-
[show abstract]
[hide abstract]
ABSTRACT: We present analysis of both the short-term optical and long-term multiwavelength variability of CTA 102. In 2004, this object was observed in an intense optical flaring state. Extensive R-band microvariability observations were carried out during this high state. In 2005, we obtained several weeks of contemporaneous radio, optical, and X-ray observations of CTA 102. These observations recorded distinct flaring activity in all three wavebands. Subsequent analysis revealed that this object may appear redder when in a brighter optical state, and that the X-ray, optical, and radio activity do not appear to be correlated. The shape of the observed spectral energy distributions suggests that both synchrotron-related and external inverse Compton processes may contribute to the X-ray emission. Our results are also compared to other results on this object and archival microvariability observations. It appears that more rapid, dramatic microvariability events occur when CTA 102 is in an elevated optical flux state.
The Astronomical Journal 11/2009; 138(6):1902. · 4.03 Impact Factor
-
Ritaban Chatterjee,
Alan P. Marscher,
Svetlana G. Jorstad,
Alice R. Olmstead,
Ian M. McHardy,
Margo F. Aller,
Hugh D. Aller,
Anne Lahteenmaki,
Merja Tornikoski,
Talvikki Hovatta, [......],
Shoji Masatoshi,
Thomas R. Miller,
Hong-Jian Pan,
Eric A. Petersen,
Bradley W. Peterson,
Zhiqiang Shen,
Dmitriy V. Strelnikov,
Jun Tao,
Aaron E. Watkins,
Kathleen Wheeler
[show abstract]
[hide abstract]
ABSTRACT: We present the results of extensive multi-frequency monitoring of the radio galaxy 3C 120 between 2002 and 2007 at X-ray, optical, and radio wave bands, as well as imaging with the Very Long Baseline Array (VLBA). Over the 5 yr of observation, significant dips in the X-ray light curve are followed by ejections of bright superluminal knots in the VLBA images. Consistent with this, the X-ray flux and 37 GHz flux are anti-correlated with X-ray leading the radio variations. This implies that, in this radio galaxy, the radiative state of accretion disk plus corona system, where the X-rays are produced, has a direct effect on the events in the jet, where the radio emission originates. The X-ray power spectral density of 3C 120 shows a break, with steeper slope at shorter timescale and the break timescale is commensurate with the mass of the central black hole based on observations of Seyfert galaxies and black hole X-ray binaries. These findings provide support for the paradigm that black hole X-ray binaries and active galactic nuclei are fundamentally similar systems, with characteristic time and size scales linearly proportional to the mass of the central black hole. The X-ray and optical variations are strongly correlated in 3C 120, which implies that the optical emission in this object arises from the same general region as the X-rays, i.e., in the accretion disk-corona system. We numerically model multi-wavelength light curves of 3C 120 from such a system with the optical-UV emission produced in the disk and the X-rays generated by scattering of thermal photons by hot electrons in the corona. From the comparison of the temporal properties of the model light curves to that of the observed variability, we constrain the physical size of the corona and the distances of the emitting regions from the central BH. Comment: Accepted for publication in the Astrophysical Journal. 28 pages, 21 figures, 2 tables
09/2009;
-
[show abstract]
[hide abstract]
ABSTRACT: We present results from a multiyear monitoring campaign of the broad-line radio galaxy 3C 120, using the Rossi X-ray Timing Explorer for nearly five years of observations. Additionally, we present coincident optical monitoring using data from several ground-based observatories. Both the X-ray and optical emission are highly variable and appear to be strongly correlated, with the X-ray emission leading the optical by 28 days. The X-ray power density spectrum is best fit by a broken power law, with a low-frequency slope of –1.2, breaking to a high-frequency slope of –2.1, and a break frequency of log νb = –5.75 Hz, or 6.5 days. This value agrees well with the value expected based on 3C 120's mass and accretion rate. We find no evidence for a second break in the power spectrum. Combined with a moderately soft X-ray spectrum (Γ = 1.8) and a moderately high accretion rate (), this indicates that 3C 120 fits in well with the high/soft variability state found in most other active galactic nuclei. Previous studies have shown that the spectrum has a strong Fe Kα line, which may be relativistically broadened. The presence of this line, combined with a power spectrum similar to that seen in Seyfert galaxies, suggests that the majority of the X-ray emission in this object arises in or near the disk, and not in the jet.
