BL Lac Object PKS Research Articles

X-ray intensity variations in BL Lac sources H2155-304 and PKS 0548-322

The X-ray Observations of two BL Lac Objects H2155-304 and PKS 0548-322 made with HRI and MPC on the Einstein Observatory show intensity variations on time scale of hours in both the sources. X-ray spectra of the two BL Lacs are derived. Limits on the mass of the accreting compact objects are obtained from time scale and magnitude of variations. Implications of the results are briefly discussed.

X-ray bursting activity in the BL Lacertae object PKS 2155-304

The bright BL Lac object PKS 2155-304 (mv=13; z=0.117) was observed with EXOSAT at five epochs (1983 Oct. 31, Nov. 30, 1984 Nov. 6, 7 and 11), for a total of about 30 hours of exposure time. Here we present data and results obtained with the Low Energy (LE) telescopes, in the band 0.05–2. keV, and with the Medium Energy (ME) argon proportional counters in the range 1.–6. keV.

X-ray variability of the bright BL Lac object PKS 2155-304

We have observed the BL Lac object PKS 2155-304 with the EXOSAT observatory and with IUE on 1983 October 31 and November 29. At the same time, optical photometry has been obtained. Variability has been observed both on a time scale of hours during the October 31 observation and on the time scale of one month. During the November 29 observation the source was 2 times brighter than in the previous observation, but no spectral modification is found between the two observations. The source has been also detected in the ME instrument and an energy spectrum has been fitted with a power law. A marginal detection in the ME Xenon counters suggests a flattening of the spectrum in the high energy band. These X-ray data extending over three decades in energy are compared with the simultaneous UV and optical observations.

Time Variability of X-Ray Spectra in BL Lac Objects

The X-ray spectra of the BL Lac objects PKS 0548-322 and 3C 66A are presented. It is found that PKS 0548-322 has probably undergone a spectral change since 1977 September, when it was observed by Riegler et al. [1]. 3C 66A presents a strong flux variability, and an X-ray spectral slope increasing when the flux decreases.

The X-ray spectra of the BL Lacertae objects PKS 0548 - 322 and 3C 66A

Einstein Observatory simultaneous imaging proportional counter and monitor proportional counter data are combined in order to derive the energy spectra of the BL Lac objects PKS 0548-322 and 3C 66A between 0.2 and 10 keV. While the latter is found to be variable in both intensity and spectral shape, the former, although constant in the present data, is found to have experienced a spectrum variation in view of results from other experiments. Attention is given to the implications of flux and spectral variability in BL Lac objects for models of X-ray emission mechanisms. It is suggested that the wide spread of the spectral index distribution is due to the detection of the highly variable synchrotron-produced X-rays that are generally undetected in QSOs.

Detection of Lyman continuum absorption in the BL Lacertae object PKS 0735+178

view Abstract Citations (15) References (15) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Detection of Lyman continuum absorption in the BL Lacertae object PKS0735+178. Bregman, J. N. ; Glassgold, A. E. ; Huggins, P. J. Abstract The detection of the Lyman edge in the BL Lac object PKS 0735+178 at the absorption red shift determined by optical measurements leads to a lower limit for the column density of atomic hydrogen, N(H I) not less than 4(17)/sq cm. The Lyman-alpha absorption line appears to have been detected, but only an approximate upper limit can be obtained from the data, of the order of 2(19)/sq cm. This amount of atomic hydrogen is less than that for a line of sight through the disk of a normal spiral galaxy. It is suggested that the absorbing material exists either in the halo of a galaxy or in the tenuous, extended, gaseous disk of a galaxy. Publication: The Astrophysical Journal Pub Date: October 1981 DOI: 10.1086/159253 Bibcode: 1981ApJ...249...13B Keywords: Bl Lacertae Objects; Lyman Spectra; Quasars; Ultraviolet Absorption; Absorption Spectra; Gas Density; Hydrogen Atoms; Iue; Red Shift; Astronomy full text sources ADS | data products SIMBAD (1) NED (1) MAST (1)

Variable X-ray spectra of BL Lacertae objects - HEAO 1 observations of PKS 0548 - 322 and 2A 1219 + 305

X-ray spectra for the BL Lac objects PKS 0548-322 and 2A 1219+305 measured with the HEAO-1 A2 detectors during pointing maneuvers on September 30, 1978 and May 31, 1978 respectively are presented. Both fit single power law components with low energy absorption. For 2A 1219+305, a thermal bremsstrahlung form gives an unacceptable fit. From a comparison with other statistically poorer observations taken at 6 month intervals while the satellite was in its normal scanning mode, it is found that the sources exhibit spectral variability. A summary of measurements of the 5 BL Lac objects detected with the A2 experiment is presented and it is concluded that X-ray spectral changes in this class of source are common. Their general X-ray spectral characteristics distinguish BL Lac objects from other classes of X-ray emitting active galactic nuclei. Analysis of their total spectra indicates that most of the energy is emitted in the 5 to 100 eV band.

Far-red surface photometry of the X-ray emitting BL Lacertae object PKS 0548-322

view Abstract Citations (21) References (35) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Far-red surface photometry of the X-ray emitting BL Lacertae object PKS 0548-322. Weistrop, D. ; Smith, B. A. ; Reitsema, H. J. Abstract Surface photometry of the X-ray emitting BL Lac object PKS 0548-322 at V, 0.75 i m, and 1.01 m is presented. The observations can be reproduced by models consisting of a point source plus elliptical galaxy with de Vaucouleurs intensity distribution. The absolute magnitude Mv = -22.1 mag and spectral flux distribution of the galaxy indicate that it is a giant elliptical. The visible and far-red spectral index of the point source is a = 0.3 + 0.2, where Fv V - a The spectral flux distribution in the radio, optical, and high-energy X-ray regions suggests the radio and optical radiation is due to synchrotron emission, while the high-energy X-ray flux may be due to inverse Compton scattering. Subject headings: BL Lacertae objects - galaxies: nuclei - galaxies: photometry - synchrotron radiation - X-rays: sources Publication: The Astrophysical Journal Pub Date: October 1979 DOI: 10.1086/157410 Bibcode: 1979ApJ...233..504W Keywords: Astronomical Photometry; Bl Lacertae Objects; Synchrotron Radiation; X Ray Sources; Compton Effect; Elliptical Galaxies; Galactic Nuclei; Radiant Flux Density; Spectral Energy Distribution; Astronomy; BL Lacertae Objects:Surface Photometry; BL Lacertae Objects:Synchrotron Radiation; BL Lacertae Objects:X Rays full text sources ADS |

Structure of radio sources with remarkably flat spectra - PKS 0735+178

Three incoherent synchrotron models are used to account for the very flat radio spectrum of the BL Lac object PKS 0735+178. The first interpretation is that the spectrum results from optically-thin synchrotron emission from relativistic electrons with a particular energy distribution. The second posits a single nonuniform, self-absorbed source generated by a wind flowing from a central object. The third suggests that sources with flat spectra are caused by the presence of multiple (three or more) discrete uniform components, and that the magnetic field and relativistic electron distribution for each source is correlated with the size of the individual components. It is proposed that the last model is the most tenable explanation of the phenomenon, and multi-frequency VLBI observations are suggested for the evaluation of the detailed structure of compact radio sources.