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NASA Technical Reports Server (NTRS) 20150010753: Spectral and Timi... |
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by NASA Technical Reports Server (NTRS) |
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The symbiotic X-ray binary (SyXB) 4U 1954+319 is a rare |
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system hosting a peculiar neutron star (NS) and an M-type |
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optical companion. Its approx. 5.4 hr NS spin period is |
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the longest among all known accretion-powered pulsars and |
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exhibited large (is approx. 7%) fluctuations over 8 yr. A |
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spin trend transition was detected with Swift/BAT around |
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an X-ray brightening in 2012. The source was in quiescent |
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and bright states before and after this outburst based on |
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60 ks Suzaku observations in 2011 and 2012. The observed |
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continuum is well described by a Comptonized model with |
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the addition of a narrow 6.4 keV Fe-K alpha line during |
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the outburst. Spectral similarities to slowly rotating |
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pulsars in high-mass X-ray binaries, its high pulsed |
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fraction (approx. 60%-80%), and the location in the |
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Corbet diagram favor high B-field (approx. greater than |
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10(exp12) G) over a weak field as in low-mass X-ray |
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binaries. The observed low X-ray luminosity (10(exp33)- |
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10(exp35) erg s(exp-1)), probable wide orbit, and a slow |
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stellar wind of this SyXB make quasi-spherical accretion |
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in the subsonic settling regime a plausible model. |
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Assuming a approx. 10(exp13) G NS, this scheme can |
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explain the approx. 5.4 hr equilibrium rotation without |
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employing the magnetar-like field (approx. 10(exp16) G) |
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required in the disk accretion case. The timescales of |
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multiple irregular flares (approx. 50 s) can also be |
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attributed to the free-fall time from the Alfv en shell |
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for a approx. 10(exp13) G field. A physical |
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interpretation of SyXBs beyond the canonical binary |
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classifications is discussed. |
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Date Published: 2016-11-17 04:40:22 |
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Identifier: NASA_NTRS_Archive_20150010753 |
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Item Size: 36639726 |
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Language: english |
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Media Type: texts |
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