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Browsing by Author "Christensen, F. E."

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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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    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%.