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Relativistic kinematics and superluminal effects in compact extragalactic radio sources are considered. A relativistic blast-wave model is applied to an outburst observed in the BL Lac object AO 0235+164. It is shown that the model can explain in detail the observed nature of variable extragalactic radio sources.
Observations in the X-ray, UV, visible, IR and radio regions of the BL Lac object Mrk 501 made over the course of two months are reported. The measurements were made with the A2 experiment on HEAO 1 (X-ray), the SWP and LWR cameras on IUE (UV), the 5-m Hale telescope (visible), the 2.5-m telescope at Mount Wilson (IR), the NRAO 92-m radio telescope at Green Bank (4750 MHz) and the 46-m radio telescope at the Algonquin Observatory (10275 and 10650 MHz). The quasi-simultaneously observed spectral slope is found to be positive and continuous from the X-ray to the UV, but to gradually flatten and possibly turn down from the mid-UV to the visible; the optical-radio emission cannot be accounted for by a single power law. The total spectrum is shown to be compatible with a synchrotron self-Compton emission mechanism, while the spectrum from the visible to the X-ray is consistent with synchrotron radiation or inverse-Compton scattering by a hot thermal electron cloud. The continuity of the spectrum from the UV to the X-ray is noted to imply a total luminosity greater than previous estimates by a factor of 3-4.
A program to obtain IUE spectra and optical photometry and spectra of three RS CVn-type binaries (HR 1099, II Peg, and AR Lac) and the prototype BY Dra system is reported. The systems were monitored for at least one orbital phase, and periodic variations in emission line flux from II Peg and HR 1099, indicative of notational modulation of an active region on these stars were detected. It is found that for II Peg the active region is in phase with photometric minimum as expected, but for HR 1099 ultraviolet emission maximum occurs at the time of photometric maximum.
X-ray emission from two BL Lacertae objects (H2155-304 and PKS 0548-322) has been studied with the High-Resolution Imager and Monitor Proportional Counter (MPC) on the Einstein Observatory. The high-spatial-resolution observations confirm the identification of these X-ray sources with the BL Lac objects and give a source size less than about 2 arcsec. Variations in the X-ray intensity and spectrum of these sources were detected over time scales of a few hours from analysis of the MPC observations.
The object H0323+022 (Doxsey et al. 1983) has been shown to be a BL Lac object by virtue of a diversity of observational characteristics at radio, optical, and X-ray wavelengths, in agreement with the conclusion of Margon and Jacoby (1984). Multi-frequency coordinated observations of this highly variable object with EXOSAT in September 1984 found it to be in a faint quiescent state (approximately 1/3 micron-Jy at approximately 5 keV and V = 16.55). Preliminary results from the latter observations are presented.
Multicolor wide-band photometry of five active stars is presented. The observations were carried out at several places before, during and after the period of IUE observations for the purpose of determining the location, sizes, and evolution of photospheric spots at the time when chromospheric, transition region, and coronal activity data were obtained from UV and radio observations. II Peg, BY Dra, and AU Mic show fairly stable quasi-sinusoidal light curves, while AR Lac and V 711 Tau show double-peaked light curves. For V 711 Tau, a remarkable evolution of the spotted area extent and/or longitude distribution is found. Small, but definite color variations that are consistent with the cool spot hypothesis have also been detected for BY Dra, II Peg and V 711 Tau.
General arguments for relativistic beaming in BL Lac objects are reviewed. These include overproduction of X-rays and fast time variability. Comments are made about the relationship of the X-ray continuum to that at lower frequencies, and observational evidence for and against continuum radiation being relativistically beamed is discussed. Finally, there is discussion of the influence of geometrical effects on predictions for time variability as a function of frequency in the context of inhomogeneous synchrotron self-Compton jet models.
