view Abstract Citations (108) References (55) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Multiwavelength Monitoring of the BL Lacertae Object PKS 2155-304. I. The IUE Campaign Urry, C. M. ; Maraschi, L. ; Edelson, R. ; Koratkar, A. ; Krolik, J. ; Madejski, G. ; Pian, E. ; Pike, G. ; Reichert, G. ; Treves, A. ; Wamsteker, W. ; Bohlin, R. ; Bregman, J. ; Brinkmann, W. ; Chiappetti, L. ; Courvoisier, T. ; Filippenko, A. V. ; Fink, H. ; George, I. M. ; Kondo, Y. ; Martin, P. G. ; Miller, H. R. ; O'Brien, P. ; Shull, J. M. ; Sitko, M. ; Szymkowiak, A. E. ; Tagliaferri, G. ; Wagner, S. ; Warwick, R. Abstract Daily monitoring of PKS 2155 - 304 with the IUE satellite throughout 1991 November has revealed dramatic, large-amplitude, rapid variations in the ultraviolet flux of this BL Lac object. Many smaller, rapid flares are superposed on a general doubling of the intensity. During the 5^d^ period when sampling was roughly continuous, the rapid flaring had an apparent quasi-periodic nature, with peaks repeating every ~0.7^d^. The short- and long-wavelength ultraviolet light curves are well correlated with each other, and with the optical light curve deduced from the Fine Error Sensor (FES) on IUE. The formal lag is zero, but the cross- correlation is asymmetric in the sense that the shorter wavelength emission leads the longer. The ultraviolet spectral shape varies a small but significant amount. The correlation between spectral shape and intensity is complicated; an increase in intensity is associated with spectral hardening, but lags behind the spectral change by ~1 day. The sign of the correlation is consistent with the nonthermal acceleration processes expected in relativistic plasmas, so that the present results are consistent with relativistic jet models, which can also account for quasi-periodic flaring. In contrast, currently proposed accretion disk models are strongly ruled out by the simultaneous optical and ultraviolet variability. Publication: The Astrophysical Journal Pub Date: July 1993 DOI: 10.1086/172864 arXiv: arXiv:astro-ph/9304003 Bibcode: 1993ApJ...411..614U Keywords: Accretion Disks; Active Galactic Nuclei; Active Galaxies; Bl Lacertae Objects; Iue; Light Curve; Ultraviolet Spectra; Astronomical Models; Blazars; Brightness Temperature; Relativistic Plasmas; Astrophysics; Astrophysics E-Print: 27 pages, plain TeX, STScI Preprint 714 full text sources arXiv | ADS | data products SIMBAD (3) NED (1) MAST (1) INES (1) Related Materials (3) Part 2: 1994A&A...288..433B Part 3: 1995ApJ...438..108C Part 4: 1995ApJ...438..120E
view Abstract Citations (23) References (28) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Ultraviolet and X-ray observations of the BL Lac PKS 0548-322. Urry, C. M. ; Mushotzky, R. F. ; Kondo, Y. ; Hackney, K. R. H. ; Hackney, R. L. Abstract Spectrophotometric observations of the BL Lac object PKS 0548-322 were made with ultraviolet and X-ray instruments on the IUE and HEAO-2 satellites. Two observations in each spectral region, one set of which was obtained simultaneously are presented. A power law of energy index approximately 1.0 gives a good description of the data from ultraviolet through X-ray frequencies. This source is reported to be variable on short timescales (Gilmore 1980); the implications of the spectral properties and apparent variability are discussed in light of a relativistic jet model. Findings support the jet picture of BL Lac objects. Publication: The Astrophysical Journal Pub Date: October 1982 DOI: 10.1086/160311 Bibcode: 1982ApJ...261...12U Keywords: Astronomical Spectroscopy; Bl Lacertae Objects; Ultraviolet Spectra; X Ray Spectra; Heao 2; Infrared Spectra; Iue; Quasars; Relativistic Theory; Spectrum Analysis; Astrophysics full text sources ADS | data products SIMBAD (4) NED (4) MAST (1) INES (1)
