A SUZAKU OBSERVATION OF NGC 4593: ILLUMINATING THE TRUNCATED DISK

Journal Article · Sun Nov 01 04:00:00 EST 2009 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/705/1/496· OSTI ID:21378378

Markowitz, A G ^[1]; Reeves, J N ^[2]

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1. Center for Astrophysics and Space Sciences, University of California, San Diego, M.C. 0424, La Jolla, CA, 92093-0424 (United States)
2. Astrophysics Group, School of Physical and Geographical Sciences, Keele University, Keele, Staffordshire, ST5 5BG (United Kingdom)

We report results from a 2007 Suzaku observation of the Seyfert 1 AGN NGC 4593. The narrow Fe Kalpha emission line has a FWHM width approx 4000 km s{sup -1}, indicating emission from approx> 5000 R {sub g}. There is no evidence for a relativistically broadened Fe K line, consistent with the presence of a radiatively efficient outer disk which is truncated or transitions to an interior radiatively inefficient flow. The Suzaku observation caught the source in a low-flux state; comparison to a 2002 XMM-Newton observation indicates that the hard X-ray flux decreased by 3.6, while the Fe Kalpha line intensity and width sigma each roughly halved. Two model-dependent explanations for the changes in Fe Kalpha line profile are explored. In one, the Fe Kalpha line width has decreased from approx10,000 to approx4000 km s{sup -1} from 2002 to 2007, suggesting that the thin disk truncation/transition radius has increased from 1000-2000 to approx>5000 R {sub g}. However, there are indications from other compact accreting systems that such truncation radii tend to be associated only with accretion rates relative to Eddington much lower than that of NGC 4593. In the second model, the line profile in the XMM-Newton observation consists of a time-invariant narrow component plus a broad component originating from the inner part of the truncated disk (approx300 R {sub g}) which has responded to the drop in continuum flux. The Compton reflection component strength R is approx 1.1, consistent with the measured Fe Kalpha line total equivalent width with an Fe abundance 1.7 times the solar value. The modest soft excess, modeled well by either thermal bremsstrahlung emission or by Comptonization of soft seed photons in an optical thin plasma, has fallen by a factor of approx20 from 2002 to 2007, ruling out emission from a region 5 lt-yr in size.

• OSTI ID: 21378378
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 705; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ABUNDANCE
BOSONS
BREMSSTRAHLUNG
COSMIC RAY SOURCES
COSMIC X-RAY SOURCES
ELECTROMAGNETIC RADIATION
ELEMENTARY PARTICLES
EMISSION
GALAXIES
HARD X RADIATION
IONIZING RADIATIONS
LINE WIDTHS
MASSLESS PARTICLES
PHOTONS
PLASMA
RADIATIONS
X RADIATION
X-RAY GALAXIES