THE REFLARES and OUTBURST EVOLUTION in the ACCRETING MILLISECOND PULSAR SAX J1808.4-3658: A DISK TRUNCATED NEAR CO-ROTATION?

A. Patruno, D. Maitra, P. A. Curran, C. D'Angelo, J. K. Fridriksson, Dave Russell, M. Middleton, R. Wijnands

Research output: Contribution to journalArticle

Abstract

The accreting millisecond X-ray pulsar SAX J1808.43658 shows peculiar low luminosity states known as "reflares" after the end of the main outburst. During this phase the X-ray luminosity of the source varies by up to three orders of magnitude in less than 12 days. The lowest X-ray luminosity observed reaches a value of ∼1032 erg s-1, only a factor of a few brighter than its typical quiescent level. We investigate the 2008 and 2005 reflaring state of SAX J1808.43658 to determine whether there is any evidence for a change in the accretion flow with respect to the main outburst. We perform a multiwavelength photometric and spectral study of the 2005 and 2008 reflares with data collected during an observational campaign covering the near-infrared, optical, ultra-violet and X-ray band. We find that the NIR/optical/UV emission, expected to come from the outer accretion disk, shows variations in luminosity over an order of magnitude. The corresponding X-ray luminosity variations are instead much deeper, spanning about 23 orders of magnitude. The X-ray spectral state observed during the reflares does not change substantially with X-ray luminosity, indicating a rather stable configuration of the accretion flow. We investigate the most likely configuration of the innermost regions of the accretion flow and we infer an accretion disk truncated at or near the co-rotation radius. We interpret these findings as due to either a strong outflow (due to a propeller effect) or a trapped disk (with limited/no outflow) in the inner regions of the accretion flow.

Original languageEnglish (US)
Article number100
JournalAstrophysical Journal
Volume817
Issue number2
DOIs
StatePublished - Feb 1 2016

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corotation
pulsars
accretion
luminosity
x rays
accretion disks
outburst
outflow
propellers
configurations
erg
near infrared
coverings
radii

Keywords

  • accretion, accretion disks
  • pulsars: general
  • pulsars: individual (SAX J1808.43658)
  • stars: neutron
  • X-rays: binaries

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

THE REFLARES and OUTBURST EVOLUTION in the ACCRETING MILLISECOND PULSAR SAX J1808.4-3658 : A DISK TRUNCATED NEAR CO-ROTATION? / Patruno, A.; Maitra, D.; Curran, P. A.; D'Angelo, C.; Fridriksson, J. K.; Russell, Dave; Middleton, M.; Wijnands, R.

In: Astrophysical Journal, Vol. 817, No. 2, 100, 01.02.2016.

Research output: Contribution to journalArticle

Patruno, A. ; Maitra, D. ; Curran, P. A. ; D'Angelo, C. ; Fridriksson, J. K. ; Russell, Dave ; Middleton, M. ; Wijnands, R. / THE REFLARES and OUTBURST EVOLUTION in the ACCRETING MILLISECOND PULSAR SAX J1808.4-3658 : A DISK TRUNCATED NEAR CO-ROTATION?. In: Astrophysical Journal. 2016 ; Vol. 817, No. 2.
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AU - Maitra, D.

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AU - D'Angelo, C.

AU - Fridriksson, J. K.

AU - Russell, Dave

AU - Middleton, M.

AU - Wijnands, R.

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AB - The accreting millisecond X-ray pulsar SAX J1808.43658 shows peculiar low luminosity states known as "reflares" after the end of the main outburst. During this phase the X-ray luminosity of the source varies by up to three orders of magnitude in less than 12 days. The lowest X-ray luminosity observed reaches a value of ∼1032 erg s-1, only a factor of a few brighter than its typical quiescent level. We investigate the 2008 and 2005 reflaring state of SAX J1808.43658 to determine whether there is any evidence for a change in the accretion flow with respect to the main outburst. We perform a multiwavelength photometric and spectral study of the 2005 and 2008 reflares with data collected during an observational campaign covering the near-infrared, optical, ultra-violet and X-ray band. We find that the NIR/optical/UV emission, expected to come from the outer accretion disk, shows variations in luminosity over an order of magnitude. The corresponding X-ray luminosity variations are instead much deeper, spanning about 23 orders of magnitude. The X-ray spectral state observed during the reflares does not change substantially with X-ray luminosity, indicating a rather stable configuration of the accretion flow. We investigate the most likely configuration of the innermost regions of the accretion flow and we infer an accretion disk truncated at or near the co-rotation radius. We interpret these findings as due to either a strong outflow (due to a propeller effect) or a trapped disk (with limited/no outflow) in the inner regions of the accretion flow.

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