X-ray Spectral Survey of WGACAT Quasars, II: Optical and Radio Properties of Quasars with Low Energy X-ray Cut-offs

We have selected quasars with X-ray colors suggestive of a low energy cut-off, from the ROSAT PSPC pointed archive. We examine the radio and optical properties of these 13 quasars. Five out of the seven quasars with good optical spectra show associated optical absorption lines, with two having high delta-v candidate systems. Two other cut-off quasars show reddening associated with the quasar. We conclude that absorption is highly likely to be the cause of the X-ray cut-offs, and that the absorbing material associated with the quasars, not intervening along the line-of-sight. The suggestion that Gigahertz Peaked Sources are associated with X-ray cut-offs remains unclear with this expanded sample.Comment: 17 pages, LaTeX, including 2 Tables and 1 figure. Ap.J. in pres

150 keV Emission from PKS2149-306 with BeppoSAX

A BeppoSAX observation of the z=2.34 quasar PKS2149-306 produced a strong signal in the high energy PDS instrument up to a maximum observed energy of nearly 50 keV, 150 keV in the quasar frame. The Beppo-SAX spectrum spans almost 3 decades (0.3-150 keV, quasar frame) and shows an extremely hard (alpha=0.4+/-0.05) X-ray spectrum above 3 keV (comparable to the X-ray background slope), and either a softer (alpha=1.0(+0.6, -0.3)) low energy component, or an ionized absorber at zero redshift. No evidence is seen of an Fe-K emission line (EW<167 eV at 6.5 keV quasar frame) or a Compton hump (R<0.3). A bremsstrahlung fit gives kT(rest)=46(+32, -16) keV, similar to the X-ray background value, and a high energy cut-off power law requires E(cut)>120 keV (quasar frame). The SED of PKS 2149-306 shows two peaks at ~ 10(12+/-0.5}Hz and \~10(21+/-1.0)Hz (~ 0.3 mm and ~ 4 MeV), strongly resembling a low energy cutoff BL~Lac object (LBL). The ratio of the two peaks shows an extreme Compton dominance (C_D=1.4+/- 0.4), as in flat spectrum radio quasars (FSRQs). The presence of an additional `optical/UV big bump' component may provide photons that cool the jet, suppressing the radio emission.Comment: 18 pages, 3 figures. LaTeX, with AAS .sty file aasms4. Revised to correct a stupid mistake affecting the Fe-K EW. The results now agree with the ASCA data from Yaqoob et a

Radio Frequency Spectra of 388 Bright 74 MHz Sources

As a service to the community, we have compiled radio frequency spectra from the literature for all sources within the VLA Low Frequency Sky Survey (VLSS) that are brighter than 15 Jy at 74 MHz. Over 160 references were used to maximize the amount of spectral data used in the compilation of the spectra, while also taking care to determine the corrections needed to put the flux densities from all reference on the same absolute flux density scale. With the new VLSS data, we are able to vastly improve upon previous efforts to compile spectra of bright radio sources to frequencies below 100 MHz because (1) the VLSS flux densities are more reliable than those from some previous low frequency surveys and (2) the VLSS covers a much larger area of the sky (declination >-30 deg.) than many other low frequency surveys (e.g., the 8C survey). In this paper, we discuss how the spectra were constructed and how parameters quantifying the shapes of the spectra were derived. Both the spectra and the shape parameters are made available here to assist in the calibration of observations made with current and future low frequency radio facilities.Comment: Accepted to ApJ

Multiwavelength observations of PKS 2255-282

During high radio frequency active galactic nucleus monitoring, we observed a major millimeter wave outburst from PKS 2255-282 in 1997 and initiated a campaign for multifrequency radio monitoring and VLBI imaging of the source. In 1998 January the EGRET instrument on board the Compton Gamma Ray Observatory detected a bright high-energy γ-ray outburst from its direction. Thus, we had the unique opportunity to monitor the source in detail at various radio frequencies already before the detection of the γ-ray outburst. We also initiated multiwavelength follow-up observations. In this paper we present multiwavelength data for PKS 2255-282 before and after the γ-ray outburst. Further, based on the observations, we estimate some physical parameters for this source and discuss the various emission mechanisms possibly involved during this outburst.M. Tornikoski, S. J. Tingay, A. Mücke, A. Chen, V. Connaughton, D. L. Jauncey, M. Johnston-Hollitt, J. Kemp, E. A. King, P. McGee, F. Rantakyrö, D. Rayner, O. Reimer, and A. K. Tzioumi