The results from the X-ray observations of two BL Lacertae objects, H2155-304 and PKS0548-322, are presented. The observations were carried out with the HEAO-1 A2 Low Energy Detectors, the High Resolution Imager, and the Monitor Proportional Counter aboard the Einstein Observatory. Correlated X-ray intensity variations of about 20 percent in the 0.15-3.5 keV energy band and about 40 percent in the 1.5-10 keV energy band are observed in H2155-304 over a period of about 8 hr. A factor of two change in the intensity of PKS0548-322 in the 3.5-10 keV energy interval is also detected over a time interval of 1 hr. Variations in the X-ray intensity over a timescale of months and the hardening of the spectrum with increasing intensity are seen in the HEAO-1 A2 data on H2155-304. The shortest observed timescale for the variability is used to derive an upper limit on the mass of the central accreting source in the two BL Lac objects studied here.
Ground-based optical and IUE satellite-ultraviolet observations of three RS CVn stars are combined with density sensitive line ratios and differential emission measure curves to describe the physical conditions in their outer atmospheres. Solar-like densities are found to be representative of average conditions on two of the stars, V 711 Tau and AR Lac. The total radiative losses from these two stars are estimated and found to be larger than the sun by at least two orders of magnitude. Consideration of the volume emitting in two of the principal transition region lines suggests a possible relation between the disk 'filling factor' for these two lines and the dynamo-related Rossby number. Only one hemisphere of the star II Peg, the one showing least evidence of starspots, is similar. On the opposite hemisphere the presence of a discrete emitting region is deduced which is almost coincident in phase with the passage of the dominant optical spot group across the visible disk. The dimensions of this region, and an illustrative interpretation in terms of a large emitting magnetic loop, are discussed. It is compared to large active region loops on the sun.
A program to obtain simultaneous multifrequency spectra of BL Lacertae objects that are known X-ray sources is discussed. The IUE spectra are generally featureless and well-fitted by power law models. For the faintest exposures, Gaussian extraction of the spectrum can greatly impove the signal-to-noise. Most program objects vary in the ultraviolet, although the time scales are not known because of limited observing time. The broadband spectra of BL Lacs exhibit a range of characteristics but the curvature is always downward and the shape is generally smooth. This can be interpreted as synchrotron emission from a relativistic jet; different jet models are possible, and each allows a range of values for the bulk velocity, magnetic field strength, and electron density. Synchrotron models are not required, however an accretion disk model also gives a good fit to the ultraviolet-through-X-ray continuum.
The Uhuru X-ray source 4U1722 + 11 was observed using the microchannel-plate detector (High Resolution Imager) on the Einstein Observatory, and its coordinates measured to a precision of about 5 arcsec. A 16th-magnitude stellar object within the error circle was observed spectroscopically at CTIO, and at the AAT, and found to have a featureless continuum. Subsequent radio observations at the VLA have established that the object is a radio source at the level of 60 mJy, and optical polarization measurements have determined that the source exhibits variable polarization at the level of 10 percent. On the basis of these observations, it is concluded that 4U1722 + 11 is a member of the class of objects known as X-ray selected blazars of BL Lac objects.
The eclipsing RS CVn system AR Lac (G2IV + K0IV) has been observed continuously for one 2-day binary cycle with the Exosat observatory. Below 1 keV, a factor of two intensity modulation is seen with a flat bottomed minimum around the time of primary eclipse and a shallow dip preceeding primary eclipse. Above 1 keV, where only emission with temperatures greater than 10 exp 7 K would be detected, no orbital modulation or eclipse is seen. This suggests that the greater than 20 million degree emission comes from a large region, comparable in size to the binary separation. The modulation in the less than 1 keV lightcurve has been modeled by chi-squared fitting to X-ray bright spots and by using maximum entropy deconvolution. The lower temperature emission is found to originate in compact regions with a pressure and temperature similar to that of the flaring sun.
Using the Canada-France-Hawaii Telescope, we have imaged a complete, flux-limited sample of Einstein Medium Sensitivity Survey BL Lacertae objects in order to study the properties of BL Lac host galaxies and to use quantitative methods to determine the richness of their galaxy cluster environments.
