WEAK HARD X-RAY EMISSION FROM TWO BROAD ABSORPTION LINE QUASARS OBSERVED WITH NuSTAR: COMPTON-THICK ABSORPTION OR INTRINSIC X-RAY WEAKNESS?

被引：56

作者：

Luo, B. ^{[1
,2
]}

Brandt, W. N. ^{[1
,2
]}

Alexander, D. M. ^{[3
]}

Harrison, F. A. ^{[4
]}

Stern, D. ^{[5
]}

Bauer, F. E. ^{[6
,7
]}

Boggs, S. E. ^{[8
]}

Christensen, F. E. ^{[9
]}

Comastri, A. ^{[10
]}

Craig, W. W. ^{[8
,11
]}

Fabian, A. C. ^{[12
]}

Farrah, D. ^{[13
]}

Fiore, F. ^{[14
]}

Fuerst, F. ^{[4
]}

Grefenstette, B. W. ^{[4
]}

Hailey, C. J. ^{[15
]}

Hickox, R. ^{[3
,16
]}

Madsen, K. K. ^{[4
]}

Matt, G. ^{[17
]}

Ogle, P. ^{[18
]}

Risaliti, G. ^{[19
,20
]}

Saez, C. ^{[6
]}

Teng, S. H. ^{[21
]}

Walton, D. J. ^{[4
]}

Zhang, W. W. ^{[22
]}

机构：

[1] Penn State Univ, Dept Astron & Astrophys, University Pk, PA 16802 USA

[2] Penn State Univ, Inst Gravitat & Cosmos, University Pk, PA 16802 USA

[3] Univ Durham, Dept Phys, Durham DH1 3LE, England

[4] CALTECH, Cahill Ctr Astron & Astrophys, Pasadena, CA 91125 USA

[5] CALTECH, Jet Prop Lab, Pasadena, CA 91109 USA

[6] Pontificia Univ Catolica Chile, Dept Astron & Astrofis, Santiago 22, Chile

[7] Space Sci Inst, Boulder, CO 80301 USA

[8] Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA

[9] Tech Univ Denmark, DTU Space Natl Space Inst, DK-2800 Lyngby, Denmark

[10] INAF, Osservatorio Astron Bologna, I-40127 Bologna, Italy

[11] Lawrence Livermore Natl Lab, Livermore, CA 94550 USA

[12] Univ Cambridge, Inst Astron, Cambridge CB3 0HA, England

[13] Virginia Tech, Dept Phys, Blacksburg, VA 24061 USA

[14] Osserv Astron Roma, I-00040 Monte Porzio Catone, Italy

[15] Columbia Univ, Columbia Astrophys Lab, New York, NY 10027 USA

[16] Dartmouth Coll, Dept Phys & Astron, Hanover, NH 03755 USA

[17] Univ Roma Tre, Dipartimento Matemat & Fis, I-00146 Rome, Italy

[18] CALTECH, IPAC, Pasadena, CA 91125 USA

[19] INAF, Osservatorio Astrofis Arcetri, I-50125 Florence, Italy

[20] Harvard Smithsonian Ctr Astrophys, Cambridge, MA 02138 USA

[21] NASA, Goddard Space Flight Ctr, Observat Cosmol Lab, Greenbelt, MD 20771 USA

[22] NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA

来源：

ASTROPHYSICAL JOURNAL | 2013年 / 772卷 / 02期

基金：

美国国家航空航天局;

关键词：

accretion; accretion disks; galaxies: active; galaxies: nuclei; quasars: absorption lines; quasars: emission lines; X-rays: general; ACTIVE GALACTIC NUCLEI; DIGITAL SKY SURVEY; SPECTRAL ENERGY-DISTRIBUTIONS; OPTICALLY SELECTED QUASARS; XMM-NEWTON SPECTROSCOPY; ACCRETION DISK WINDS; SEYFERT; GALAXIES; CHANDRA SURVEY; ULTRAVIOLET-ABSORPTION; CONFIDENCE-LIMITS;

D O I：

10.1088/0004-637X/772/2/153

中图分类号：

P1 [天文学];

学科分类号：

0704 ;

摘要：

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%.

引用

页数：17

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