The Astrophysical Journal 04/2009; 696(1):601. · 6.02 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We present results from a multi-year monitoring campaign of the broad-line radio galaxy 3C 120, using the Rossi X-ray Timing Explorer (RXTE) for nearly five years of observations. Additionally, we present coincident optical monitoring using data from several ground-based observatories. Both the X-ray and optical emission are highly variable and appear to be strongly correlated, with the X-ray emission leading the optical by 28 days. The X-ray power density spectrum is best fit by a broken power law, with a low-frequency slope of -1.2, breaking to a high-frequency slope of -2.1, and a break frequency of log nu_b=-5.75 Hz, or 6.5 days. This value agrees well with the value expected based on 3C 120's mass and accretion rate. We find no evidence for a second break in the power spectrum. Combined with a moderately soft X-ray spectrum (Gamma=1.8) and a moderately high accretion rate (mdot / mdot_Edd ~ 0.3), this indicates that 3C 120 fits in wellwith the high/soft variability state found in most other AGNs. Previous studies have shown that the spectrum has a strong Fe K-alpha line, which may be relativistically broadened. The presence of this line, combined with a power spectrum similar to that seen in Seyfert galaxies, suggests that the majority of the X-ray emission in this object arises in or near the disk, and not in the jet. Comment: 19 pages, 6 figures. Accepted for publication in ApJ
02/2009;
-
[show abstract]
[hide abstract]
ABSTRACT: We present the results of a 3 year monitoring campaign of the Seyfert 1 galaxy Markarian 509, using X-ray data from the Rossi X-Ray Timing Explorer and optical data taken by the SMARTS consortium. Both light curves show significant variations and are strongly correlated with the optical flux leading the X-ray flux by 15 days. The X-ray power spectrum shows a steep high-frequency slope of –2.0, breaking to a slope of –1.0 at a timescale of 34 days. The lag from optical to X-ray emission is most likely caused by variations in the accretion disk propagating inward.
The Astrophysical Journal 12/2008; 677(2):880. · 6.02 Impact Factor
-
Ritaban Chatterjee,
Svetlana G. Jorstad,
Alan P. Marscher,
Haruki Oh,
Ian M. McHardy,
Margo F. Aller,
Hugh D. Aller,
Thomas J. Balonek,
H. Richard Miller, Wesley T. Ryle,
Gino Tosti,
Omar Kurtanidze,
Maria Nikolashvili,
Valeri M. Larionov,
and Vladimir A. Hagen-Thorn
[show abstract]
[hide abstract]
ABSTRACT: We present the results of extensive multi-wave band monitoring of the blazar 3C 279 between 1996 and 2007 at X-ray energies (2-10 keV), optical R band, and 14.5 GHz, as well as imaging with the Very Long Baseline Array (VLBA) at 43 GHz. In all bands the power spectral density corresponds to "red noise" that can be fit by a single power law over the sampled timescales. Variations in flux at all three wave bands are significantly correlated. The time delay between high- and low-frequency bands changes substantially on timescales of years. A major multifrequency flare in 2001 coincided with a swing of the jet toward a more southerly direction, and in general the X-ray flux is modulated by changes in the position angle of the jet near the core. The flux density in the core at 43 GHz—increases in which indicate the appearance of new superluminal knots—are significantly correlated with the X-ray flux. We decompose the X-ray and optical light curves into individual flares, finding that X-ray leads optical variations (XO) in six flares, the reverse (OX) occurs in three flares, and there is essentially zero lag in four flares. Upon comparing theoretical expectations with the data, we conclude that (1) XO flares can be explained by gradual acceleration of radiating electrons to the highest energies, (2) OX flares can result from either light-travel delays of the seed photons (synchrotron self-Compton scattering) or gradients in maximum electron energy behind shock fronts, and (3) events with similar X-ray and optical radiative energy output originate well upstream of the 43 GHz core, while those in which the optical radiative output dominates occur at or downstream of the core.
