrophysics
Report/Patent Number
GSFC-E-DAA-TN15986
Funding Number(s)
CONTRACT_GRANT: NNG06EO90A
Distribution Limits
Public
Copyright
Other
Keywords
stars: magnetic field
4U 1907+09)
oscillations
pulsars: individual (4U 1538 - 522

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