Multiwavelength behaviour of the blazar OJ 248 from radio to γ-rays★

Abstract

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 GLAST-AGILE Support Program (GASP) of the Whole Earth Blazar Telescope (WEBT), as well as data from the Swift (optical-UV and X-rays) and Fermi (γ-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 γ-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%, but it reaches ∼ 19% during the early stage of the 2012-2013 outburst. A vague correlation of P with brightness is observed. There is no preferred electric vector polarisation 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 × 10 −15 erg cm −2 s −1 and a full width at half-maximum of 2053 km s −1 .

Multiwavelength behaviour of the blazar 3C 279: decade-long study from γ-ray to radio

“…Less pronounced line flux variability in the spectra of several blazars has also been reported by Isler et al (2015). In contrast, stability of emissionline fluxes has been reported in several previous studies: 3C 454.3 (Raiteri et al 2008), PKS 1222+216 (Smith et al 2011), 4C 38.41 (Raiteri et al 2012, OJ 248 (Carnerero et al 2015), and CTA 102 (Larionov et al 2016b).…”

Synchrotron emission from the blazar PG 1553+113. An analysis of its flux and polarization variability

“…Wide rotations of the radio and optical EVPA have been observed in blazars for more than 30 years (e.g. Ledden & Aller 1979;Aller, Hodge & Aller 1981;Kikuchi et al 1988;Marscher et al 2008;Larionov et al 2008;Marscher et al 2010;Raiteri et al 2012;Sasada et al 2012;Raiteri et al 2013;Carnerero et al 2015;Blinov et al 2015;Larionov et al 2016). Sometimes they are coincident with γ-ray flares.…”

Multiwavelength photometric and spectropolarimetric analysis of the FSRQ 3C 279

“…Therefore, the method is most accurate for densely sampled data sets. Some authors use as little as five days as a limit over which to apply the shifting method (Jorstad 2009;Carnerero et al 2015). The data we use is only very densely sampled (∼1 observation/day) in small time bins(∼5-10 days at a time), and the average time in between time bins is three weeks.…”

“…Blinov et al 2015, and references therein), however, this can also be a function of the activity E-mail: victorp@inaoep.mx state of the source (e.g. Itoh et al 2015;Carnerero et al 2015;Bhatta et al 2015, and references therein).…”