BeppoSAXObservations of Synchrotron X‐Ray Emission from Radio Quasars

Abstract

We present new BeppoSAX Low Energy Concentrator Spectrometer (LECS), Medium Energy Concentrator Spectrometer (MECS), and Phoswich Detector System (PDS) observations of four flat-spectrum radio quasars (FSRQs) having effective spectral indices ro and ox typical of high-energy peaked BL Lac objects. Our sources have X-ray-to-radio flux ratios on average $70 times larger than '' classical '' FSRQs and lie at the extreme end of the FSRQ X-ray-to-radio flux ratio distribution. The collected data cover the energy range 0.1-10 keV (observer's frame), reaching $100 keV for one object. The BeppoSAX band in one of our sources, RGB J1629+4008, is dominated by synchrotron emission peaking at $2 Â 10 16 Hz, as also shown by its steep (energy index X $ 1:5) spectrum. This makes this object the first known FSRQ whose X-ray emission is not due to inverse Compton radiation. Two other sources display a flat BeppoSAX spectrum ( X $ 0:7), with weak indications of steepening at low X-ray energies. The combination of BeppoSAX and ROSAT observations, (nonsimultaneous) multifrequency data, and a synchrotron inverse Compton model suggests synchrotron peak frequencies %10 15 Hz, although a better coverage of their spectral energy distributions is needed to provide firmer values. If confirmed, these values would be typical of '' intermediate '' BL Lac objects for which the synchrotron and inverse Compton components overlap in the BeppoSAX band. Our sources, although firmly in the radio-loud regime, have powers more typical of high-energy peaked BL Lac objects than of FSRQs, and indeed their radio powers put them near the low-luminosity end of the FSRQ luminosity function. We discuss this in terms of an anticorrelation between synchrotron peak frequency and total power, based on physical arguments, and also as possibly due to a selection effect.

BeppoSAXView of Radio‐loud Active Galactic Nuclei

“…A possible counterexample is RGB J1629+4008, which shows a very soft (À $ 2:6) spectrum. Padovani et al (2002) explained the X-ray spectrum of this object as being dominated by synchrotron radiation, suggesting the existence of FSRQs sources with properties similar to highenergy-peaked BL Lacertae (HBL) objects. On the other hand, the optical classification as a narrow-line Seyfert 1 galaxy (NLS1) on the basis of its H line width (Grupe et al 2004) could explain the steep soft X-ray spectrum as being due to thermal emission, possibly from an accretion disk.…”

The Deep X‐Ray Radio Blazar Survey. III. Radio Number Counts, Evolutionary Properties, and Luminosity Function of Blazars

“…The sources of a given survey occupy a region of the flux-flux plane, whose bottom left corner is shown in the figure. The long-dashed line in the figure (X-ray to radio flux ratio f X /f r ¼ 10 À11:5 ergs cm À2 s À1 Jy À1 or rX $ 0:78) divides high-energy peaked from low-energy peaked blazars (both BL Lac objects and FSRQs; see Padovani et al 2002Padovani et al , 2003 Figure 3 clearly illustrates the limitations of surveys with double radio/X-ray flux limits. A survey whose limits fall quite far from both dotted lines will not provide a complete picture of the blazar population.…”

Properties of flat-spectrum radio-loud narrow-line Seyfert 1 galaxies

“…J0814+5609, J1047+4725, J1548+3511, J1629+4007) with fairly good sampling because of previous specific interest. For example, J1629+4007 was long observed because it was thought to be an example of a high-frequency peaked FSRQ (Padovani et al 2002, Falcone et al 2004. It is evident from the SED (Fig.…”