A decade in the life of EXO 2030+375: a multiwavelength study of an accreting X-ray pulsar
A decade in the life of EXO 2030+375: a multiwavelength study of an accreting X-ray pulsar
Using BATSE and RXTE observations from 1991 April to 2001 August, we have detected 71 outbursts from 82 periastron passages of EXO 2030+375, a 42 s transient X-ray pulsar with a Be star companion, including several outbursts from 1993 August to 1996 April, when the source was previously believed to be quiescent. Combining BATSE, RXTE, and EXOSAT data, we have derived an improved orbital solution. Applying this solution results in a smooth profile for the spin-up rate during the giant outburst and results in evidence for a correlation between the spin-up rate and observed flux in the brighter BATSE outbursts. Infrared and Hα measurements show a decline in the density of the circumstellar disk around the Be star. This decline is followed by a sudden drop in the X-ray flux and a turnover from a spin-up trend to spin-down in the frequency history. This is the first Be/X-ray binary that shows an extended interval, about 2.5 yr, in which the global trend is spin-down, but the outbursts continue. In 1995 the orbital phase of EXO 2030+375's outbursts shifted from peaking about 6 days after periastron to peaking before periastron. The outburst phase slowly recovered to peaking at about 2.5 days after periastron. We interpret this shift in orbital phase followed by a slow recovery as evidence of a global one-armed oscillation propagating in the Be disk. This is further supported by changes in the shape of the Hα profile, which are commonly believed to be produced by a reconfiguration of the Be disk. The truncated viscous decretion disk model provides an explanation for the long series of normal outbursts and the evidence of an accretion disk in the brighter normal outbursts. Long-term multiwavelength observations such as these clearly add considerably to our knowledge of Be/X-ray binaries and the relationship among optical, infrared, and X-ray observations.
accretion, accretion disks, stars, pulsars, individual, alphanumeric, EXO 2030+375, stars: neutron, x-rays: binaries, x-rays: individual (EXO 2030+375)
287-302
Wilson, C.A.
9f6f5364-62b4-4d76-9564-c25dd6b0f9e8
Finger, M.H.
3b33865b-a7a3-44a7-a2f0-05cda0423a92
Coe, M.J.
04dfb23b-1456-46a3-9242-5cee983471d5
Laycock, S.
3021ea8f-9d14-4cda-93cd-6776c37ed386
Fabregat, J.
56633b5f-ba82-45c2-bfb2-b2e30bfdd92e
1 May 2002
Wilson, C.A.
9f6f5364-62b4-4d76-9564-c25dd6b0f9e8
Finger, M.H.
3b33865b-a7a3-44a7-a2f0-05cda0423a92
Coe, M.J.
04dfb23b-1456-46a3-9242-5cee983471d5
Laycock, S.
3021ea8f-9d14-4cda-93cd-6776c37ed386
Fabregat, J.
56633b5f-ba82-45c2-bfb2-b2e30bfdd92e
Wilson, C.A., Finger, M.H., Coe, M.J., Laycock, S. and Fabregat, J.
(2002)
A decade in the life of EXO 2030+375: a multiwavelength study of an accreting X-ray pulsar.
Astrophysical Journal, 570 (1), .
(doi:10.1086/339739).
Abstract
Using BATSE and RXTE observations from 1991 April to 2001 August, we have detected 71 outbursts from 82 periastron passages of EXO 2030+375, a 42 s transient X-ray pulsar with a Be star companion, including several outbursts from 1993 August to 1996 April, when the source was previously believed to be quiescent. Combining BATSE, RXTE, and EXOSAT data, we have derived an improved orbital solution. Applying this solution results in a smooth profile for the spin-up rate during the giant outburst and results in evidence for a correlation between the spin-up rate and observed flux in the brighter BATSE outbursts. Infrared and Hα measurements show a decline in the density of the circumstellar disk around the Be star. This decline is followed by a sudden drop in the X-ray flux and a turnover from a spin-up trend to spin-down in the frequency history. This is the first Be/X-ray binary that shows an extended interval, about 2.5 yr, in which the global trend is spin-down, but the outbursts continue. In 1995 the orbital phase of EXO 2030+375's outbursts shifted from peaking about 6 days after periastron to peaking before periastron. The outburst phase slowly recovered to peaking at about 2.5 days after periastron. We interpret this shift in orbital phase followed by a slow recovery as evidence of a global one-armed oscillation propagating in the Be disk. This is further supported by changes in the shape of the Hα profile, which are commonly believed to be produced by a reconfiguration of the Be disk. The truncated viscous decretion disk model provides an explanation for the long series of normal outbursts and the evidence of an accretion disk in the brighter normal outbursts. Long-term multiwavelength observations such as these clearly add considerably to our knowledge of Be/X-ray binaries and the relationship among optical, infrared, and X-ray observations.
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More information
Published date: 1 May 2002
Additional Information:
This paper provides important constrains on accretion mechanisms from the circumstellar disk of a Be star on to a compainon neutron star. The crucial database of observations was accrued under Coe's guidance, who also led on the interpretation of the optical spectra.
Keywords:
accretion, accretion disks, stars, pulsars, individual, alphanumeric, EXO 2030+375, stars: neutron, x-rays: binaries, x-rays: individual (EXO 2030+375)
Identifiers
Local EPrints ID: 37631
URI: http://eprints.soton.ac.uk/id/eprint/37631
ISSN: 0004-637X
PURE UUID: 1be6c382-1ef4-4646-a44a-2ee52367423a
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Date deposited: 25 May 2006
Last modified: 16 Mar 2024 02:35
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Contributors
Author:
C.A. Wilson
Author:
M.H. Finger
Author:
S. Laycock
Author:
J. Fabregat
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