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Title: The nature of transition blazars

Blazars are classically divided into the BL Lacertae (BLL) and flat-spectrum radio quasar (FSRQ) subclasses, corresponding to radiatively inefficient and efficient accretion regimes, respectively, largely based on the equivalent width (EW) of their optical broad emission lines (BELs). However, EW-based classification criteria are not physically motivated, and a few blazars have previously transitioned' from one subclass to the other. We present the first systematic search for these transition blazars in a sample of 602 unique pairs of repeat spectra of 354 blazars in the Sloan Digital Sky Survey, finding six clear cases. These transition blazars have bolometric Eddington ratios of ∼0.3 and low-frequency synchrotron peaks, and are thus FSRQ-like. We show that the strong EW variability (up to an unprecedented factor of >60) is due to swamping of the BELs from variability in jet continuum emission, which is stronger in amplitude and shorter in timescale than typical blazars. Although these transition blazars appear to switch between FSRQ and BLL according to the phenomenologically based EW scheme, we show that they are most likely rare cases of FSRQs with radiatively efficient accretion flows and especially strongly beamed jets. These results have implications for the decrease of the apparent BLL population atmore » high redshifts, and may lend credence to claims of a negative BLL redshift evolution.« less
Authors:
;  [1] ;  [2] ; ;  [3] ;  [4] ;  [5]
  1. Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195 (United States)
  2. Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109 (United States)
  3. Department of Astronomy and Astrophysics, 525 Davey Lab, The Pennsylvania State University, University Park, PA 16802 (United States)
  4. Department of Physics, University of Washington, Seattle, WA 98195-1560 (United States)
  5. Department of Physics and Astronomy 3905, University of Wyoming, 1000 East University, Laramie, WY 82071 (United States)
Publication Date:
OSTI Identifier:
22370090
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 797; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; BEAMS; BL LACERTAE OBJECTS; BOLOMETERS; CLASSIFICATION; EMISSION; GALAXIES; QUASARS; RED SHIFT; SPECTRA; STAR EVOLUTION; SYNCHROTRON RADIATION