THE X-RAY ENERGY DEPENDENCE OF THE RELATION BETWEEN OPTICAL AND X-RAY EMISSION IN QUASARS

Journal Article · Sun Jan 10 00:00:00 EST 2010 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/708/2/1388· OSTI ID:21392375

Young, M; Elvis, M; Risaliti, G ^[1]

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1. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)

We develop a new approach to the well-studied anti-correlation between the optical-to-X-ray spectral index, alpha{sub ox}, and the monochromatic optical luminosity, l{sub opt}. By cross-correlating the Sloan Digital Sky Survey DR5 quasar catalog with the XMM-Newton archive, we create a sample of 327 quasars with X-ray signal-to-noise ratio (S/N) > 6, where both optical and X-ray spectra are available. This allows alpha{sub ox} to be defined at arbitrary frequencies, rather than the standard 2500 A and 2 keV. We find that while the choice of optical wavelength does not strongly influence the alpha{sub ox}-l{sub opt} relation, the slope of the relation does depend on the choice of X-ray energy. The slope of the relation becomes steeper when alpha{sub ox} is defined at low (approx1 keV) X-ray energies. This change is significant when compared to the slope predicted by a decrease in the baseline over which alpha{sub ox} is defined. The slopes are also marginally flatter than predicted at high (approx10 keV) X-ray energies. Partial correlation tests show that while the primary driver of alpha{sub ox} is l{sub opt}, the Eddington ratio correlates strongly with alpha{sub ox} when l{sub opt} is taken into account, so accretion rate may help explain these results. We combine the alpha{sub ox}-l{sub opt} and GAMMA-L{sub bol}/L{sub Edd} relations to naturally explain two results: (1) the existence of the GAMMA-l{sub x} relation as reported in Young et al., and (2) the lack of a GAMMA-l{sub opt} relation. The consistency of the optical/X-ray correlations establishes a more complete framework for understanding the relation between quasar emission mechanisms. We also discuss two correlations with the hard X-ray bolometric correction, which we show correlates with both alpha{sub ox} and Eddington ratio. This confirms that an increase in accretion rate correlates with a decrease in the fraction of up-scattered disk photons.

• OSTI ID: 21392375
• Journal Information: Astrophysical Journal, Vol. 708, Issue 2; Other Information: DOI: 10.1088/0004-637X/708/2/1388; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ACCRETION DISKS
BOLOMETERS
CATALOGS
ENERGY DEPENDENCE
GALAXIES
HARD X RADIATION
KEV RANGE 01-10
LUMINOSITY
MONOCHROMATIC RADIATION
PHOTON EMISSION
PHOTONS
QUASARS
SIGNAL-TO-NOISE RATIO
X-RAY SPECTRA
BOSONS
COSMIC RADIO SOURCES
DIMENSIONLESS NUMBERS
DOCUMENT TYPES
ELECTROMAGNETIC RADIATION
ELEMENTARY PARTICLES
EMISSION
ENERGY RANGE
IONIZING RADIATIONS
KEV RANGE
MASSLESS PARTICLES
MEASURING INSTRUMENTS
OPTICAL PROPERTIES
PHYSICAL PROPERTIES
RADIATIONS
SPECTRA
X RADIATION