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

Journal Article · Sun Jan 10 04:00:00 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, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 708; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

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