The Astrophysical Journal 12/2008; 689(1):79. · 6.02 Impact Factor
-
Angela Osterman Meyer,
H. Richard Miller,
Kevin Marshall, Wesley T. Ryle,
Hugh Aller,
Margo Aller,
John P. McFarland,
Joseph T. Pollock,
Daniel E. Reichart,
J. Adam Crain,
Kevin M. Ivarsen,
Aaron P. LaCluyze,
and Melissa C. Nysewander
[show abstract]
[hide abstract]
ABSTRACT: Coordinated X-ray, optical, and radio observations of the blazar PKS 1622-297 were obtained during a three-week campaign in 2006 using the Rossi X-Ray Timing Explorer (RXTE), the University of Michigan Radio Astronomy Observatory, and optical telescopes at Cerro Tololo Inter-American Observatory. The RXTE observations indicate that this object is a comparatively weak X-ray emitter for a Flat-Spectrum Radio Quasar. The observed broadband spectral shape indicates that X-rays were most likely produced by the Inverse Compton processes. Optical observations of this object produced unexpected results in that this object appeared redder when in a bright state and bluer when in a faint state, contrary to the observed behavior of BL Lac objects.
The Astronomical Journal 08/2008; 136(3):1398. · 4.03 Impact Factor
-
Alan P Marscher,
Svetlana G Jorstad,
Francesca D D'Arcangelo,
Paul S Smith,
G Grant Williams,
Valeri M Larionov,
Haruki Oh,
Alice R Olmstead,
Margo F Aller,
Hugh D Aller, [......],
Esko Valtaoja,
Vladimir A Hagen-Thorn,
Eugenia N Kopatskaya,
Walter K Gear,
Gino Tosti,
Omar Kurtanidze,
Maria Nikolashvili,
Lorand Sigua,
H Richard Miller, Wesley T Ryle
[show abstract]
[hide abstract]
ABSTRACT: Blazars are the most extreme active galactic nuclei. They possess oppositely directed plasma jets emanating at near light speeds from accreting supermassive black holes. According to theoretical models, such jets are propelled by magnetic fields twisted by differential rotation of the black hole's accretion disk or inertial-frame-dragging ergosphere. The flow velocity increases outward along the jet in an acceleration and collimation zone containing a coiled magnetic field. Detailed observations of outbursts of electromagnetic radiation, for which blazars are famous, can potentially probe the zone. It has hitherto not been possible to either specify the location of the outbursts or verify the general picture of jet formation. Here we report sequences of high-resolution radio images and optical polarization measurements of the blazar BL Lacertae. The data reveal a bright feature in the jet that causes a double flare of radiation from optical frequencies to TeV gamma-ray energies, as well as a delayed outburst at radio wavelengths. We conclude that the event starts in a region with a helical magnetic field that we identify with the acceleration and collimation zone predicted by the theories. The feature brightens again when it crosses a standing shock wave corresponding to the bright 'core' seen on the images.
Nature 05/2008; 452(7190):966-9. · 36.28 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The TeV blazar PKS 2155--304 was the subject of an intensive 2 week optical and near-infrared observing campaign in 2004 August with the CTIO 0.9m telescope. During this time, simultaneous X-ray data from RXTE were also obtained. We compare the results of our observations to the results from two previous simultaneous multiwavelength campaigns on PKS 2155-304. We conclude that the correlation between the X-ray and UV/optical variability is strongest and the time lag is shortest (only a few hours) when the object is brightest. As the object becomes fainter, the correlations are weaker and the lags longer, increasing to a few days. Based on the results of four campaigns, we find evidence for a linear relationship between the mean optical brightness and lag time of X-ray and UV/optical events. Furthermore, we assert that this behavior, along with the different multiwavelength flare lag times across different flux states is consistent with a highly relativistic shock propagating down the jet producing the flares observed during a high state. In a quiescent state, the variability is likely to be due to a number of factors including both the jet and contributions outside of the jet, such as the accretion disk. Comment: 23 pages, 8 figures, to be published in the Astrophysical Journal, volume 671
11/2007;
