2008ApJ...675.1424C -
Astrophys. J., 675, 1424-1435 (2008/March-2)
A comparison of the variability of the symbiotic X-ray binaries GX 1+4, 4U 1954+31, and 4U 1700+24 from Swift BAT and RXTE ASM observations.
CORBET R.H.D., SOKOLOSKI J.L., MUKAI K., MARKWARDT C.B. and TUELLER J.
Abstract (from CDS):
We present an analysis of the X-ray variability of three symbiotic X-ray binaries, GX 1+4, 4U 1700+24, and 4U 1954+31, using observations made with the Swift Burst Alert Telescope (BAT) and the Rossi X-Ray Timing Explorer (RXTE) All-Sky Monitor (ASM). Observations of 4U 1954+31 with the Swift BAT show modulation at a period near 5 hr. Models to explain this modulation are discussed, including the presence of an exceptionally slow X-ray pulsar in the system and accretion instabilities. We conclude that the most likely interpretation is that 4U 1954+31 contains one of the slowest known X-ray pulsars. Unlike 4U 1954+31, neither GX 1+4 nor 4U 1700+24 show any evidence for modulation on a timescale of hours. An analysis of the RXTE ASM light curves of GX 1+4, 4U 1700+24, and 4U 1954+31 does not show the presence of periodic modulation in any source, with the exception of a possible detection of the 5 hr period in 4U 1954+31, although there is considerable variability on long timescales for all three sources. There is no modulation in GX 1+4 on either the optical 1161 day orbital period or a previously reported 304 day X-ray period. For 4U 1700+24 we do not confirm the 404 day X-ray period previously proposed for this source from a shorter duration ASM light curve. We conclude that all three sources have substantial low-frequency noise in their power spectra that may give the appearance of periodic modulation if this noise is not properly accounted for, particularly if short-duration light curves are examined.
Abstract Copyright:
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Journal keyword(s):
Stars: Binaries: Symbiotic - Stars: Individual: Alphanumeric: GX 1+4 - stars: individual (4U 1954+31) - stars: individual (4U 1700+24) - Stars: Neutron - X-Rays: Binaries
Simbad objects:
14
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