Publication Date:
2015-05-10
Description:
We present an analysis of the multiwavelength behaviour of the blazar OJ 248 at z = 0.939 in the period 2006–2013. We use low-energy data (optical, near-infrared, and radio) obtained by 21 observatories participating in the Gamma-Ray Large Area Space Telescope (GLAST)- AGILE Support Program of the Whole Earth Blazar Telescope, as well as data from the Swift (optical–UV and X-rays) and Fermi (-rays) satellites, to study flux and spectral variability and correlations among emissions in different bands. We take into account the effect of absorption by the Damped Lyman α intervening system at z = 0.525. Two major outbursts were observed in 2006–2007 and in 2012–2013 at optical and near-IR wavelengths, while in the high-frequency radio light curves prominent radio outbursts are visible peaking at the end of 2010 and beginning of 2013, revealing a complex radio–optical correlation. Cross-correlation analysis suggests a delay of the optical variations after the -ray ones of about a month, which is a peculiar behaviour in blazars. We also analyse optical polarimetric and spectroscopic data. The average polarization percentage P is less than 3 per cent, but it reaches ~19 per cent during the early stage of the 2012–2013 outburst. A vague correlation of P with brightness is observed. There is no preferred electric vector polarization angle and during the outburst the linear polarization vector shows wide rotations in both directions, suggesting a complex behaviour/structure of the jet and possible turbulence. The analysis of 140 optical spectra acquired at the Steward Observatory reveals a strong Mg ii broad emission line with an essentially stable flux of 6.2 x 10 – 15 erg cm – 2 s – 1 and a full width at half-maximum of 2053 km s – 1 .
Print ISSN:
0035-8711
Electronic ISSN:
1365-2966
Topics:
Physics
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