X-raying the ultraluminous infrared starburst galaxy and broad absorption line QSO Markarian 231 with Chandra

S. C. Gallagher, W. N. Brandt, G. Chartas, G. P. Garmire, R. M. Sambruna

Research output: Contribution to journalArticle

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Abstract

With 40 ks of Chandra ACIS-S3 exposure, new information on both the starburst and QSO components of the X-ray emission of Markarian 231, an ultraluminous infrared galaxy and broad absorption line QSO, has been obtained. The bulk of the X-ray luminosity is emitted from an unresolved nuclear point source, and the spectrum is remarkably hard, with the majority of the flux emitted above 2 keV. Most notably, significant nuclear variability (a decrease of ∼45% in approximately 6 hr) at energies above 2 keV indicates that Chandra has probed within light-hours of the central black hole. Although we concur with Maloney & Reynolds that the direct continuum is not observed, this variability coupled with the 188 eV upper limit on the equivalent width of the Fe Kα emission line argues against the reflection-dominated model put forth by these authors based on their ASCA data. Instead, we favor a model in which a small, Compton-thick absorber blocks the direct X-rays, and only indirect, scattered X-rays from multiple lines of sight can reach the observer. Extended soft, thermal emission encompasses the optical extent of the galaxy and exhibits resolved structure. An off-nuclear X-ray source with a 0.35-8.0 keV luminosity of LX = 7 × 1039 ergs s -1, consistent with the ultraluminous X-ray sources in other nearby starbursts, is detected. We also present an unpublished Faint Object Spectrograph spectrum from the Hubble Space Telescope archive showing the broad C IV absorption.

Original languageEnglish (US)
Pages (from-to)655-670
Number of pages16
JournalAstrophysical Journal
Volume569
Issue number2 I
DOIs
StatePublished - Apr 20 2002

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starburst galaxies
quasars
x rays
luminosity
galaxies
faint objects
thermal emission
Hubble Space Telescope
erg
line of sight
point sources
spectrographs
point source
absorbers
continuums
energy

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Gallagher, S. C. ; Brandt, W. N. ; Chartas, G. ; Garmire, G. P. ; Sambruna, R. M. / X-raying the ultraluminous infrared starburst galaxy and broad absorption line QSO Markarian 231 with Chandra. In: Astrophysical Journal. 2002 ; Vol. 569, No. 2 I. pp. 655-670.
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X-raying the ultraluminous infrared starburst galaxy and broad absorption line QSO Markarian 231 with Chandra. / Gallagher, S. C.; Brandt, W. N.; Chartas, G.; Garmire, G. P.; Sambruna, R. M.

In: Astrophysical Journal, Vol. 569, No. 2 I, 20.04.2002, p. 655-670.

Research output: Contribution to journalArticle

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T1 - X-raying the ultraluminous infrared starburst galaxy and broad absorption line QSO Markarian 231 with Chandra

AU - Gallagher, S. C.

AU - Brandt, W. N.

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AU - Sambruna, R. M.

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N2 - With 40 ks of Chandra ACIS-S3 exposure, new information on both the starburst and QSO components of the X-ray emission of Markarian 231, an ultraluminous infrared galaxy and broad absorption line QSO, has been obtained. The bulk of the X-ray luminosity is emitted from an unresolved nuclear point source, and the spectrum is remarkably hard, with the majority of the flux emitted above 2 keV. Most notably, significant nuclear variability (a decrease of ∼45% in approximately 6 hr) at energies above 2 keV indicates that Chandra has probed within light-hours of the central black hole. Although we concur with Maloney & Reynolds that the direct continuum is not observed, this variability coupled with the 188 eV upper limit on the equivalent width of the Fe Kα emission line argues against the reflection-dominated model put forth by these authors based on their ASCA data. Instead, we favor a model in which a small, Compton-thick absorber blocks the direct X-rays, and only indirect, scattered X-rays from multiple lines of sight can reach the observer. Extended soft, thermal emission encompasses the optical extent of the galaxy and exhibits resolved structure. An off-nuclear X-ray source with a 0.35-8.0 keV luminosity of LX = 7 × 1039 ergs s -1, consistent with the ultraluminous X-ray sources in other nearby starbursts, is detected. We also present an unpublished Faint Object Spectrograph spectrum from the Hubble Space Telescope archive showing the broad C IV absorption.

AB - With 40 ks of Chandra ACIS-S3 exposure, new information on both the starburst and QSO components of the X-ray emission of Markarian 231, an ultraluminous infrared galaxy and broad absorption line QSO, has been obtained. The bulk of the X-ray luminosity is emitted from an unresolved nuclear point source, and the spectrum is remarkably hard, with the majority of the flux emitted above 2 keV. Most notably, significant nuclear variability (a decrease of ∼45% in approximately 6 hr) at energies above 2 keV indicates that Chandra has probed within light-hours of the central black hole. Although we concur with Maloney & Reynolds that the direct continuum is not observed, this variability coupled with the 188 eV upper limit on the equivalent width of the Fe Kα emission line argues against the reflection-dominated model put forth by these authors based on their ASCA data. Instead, we favor a model in which a small, Compton-thick absorber blocks the direct X-rays, and only indirect, scattered X-rays from multiple lines of sight can reach the observer. Extended soft, thermal emission encompasses the optical extent of the galaxy and exhibits resolved structure. An off-nuclear X-ray source with a 0.35-8.0 keV luminosity of LX = 7 × 1039 ergs s -1, consistent with the ultraluminous X-ray sources in other nearby starbursts, is detected. We also present an unpublished Faint Object Spectrograph spectrum from the Hubble Space Telescope archive showing the broad C IV absorption.

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