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Possible Detection of an Emission Cyclotron Resonance Scattering Feature from the Accretion-Powered Pulsar 4U 1626-67We present analysis of 4U 1626-67, a 7.7 s pulsar in a low-mass X-ray binary system, observed with the hard X-ray detector of the Japanese X-ray satellite Suzaku in 2006 March for a net exposure of ~88 ks. The source was detected at an average 10-60 keY flux of approx 4 x 10-10 erg / sq cm/ s. The phase-averaged spectrum is reproduced well by combining a negative and positive power-law times exponential cutoff (NPEX) model modified at approx 37 keY by a cyclotron resonance scattering feature (CRSF). The phase-resolved analysis shows that the spectra at the bright phases are well fit by the NPEX with CRSF model. On the other hand. the spectrum in the dim phase lacks the NPEX high-energy cutoff component, and the CRSF can be reproduced by either an emission or an absorption profile. When fitting the dim phase spectrum with the NPEX plus Gaussian model. we find that the feature is better described in terms of an emission rather than an absorption profile. The statistical significance of this result, evaluated by means of an F test, is between 2.91 x 10(exp -3) and 1.53 x 10(exp -5), taking into account the systematic errors in the background evaluation of HXD-PIN. We find that the emission profile is more feasible than the absorption one for comparing the physical parameters in other phases. Therefore, we have possibly detected an emission line at the cyclotron resonance energy in the dim phase.
Document ID
20120016469
Acquisition Source
Goddard Space Flight Center
Document Type
Reprint (Version printed in journal)
Authors
Iwakiri, W. B.
(Saitama Univ. Saitama, Japan)
Terada, Y.
(Saitama Univ. Saitama, Japan)
Tashiro, M. S.
(Saitama Univ. Saitama, Japan)
Mihara, T.
(Institute of Physical and Chemical Research Saitama, Japan)
Angelini, L.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Yamada, S.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Enoto, T.
(Kavli Inst. for Particle Astrophysics and Cosmology Stanford, CA, United States)
Makishima, K.
(Tokyo Univ. Japan)
Nakajima, M.
(Nihon Univ. Chiba, Japan)
Yoshida, A.
(Aoyamagakuin Univ. Sagamihara, Japan)
Date Acquired
August 26, 2013
Publication Date
May 2, 2012
Publication Information
Publication: The Astrophysical Journal
Volume: 751
Issue: 1
Subject Category
Astronomy
Report/Patent Number
GSFC.JA.7322.2012
Distribution Limits
Public
Copyright
Other

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