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Browsing by Author "Brandt, W. N."

Now showing 1 - 5 of 5
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    Consistent Analysis of the AGN LF in X-Ray and MIR in the XMM-LSS Field
    Runburg, Jack; Farrah, Duncan; Sajina, Anna; Lacy, Mark; Lidua, Jenna; Hatziminaoglou, Evanthia; Brandt, W. N.; Chen, Chien-Ting J.; Nyland, Kristina; Shirley, Raphael; Clements, D. L.; Pitchford, Lura K. (IOP, 2022-01-01)
    The luminosity function of active galactic nuclei (AGN) probes the history of supermassive black hole assembly and growth across cosmic time. To mitigate selection biases, we present a consistent analysis of the AGN luminosity functions (LFs) derived for both X-ray and mid-infrared (MIR) selected AGN in the XMM-Large Scale Structure field. There are 4268 AGN used to construct the MIR luminosity function (IRLF) and 3427 AGN used to construct the X-ray luminosity function (XLF), providing the largest census of the AGN population out to z = 4 in both bands with significant reduction in uncertainties. We are able for the first time to see the knee of the IRLF at z > 2 and observe a flattening of the faint-end slope as redshift increases. The bolometric luminosity density, a proxy for the cosmic black hole accretion history, computed from our LFs, shows a peak at z approximate to 2.25, consistent with recent estimates of the peak in the star formation rate density (SFRD). However, at earlier epochs, the AGN luminosity density is flatter than the SFRD. If confirmed, this result suggests that the build up of black hole mass outpaces the growth of stellar mass in high-mass systems at z greater than or similar to 2.5. This is consistent with observations of redshift z similar to 6 quasars that lie above the local M - sigma relationship. The luminosity density derived from the IRLF is higher than that from the XLF at all redshifts. This is consistent with the dominant role of obscured AGN activity in the cosmic growth of supermassive black holes.
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    The nuclear spectroscopic telescope array (NuSTAR) high-energy x-ray mission
    Harrison, F. A.; Craig, W. W.; Christensen, F. E.; Hailey, C. J.; Zhang, W. W.; Boggs, S. E.; Stern, D.; Cook, W. R.; Forster, K.; Giommi, P.; Grefenstette, B. W.; Kim, Y.; Kitaguchi, T.; Koglin, J. E.; Madsen, K. K.; Mao, P. H.; Miyasaka, H.; Mori, K.; Perri, M.; Pivovaroff, M. J.; Puccetti, S.; Rana, V. R.; Westergaard, N. J.; Willis, J.; Zoglauer, A.; An, H. J.; Bachetti, M.; Barriere, N. M.; Bellm, E. C.; Bhalerao, V.; Brejnholt, N. F.; Fuerst, F.; Liebe, C. C.; Markwardt, C. B.; Nynka, M.; Vogel, J. K.; Walton, D. J.; Wik, D. R.; Alexander, D. M.; Cominsky, L. R.; Hornschemeier, A. E.; Hornstrup, A.; Kaspi, V. M.; Madejski, G. M.; Matt, G.; Molendi, S.; Smith, D. M.; Tomsick, J. A.; Ajello, M.; Ballantyne, D. R.; Balokovic, M.; Barret, D.; Bauer, F. E.; Blandford, R. D.; Brandt, W. N.; Brenneman, L. W.; Chiang, J.; Chakrabarty, D.; Chenevez, J.; Comastri, A.; Dufour, F.; Elvis, M.; Fabian, A. C.; Farrah, D.; Fryer, C. L.; Gotthelf, E. V.; Grindlay, J. E.; Helfand, D. J.; Krivonos, R.; Meier, D. L.; Miller, J. M.; Natalucci, L.; Ogle, P.; Ofek, E. O.; Ptak, A.; Reynolds, S. P.; Rigby, J. R.; Tagliaferri, G.; Thorsett, S. E.; Treister, E.; Urry, C. M. (IOP Publishing Ltd., 2013-06)
