Browsing by Author "Gandhi, P."
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- ItemA GROWTH-RATE INDICATOR FOR COMPTON-THICK ACTIVE GALACTIC NUCLEI(2016) Brightman, M.; Masini, A.; Ballantyne, D. R.; Balokovic, M.; Brandt, W. N.; Chen, C. -T.; Comastri, A.; Farrah, D.; Gandhi, P.; Harrison, F. A.; Ricci, C.; Stern, D.; Walton, D. J.Due to their heavily obscured central engines, the growth rate of Compton-thick (CT) active galactic nuclei (AGNs) is difficult to measure. A statistically significant correlation between the Eddington ratio, lambda(Edd), and the X-ray power-law index, Gamma, observed in unobscured AGNs offers an estimate of their growth rate from X-ray spectroscopy (albeit with large scatter). However, since X-rays undergo reprocessing by Compton scattering and photoelectric absorption when the line of sight to the central engine is heavily obscured, the recovery of the intrinsic Gamma is challenging. Here we study a sample of local, predominantly CT megamaser AGNs, where the black hole mass, and thus Eddington luminosity, are well known. We compile results of the X-ray spectral fitting of these sources with sensitive high-energy (E > 10 keV) NuSTAR data, where X-ray torus models, which take into account the reprocessing effects have been used to recover the intrinsic Gamma values and X-ray luminosities, L-X. With a simple bolometric correction to L-X to calculate lambda(Edd), we find a statistically significant correlation between Gamma and lambda(Edd) (p = 0.007). A linear fit to the data yields Gamma = (0.41 +/- 0.18)log(10)lambda(Edd) + (2.38 +/- 0.20), which is statistically consistent with results for unobscured AGNs. This result implies that torus modeling successfully recovers the intrinsic AGN parameters. Since the megamasers have low-mass black holes (M-BH approximate to 10(6)-10(7) M-circle dot) and are highly inclined, our results extend the Gamma-lambda(Edd) relationship to lower masses and argue against strong orientation effects in the corona, in support of AGN unification. Finally this result supports the use of Gamma as a growth-rate indicator for accreting black holes, even for CT AGNs.
- ItemA New Compton-thick AGN in Our Cosmic Backyard: Unveiling the Buried Nucleus in NGC 1448 with NuSTAR(2017) Annuar, A.; Alexander, D.; Gandhi, P.; Lansbury, G.; Asmus, D.; Ballantyne, D.; Bauer, Franz Erik; Boggs, S.; Boorman, P.; Brandt W.; Brightman, M.|Christensen, F.; Craig, W.; Farrah, D.; Goulding, A.; Hailey, C.; Harrison, F.; Koss, M.; Lamassa, S.; Murray, S.; Ricci, Claudio; Rosario, D.; Stanley, F.; Stern, D.; Zhang, W.
- ItemA new population of compton-thick AGNs identified using the spectral curvature above 10 keV.(2016) Koss, M.; Bauer, Franz Erik; Ricci, Claudio; Treister, Ezequiel; Assef T., Roberto; Balokovic, M.; Stern, Daniel.; Gandhi, P.; Lamperti, I.; Alexander, D. M.
- ItemBroad-band X-ray spectral analysis of the Seyfert 1 galaxy GRS 1734-292(2017) Tortosa, A.; Marinucci, A.; Matt, G.; Bianchi, S.; La Franca, F.; Ballantyne, D. R.; Boorman, P. G.; Fabian, A. C.; Farrah, D.; Ricci, Claudio; Fuerst, F.; Gandhi, P.; Harrison, F. A.; Koss, M. J.; Stern, D.; Ursini, F.; Walton, D. J.
- ItemCompton-thick accretion in the local universe(2015) Ricci, Claudio; Ueda, Y.; Koss, M.; Trakhtenbrot, B.; Bauer, Franz Erik; Gandhi, P.
