Radio-Gamma-ray connection and spectral evolution in 4C +49.22 (S4 1150+49): the Fermi, Swift and Planck view

TL;DR

This study analyzes multi-wavelength observations of the blazar 4C 49.22 during a gamma-ray flare, revealing correlated variability across bands and spectral features typical of BL Lac objects, with models fitting the spectral energy distribution.

Contribution

It provides a comprehensive multi-epoch, multi-wavelength analysis of a gamma-ray flare in 4C 49.22, including spectral modeling with single and two-zone emission models.

Findings

Detection of correlated variability across microwave to X-ray bands during the flare.

Spectral features more typical of BL Lac objects observed in a flat spectrum radio quasar.

Successful modeling of the spectral energy distribution with single and two-zone emission models.

Abstract

The Large Area Telescope on board the Fermi Gamma-ray Space Telescope detected a strong gamma-ray flare on 2011 May 15 from a source identified as 4C 49.22, a flat spectrum radio quasar also known as S4 1150+49. This blazar, characterised by a prominent radio-optical-X-ray jet, was in a low gamma-ray activity state during the first years of Fermi observations. Simultaneous observations during the quiescent, outburst and post-flare gamma-ray states were obtained by Swift, Planck and optical-IR-radio telescopes (INAOE, Catalina CSS, VLBA, Metsahovi). The flare is observed from microwave to X-ray bands with correlated variability and the Fermi, Swift and Planck data for this FSRQ show some features more typical of BL Lac objects, like the synchrotron peak in the optical band that outshines the thermal blue-bump emission, and the X-ray spectral softening. Multi-epoch VLBA observations show the ejection of a new component close in time with the GeV gamma-ray flare. The radio-to-gamma-ray spectral energy distribution is modeled and fitted successfully for the outburst and the post-flare epochs using either a single flaring blob with two emission processes (synchrotron self Compton, and external-radiation Compton), and a two-zone model with SSC-only mechanism.