    The Nuclear Spectroscopic Telescope Array (NuSTAR) mission, launched on 2012 June 13, is the first focusing high-energy X-ray telescope in orbit. NuSTAR operates in the band from 3 to 79 keV, extending the sensitivity of focusing far beyond the similar to 10 keV high-energy cutoff achieved by all previous X-ray satellites. The inherently low background associated with concentrating the X-ray light enables NuSTAR to probe the hard X-ray sky with a more than 100-fold improvement in sensitivity over the collimated or coded mask instruments that have operated in this bandpass. Using its unprecedented combination of sensitivity and spatial and spectral resolution, NuSTAR will pursue five primary scientific objectives: (1) probe obscured active galactic nucleus (AGN) activity out to the peak epoch of galaxy assembly in the universe (at z less than or similar to 2) by surveying selected regions of the sky; (2) study the population of hard X-ray-emitting compact objects in the Galaxy by mapping the central regions of the Milky Way; (3) study the non-thermal radiation in young supernova remnants, both the hard X-ray continuum and the emission from the radioactive element Ti-44; (4) observe blazars contemporaneously with ground-based radio, optical, and TeV telescopes, as well as with Fermi and Swift, to constrain the structure of AGN jets; and (5) observe line and continuum emission from core-collapse supernovae in the Local Group, and from nearby Type Ia events, to constrain explosion models. During its baseline two-year mission, NuSTAR will also undertake a broad program of targeted observations. The observatory consists of two co-aligned grazing-incidence X-ray telescopes pointed at celestial targets by a three-axis stabilized spacecraft. Deployed into a 600 km, near-circular, 6 degrees inclination orbit, the observatory has now completed commissioning, and is performing consistent with pre-launch expectations. NuSTAR is now executing its primary science mission, and with an expected orbit lifetime of 10 yr, we anticipate proposing a guest investigator program, to begin in late 2014.
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    Space Telescope and Optical Reverberation Mapping Project. X. Understanding the Absorption-line Holiday in NGC 5548
    Dehghanian, M.; Ferland, G. J.; Kriss, G. A.; Peterson, B. M.; Mathur, S.; Mehdipour, M.; Guzman, F.; Chatzikos, M.; van Hoof, P. A. M.; Williams, R. J. R.; Arav, Nahum; Barth, A. J.; Bentz, M. C.; Bisogni, S.; Brandt, W. N.; Crenshaw, D. M.; Dalla Bonta, E.; De Rosa, G.; Fausnaugh, M. M.; Gelbord, J. M.; Goad, M. R.; Gupta, A.; Horne, Keith; Kaastra, J.; Knigge, C.; Korista, K. T.; McHardy, I. M.; Pogge, R. W.; Starkey, D. A.; Vestergaard, M. (2019-06-01)
    The Space Telescope and Optical Reverberation Mapping Project (AGN STORM) on NGC 5548 in 2014 is one of the most intensive multiwavelength AGN monitoring campaigns ever. For most of the campaign, the emission-line variations followed changes in the continuum with a time lag, as expected. However, the lines varied independently of the observed UV-optical continuum during a 60-70 day "holiday," suggesting that unobserved changes to the ionizing continuum were present. To understand this remarkable phenomenon and to obtain an independent assessment of the ionizing continuum variations, we study the intrinsic absorption lines present in NGC 5548. We identify a novel cycle that reproduces the absorption line variability and thus identify the physics that allows the holiday to occur. In this cycle, variations in this obscurer's line-of-sight covering factor modify the soft X-ray continuum, changing the ionization of helium Ionizing radiation produced by recombining helium then affects the level of ionization of some ions seen by the Hubble Space Telescope. In particular, high-ionization species are affected by changes in the obscurer covering factor, which does not affect the optical or UV continuum, and thus appear as uncorrelated changes, a "holiday." It is likely that any other model that selectively changes the soft X-ray part of the continuum during the holiday can also explain the anomalous emission-line behavior observed.