- ItemDetermining the covering factor of compton-thick active galactic nuclei with NuSTAR(2015) Brightman, M.; Balokovic, M.; Stern, D.; Arevalo, P.; Ballantyne, D. R.; Bauer, Franz Erik; Bogg, S. E.; Craig, W. W.; Christensen, F. E.; Comastri, A.; Gandhi, P.; Hailey, C. J.; Harrison, F. A.; Hickox, R. C.; Koss, M.; Lamassa, S.; Fuerst, F.; Puccetti, S.; Rivers, E.; Vasudevan, R.; Walton, D. J.; Zhang, W. W.
- ItemHard X-Ray-selected AGNs in Low-mass Galaxies from the NuSTAR Serendipitous Survey(2017) Chen, C. T. J.; Brandt, W. N.; Reines, A. E.; Lansbury, G.; Stern, D.; Alexander, D. M.; Bauer, Franz Erik; Ricci, Claudio; Del Moro, A.; Gandhi, P.; Harrison, F. A.; Hickox, R. C.; Koss, M. J.; Lanz, L.; Koss, M. J.; Lanz, L.; Luo, B.; Ricci, Claudio
- ItemIC 3639—A NEW BONA FIDE COMPTON-THICK AGN UNVEILED BY NuSTAR(2016) Boorman, Peter G.; Gandhi, P.; Alexander, D. M.; Annuar, A.; Ballantyne, D. R.; Bauer, Franz Erik; Boggs, S. E.; Brandt, W. N.; Brightman, M.; Christensen, F. E.; Craig, W. W.; Farrah, D.; Hailey, C. J.; Harrison, F. A.; Hönig, S. F.; Koss, M.; LaMassa, S. M.; Masini, A. C.; Ricci, G.; Risaliti, D.; Stern, W.; Zhang, W.
- ItemIC 751: A New Changing Look AGN Discovered by NuSTAR.(2016) Ricci, Claudio; Bauer, Franz Erik; Treister, Ezequiel; Arévalo, Patricia.; Boggs, Steven E.; Brandt, W. N.; Christensen, F. E.; Craig, W. W.; Gandhi, P.; Hailey, C. J.; Harrison, F. A.
- ItemInvestigating the Evolution of the Dual AGN System ESO 509-IG066.(2017) Kosec, P.; Ricci, Claudio; Treister, Ezequiel; Privon, G. C.; Brightman, M.; Stern, D.; Müller-Sánchez, Francisco; Koss, M.; Oh, K.; Assef T., Roberto; Gandhi, P.
- ItemNew spectral model for constraining torus covering factors from broadband X-ray spectra of active galactic nuclei(2018) Baloković, M.; Brightman, M.; Harrison, F.A.; Comastri, A.; Ricci, Claudio; Buchner, J.; Gandhi, P.; Farrah, D.; Stern, D.
- ItemNuSTAR catches the unveiling nucleus of NGC 1068(2016) Bauer, Franz Erik; Ricci, Claudio; Marinucci, A.; Bianchi, S.; Matt, G.; Alexander, D.; Balokovic, M.; Brandt, W.; Gandhi, P.; Guainazzi, M.; Harrison, F.; Iwasawa, K.; Koss, M.; Madsen, K.; Nicastro, F.; Puccetti, S.; Stern, D.; Walton, D.
