Fermi-LAT and multi-wavelength observations of the flaring activity of PKS 1510-089 between September 2008 and June 2009
Abstract
We report on the MW observations of PKS 1510-089 (z=0.361) during a period of about 11 months, when the source exhibited a relevant evolution of its broad-band spectral energy distribution (SED), characterized by a complex variability both at Optical/UV and gamma-ray energies, with time scales detected down to the level of 6/12 hours. The brightest gamma-ray isotropic luminosity, recorded on 2009-03-26, was of about 2 x 1048 erg s-1 . The spectrum, in the Fermi-LAT energy range, shows a mild curvature well described by a log-parabolic law, and can be understood as signature of the Klein-Nishina effect. The gamma-ray flux has a complex correlation with the other wavelengths. There is no correlation at all with the X-ray band, a week correlation with the UV, and a relevant correlation with the optical flux. Moreover, the gamma-ray flux seems to lead the optical one of about 13 days. Using UV data we estimated a black hole mass of about 5.6 x 108 solar masses, and an accretion rate of about 0.5 solar masses/year. Although the power in the thermal and non-thermal outputs is smaller if compared to the very luminous and distant flat spectrum radio quasars (FSQR), PKS 1510-089 exhibits a quite large Compton dominance and prominent a big blue bump (BBB) signature, as observed in the most powerful gamma-ray quasars. This objects could be a representative of an aged FSQR, hence the analysis here presented is relevant in order to understand the evolution of these objects. We remark the puzzling feature of the BBB UV shape. Indeed, we note that the BBB was still prominent during the historical maximum optical state in May 2009, although the optical/UV spectral index was softer compared to that in quiescent state. This seems to be not fully compatible with a pure BBB emission, with the BBB supposed to be completely dominated by the synchrotron emission during the highest optical state. We model the broadband spectrum assuming a leptonic scenario in which the high energy bump is dominated by the inverse Compton scattering of soft photons produced by the accretion disk and scattered toward the jet by the broad line region. The resulting model-dependent jet energetic content is compatible with the jet being powered by the accretion disk, with a total efficiency within the Kerr black hole limit. The analysis here presented, shows the great relevance of the MW monitoring of blazars, despite of the gamma-ray triggering activity. Indeed, only comparing the flaring and quiescent states, and understanding the evolution of the physical parameters as a function of the flaring activity, it is possible to discriminate among the possible physical scenarios.
- Publication:
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38th COSPAR Scientific Assembly
- Pub Date:
- 2010
- Bibcode:
- 2010cosp...38.2244T