view Abstract Citations (159) References (48) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Correlated Hard X-Ray and Ultraviolet Variability in NGC 5548 Clavel, J. ; Nandra, K. ; Makino, F. ; Pounds, K. A. ; Reichert, G. A. ; Urry, C. M. ; Wamsteker, W. ; Peracaula-Bosch, M. ; Stewart, G. C. ; Otani, C. Abstract We present the result of a series of contemporaneous (within one day) hard X-ray (Ginga) and ultraviolet (IUE) observations of the Seyfert 1 galaxy NGC 5548. Nine of these observations were carried out over a period of 51 days in 1990 May-July, and two in 1989. An additional simultaneous IUE-EXOSAT observation obtained on 1984 May 21 is also analyzed. In 1989-1990, the 1350 A continuum and 2-10 keV flux both varied by a factor 2.6 in a highly correlated (at better than the 99% confidence level) fashion. Adding the single 1984 data point significantly weakens the correlation, since the UV flux was 3.5 times larger then than its average 1990 value, while the X-ray flux was only 70% higher. In 1990 the UV and X-ray flux variations appear to be simultaneous to within a few (<= 6) days. These results, together with the simultaneity of the variations at 5000 and 1350 A, are incompatible with the standard geometrically thin accretion disk model. To salvage the disk model, one must postulate the existence of at least two continuum emission components in the UV-optical regime. The first one arises from thermal reprocessing of the X-ray impinging on and absorbed by the disk, while the other represents the thermal emission generated by viscous processes inside the disk itself. In this scheme, the reprocessed component varies in phase with the hard X-rays and accounts for the bulk of the UV emission when NGC 5548 is in a low to intermediate state of brightness, while larger amplitude variations are driven by a change in the amount of gravitational energy released locally inside the disk. The thermal reprocessing region extends to at least 200 Schwarzschild radii, much further out than the UV-emitting region in a standard disk without reprocessing. Since the relationship between the UV and the X-ray source in NGC 5548 is phenomenologically identical to that in NGC 4151, this scheme may be applicable to Seyfert galaxies as a class. Publication: The Astrophysical Journal Pub Date: July 1992 DOI: 10.1086/171490 Bibcode: 1992ApJ...393..113C Keywords: Galactic Clusters; Ginga Satellite; Iue; Seyfert Galaxies; X Ray Sources; Accretion Disks; Astronomical Models; Potassium; Thermal Emission; Ultraviolet Radiation; Astrophysics; GALAXIES: INDIVIDUAL NGC NUMBER: NGC 5548; GALAXIES: SEYFERT; ULTRAVIOLET: GALAXIES; X-RAYS: GALAXIES full text sources ADS | data products SIMBAD (5) NED (1) MAST (1) INES (1)
Hubble Space Telescope (HST) observations have led to the discovery of the optical counterpart of the radio jet of PKS 2201+044 and to a detailed analysis of the optical jets of PKS 0521-365 and 3C 371. At HST spatial resolution these jets are well resolved, displaying knotty morphologies. When compared with radio maps of appropriate resolution, a clear one-to-one correspondence between optical and radio structures is found, showing that all detected optical structures are indeed related to the radio synchrotron emission. Photometry of the brightest knots shows that the radio-to-optical spectral index and the derived intensity of the equipartition magnetic field are approximately constant along the jet. Thus, present observations suggest that the electron energy distribution does not change significantly all along the jet.
Supermassive black holes weighing up to ~109 M ⊙ are in place by z ~ 7, when the age of the universe is 1 Gyr. This implies a time crunch for their growth, since such high masses cannot be easily reached in standard accretion scenarios. Here, we explore the physical conditions that would lead to optimal growth wherein stable super-Eddington accretion would be permitted. Our analysis suggests that the preponderance of optimal conditions depends on two key parameters: the black hole mass and the host galaxy central gas density. In the high-efficiency region of this parameter space, a continuous stream of gas can accrete onto the black hole from large to small spatial scales, assuming a global isothermal profile for the host galaxy. Using analytical initial mass functions for black hole seeds, we find an enhanced probability of high-efficiency growth for seeds with initial masses 104 M ⊙. Our picture suggests that a large population of high-z lower-mass black holes that formed in the low-efficiency region, with low duty cycles and accretion rates, might remain undetectable as quasars, since we predict their bolometric luminosities to be 1041 erg s−1. The presence of these sources might be revealed only via gravitational wave detections of their mergers.
We report CGRO, RXTE, ASCA, ROSAT, IUE, HST and ground-based observations of a large flare in 3C 279 in February 1996. X-rays and γ-rays peaked simultaneously (within one day). We show simultaneous spectral energy distributions prior to and near the flare peak. The γ-ray flare was the brightest ever observed in this source.