- ItemNuSTAR observations of four nearby X-ray faint AGNs: low luminosity or heavy obscuration?(OUP, 2020) Annuar, A.; Alexander, D. M.; Gandhi, P.; Lansbury, G. B.; Asmus, D.; Balokovic, M.; Ballantyne, D. R.; Bauer, Franz Erik; Boorman, P. G.; Brandt, W. N.; Brightman, M.; Chen, C. T. J.; Del Moro, A.; Farrah, D.; Harrison, F. A.; Koss, M. J.; Lanz, L.; Marchesi, S.; Masini, A.; Nardini, E.; Ricci, Claudio; Stern, D.; Zappacosta, L.We present NuSTAR (Nuclear Spectroscopic Telescope Array) observations of four active galactic nuclei (AGNs) located within 15 Mpc. These AGNs, namely ESO 121-G6, NGC 660, NGC 3486, and NGC 5195, have observed X-ray luminosities of L 2–10 keV,obs ≲ 10 39 erg s −1 , classifying them as low-luminosity AGN (LLAGN). We perform broad-band X-ray spectral analysis for the AGN by combining our NuSTAR data with Chandra or XMM–Newton observations to directly measure their column densities (N H ) and infer their intrinsic power. We complement our X-ray data with archival and new high-angular resolution mid-infrared (mid-IR) data for all objects, except NGC 5195. Based on our X-ray spectral analysis, we found that both ESO 121-G6 and NGC 660 are heavily obscured (N H > 10 23 cm −2 ; L 2–10 keV,int ∼ 10 41 erg s −1 ), and NGC 660 may be Compton thick. We also note that the X-ray flux and spectral slope for ESO 121-G6 have significantly changed over the last decade, indicating significant changes in the obscuration and potentially accretion rate. On the other hand, NGC 3486 and NGC 5195 appear to be unobscured and just mildly obscured, respectively, with L 2–10 keV,int < 10 39 erg s −1 , i.e. genuine LLAGN. Both of the heavily obscured AGNs have L bol > 10 41 erg s −1 and λ Edd ≳ 10 −3 , and are detected in high-angular resolution mid-IR imaging, indicating the presence of obscuring dust on nuclear scale. NGC 3486, however, is undetected in high-resolution mid-IR imaging, and the current data do not provide stringent constraints on the presence or absence of obscuring nuclear dust in the AGN.
- ItemNuSTAR observations of heavily obscured quasars at z 0.5(2014) Lansbury, G.B.; Alexander, D.M.; Del Moro, A.; Gandhi, P.; Assef, R.J.; Stern, D.; Aird, J.; Ballantyne, D.R.; Balokovic, M.; Bauer, Franz Erik
- ItemNuStar observations of the compton-thick active galactic nucleus and ultraluminous X-Ray source candidate in NGC 5643(2015) Annuar, A.; Gandhi, P.; Alexander, D.; Lansbury, G.; Arévalo, P.; Ballantyne, D.; Balokovic, M.; Boggs, S.; Brandt, W.; Brightman, M.; Christensen, F.; Craig, W.; Del Moro, A.; Hailey, C.; Harrison, F.; Bauer, Franz Erik
- ItemNuSTAR observations of water megamaser AGN(2016) Masini, A.; Comastri, A.; Baloković, M.; Zaw, I.; Puccetti, S.; Ballantyne, D. R.; Bauer, Franz Erik; Boggs, S. E.; Brandt, W. N.; Brightman, M.; Christensen, F. E.; Craig, W. W.; Gandhi, P.; Hailey, C. J.; Harrison, F. A.; Koss, M. J.; Madejski, G.; Ricci, Claudio; Rivers, E.; Stern, D.
- ItemNuStar reveals extreme absorption in z < 0.5 type 2 quasars(2015) Lansbury, G.; Gandhi, P.; Alexander, D.; Assef, R.; Aird, J.; Annuar, A.; Ballantyne, D.; Balokovic, M.; Bauer, Franz Erik; Boggs, S.; Brandt, W.; Brightman, M.; Christensen, F.; Civano, F.; Comastri, A.; Craig, W.
- ItemNuStar spectroscopy of multiI-component X-Ray reflection from NGC 1068(2015) Bauer, Franz Erik; Arévalo, P.; Walton, D.; Koss, M.; Puccetti, S.; Gandhi, P.; Stern, D.; Alexander, D.; Balokovic, M.; Boggs, S.; Brandt, W.; Brightman, M.; Christensen, F.; Comastri, A.; Craig, W.; Del Moro, A.
- ItemNuSTAR unveils a Compton-thick type 2 quasar in Mrk 34(2014) Gandhi, P.; Lansbury, G.; Alexander, D.; Stern, D.; Arevalo, P.; Ballantyne, D.; Balokovic, M.; Bauer, Franz Erik; Boggs, S.; Brandt, W.
- Item[O iii] lambda5007 and X-ray properties of a complete sample of hard X-ray selected AGNs in the local Universe(2015) Ueda, Y.; Hashimoto, Y.; Ichikawa, K.; Ishino, Y.; Kniazev, A.; Vaeisaenen, P.; Ricci, Claudio; Berney, S.; Gandhi, P.; Koss, M.