G. A. Kriss
A5090292864- Astrophysical Phenomena and Observations
- Galaxies: Formation, Evolution, Phenomena
- Astronomy and Astrophysical Research
- Gamma-ray bursts and supernovae
- Stellar, planetary, and galactic studies
- Astrophysics and Cosmic Phenomena
- Astrophysics and Star Formation Studies
- Astronomical Observations and Instrumentation
- Adaptive optics and wavefront sensing
- Photocathodes and Microchannel Plates
- Solar and Space Plasma Dynamics
- Calibration and Measurement Techniques
- Atmospheric Ozone and Climate
- Pulsars and Gravitational Waves Research
- Particle Accelerators and Free-Electron Lasers
- Astro and Planetary Science
- Geophysics and Gravity Measurements
- Magnetic confinement fusion research
- X-ray Spectroscopy and Fluorescence Analysis
- Radio Astronomy Observations and Technology
- Particle Detector Development and Performance
- Ionosphere and magnetosphere dynamics
- Spectroscopy and Laser Applications
- Nuclear Physics and Applications
- Spacecraft and Cryogenic Technologies
Space Telescope Science Institute
2015-2024
Johns Hopkins University
2007-2017
Michigan Science Center
2004-2016
University of Baltimore
2011-2015
Max Planck Society
2015
Max Planck Institute for Radio Astronomy
2015
Bloomberg (United States)
1998-2013
Mount Stromlo Observatory
2009
Observatoire astronomique de Strasbourg
2009
IBM (United States)
2006
The Far Ultraviolet Spectroscopic Explorer satellite observes light in the far-ultraviolet spectral region, 905-1187 Å, with a high resolution. instrument consists of four co-aligned prime-focus telescopes and Rowland spectrographs microchannel plate detectors. Two telescope channels use Al : LiF coatings for optimum reflectivity between approximately 1000 1187 other two SiC optimized throughput 905 1105 Å. gratings are holographically ruled to correct largely astigmatism minimize scattered...
We use a sample of 332 Hubble Space Telescope spectra 184 quasi-stellar objects (QSOs) with z > 0.33 to study the typical ultraviolet spectral properties QSOs, emphasis on ionizing continuum. Our is nearly twice as large that from previous work by W. Zheng and colleagues provides much better coverage in extreme-ultraviolet (EUV). The overall composite continuum can be described power law index αEUV = -1.76 ± 0.12 (fν ∝ να) between 500 1200 Å. corresponding results for subsamples radio-quiet...
We construct a composite quasar spectrum from 284 HST FOS spectra of 101 quasars with redshifts z > 0.33. The covers the wavelengths between 350 and 3000 Å in rest frame, peak S/N level ~130 per at ~1200 Å. Since ~90% sample have redshift < 1.5, is suitable for studying wavelength region shortward Lyα without large effects intervening forest absorption. Data waveband 600 are mainly 1.5 quasars, which significant corrections accumulated Lyman-series line continuum absorption been applied.
view Abstract Citations (502) References (43) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Steps toward Determination of the Size and Structure Broad-Line Region in Active Galactic Nuclei. I. an 8 Month Campaign Monitoring NGC 5548 with IUE Clavel, J. ; Reichert, G. A. Alloin, D. Crenshaw, M. Kriss, Krolik, H. Malkan, Netzer, Peterson, B. Wamsteker, W. Altamore, Baribaud, T. Barr, P. Beck, S. Binette, L. Bromage, E. Brosch, N. Diaz, Filippenko, V. Fricke,...
