Browsing by Author "Stern, Daniel "

Now showing 1 - 6 of 6
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    A NuStar survey of nearby ultraluminous infrared galaxies
    (2015) Teng, Stacy H.; Rigby, Jane R.; Stern, Daniel; Ptak, Andrew; Alexander, D. M.; Bauer, Franz Erik; Boggs, Stephen E.; Brandt, W. Niel; Christensen, Finn E.; Comastri, Andrea
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    BASS-XL: X-ray variability properties of unobscured active galactic nuclei
    (2023) Tortosa, Alessia; Ricci, Claudio; Arevalo, Patricia; Koss, Michael J.; Bauer, Franz E.; Trakhtenbrot, Benny; Mushotzky, Richard; Temple, Matthew J.; Ricci, Federica; Lilayu, Alejandra Rojas; Kawamuro, Taiki; Caglar, Turgay; Liu, Tingting; Harrison, Fiona; Oh, Kyuseok; Powell, Meredith Clark; Stern, Daniel; Urry, Claudia Megan
    We investigate the X-ray variability properties of Seyfert 1 Galaxies belonging to the BAT AGN Spectroscopic Survey (BASS). The sample includes 151 unobscured (N-H < 10(22) cm(-2)) AGNs observed with XMM-Newton for a total exposure time of similar to 27 ms, representing the deepest variability study done so far with high signal-to-noise XMM-Newton observations, almost doubling the number of observations analysed in previous works. We constrain the relation between the normalized excess variance and the 2-10 keV AGN luminosities, black hole masses, and Eddington ratios. We find a highly significant correlation between sigma(2)(NXS) and M-BH, with a scatter of similar to 0.85 dex. For sources with high L2-10 this correlation has a lower normalization, confirming that more luminous (higher mass) AGNs show less variability. We explored the sigma(2)(NXS) versus M-BH relation for the sub-sample of sources with M-BH estimated via the 'reverberation mapping' technique, finding a tighter anticorrelation, with a scatter of similar to 0.65 dex. We examine how the sigma(2)(NXS) changes with energy by studying the relation between the variability in the hard (3-10 keV) and the soft (0.2-1 keV)/medium (1-3 keV) energy bands, finding that the spectral components dominating the hard energy band are more variable than the spectral components dominating in softer energy bands, on time-scales shorter than 10 ks.
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    BASS. XXIX. The Near-infrared View of the Broad-line Region (BLR): The Effects of Obscuration in BLR Characterization
    (2022) Ricci, Federica ; Treister, Ezequiel ; Bauer, Franz E.; Mejía-Restrepo, Julian E. ; Koss, Michael J. ; den Brok, Jakob S. ; Baloković, Mislav ; Bär, Rudolf ; Bessiere, Patricia ; Caglar, Turgay ; Harrison, Fiona ; Ichikawa, Kohei ; Kakkad, Darshan; Lamperti, Isabella ; Mushotzky, Richard ; Oh, Kyuseok ; Powell, Meredith C. ; Privon, George C. ; Ricci, Claudio ; Riffel, Rogerio ; Rojas, Alejandra F. ; Sani, Eleonora ; Smith, Krista L. ; Stern, Daniel ; Trakhtenbrot, Benny ; Urry, C. Megan ; Veilleux, Sylvain
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    BASS. XXVIII. Near-infrared Data Release 2: High-ionization and Broad Lines in Active Galactic Nuclei
    (2022) den Brok, Jakob S.; Koss, Michael J.; Trakhtenbrot, Benny; Stern, Daniel; Cantalupo, Sebastiano; Lamperti, Isabella; Ricci, Federica; Ricci, Claudio; Oh, Kyuseok; Bauer, Franz E.; Riffel, Rogerio; Rodriguez-Ardila, Alberto; Baer, Rudolf; Harrison, Fiona; Ichikawa, Kohei; Mejia-Restrepo, Julian E.; Mushotzky, Richard; Powell, Meredith C.; Boissay-Malaquin, Rozenn; Stalevski, Marko; Treister, Ezequiel; Urry, C. Megan; Veilleux, Sylvain
