Accretion column eclipses in the X-ray pulsars GX 1+4 and RX J0812.4-3114
Version 2 2024-09-17, 02:10Version 2 2024-09-17, 02:10
Version 1 2023-05-16, 12:55Version 1 2023-05-16, 12:55
journal contribution
posted on 2024-09-17, 02:10authored byD Galloway, AB Giles, K Wu, JG Greenhill
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.
History
Publication title
Monthly Notices of the Royal Astronomical Society
Volume
325
Issue
1
Pagination
419-425
ISSN
0035-8711
Department/School
Physics
Publisher
Blackwell Science Ltd
Publication status
Published
Place of publication
Oxford
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