This report summarizes the activities related to two ROSAT investigations: (1) x-ray properties of radio galaxies thought to contain BL Lac type nuclei; and (2) x-ray spectra of a complete sample of flat-spectrum radio sources. The following papers describing the research are provided as attachments: Multiple X-ray Emission Components in Low Power Radio Galaxies; New X-ray Results on Radio Galaxies; Analysis Techniques for a Multiwavelength Study of Radio Galaxies; Separation of X-ray Emission Components in Radio Galaxies; X-ray Emission in Powerful Radio Galaxies and Quasars; Extended and Compact X-ray Emission in Powerful Radio Galaxies; and X-ray Spectra of a Complete Sample of Extragalactic Core-dominated Radio Sources.
We present high dyanamic range (greater than 10 000:1) Very Large Array (VLA) maps of four highly c ore-dominated BL Lacertae Objects (PKS 0735+178, OJ 287, 1219+285, and PKS 1413+135), all of which had been reported previously as being unresolved at dynamic ranges approximately 1000-3000:1. Three of the four possess low surface brightness kpc-scale structure, with extended power levels and morphologies reasonable for FR 1 radio galaxies. One, however (PKS 1413+135), possesses no extended structure at dynamic range 9600:1. Only one of the sources exhibits aligned Very Large Array (VLA) and VLBI structures, suggesting bends on approximately 100-1000 pc size scales for the other two. As these four have extremely high core-to-extended flux ratios (f approximately 30-5000), they provide an extreme test of unified schemes. By deriving minimum constraints for the beaming angles and Lorentz factors which are required to produce the degrees of core dominance seen, we find that the three extended radio sources are consistent with being beamed FR 1 radio galaxies. PKS 1413+135 remains an anomalous BL Lac Object for several reasons.
The following publications are included and serve as the final report: The X-ray Spectrum of Abell 665; Clusters of Galaxies; Ginga Observation of an Oxygen-rich Supernova Remnant; Ginga Observations of the Coma Cluster and Studies of the Spatial Distribution of Iron; A Measurement of the Hubble Constant from the X-ray Properties and the Sunyaev-Zel'dovich Effect of Abell 2218; Non-polytropic Model for the Coma Cluster; and Abundance Gradients in Cooling Flow Clusters: Ginga LAC (Large Area Counter) and Einstein SSS (Solid State Spectrometer) Spectra of A496, A1795, A2142, and A2199.
The Burst and Transient Source Experiment (BATSE) on the Compton Gamma-Ray Observatory has been shown to be sensitive to non-transient hard X-ray sources in our galaxy, down to flux levels of 100 mCrab for daily measurements, 3 mCrab for integrations over several years. We use the continuous BATSE database and the Earth Occultation technique to extract average flux values between 20 and 200 keV from complete and radio- and X-ray- selected BL Lac samples over a 2 year period.
This grant covered the analysis and interpretation of astrophysical data obtained with the XMM-Newton satellite mission. BL Lac objects are active galactic nuclei that exhibit unusually strong polarization and variability, and are also missing the usual strong optical/ultraviolet emission lines. They are typically strong X-ray sources, but this is the first survey gathering high-quality spectral data from a significant number of these objects. The observations were successful, and all data (for objects in this proposal as well as that of Dr. Perlman s) were of very good quality, as expected. We find that the X-ray spectra of most of these objects are well described by a power-law after allowing for low-energy absorption that can be attributed to neutral gas in the line of sight, presumably located in our own Galaxy. However, in some cases we see indications of a deviation from power-law behavior in the sense that the spectrum appears to be steepening (softening) to higher energies. We are developing a theoretical model in which the steepening is a result of energy-dependent cooling of the radiating particles.We searched for discrete spectral features that might be intrinsic to the objects or their host galaxies, but we found none at the level of sensitivity provided by these data. These are interestingly strong upper bounds.