Browsing by Author "Gallagher, S. C."

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    NuSTAR Observations of Intrinsically X-Ray Weak Quasar Candidates: An Obscuration-only Scenario
    (2022) Wang, Chaojun; Luo, B.; Brandt, W. N.; Alexander, D. M.; Bauer, F. E.; Gallagher, S. C.; Huang, Jian; Liu, Hezhen; Stern, D.
    We utilize recent NuSTAR observations (co-added depth approximate to 55-120 ks) of PG 1001+054, PG 1254+047, and PHL 1811 to constrain their hard X-ray (greater than or similar to 5 keV) weakness and spectral shapes and thus to investigate the nature of their extreme X-ray weakness. These quasars showed very weak soft X-ray emission, and they were proposed to be intrinsically X-ray weak, with the X-ray coronae producing weak continuum emission relative to their optical/UV emission. However, the new observations suggest an alternative explanation. The NuSTAR 3-24 keV spectral shapes for PG 1001+054 and PHL 1811 are likely flat (effective power-law photon indices Gamma(eff )= 1.0(-0.6)(+0.5) and Gamma(eff )= 1.4(-0.7)(+0.8) respectively), while the shape is nominal for PG 1254+047 ( Gamma(eff) = 1.8 +/- 0.3). PG 1001+054 and PHL 1811 are significantly weak at hard X-ray energies (by factors of approximate to 26-74 at rest-frame 8 keV) compared to the expectations from their optical/UV emission, while PG 1254+047 is only hard X-ray weak by a factor of approximate to 3. We suggest that X-ray obscuration is present in all three quasars. We propose that, as an alternative to the intrinsic X-ray weakness + X-ray obscuration scenario, the soft and hard X-ray weakness of these quasars can be uniformly explained under an obscuration-only scenario. This model provides adequate descriptions of the multiepoch soft and hard X-ray data of these quasars, with variable column density and leaked fraction of the partial covering absorber. We suggest that the absorber is the clumpy dust-free wind launched from the accretion disk. These quasars probably have super-Eddington accretion rates that drive powerful and high-density winds.
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    The X-rays wind connection in PG 2112+059
    (2021) Saez, C.; Brandt, W. N.; Bauer, F. E.; Chartas, G.; Misawa, T.; Hamann, F.; Gallagher, S. C.
    We study the connection between the X-ray and ultraviolet (UV) properties of the broad absorption line (BAL) wind in the highly X-ray variable quasar PG 2112+059 by comparing Chandra-ACIS data with contemporaneous UV HST/STIS spectra in three different epochs. We observe a correlation whereby an increase in the equivalent widths (EWs) of the BALs is accompanied by a redder UV spectrum. The growth in the BAL EWs is also accompanied by a significant dimming in soft X-ray emission (less than or similar to 2keV), consistent with increased absorption. Variations in the hard X-ray emission (less than or similar to 2 keV) are only accompanied by minor spectral variations of the UV-BALs and do not show significant changes in the EWof BALs. These trends suggest a wind-shield scenario where the outflow inclination with respect to the line of sight is decreasing and/or the wind mass is increasing. These changes elevate the covering fraction and/or column densities of the BALs and are likely accompanied by a nearly contemporaneous increase in the column density of the shield.