摘要:

The rich X‐ray light curves of blazars obtained with RXTE allow meaningful correlation analyses with longer wavelengths. This reveals strong connections of variations across the electromagnetic spectrum. In 3C 279, PKS 1510‐089, and BL Lac, the characteristics of the X‐ray variability change along with the projected direction of the compact jet. Outbursts in the radio, IR, or optical often precede flares at high energies. A period of pronounced variability in BL Lac in late 2000 occurs at both optical and X‐ray frequencies, with the X‐ray spectral index steepening. A superluminal radio knot is ejected during this event. The implication of our monitoring results is that the IR to X‐ray (as well as &ggr;‐ray) emission is cospatial with the compact radio jet, most likely occurring in the superluminal knots. In the radio galaxy 3C 120, in which the X‐rays probably come mainly from a hot accretion‐disk corona, the appearance of superluminal radio knots follows (by 4 weeks) dips in the X‐ray emission, as in microquasars but on longer timescales. The delay implies that the core of the radio jet, as seen in mm‐wave VLBA images, lies at least 0.4 pc from the central engine, consistent with models in which the jet flow accelerates far from the black hole. The quasar 3C 273 may be an interesting hybrid case in which contributions to the X‐ray emission may come from both the jet and corona. The power spectral density has a low‐frequency break that, in analogy with black‐hole binary systems, implies a mass of the central black hole of 3 – 6 × 108M⊙, similar to that obtained by reverberation mapping of emission‐line variability. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1781021

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

In this paper we review the very large contribution made by RXTE to our understanding of Active Galaxies (AGN). We discuss the relationship between AGN and Galactic Black Hole X‐ray binary systems (GBHs) and show, by comparison of their powerspectral densities (PSDs) that some AGN are the equivalent of GBHs in their ‘high’ state, rather than in their ‘low’ state as has previously been assumed. We plot the timescale at which the PSD slope steepens from −1 to −2 against the black hole mass for a sample of AGN, and for Cyg X‐1 in its high and low states. We find it is not possible to fit all AGN to the same linear scaling of break timescale with black hole mass. However broad line AGN are consistent with a linear scaling of break timescale with mass from Cyg X‐1 in its low state and NLS1 galaxies scale better with Cyg X‐1 in its high state, although there is an exception, NGC3227. We suggest that the relationship between black hole mass and break timescale is a function of another underlying parameter which may be accretion rate or black hole spin or, probably, both. We examine X‐ray spectral variability and show how simple ‘flux‐flux’ plots can distinguish between ‘two‐component’ and ‘spectral pivoting’ models. We also examine the relationship between the X‐ray emission and that in other wavebands. In the case of X‐ray/optical variability we show how cooler discs in AGN with larger mass black holes lead to greater proximity of the X‐ray and optical emission regions and hence to more highly correlated variability. The very large amplitude of optical variability then rules out reprocessing as the origin of the optical emission. We show how the radio emission in NGC 4051 is strongly correlated with the X‐ray emission, implying some contribution to the X‐ray emission from a jet for which there is some evidence in radio images. We point out, however, that we have only studied in detail the X‐ray variability of a handful of AGN. There is a strong requirement to extend such studies to unbiased samples of many hundreds of AGN and so a strong need for a very sensitive (<mCrab in a day), long lived (∼10 years) all sky monitor. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1781022

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Using the Rossi X‐ray Timing Experiment (RXTE), we have observed both the Seyfert 1 galaxy Akn 120 and the broad‐line radio galaxy 3C 120. Monitoring observations spanning 2 years plus intensive stares spanning several days have been obtained for both objects. These data have allowed us to construct the power density spectrum (PDS) for each object. Covering more than 4 decades in temporal frequency, the PDS for 3C 120 represents the first such measurement for a radio loud galaxy. The PDS for 3C 120 shows a steep power law at high frequencies, which turns over at low frequencies. Akn 120 also has a power law shape in its PDS. Using the PDS of Cygnus X‐1, we estimate the masses for both of these objects. Optical data and cross correlation functions are also presented for Akn 120. The long‐term light curve of Akn 120 shows a strong correlation with optical data, with zero time lag. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1781023

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The Tartarus database contains products for 529ASCAobservations of active galactic nuclei. We have been updating Tartarus to include observing sequences conducted after 1999 January. The revised database will contain products for 375 objects, with a total of 614 observing sequences. We have begun a systematic timing analysis of the Tartarus light curves. We present here some preliminary results of an investigation into the relation between excess variance and black‐hole mass. Having optimised our analysis to minimize the scatter in the variance measurements, we find that the narrow‐line active galactic nuclei follow roughly the same relation as the broad‐line objects. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1781024