Supermassive black holes in the nuclei of active galaxies expel large amounts matter through powerful winds ionized gas. The archetypal galaxy NGC 5548 has been studied for decades, and high-resolution X-ray UV observations have previously shown a persistent outflow. An observing campaign 2013 with six space observatories shows nucleus to be obscured by long-lasting, clumpy stream gas never seen before. It blocks 90% soft emission causes simultaneous deep, broad absorption troughs. outflow...
view Abstract Citations (355) References (10) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS HST FOS Spectroscopy of M87: Evidence for a Disk Ionized Gas around Massive Black Hole Harms, Richard J. ; Ford, Holland C. Tsvetanov, Zlatan I. Hartig, George F. Dressel, Linda L. Kriss, Gerard A. Bohlin, Ralph Davidsen, Arthur Margon, Bruce Kochhar, Ajay K. Using the Faint Object Spectrograph on Hubble Space Telescope (HST) to observe central region M87, we have...
view Abstract Citations (315) References (26) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Narrowband HST Images of M87: Evidence for a Disk Ionized Gas around Massive Black Hole Ford, Holland C. ; Harms, Richard J. Tsvetanov, Zlatan I. Hartig, George F. Dressel, Linda L. Kriss, Gerard A. Bohlin, Ralph Davidsen, Arthur Margon, Bruce Kochhar, Ajay K. We present WFPC2 narrowband Hα + [N II] images M87 which show small disk ionized gas with apparent spiral...
We present results from a 900 ks exposure of NGC 3783 with the High-Energy Transmission Grating Spectrometer on board Chandra X-Ray Observatory. The resulting X-ray spectrum, which covers 0.5-10 keV energy range, has best combination signal-to-noise ratio and resolution ever obtained for an AGN. This spectrum reveals absorption lines H-like He-like ions N, O, Ne, Mg, Al, Si, S. There are also possible Ar Ca as well C. identify inner-shell lower ionization such Si VII-Si XII S XII-S XIV. iron...
view Abstract Citations (378) References (39) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Ultraviolet Variability of NGC 5548: Dynamics the Continuum Production Region and Geometry Broad-Line Krolik, J. H. ; Horne, Keith Kallman, T. R. Malkan, M. A. Edelson, Kriss, G. We used data obtained in 1989-1990 IUE monitoring 5548 to derive a mean shape for ionizing spectrum; line profiles; continuum fluctuation power spectrum three UV bands; cross-correlation...
Although soft X-ray absorption features in AGNs were discovered almost ten years ago, the nature and location of gas creating them has remained controversial. Guided by results recent high-resolution spectroscopy, we argue that these are created a multitemperature wind whose source matter is photoionized evaporation from inner edge obscuring torus often found surrounding an AGN. Photoionized presence copious mass locks ratio ionizing intensity to pressure critical value. However, broad range...
view Abstract Citations (284) References (32) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Steps toward Determination of the Size and Structure Broad-Line Region in Active Galactic Nuclei. VIII. an Intensive HST, IUE, Ground-based Study NGC 5548 Korista, K. T. ; Alloin, D. Barr, P. Clavel, J. Cohen, R. Crenshaw, M. Evans, I. N. Horne, Koratkar, A. Kriss, G. Krolik, H. Malkan, Morris, S. L. Netzer, O'Brien, Peterson, B. Reichert, Rodriguez-Pascual,...
We have produced the next generation of quasar spectral energy distributions (SEDs), essentially updating work Elvis et al. (1994) by using high-quality data obtained with several space and ground-based telescopes, including NASA's Great Observatories. present an atlas SEDs 85 optically bright, non-blazar quasars over electromagnetic spectrum from radio to X-rays. The heterogeneous sample includes 27 radio-quiet 58 radio-loud quasars. Most objects quasi-simultaneous ultraviolet-optical...
The Far Ultraviolet Spectroscopic Explorer (FUSE) has surveyed a large sample (>100) of active galactic nuclei (AGNs) in the low-redshift universe (z < 1). Its response at short wavelengths makes it possible to measure directly far-ultraviolet spectral properties quasi-stellar objects (QSOs) and Seyfert 1 galaxies z 0.3. Using archival FUSE spectra, we form composite extreme-ultraviolet (EUV) spectrum QSOs ≤ 0.67. After consideration many sources systematic error our analysis, find that...
view Abstract Citations (240) References (47) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The X-ray emitting gas in poor clusters with central dominant galaxies. Kriss, G. A. ; Cioffi, D. F. Canizares, C. R. observations of 16 containing galaxies have been performed the IPC Einstein Observatory. Twelve were detected, and each case emission is centered on galaxy. For six brightest clusters, authors find extended that smooth, centrally peaked, reasonably...
