X-ray Properties of Intermediate-Mass Black Holes in Active Galaxies. II. X-ray-Bright Accretion and Possible Evidence for Slim Disks Export

@article{citeulike:4181157, abstract = {We present X-ray properties of optically-selected intermediate-mass (\~{}10^5--10^6 M\_Sun) black holes (BHs) in active galaxies (AGNs), using data from the Chandra X-Ray Observatory. Our observations are a continuation of a pilot study by Greene \& Ho (2007). Of the 8 objects observed, 5 are detected with X-ray luminosities in the range L\_0.5-2 keV = 10^41--10^43 erg s^-1, consistent with the previously observed sample. Objects with enough counts to extract a spectrum are well fit by an absorbed power law. We continue to find a range of soft photon indices 1 \< \Gamma\_s \< 2.7, where N(E) \propto E^-\Gamma\_s, consistent with previous AGN studies, but generally flatter than other narrow-line Seyfert 1 active nuclei (NLS1s). The soft photon index correlates strongly with X-ray luminosity and Eddington ratio, but does not depend on BH mass. There is no justification for the inclusion of any additional components, such as a soft excess, although this may be a function of the relative inefficiency of detecting counts above 2 keV in these relatively shallow observations. As a whole, the X-ray-to-optical spectral slope \alpha\_ox is flatter than in more massive systems, even other NLS1s. Only X-ray-selected NLS1s with very high Eddington ratios share a similar \alpha\_ox. This is suggestive of a physical change in the accretion structure at low masses and at very high accretion rates, possibly due to the onset of slim disks. Although the detailed physical explanation for the X-ray loudness of these intermediate-mass BHs is not certain, it is very striking that targets selected on the basis of optical properties should be so distinctly offset in their broader spectral energy distributions.}, archivePrefix = {arXiv}, author = {Desroches, Louis-Benoit and Greene, Jenny E. and Ho, Luis C.}, citeulike-article-id = {4181157}, citeulike-linkout-0 = {http://arxiv.org/abs/0903.2257}, citeulike-linkout-1 = {http://arxiv.org/pdf/0903.2257}, day = {12}, eprint = {0903.2257}, keywords = {agns, bhs, xray}, month = {Mar}, posted-at = {2009-03-16 11:03:38}, priority = {2}, title = {X-ray Properties of Intermediate-Mass Black Holes in Active Galaxies. II. X-ray-Bright Accretion and Possible Evidence for Slim Disks}, url = {http://arxiv.org/abs/0903.2257}, year = {2009} }

TY - JOUR ID - citeulike:4181157 L3 - citeulike-article-id:4181157 N2 - We present X-ray properties of optically-selected intermediate-mass (~10^5--10^6 M_Sun) black holes (BHs) in active galaxies (AGNs), using data from the Chandra X-Ray Observatory. Our observations are a continuation of a pilot study by Greene & Ho (2007). Of the 8 objects observed, 5 are detected with X-ray luminosities in the range L_0.5-2 keV = 10^41--10^43 erg s^-1, consistent with the previously observed sample. Objects with enough counts to extract a spectrum are well fit by an absorbed power law. We continue to find a range of soft photon indices 1 < \Gamma_s < 2.7, where N(E) \propto E^-\Gamma_s, consistent with previous AGN studies, but generally flatter than other narrow-line Seyfert 1 active nuclei (NLS1s). The soft photon index correlates strongly with X-ray luminosity and Eddington ratio, but does not depend on BH mass. There is no justification for the inclusion of any additional components, such as a soft excess, although this may be a function of the relative inefficiency of detecting counts above 2 keV in these relatively shallow observations. As a whole, the X-ray-to-optical spectral slope \alpha_ox is flatter than in more massive systems, even other NLS1s. Only X-ray-selected NLS1s with very high Eddington ratios share a similar \alpha_ox. This is suggestive of a physical change in the accretion structure at low masses and at very high accretion rates, possibly due to the onset of slim disks. Although the detailed physical explanation for the X-ray loudness of these intermediate-mass BHs is not certain, it is very striking that targets selected on the basis of optical properties should be so distinctly offset in their broader spectral energy distributions. TI - X-ray Properties of Intermediate-Mass Black Holes in Active Galaxies. II. X-ray-Bright Accretion and Possible Evidence for Slim Disks KW - agns KW - bhs KW - xray AU - Desroches, Louis-Benoit AU - Greene, Jenny AU - Ho, Luis PY - 2009/Mar/12/ UR - http://arxiv.org/abs/0903.2257 ER -