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The Astrophysical Journal


The Astrophysical Journal Volume 751 Number 1

W. B. Iwakiri et al. 2012 ApJ 751 35 doi:10.1088/0004-637X/751/1/35

POSSIBLE DETECTION OF AN EMISSION CYCLOTRON RESONANCE SCATTERING FEATURE FROM THE ACCRETION-POWERED PULSAR 4U 1626–67

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W. B. Iwakiri1, Y. Terada1, T. Mihara2, L. Angelini3, M. S. Tashiro1, T. Enoto4, S. Yamada3, K. Makishima5, M. Nakajima6, and A. Yoshida7

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Abstract References Cited By Metrics

We 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 keV flux of ~4 × 10–10 erg cm–2 s–1. The phase-averaged spectrum is reproduced well by combining a negative and positive power-law times exponential cutoff (NPEX) model modified at ~37 keV 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 × 10–3 and 1.53 × 10–5, 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.


Keywords

pulsars: individual (4U 1626–67); stars: magnetic field; X-rays: binaries; X-rays: stars


Dates

Issue 1 (2012 May 20)

Received 2011 September 23, accepted for publication 2012 March 16

Published 2012 May 2

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