    We present the BAT AGN Spectroscopic Survey (BASS) Near-infrared Data Release 2 (DR2), a study of 168 nearby ((z) over bar = 0.04, z < 0.6) active galactic nuclei (AGN) from the all-sky Swift Burst Array Telescope X-ray survey observed with the Very Large Telescope (VLT)/X-shooter in the near-infrared (NIR; 0.8-2.4 mu m). We find that 49/109 (45%) Seyfert 2 and 35/58 (60%) Seyfert 1 galaxies observed with VLT/X-shooter show at least one NIR high-ionization coronal line (CL; ionization potential chi > 100 eV). Comparing the emission of the [Si VI] lambda 1.9640 CL with the X-ray emission for the DR2 AGN, we find a significantly tighter correlation, with a lower scatter (0.37 dex) than that for the optical [O III] lambda 5007 line (0.71 dex). We do not find any correlation between CL emission and the X-ray photon index Gamma. We find a clear trend of line blueshifts with increasing ionization potential in several CLs, such as [Si VI] lambda 1.9640, [Si X] lambda 1.4300, [S VIII] lambda 0.9915, and [S IX] lambda 1.2520, indicating the radial structure of the CL region. Finally, we find a strong underestimation bias in black hole mass measurements of Sy 1.9 using broad H alpha due to the presence of significant dust obscuration. In contrast, the broad Pa alpha and Pa beta emission lines are in agreement with the M-sigma relation. Based on the combined DR1 and DR2 X-shooter sample, the NIR BASS sample now comprises 266 AGN with rest-frame NIR spectroscopic observations, the largest set assembled to date.
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    Growing supermassive black holes in the late stages of galaxy mergers are heavily obscured.
    (2017) Ricci, Claudio; Bauer, Franz Erik; Treister, Ezequiel; Privon, G. C.; Schawinski, K.; Blecha, L.; Arevalo, P.; Armus, Lee; Harrison, F.; Ho, L. C.; Iwasawa, K.; Sanders, David B.; Stern, Daniel
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    HARD X-RAY MORPHOLOGICAL AND SPECTRAL STUDIES OF THE GALACTIC CENTER MOLECULAR CLOUD SGR B2: CONSTRAINING PAST SGR A☆ FLARING ACTIVITY
    (2015) Zhang, Shuo; Hailey, Charles J.; Mori, Kaya; Clavel, Maica; Terrier, Regis; Ponti, Gabriele; Goldwurm, Andrea; Bauer, Franz E.; Boggs, Steven E.; Christensen, Finn E.; Craig, William W.; Harrison, Fiona A.; Hong, Jaesub; Nynka, Melania; Soldi, Simona; Stern, Daniel; Tomsick, John A.; Zhang, William W.
    In 2013, NuSTAR observed the Sgr B2 region and for the first time resolved its hard X-ray emission on subarcminute scales. Two prominent features are detected above 10 keV:. a newly emerging cloud, G0.66-0.13, and the central 90 '' radius region containing two compact cores, Sgr B2(M) and Sgr B2(N), surrounded by diffuse emission. It is inconclusive whether the remaining level of Sgr. B2 emission is still decreasing or has reached a constant background level. A decreasing X-ray emission can be best explained by the X-ray reflection nebula scenario, where the cloud reprocesses a past giant outburst from Sgr A(star). In the X-ray reflection nebula (XRN) scenario, the 3-79 keV Sgr. B2 spectrum allows us to self-consistently test the XRN model using both the Fe K alpha line and the continuum emission. The peak luminosity of the past Sgr A(star) outburst is constrained to L3-79keV similar to 5 x 10(38) ergs s(-1). A newly discovered cloud feature, G0.66-0.13, shows different timing variability. We suggest that it could be a molecular clump located in the Sgr B2 envelope reflecting the same Sgr A(star) outburst. In contrast, if the Sgr. B2 X-ray emission has reached a constant background level, it would imply an origin of low-energy cosmic-ray (CR) proton bombardment. In this scenario, from the NuSTAR measurements we infer a CR ion power of dW/dt = (1 - 4) x 10(39) erg s(-1) and a CR ionization rate of zeta(H) = (6 - 10) x 10(-15) H-1 s(-1). measurements can become powerful tools to constrain the GC CR population.