MAGIC gamma-ray and multi-frequency observations of flat spectrum radio quasar PKS 1510−089 in early 2012

Abstract

Aims. Amongst more than fifty blazars detected in very high energy (VHE, E > 100 GeV) γ rays, only three belong to the subclass of flat spectrum radio quasars (FSRQs). The detection of FSRQs in the VHE range is challenging, mainly because of their soft spectra in the GeV-TeV regime. MAGIC observed PKS 1510−089 (z = 0.36) starting 2012 February 3 until April 3 during a high activity state in the high energy (HE, E > 100 MeV) γ-ray band observed by AGILE and Fermi. MAGIC observations result in the detection of a source with significance of 6.0 standard deviations (σ). We study the multi-frequency behaviour of the source at the epoch of MAGIC observation, collecting quasi-simultaneous data at radio and optical (GASP-WEBT and F-Gamma collaborations, REM, Steward, Perkins, Liverpool, OVRO, and VLBA telescopes), X-ray (Swift satellite), and HE γ-ray frequencies. Methods. We study the VHE γ-ray emission, together with the multi-frequency light curves, 43 GHz radio maps, and spectral energy distribution (SED) of the source. The quasi-simultaneous multi-frequency SED from the millimetre radio band to VHE γ rays is modelled with a one-zone inverse Compton model. We study two different origins of the seed photons for the inverse Compton scattering, namely the infrared torus and a slow sheath surrounding the jet around the Very Long Baseline Array (VLBA) core. Results. We find that the VHE γ-ray emission detected from PKS 1510−089 in 2012 February-April agrees with the previous VHE observations of the source from 2009 March-April. We find no statistically significant variability during the MAGIC observations on daily, weekly, or monthly time scales, while the other two known VHE FSRQs (3C 279 and PKS 1222+216) have shown daily scale to sub-hour variability. The γ-ray SED combining AGILE, Fermi and MAGIC data joins smoothly and shows no hint of a break. The multi-frequency light curves suggest a common origin for the millimetre radio and HE γ-ray emission, and the HE γ-ray flaring starts when the new component is ejected from the 43 GHz VLBA core and the studied SED models fit the data well. However, the fast HE γ-ray variability requires that within the modelled large emitting region, more compact regions must exist. We suggest that these observed signatures would be most naturally explained by a turbulent plasma flowing at a relativistic speed down the jet and crossing a standing conical shock.

Flat Spectrum Radio Quasars through the MAGIC glasses

“…[4] and February-April 2012 by MAGIC [5]. The flux and spectra of the two observations agree within the errors.…”

“…The MWL SED of FSRQs typically peaks at lower energies [1], making the detection of such targets challenging in VHE. Up to now, only 5 FSRQs have been detected in the VHE band: 3C 279 [2,3], PKS 1510-089 [4,5], PKS 1222+216 [6], S3 0218+357 [7] and PKS 1441+25 [9,10].…”

Kinematics of Parsec-scale Jets of Gamma-Ray Blazars at 43 GHz within the VLBA-BU-BLAZAR Program

“…The propagation of knot B2 down the jet was analyzed in Marscher et al (2010) in connection with the strong γ-ray outburst in 2009. The appearance of B4 in the jet coincides with another high γ-ray state of the quasar in the autumn of 2011 (Orienti et al 2013), while the ejection of B5 occurred simultaneously with a TeV flare detected by MAGIC (Aleksić et al 2014b). Knots B4 and B5 correspond to K11 and K12 discussed in Aleksić et al (2014b), respectively.…”

“…The appearance of B4 in the jet coincides with another high γ-ray state of the quasar in the autumn of 2011 (Orienti et al 2013), while the ejection of B5 occurred simultaneously with a TeV flare detected by MAGIC (Aleksić et al 2014b). Knots B4 and B5 correspond to K11 and K12 discussed in Aleksić et al (2014b), respectively. Although the β app of B4 is slightly different from that of K11, the latter is caused by the deceleration of B4 at later epochs.…”

“…Multiwavelength (MW) campaigns of simultaneous monitoring from the γ-ray to the radio bands have become routine (e.g., Abdo et al 2010a;Raiteri et al 2011;Hayashida et al 2012;Larionov et al 2013;Aleksić et al 2014bAleksić et al , 2015Wehrle et al 2016). In addition, regular imaging observations of AGN jets at 15GHz (the MOJAVE program 9 ) and monitoring of γ-ray blazars at 43GHz (the VLBA-BU-BLAZAR program 10 ) with the VLBA have been established to probe the jets of blazars.…”