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

For light curves sampled on an uneven grid of observation times, the shape of the power density spectrum (PDS) includes severe distortion effects due to the window function, and simulations of light curves are indispensable to recover the true PDS. We present an improved method for comparing light curves generated from a PDS model to the measured data and apply it to a 50‐day longRXTEobservations of NGC 4945, a Seyfert 2 galaxy with well‐determined mass from megamaser observations. The improvements over previously reported investigations include the adjustment of the PDS model normalization for each simulated light curve in order to directly investigate how well the chosen PDS shape describes the source data. We furthermore implement a robust goodness‐of‐fit measure that does not depend on the form of the variable used to describe the power in the periodogram. We conclude that a knee‐type function (smoothly broken power law) describes the data better than a simple power law; the best‐fit break frequency is ∼ 10−6Hz. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1781025

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

We investigate the model of an accretion disk illuminated locally by hard X‐rays. The X‐ray source is in the form of the hot flares most probably produced via magnetic field reconnection. Flares are accompanied by hot spots created at the accretion disk surface by illumination. We compute the local reflected (spot) spectrum using the codes TITAN/NOAR. In our computations we are able to model the change of intensities of X‐ray emission lines from 0.1 keV up to the most prominent iron K&agr;line due to appearance of flares. The global spectrum is obtained assuming a distribution of flares, where each flare has assumed effective life time. In such a case we follow the line profile modified due to relativistic smearing in Kerr metric. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1781026

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

We model synchrotron and inverse Compton flares in blazars from radio to X‐rays and gamma‐rays. We take into account the internal structure and geometry of the source (energy stratification) caused by particle acceleration at shock wave fronts and synchrotron energy losses. We also consider the effects of light‐travel time of the synchrotron emission that supplies the seed photons for synchrotron self‐Compton scattering. These internal light‐travel delays may lead to a lag of the higher energy flare with respect to variations at lower frequencies. In the model, a flare in the jet follows a collision between moving and stationary shocks. The collision leads to the creation of forward and reverse shocks, both advecting down the jet along with the shocked plasma, but moving in opposite directions in the shocked plasma rest frame. The double shock‐wave structure of the emission region could be apparent in the flare profile and can provide an explanation for large time delays between synchrotron and inverse Compton flares. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1781027

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

We have performed two campaigns of intensive monitoring of the blazars 3C 273, 3C 279, and PKS 1510‐089 in the X‐ray, optical, near‐IR, and radio regions in March and April 2002. The quasar 3C 279 reveals significant interday variability at all wavelengths. The quasar 3C 273 shows smooth variations in the X‐ray and near‐IR regions on time scales of 2–3 days. For both quasars the results indicate close connection between X‐ray and near‐IR emission with a delay of X‐rays from 0 to 3 days. The quasar PKS 1510‐089 was in a low emission state at all frequencies during the campaigns. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1781028

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

I present an observational review of the five accretion‐driven millisecond X‐ray pulsars currently known, focusing on the results obtained with theRossi X‐ray Timing Explorer(RXTE) satellite. A prominent place in this review is given to the first such system discovered, SAX J1808.4‐3658. Currently four outbursts have been detected from this source, three of which have been studied usingRXTE. This makes this source the best studied example of all accretion‐driven millisecond pulsars. Its October 2002 outburst is of particular interest because of the discovery of kilohertz quasi‐periodic oscillations and burst oscillations during its thermonuclear X‐ray bursts. The other four accreting millisecond pulsars were discovered within the last two years and only limited results have been published so far. A more extended review can be found at http://zon.wins.uva.nl/∼rudy/admxp/ © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1781029

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

RXTEhas discovered a flurry of new accreting millisecond pulsars in the past two years, based on dedicated and all‐sky monitoring. How couldRXTEand an enhanced future timing mission capitalize on these successes? I argue that the major issues to tackle are binary orbit and spin evolution. There is enough potential uncertainty in the models that drive binary evolution that it is worth attempting to detect orbital period changes in millisecond pulars. WithRXTEit is possible to measure the orbital phase to within a few to a few hundred microperiods, and that can be improved by a factor of ∼ 3 with an enhanced timing mission with ∼10 times the collecting area. This in turn will make it possible to feasibly detect significant orbital period changes within a few years baseline. Neutron star spin torques due to accretion are also important, since they are presumably the mechanism by which low mass X‐ray binaries are spun up to millisecond pulsars in the first place. The current ambiguous data on spin torques suggests that further, more ambitious studies are required. I also discuss several other issues, such as pulse phased spectroscopy, which may improve our knowledge of the neutron star equation of state. I conclude with a brief presentation of the “ideal” millisecond pulsar observatory. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1781030

出版商:AIP    

年代:1904

数据来源: AIP