Browsing by Author "Chen, C. -T."

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    A 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.
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    REVERBERATION MAPPING OF THE SEYFERT 1 GALAXY NGC7469
    (2014) Peterson, B. M.; Grier, C. J.; Horne, Keith; Pogge, R. W.; Bentz, M. C.; De Rosa, G.; Denney, K. D.; Martini, Paul; Sergeev, S. G.; Kaspi, S.; Minezaki, T.; Zu, Y.; Kochanek, C. S.; Siverd, R. J.; Shappee, B.; Salvo, C. Araya; Beatty, T. G.; Bird, J. C.; Bord, D. J.; Borman, G. A.; Che, X.; Chen, C. -T.; Cohen, S. A.; Dietrich, M.; Doroshenko, V. T.; Drake, T.; Efimov, Yu. S.; Free, N.; Ginsburg, I.; Henderson, C. B.; King, A. L.; Koshida, S.; Mogren, K.; Molina, M.; Mosquera, A. M.; Motohara, K.; Nazarov, S. V.; Okhmat, D. N.; Pejcha, O.; Rafter, S.; Shields, J. C.; Skowron, D. M.; Skowron, J.; Valluri, M.; van Saders, J. L.; Yoshii, Y.
    A large reverberation-mapping study of the Seyfert 1 galaxy NGC7469 has yielded emission-line lags for H beta lambda 4861 and He He II lambda 4686 and a central black hole mass measurement M-BH approximate to 1 x 10(7)M(circle dot) , consistent with previous measurements. A very low level of variability during the monitoring campaign precluded meeting our original goal of recovering velocity-delay maps from the data, but with the new H beta measurement, NGC7469 is no longer an outlier in the relationship between the size of the H beta-emitting broad-line region and the luminosity of the active galactic nucleus. It was necessary to detrend the continuum and H beta and He He II lambda 4686 line light curves and those from archival UV data for different time-series analysis methods to yield consistent results.