We present UBVRIz' optical images taken with MOSAIC on the CTIO 4 m telescope of the 0.32 deg2 Extended Hubble Deep Field-South. This is one of four fields comprising the MUSYC survey, which is optimized for the study of galaxies at z = 3, active galactic nucleus (AGN) demographics, and Galactic structure. Our methods used for astrometric calibration, weighted image combination, and photometric calibration in AB magnitudes are described. We calculate corrected aperture photometry and its uncertainties and find through tests that these provide a significant improvement upon standard techniques. Our photometric catalog of 62,968 objects is complete to a total magnitude of RAB = 25, with R-band counts consistent with results from the literature. We select z ≃ 3 Lyman break galaxy (LBG) candidates from their UVR colors and find a sky surface density of 1.4 arcmin-2 and an angular correlation function w(θ) = (2.3 ± 1.0)θ-0.8, consistent with previous findings that high-redshift Lyman break galaxies reside in massive dark matter halos. Our images and catalogs are available online.
view Abstract Citations (519) References (77) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Complete Sample of 1 Jansky BL Lacertae Objects. I. Summary Properties Stickel, M. ; Padovani, P. ; Urry, C. M. ; Fried, J. W. ; Kuehr, H. Abstract This paper describes the first homogeneous, flux-limited sample of radio-selected BL Lac objects, taken from the 1 Jy survey of Kuhr et al. These 34 BL Lac objects comprise the only well-defined sample of BL Lac objects outside the X-ray band. The selection criteria include flat radio spectra, optical counterparts visible on Sky Survey Plates, and optical emission lines weaker than 5 A equivalent width in the rest frame. With two exceptions, all of the BL Lac objects also have high optical polarization, P_opt_ > 3%. Redshifts from weak emission lines, usually narrow [O II] λ3727, [O III] λ5007, or broad Mg II λ2798, are available for ~ 3/4 of the sample. The nearby (z < 0.2) BL Lac objects, at least, sit in elliptical galaxies and may occur in groups or small clusters of galaxies. Gravitational lensing appears to affect one of the high-redshift (z >~ 0.5) BL Lac objects and could be important in others as well. The radio number counts derived from the 1 Jy BL Lac sample are roughly Euclidean over the range between 1 and ~ 5 Jy, and there is evidence for evolution at the 2 σ level. The local radio luminosity function of BL Lac objects is derived and the total number density for P_5 GHz_ >~ 6 x 10^31^ ergs s^-1^ Hz^-1^ is ~ 40 Gpc^-3^. Publication: The Astrophysical Journal Pub Date: June 1991 DOI: 10.1086/170133 Bibcode: 1991ApJ...374..431S Keywords: Bl Lacertae Objects; Emission Spectra; Gravitational Lenses; Radio Sources (Astronomy); Sky Surveys (Astronomy); Brightness Distribution; Galactic Radiation; Red Shift; Astrophysics; BL LACERTAE OBJECTS; GRAVITATIONAL LENSES; LUMINOSITY FUNCTION; RADIO SOURCES: GALAXIES full text sources ADS | data products SIMBAD (34) NED (34) Related Materials (1) Part 2: 1993A&AS...98..393S
Abstract We present the third catalog release of the wide-area (31.3 deg 2 ) Stripe 82 X-ray survey. This catalog combines previously published X-ray source properties with multiwavelength counterparts and photometric redshifts, presents 343 new spectroscopic redshifts, and provides black hole masses for 1297 Type 1 active galactic nuclei (AGN). With spectroscopic redshifts for 3457 out of 6181 Stripe 82X sources, the survey has a spectroscopic completeness of 56%. This completeness rises to 90% when considering the contiguous portions of the Stripe 82X survey with homogeneous X-ray coverage at an optical magnitude limit of r < 22. Within that portion of the survey, 23% of AGN can be considered obscured by being either a Type 2 AGN, reddened ( R − K > 4, Vega), or X-ray obscured with a column density of N H > 10 22 cm −2 . Unlike other surveys, there is only an 18% overlap between Type 2 and X-ray obscured AGN. We calculated black hole masses for Type 1 AGN that have Sloan Digital Sky Survey spectra using virial mass estimators calibrated on the H β , Mg ii , H α , and C iv emission lines. We find wide scatter in these black hole mass estimates, indicating that statistical analyses should use black hole masses calculated from the same formula to minimize bias. We find that the AGN with the highest X-ray luminosities are accreting at the highest Eddington ratios, consistent with the picture that most black hole mass accretion happens in the phase when the AGN is luminous ( L 2−10keV > 10 45 erg s −1 ).
