X-RAY OBSERVATIONAL SIGNATURE OF A BLACK HOLE ACCRETION DISK IN AN ACTIVE GALACTIC NUCLEUS RX J1633+4718

Journal Article · Mon Nov 01 00:00:00 EDT 2010 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/723/1/508· OSTI ID:21467181

Yuan, W; Liu, B F ^[1]; Zhou, H

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1. National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 (China)

We report the discovery of a luminous ultra-soft X-ray excess in a radio-loud narrow-line Seyfert 1 galaxy, RX J1633+4718, from archival ROSAT observations. The thermal temperature of this emission, when fitted with a blackbody, is as low as 32.5{sup +8.0}{sub -6.0} eV. This is in remarkable contrast to the canonical temperatures of {approx}0.1-0.2 keV found hitherto for the soft X-ray excess in active galactic nuclei (AGNs) and is interestingly close to the maximum temperature predicted for a postulated accretion disk in this object. If this emission is indeed blackbody in nature, the derived luminosity (3.5{sup +3.3}{sub -1.5} x 10{sup 44} erg s{sup -1}) infers a compact emitting area with a size ({approx}5 x 10{sup 12} cm or 0.33 AU in radius) that is comparable to several times the Schwarzschild radius of a black hole (BH) at the mass estimated for this AGN ({approx}3 x 10{sup 6} M{sub sun}). In fact, this ultra-steep X-ray emission can be well fitted as the (Compton scattered) Wien tail of the multi-temperature blackbody emission from an optically thick accretion disk, whose inferred parameters (BH mass and accretion rate) are in good agreement with independent estimates using the optical emission-line spectrum. We thus consider this feature as a signature of the long-sought X-ray radiation directly from a disk around a supermassive BH, presenting observational evidence for a BH accretion disk in the AGN. Future observations with better data quality, together with improved independent measurements of the BH mass, may constrain the spin of the BH.

• OSTI ID: 21467181
• Journal Information: Astrophysical Journal, Vol. 723, Issue 1; Other Information: DOI: 10.1088/0004-637X/723/1/508; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ACCRETION DISKS
BLACK HOLES
EMISSION
GALAXY NUCLEI
LUMINOSITY
MASS
SCHWARZSCHILD RADIUS
SOFT X RADIATION
X-RAY GALAXIES
COSMIC RAY SOURCES
COSMIC X-RAY SOURCES
ELECTROMAGNETIC RADIATION
GALAXIES
IONIZING RADIATIONS
OPTICAL PROPERTIES
PHYSICAL PROPERTIES
RADIATIONS
X RADIATION