2002/08/28 by Paolo Padovani, P. Padovani, L. Costamante +7
Physics and Astronomy · #Astrophysics and Cosmic Phenomena #BL Lac object #Blazar #Flux (metallurgy) #Galaxies: Formation, Evolution, Phenomena #Luminosity #Quasar #ROSAT #Radio Astronomy Observations and Technology #Spectral index #Synchrotron #astro-ph
paper · pdf · doi:10.1086/344406
published as Astrophys.J. 581 (2002) 895 · 18 pages, 9 figures. Accepted for publication in The Astrophysical Journal. Postscript file also available at http://www.stsci.edu/~padovani/xrayspectra_papers.html
arxiv created 2002/08/28 · openalex publication_date 2002/12/16 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
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 α ro and α 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 × 10 16 Hz, as also shown by its steep (energy index α 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 (α 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.