A multiphase Suzaku study of X-rays from τ Sco

R. Ignace, L. M. Oskinova, M. Jardine, J. P. Cassinelli, D. H. Cohen, J. F. Donati, R. H.D. Townsend, A. Ud-Doula

Research output: Contribution to journalArticle

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Abstract

We obtained relatively high signal-to-noise X-ray spectral data of the early massive star τ Sco (B0.2V) with the Suzaku X-ray Imaging Spectrometer (XIS) instrument. This source displays several unusual features that motivated our study: (1) redshifted absorption in UV P Cygni lines to approximately +250 km s-1 suggestive of infalling gas, (2) unusually hard X-ray emission requiring hot plasma at temperatures in excess of 10 MK whereas most massive stars showrelatively softX-rays at a fewMK, and (3) a complex photospheric magnetic field of open and closed field lines. In an attempt to understand the hard component better, X-ray data were obtained at six roughly equally spaced phases within the same epoch of τ Sco's 41 day rotation period. The XIS instrument has three operable detectors: XIS1 is back-illuminated with sensitivity down to 0.2 keV; XIS0 and XIS2 are front-illuminated with sensitivity only down to 0.4 keV and have an overall less effective area than XIS1. The XIS0 and XIS3 detectors show relatively little variability. In contrast, there is a ≈4σ detection of a ≈4% drop in the count rate of the XIS1 detector at one rotational phase. In addition, all three detectors show a ≈3% increase in count rate at the same phase. The most optimistic prediction of X-ray variability allows for a 40% change in the count rate, particularly near phases where we have pointings. Observed modulations in the X-ray light curve on the rotation cycle is an order of magnitude smaller than this,which places newstringent constraints on futuremodeling of this interestingmagnetic massive star.

Original languageEnglish (US)
Pages (from-to)1412-1420
Number of pages9
JournalAstrophysical Journal
Volume721
Issue number2
DOIs
StatePublished - Oct 1 2010

Fingerprint

massive stars
x rays
detectors
imaging spectrometers
spectrometer
early stars
sensitivity
high temperature plasmas
light curve
rays
time measurement
magnetic field
modulation
plasma
cycles
detector
prediction
predictions
gases
gas

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Ignace, R., Oskinova, L. M., Jardine, M., Cassinelli, J. P., Cohen, D. H., Donati, J. F., ... Ud-Doula, A. (2010). A multiphase Suzaku study of X-rays from τ Sco. Astrophysical Journal, 721(2), 1412-1420. https://doi.org/10.1088/0004-637X/721/2/1412
Ignace, R. ; Oskinova, L. M. ; Jardine, M. ; Cassinelli, J. P. ; Cohen, D. H. ; Donati, J. F. ; Townsend, R. H.D. ; Ud-Doula, A. / A multiphase Suzaku study of X-rays from τ Sco. In: Astrophysical Journal. 2010 ; Vol. 721, No. 2. pp. 1412-1420.
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Ignace, R, Oskinova, LM, Jardine, M, Cassinelli, JP, Cohen, DH, Donati, JF, Townsend, RHD & Ud-Doula, A 2010, 'A multiphase Suzaku study of X-rays from τ Sco', Astrophysical Journal, vol. 721, no. 2, pp. 1412-1420. https://doi.org/10.1088/0004-637X/721/2/1412

A multiphase Suzaku study of X-rays from τ Sco. / Ignace, R.; Oskinova, L. M.; Jardine, M.; Cassinelli, J. P.; Cohen, D. H.; Donati, J. F.; Townsend, R. H.D.; Ud-Doula, A.

In: Astrophysical Journal, Vol. 721, No. 2, 01.10.2010, p. 1412-1420.

Research output: Contribution to journalArticle

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T1 - A multiphase Suzaku study of X-rays from τ Sco

AU - Ignace, R.

AU - Oskinova, L. M.

AU - Jardine, M.

AU - Cassinelli, J. P.

AU - Cohen, D. H.

AU - Donati, J. F.

AU - Townsend, R. H.D.

AU - Ud-Doula, A.

PY - 2010/10/1

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N2 - We obtained relatively high signal-to-noise X-ray spectral data of the early massive star τ Sco (B0.2V) with the Suzaku X-ray Imaging Spectrometer (XIS) instrument. This source displays several unusual features that motivated our study: (1) redshifted absorption in UV P Cygni lines to approximately +250 km s-1 suggestive of infalling gas, (2) unusually hard X-ray emission requiring hot plasma at temperatures in excess of 10 MK whereas most massive stars showrelatively softX-rays at a fewMK, and (3) a complex photospheric magnetic field of open and closed field lines. In an attempt to understand the hard component better, X-ray data were obtained at six roughly equally spaced phases within the same epoch of τ Sco's 41 day rotation period. The XIS instrument has three operable detectors: XIS1 is back-illuminated with sensitivity down to 0.2 keV; XIS0 and XIS2 are front-illuminated with sensitivity only down to 0.4 keV and have an overall less effective area than XIS1. The XIS0 and XIS3 detectors show relatively little variability. In contrast, there is a ≈4σ detection of a ≈4% drop in the count rate of the XIS1 detector at one rotational phase. In addition, all three detectors show a ≈3% increase in count rate at the same phase. The most optimistic prediction of X-ray variability allows for a 40% change in the count rate, particularly near phases where we have pointings. Observed modulations in the X-ray light curve on the rotation cycle is an order of magnitude smaller than this,which places newstringent constraints on futuremodeling of this interestingmagnetic massive star.

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Ignace R, Oskinova LM, Jardine M, Cassinelli JP, Cohen DH, Donati JF et al. A multiphase Suzaku study of X-rays from τ Sco. Astrophysical Journal. 2010 Oct 1;721(2):1412-1420. https://doi.org/10.1088/0004-637X/721/2/1412