TY - JOUR
T1 - The hard X-ray spectral slope as an accretion rate indicator in radio-quiet active galactic nuclei
AU - Shemmer, Ohad
AU - Brandt, W. N.
AU - Netzer, Hagai
AU - Maiolino, Roberto
AU - Kaspi, Shai
N1 - Funding Information:
This work is based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and the US (NASA). We thank an anonymous referee for constructive comments, and George Chartas and Aaron Steffen for fruitful discussions. We gratefully acknowledge the financial support of NASA grant NNG05GP00G (O. S., W. N. B.), NASA Long Term Space Astrophysics grant NAG 5-13035 (O. S., W. N. B.), and the Zeff Fellowship at the Technion (S. K.). This work is supported by Israel Science Foundation grant 232/03.
PY - 2006/7/20
Y1 - 2006/7/20
N2 - We present new XMM-Newton observations of two luminous and high accretion rate radio-quiet active galactic nuclei (AGNs) at z ∼ 2. Together with archival X-ray and rest-frame optical spectra of three sources with similar properties, as well as 25 moderate-luminosity radio-quiet AGNs at z < 0.5, we investigate, for the first time, the dependence of the hard (≳2 keV) X-ray power-law photon index on the broad Hβ emission-line width and on the accretion rate across ∼3 orders of magnitude in AGN luminosity. Provided that the accretion rates of the five luminous sources can be estimated by extrapolating the well-known relation between the broad-line region size and luminosity to high luminosities, we find that the photon indices of these sources, while consistent with those expected from their accretion rates, are significantly higher than expected from the widths of their Hβ lines. We argue that within the limits of our sample, the hard X-ray photon index depends primarily on the accretion rate.
AB - We present new XMM-Newton observations of two luminous and high accretion rate radio-quiet active galactic nuclei (AGNs) at z ∼ 2. Together with archival X-ray and rest-frame optical spectra of three sources with similar properties, as well as 25 moderate-luminosity radio-quiet AGNs at z < 0.5, we investigate, for the first time, the dependence of the hard (≳2 keV) X-ray power-law photon index on the broad Hβ emission-line width and on the accretion rate across ∼3 orders of magnitude in AGN luminosity. Provided that the accretion rates of the five luminous sources can be estimated by extrapolating the well-known relation between the broad-line region size and luminosity to high luminosities, we find that the photon indices of these sources, while consistent with those expected from their accretion rates, are significantly higher than expected from the widths of their Hβ lines. We argue that within the limits of our sample, the hard X-ray photon index depends primarily on the accretion rate.
KW - Galaxies: active
KW - Galaxies: nuclei
KW - Quasars: emission lines
KW - Quasars: individual (Q1346-036, HE 2217-2818)
KW - X-rays: galaxies
UR - http://www.scopus.com/inward/record.url?scp=33747467577&partnerID=8YFLogxK
U2 - 10.1086/506911
DO - 10.1086/506911
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AN - SCOPUS:33747467577
SN - 0004-637X
VL - 646
SP - L29-L32
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - II
ER -