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Accretion column eclipses in the X-ray pulsars GX 1+4 and RX J0812.4-3114


Galloway, D and Giles, AB and Wu, K and Greenhill, JG, Accretion column eclipses in the X-ray pulsars GX 1+4 and RX J0812.4-3114, Monthly Notices of the Royal Astronomical Society, 325, (1) pp. 419-425. ISSN 0035-8711 (2001) [Refereed Article]

DOI: doi:10.1046/j.1365-8711.2001.04467.x


Sharp dips observed in the pulse profiles of three X-ray pulsars (GX 1+4, RX J0812.4-3114 and A 0535+26) have previously been suggested to arise from partial eclipses of the emission region by the accretion column occurring once each rotation period. We present pulse-phase spectroscopy from Rossi X-ray Timing Explorer satellite observations of GX 1+4 and RX J0812.4-3114, which for the first time confirms this interpretation. The dip phase corresponds to the closest approach of the column axis to the line of sight, and the additional optical depth of photons escaping from the column in this direction gives rise to both the decrease in flux and increase in the fitted optical depth measured at this phase. Analysis of the arrival time of individual dips in GX 1+4 provides the first measurement of azimuthal wandering of a neutron star accretion column. The column longitude varies stochastically with a standard deviation ranging between 2° and 6° depending on the source luminosity. Measurements of the phase width of the dip both from mean pulse profiles and from the individual eclipses demonstrate that the dip width is proportional to the flux. The variation is consistent with that expected if the azimuthal extent of the accretion column depends only upon the Keplerian velocity at the inner disc radius, which varies as a consequence of the accretion rate M.

Item Details

Item Type:Refereed Article
Research Division:Physical Sciences
Research Group:Astronomical sciences
Research Field:Galactic astronomy
Objective Division:Expanding Knowledge
Objective Group:Expanding knowledge
Objective Field:Expanding knowledge in the physical sciences
UTAS Author:Galloway, D (Mr Duncan Galloway)
UTAS Author:Giles, AB (Dr Barry Giles)
UTAS Author:Greenhill, JG (Dr John Greenhill)
ID Code:22119
Year Published:2001
Web of Science® Times Cited:23
Deposited By:Physics
Deposited On:2001-08-01
Last Modified:2002-05-09

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