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    Ultraviolet and X-ray Variability of the Seyfert 1.5 Galaxy Markarian 817
    Winter, L. M.; Danforth, C.; Vasudevan, R.; Brandt, W. N.; Scott, J.; Froning, C.; Keeney, B.; Shull, J. M.; Penton, S.; Mushotzky, R. F.; Schneider, D. P.; Arav, Nahum (IOP PUBLISHING LTD, 2011-02)
    We present an investigation of the ultraviolet and X-ray spectra of the Seyfert 1.5 galaxy Markarian 817. The ultraviolet analysis includes two recent observations taken with the Cosmic Origins Spectrograph (COS) in 2009 August and December, as well as archival spectra from the International Ultraviolet Explorer and the Hubble Space Telescope. Twelve Ly alpha absorption features are detected in the 1997 Goddard High Resolution Spectrograph (GHRS) and 2009 COS spectra-of these, four are associated with high-velocity clouds in the interstellar medium, four are at low significance, and the remaining four are intrinsic features, which vary between the GHRS and COS observations. The strongest intrinsic absorber in the 1997 spectrum has a systemic velocity of similar to-4250 km s(-1). The corresponding feature in the COS data is five times weaker than the GHRS absorber. The three additional weak (equivalent width from 13 to 54 m angstrom) intrinsic Lya absorbers are at systemic velocities of -4100 km s(-1), -3550 km s(-1), and -2600 km s(-1). However, intrinsic absorption troughs from highly ionized Civ and N v are not detected in the COS observations. No ionized absorption signatures are detected in the similar to 14 ks XMM-Newton EPIC spectra. The factor of five change in the intrinsic Lya absorber is most likely due to bulk motions in the absorber, since there is no drastic change in the UV luminosity of the source from the GHRS to the COS observations. In a study of the variability of Mrk 817, we find that the X-ray luminosity varies by a factor of similar to 40 over 20 years, while the UV continuum/emission lines vary by at most a factor of similar to 2.3 over 30 years. The variability of the X-ray luminosity is strongly correlated with the X-ray power-law index, but no correlation is found with the simultaneous optical/UV photometry.
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    Weak hard X-ray emission from two broad absorption line quasars observed with NuSTAR: Compton-thick absorption or intrinsic X-ray weakness?
    Luo, B.; Brandt, W. N.; Alexander, D. M.; Harrison, F. A.; Stern, D.; Bauer, F. E.; Boggs, S. E.; Christensen, F. E.; Comastri, A.; Craig, W. W.; Fabian, A. C.; Farrah, D.; Fiore, F.; Fuerst, F.; Grefenstette, B. W.; Hailey, C. J.; Hickox, R.; Madsen, K. K.; Matt, G.; Ogle, P.; Risaliti, G.; Saez, C.; Teng, S. H.; Walton, D. J.; Zhang, W. W. (IOP Publishing Ltd., 2013-08)
    We present Nuclear Spectroscopic Telescope Array (NuSTAR) hard X-ray observations of two X-ray weak broad absorption line (BAL) quasars, PG 1004+130 (radio loud) and PG 1700+518 (radio quiet). Many BAL quasars appear X-ray weak, probably due to absorption by the shielding gas between the nucleus and the accretion-disk wind. The two targets are among the optically brightest BAL quasars, yet they are known to be significantly X-ray weak at rest-frame 2-10 keV (16-120 times fainter than typical quasars). We would expect to obtain approximate to 400-600 hard X-ray (greater than or similar to 10 keV) photons with NuSTAR, provided that these photons are not significantly absorbed (N-H less than or similar to 10(24) cm(-2)). However, both BAL quasars are only detected in the softer NuSTAR bands (e.g., 4-20 keV) but not in its harder bands (e.g., 20-30 keV), suggesting that either the shielding gas is highly Compton-thick or the two targets are intrinsically X-ray weak. We constrain the column densities for both to be N-H approximate to 7 x 10(24) cm(-2) if the weak hard X-ray emission is caused by obscuration from the shielding gas. We discuss a few possibilities for how PG 1004+130 could have Compton-thick shielding gas without strong Fe K alpha line emission; dilution from jet-linked X-ray emission is one likely explanation. We also discuss the intrinsic X-ray weakness scenario based on a coronal-quenching model relevant to the shielding gas and disk wind of BAL quasars. Motivated by our NuSTAR results, we perform a Chandra stacking analysis with the Large Bright Quasar Survey BAL quasar sample and place statistical constraints upon the fraction of intrinsically X-ray weak BAL quasars; this fraction is likely 17%-40%.