Discovery of an extreme MeV blazar with the Swift burst alert telescope

R. M. Sambruna, C. B. Markwardt, R. F. Mushotzky, J. Tueller, R. Hartman, W. N. Brandt, D. P. Schneider, A. Falcone, A. Cucchiara, M. F. Aller, H. D. Aller, I. Torniainen, F. Tavecchio, L. Maraschi, M. Gliozzi, T. Takahashi

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The Burst Alert Telescope (BAT) on board Swift detected bright emission from 15-195 keV from the source SWIFT J0746.3+2548 (J0746 in the following), identified with the optically faint (R ∼ 19), z = 2.979 quasar SDSS J074625.87+244901.2. Here we present Swift and multiwavelength observations of this source. The X-ray emission from J0746 is variable on timescales of hours to weeks in 0.5-8 keV and of a few months in 15-195 keV, but there is no accompanying spectral variability in the 0.5-8 keV band. There is a suggestion that the BAT spectrum, initially very hard (photon index Γ ∼ 0.7 ), steepened to Γ ∼ 1.3 in a few months, together with a decrease of the 15-195 keV flux by a factor ∼2. The 0.5-8 keV continuum is well described by a power law with Γ ∼ 1.3 and spectral flattening below 1 keV. The latter can be described with a column density in excess of the Galactic value with intrinsic column density NHz ∼ 1022 cm-2, or with a flatter power law, implying a sharp (ΔΓ ≳1) break across 16 keV in the quasar's rest frame. The spectral energy distribution of J0746 is double-humped, with the first component peaking at IR wavelengths and the second component at MeV energies. These properties suggest that J0746 is a blazar with high gamma-ray luminosity and low peak energy (MeV), stretching the blazar sequence to an extreme.

Original languageEnglish (US)
Pages (from-to)23-35
Number of pages13
JournalAstrophysical Journal
Issue numberI
StatePublished - Jul 20 2006

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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