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Title: High-energy properties of the high-redshift flat spectrum radio quasar PKS 2149-306

We investigate the γ-ray and X-ray properties of the flat spectrum radio quasar PKS 2149-306 at redshift z = 2.345. A strong γ-ray flare from this source was detected by the Large Area Telescope on board the Fermi Gamma-ray Space Telescope satellite in 2013 January, reaching on January 20 a daily peak flux of (301 ± 36)×10 -8 ph cm -2 s -1 in the 0.1–100 GeV energy range. This flux corresponds to an apparent isotropic luminosity of (1.5±0.2)×1050 erg s -1, comparable to the highest values observed by a blazar so far. During the flare the increase of flux was accompanied by a significant change of the spectral properties. Moreover significant flux variations on a 6-h time- scale were observed, compatible with the light crossing time of the event horizon of the central black hole. The broad band X-ray spectra of PKS 2149-306 observed by Swift-XRT and NuSTAR are well described by a broken power-law model, with a very hard spectrum (Γ 1 ~1) below the break energy, at Ebreak = 2.5–3.0 keV, and Γ 2 ~ 1.4–1.5 above the break energy. The steepening of the spectrum below ~3 keV may indicate that the soft X- ray emission ismore » produced by the low-energy relativistic electrons. This is in agreement with the small variability amplitude and the lack of spectral changes in that part of the X-ray spectrum observed between the two NuSTAR and Swift joint observations. As for the other high-redshift FSRQ detected by both Fermi-LAT and Swift-BAT, the photon index of PKS 2149-306 in hard X-ray is 1.6 or lower and the average γ-ray luminosity higher than 2×1048 erg s -1.« less
Authors:
 [1] ;  [2]
  1. Univ. of Bologna (Italy); Istituto Nazionale di Astrofisica (INAF), Bologna (Italy)
  2. Istituto Nazionale di Astrofisica (INAF), Bologna (Italy)
Publication Date:
Grant/Contract Number:
AC02-76SF00515
Type:
Accepted Manuscript
Journal Name:
Monthly Notices of the Royal Astronomical Society
Additional Journal Information:
Journal Volume: 455; Journal Issue: 2; Journal ID: ISSN 0035-8711
Publisher:
Royal Astronomical Society
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, quasars: individual: PKS 2149−306, quasars: general, gamma-rays: galaxies, gamma-rays: general, X-rays: galaxies
OSTI Identifier:
1354853