摘要:

We have observed the peculiar superluminal quasar 4C 39.25 with the ROSAT PSPC at two epochs. We examine both short‐term (constant flux on intraday and several‐day timescales) and long‐term (30% increase over 2 yr) variability of the soft X‐ray emission. The entire radio to submillimeter spectrum also rose by 30% over the same period. This supports the twisted relativistic jet model for 4C 39.25 (Marscheret al. 1991), in which the Doppler beaming factor increases monotonically as the velocity vector of the superluminally moving component (here identified as the source of the X‐rays) continues to bend toward the line of sight. ©1994 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.46701

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

We report excess X‐ray absorption toward two sources with quite different redshifts: thez=2.07 quasar PKS 0528+134 and the relatively nearby (z=0.077) radio galaxy OQ 208 (1408+286). Both sources exhibit features common to Giga‐Hertz Peaked spectrum (GPS) radio sources. Excess X‐ray absorption has been found toward other high‐zsources (many also GPS sources) and interpreted as either intrinsic to the host galaxy/cluster or absorption by an intervening galaxy or cloud along the line of sight (Elviset al. 1993). VLBI and X‐ray observations reveal a distorted jet‐like structure and relativistically beamed emission region in PKS 0528+134. The detection of excess absorption over a wide redshift range favors the intrinsic absorption model. The absorbing gas may also shape the radio morphology and spectrum of a GPS sources. ©1994 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.46702

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

ROSAT is the first mission to have detected X‐ray emission in radio galaxies which are both powerful (l178 MHz≳1027W Hz−1sr−1) and distant (z≳0.4), enabling test of ‘‘unified schemes’’ through a comparison of the X‐ray and radio properties of powerful quasars and radio galaxies. These radio galaxies are faint in X‐rays, but, nevertheless, ROSAT is capable of resolving any associated X‐ray‐emitting gas of cluster dimension.We present ROSAT PSPC observations of two such radio galaxies and suggest that there is a component of unresolved X‐ray emission in powerful, high‐redshift radio galaxies which may be related to the radio core; this will be tested by ROSAT observations of other powerful radio galaxies. ©1994 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.46703

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

We compare the optical to soft X‐ray spectral energy distribution of six bright low‐redshift (0.048<z<0.155) radio‐quiet quasars with models of quasars where the soft excess is interpreted in terms of (a) optically thick thermal emission from the innermost region of an accretion disk in Schwarschild and Kerr geometries, (b) reprocessing from ionized gas. Pure disk models even in a Kerr geometry cannot easily reproduce the observed optical to soft X‐ray energy distribution. The range of parameters which give reasonable predictions is narrow: high inclinations, high accretion rates and central black hole ∼ 108M⊙. We consider modifications of the disk models: 1) an underlying power law component extending from the infrared (3 &mgr;m) to the X‐ray; 2) reprocessing of the X‐rays. The modified models can explain the optical‐UV and soft X‐ray observations. Free‐free models are discussed by Fiore in these Proceedings. ©1994 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.46655

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Preliminary results of a spectral analysis of ROSAT PSPC pointed observations for a complete sample of radio‐selected BL Lac objects (1 Jy sample) are presented. At present, data are available for 24 of the 34 sources, 20 of which have enough statistical significance to allow spectral analysis. The average spectral index for the whole group is 2.39±0.02 (weighted mean). Study with more complex models, as well as spatial and temporal analyses, are underway. ©1994 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.46656

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

We present a deepROSATPSPC image of the radio lobes of the nearby galaxy Fornax A (=NGC 1316) and find, after image processing, X‐ray emission closely mimicking the radio emission. We argue that this is the long‐sought inverse Compton radiation produced when cosmic microwave background photons are upscattered off synchrotron emitting electrons in the radio lobes. The derived magnetic field in the lobes is compared with equipartition values and we also discuss the possibility of thermal Bremsstrahlung emission as a souce of lobe X‐rays. This observation constitutes the best case for detection of inverse Compton X‐rays in radio lobes to date. ©1994 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.46657

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

We have used X‐ray and VLBI observations of twenty three BL Lac objects from the 1 Jy sample of radio bright sources to test models for the orgin of X‐ray emission in BL Lacs. We find a correlation between the X‐ray luminosity and the parsec scale radio emission, consistent with the idea that the X‐rays are relativistically beamed. A simple approximation for the synchrotron self‐Compton process has been used to estimate the minimum Doppler factor for bulk relativistic motion. Relativistic motion is implied for ∼75% of the sources, although there are no clear trends between the minimum Doppler factor and other traits. These results suggest that the soft X‐ray spectra do not contain a significant inverse‐Compton contribution, but this needs to be tested with more sophisticated models. ©1994 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.46659

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

We have made multiband observations of six candidate Optically Quiet Quasars, and confirm the inverted Spectral Energy Distribution in four. OQQs could be ordinary radio‐loud AGN whose SED is significantly modified by absorption either intrinsic to the source or along the line of sight, or the X‐rays could be dominated by a strong inverse‐Compton contribution. Our four OQQs exhibit a range of properties and more than one explanation is possible. ©1994 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.46660

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

ROSAT deep survey X‐ray sources have been identified with active galaxies (Active Galactic Nuclei and Narrow Emission‐Line galaxies) and also with early‐type, ‘‘passive galaxies’’. In this paper we discuss preliminary results of the galaxy content, both early‐type and emission‐line galaxies, of 5 ROSAT fields. ©1994 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.46661

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The x‐ray bright BL Lac object PKS2155‐304 was observed with the PSPC on two separate occasions: May 6, 1991 and November 17, 1992. There was a 45% drop in flux between the observations. The later observations were well fit with a simple power law; however, the earlier spectrum appears more complex, and requires an additional feature. We modelled this as an absorption notch or edge. Similar absorption by hot gas, apparently intrinsic to the source, has been detected with other instrumented in this and other BL Lac objects. However, we believe the source of the feature is instrumental and is probably the result of a small temporal gain shift (∼1–2%) in the response matrix. ©1994 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.46662

出版商:AIP    

年代:1994

数据来源: AIP