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Title: PKS 1954–388: RadioAstron detection on 80,000 km baselines and multiwavelength observations

Here, we present results from a multiwavelength study of the blazar PKS 1954–388 at radio, UV, X-ray, and gamma-ray energies. A RadioAstron observation at 1.66 GHz in June 2012 resulted in the detection of interferometric fringes on baselines of 6.2 Earth-diameters. This suggests a source frame brightness temperature of greater than 2 × 10 12 K, well in excess of both equipartition and inverse Compton limits and implying the existence of Doppler boosting in the core. An 8.4-GHz TANAMI VLBI image, made less than a month after the RadioAstron observations, is consistent with a previously reported superluminal motion for a jet component. Flux density monitoring with the Australia Telescope Compact Array confirms previous evidence for long-term variability that increases with observing frequency. A search for more rapid variability revealed no evidence for significant day-scale flux density variation. The ATCA light-curve reveals a strong radio flare beginning in late 2013, which peaks higher, and earlier, at higher frequencies. Comparison with the Fermi gamma-ray light-curve indicates this followed ~ 9 months after the start of a prolonged gamma-ray high-state—a radio lag comparable to that seen in other blazars. The multiwavelength data are combined to derive a Spectral Energy Distribution, which is fittedmore » by a one-zone synchrotron-self-Compton (SSC) model with the addition of external Compton (EC) emission.« less
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [1] ;  [5] ;  [6] ;  [1] ;  [2] ;  [2] ;  [5] ;  [7] ;  [8] ;  [9] ;  [10] ;  [2] ;  [11] ;  [11] ;  [12] ;  [1] more »;  [13] ;  [14] ;  [1] ;  [15] ;  [16] ;  [1] ;  [2] « less
  1. CSIRO Astronomy and Space Science, Epping, NSW (Australia)
  2. Astro Space Center of Lebedev Physical Institute, Moscow (Russia)
  3. NASA Goddard Space Flight Center (GSFC), Greenbelt, MD (United States); Catholic Univ. of America, Washington, D.C. (United States); Univ. of Maryland Baltimore County (UMBC), Baltimore, MD (United States)
  4. Stanford Univ., Stanford, CA (United States); Chungbuk National Univ., Cheongju (Republic of Korea)
  5. NASA Goddard Space Flight Center (GSFC), Greenbelt, MD (United States); Catholic Univ. of America, Washington, D.C. (United States)
  6. Aalto Univ. Metsahovi Radio Observatory, Kylmala (Finland); Aalto Univ. Dept. of Radio Science and Engineering, Aalto (Finland).
  7. Bundesamt fur Kartographie und Geodasie, Bad Kotzting (Germany)
  8. CSIRO Astronomy and Space Science, ACT (Australia)
  9. CSIRO Astronomy and Space Science, Epping, NSW (Australia); Australian National Univ., Canberra, ACT (Australia)
  10. Univ. Wurzburg, Wurzburg (Germany)
  11. Univ. of Tasmania, Hobart, TAS (Australia)
  12. Radboud Univ. Nijmegen, Nijmegen (The Netherlands)
  13. Australian National Univ., Canberra, ACT (Australia)
  14. Hartebeesthoek Radio Astronomy Observatory, Krugersdorp (South Africa)
  15. ASTRON The Netherlands Institute for Radio Astronomy, Dwingeloo (The Netherlands)
  16. Astro Space Center of Lebedev Physical Institute, Moscow (Russia); National Observatory of Athens, Penteli (Greece); Moscow State Univ., Moscow (Russia)
Publication Date:
Grant/Contract Number:
AC02-76SF00515
Type:
Accepted Manuscript
Journal Name:
Publications of the Astronomical Society of Australia
Additional Journal Information:
Journal Volume: 34; Journal ID: ISSN 1323-3580
Publisher:
CSIRO
Research Org:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; galaxies: active; galaxies: jets; gamma rays: galaxies; ISM: structure; radio continuum: galaxies
OSTI Identifier:
1355732