Recent intensive Swift monitoring of the Seyfert 1 galaxy NGC 5548 yielded 282 usable epochs over 125 days across six UV/optical bands and X-rays. This is densest extended AGN continuum sampling ever obtained, with a mean rate <0.5 day. Approximately daily HST UV was also obtained. The light curves show strong correlations (r_max = 0.57 - 0.90) clearest measurement to date interband lags. These lags are well-fit by \tau propto \lambda^4/3 wavelength dependence, normalization that indicates...
An extensive multi-satellite campaign on NGC 5548 has revealed this archetypal Seyfert-1 galaxy to be in an exceptional state of persistent heavy absorption. Our observations taken 2013-2014 with XMM-Newton, Swift, NuSTAR, INTEGRAL, Chandra, HST and two ground-based observatories have together enabled us establish that unexpected phenomenon is caused by outflowing stream weakly ionised gas (called the obscurer), extending from vicinity accretion disk broad-line region. In work we present...
Abstract Swift intensive accretion disk reverberation mapping of four AGN yielded light curves sampled ∼200–350 times in 0.3–10 keV X-ray and six UV/optical bands. Uniform reduction cross-correlation analysis these data sets yields three main results: (1) The X-ray/UV correlations are much weaker than those within the UV/optical, posing severe problems for lamp-post reprocessing model which variations a central corona drive power surrounding disk. (2) interband lags generally consistent with...
ABSTRACT We present ground-based optical photometric monitoring data for NGC 5548, part of an extended multiwavelength reverberation mapping campaign. The light curves have nearly daily cadence from 2014 January to July in nine filters ( BVRI and ugriz ). Combined with ultraviolet the Hubble Space Telescope Swift , we confirm significant time delays between continuum bands as a function wavelength, extending wavelength coverage 1158 Å z band (~9160 Å). find that lags at wavelengths longer...
We describe the first results from a six-month long reverberation-mapping experiment in ultraviolet based on 170 observations of Seyfert 1 galaxy NGC 5548 with Cosmic Origins Spectrograph Hubble Space Telescope. Significant correlated variability is found continuum and broad emission lines, amplitudes ranging ~30% to factor two lines three continuum. The variations all strong lag behind those continuum, He II 1640 lagging by ~2.5 days Lyman alpha 1215, C IV 1550, Si 1400 ~5-6 days....
We present the analysis of XMM-Newton and Swift optical-UV X-ray observations Seyfert-1/QSO Mrk 509, part an unprecedented multi-wavelength campaign, investigating nuclear environment this AGN. The data are from a series 10 about 60 ks each, spaced each other by 4 days, taken in Oct-Nov 2009. During our 509 was also observed with for period 100 monitoring behaviour source before after observations. With these we have established continuum spectrum bands investigated its variability on...
(Abridged) The simultaneous UV to X-rays/gamma rays data obtained during the multi-wavelength XMM/INTEGRAL campaign on Seyfert 1 Mrk 509 are used in this paper and tested against physically motivated broad band models. Each observation has been fitted with a realistic thermal comptonisation model for continuum emission. Prompted by correlation between soft X-ray flux, we use component excess. X-rays/gamma-rays emission of can be well these components. presence relatively hard high-energy...
We present the first results from ongoing, intensive, multi-wavelength monitoring program of luminous Seyfert 1 galaxy Mrk 817. While this AGN was, in part, selected for its historically unobscured nature, we discovered that X-ray spectrum is highly absorbed, and there are new blueshifted, broad narrow UV absorption lines, which suggest a dust-free, ionized obscurer located at inner line region partially covers central source. Despite obscuration, measure optical continuum reverberation lags...
An 8 month monitoring campaign on the Seyfert 1 galaxy Fairall 9 has been conducted with International Ultraviolet Explorer in an attempt to obtain reliable estimates of continuum-continuum and continuum-emission-line delays for a high-luminosity active galactic nucleus (AGN). While results this are more ambiguous than those previous campaigns lower luminosity sources, we find general agreement earlier results: (1) there is no measurable lag between ultraviolet continuum bands, (2) measured...