Two active states of the narrow-line gamma-ray-loud AGN GB 1310+487

Abstract

Context. Previously unremarkable, the extragalactic radio source GB 1310+487 showed a γ-ray flare on 2009 November 18, reaching a daily flux of ∼10 −6 photons cm −2 s −1 at energies E > 100 MeV and became one of the brightest GeV sources for about two weeks. Its optical spectrum shows strong forbidden-line emission while lacking broad permitted lines, which is not typical for a blazar. Instead, the spectrum resembles those of narrow emission-line galaxies. Aims. We investigate changes in the object's radio-to-GeV spectral energy distribution (SED) during and after the prominent γ-ray flare with the aim of determining the nature of the object and of constraining the origin of the variable high-energy emission. Methods. The data collected by the Fermi and AGILE satellites at γ-ray energies; Swift at X-ray and ultraviolet (UV); the Kanata, NOT, and Keck telescopes at optical; OAGH and WISE at infrared (IR); and IRAM 30 m, OVRO 40 m, Effelsberg 100 m, RATAN-600, and VLBA at radio are analyzed together to trace the SED evolution on timescales of months. Results. The γ-ray/radio-loud narrow-line active galactic nucleus (AGN) is located at redshift z = 0.638. It shines through an unrelated foreground galaxy at z = 0.500. The AGN light is probably amplified by gravitational lensing. The AGN SED shows a two-humped structure typical of blazars and γ-ray-loud narrow-line Seyfert 1 galaxies, with the high-energy (inverse-Compton) emission dominating by more than an order of magnitude over the low-energy (synchrotron) emission during γ-ray flares. The difference between the two SED humps is smaller during the low-activity state. Fermi observations reveal a strong correlation between the γ-ray flux and spectral index, with the hardest spectrum observed during the brightest γ-ray state. The γ-ray flares occurred before and during a slow rising trend in the radio, but no direct association between γ-ray and radio flares could be established. Conclusions. If the γ-ray flux is a mixture of synchrotron self-Compton and external Compton emission, the observed GeV spectral variability may result from varying relative contributions of these two emission components. This explanation fits the observed changes in the overall IR to γ-ray SED.

THE THIRD CATALOG OF ACTIVE GALACTIC NUCLEI DETECTED BY THEFERMILARGE AREA TELESCOPE

“…The SSRQ 4C+04.40 is part of a double association (with the FSRQ MG1 J120448+0408) of 3FGL J1205.4+0412. GB 1310+487 is a gamma-ray/radio-loud narrow-line AGN at z = 0.638, showing a gamma-ray flare in November 2009 and located behind the disk of an unrelated emission-line galaxy at z = 0.500 (Sokolovsky et al 2014).…”

VaST: A variability search toolkit

“…The development of VaST was mostly driven by the author's data processing needs. These evolved from a piggyback variability search in targeted CCD observations of known variable objects (Antipin et al 2005) to variability search using digitized photographic plates (Kolesnikova et al 2008, Sokolovsky et al 2014c), Swift/U-VOT data analysis (Sokolovsky 2009, Gupta et al 2012, visualization of CoRoT lightcurves (Sokolovsky et al 2010), photometry of individual active galactic nuclei (Schinzel et al 2011, Sokolovsky et al 2014d) and wide-field search for bright optical transients (Sokolovsky et al 2014b) that resulted in the discovery of Nova Sagittarii 2012 #1 (=V5589 Sgr; Korotkiy et al 2012. VaST was applied for variability search in CCD data by others including Majaess et al (2013), Lapukhin et al (2014), Kryachko et al (2015).…”

Radiation Mechanisms and Physical Properties of GeV $\gamma $-Ray Source GB 1310+487

“…The observations of radio source GB 1310+487 by the FermiLarge Area Telescope (LAT; Atwood et al 2009) have shown the intense activity in the GeV γ-rays band and the twohumped structure in its spectral energy distribution (SED; Sokolovsky et al 2014), which are the typical features of blazars. Blazars are a peculiar class of active galactic nuclei (AGNs) having relativistic jets aligned close to the line of sight.…”

“…Three different states of GB 1310+487 were presented and preliminarily discussed by Sokolovsky et al (2014). ~´--in one day lasting about three weeks.…”

“…During Flare 1 and Flare 2, the Compton dominance factors (the ratio of the high-energy hump to synchrotron hump flux, q c ) are similar to most cases of FSRQs with q 10 c > . With the simultaneous Fermi-LAT and WISEobservations, Sokolovsky et al (2014) got the q c = 12 for Flare 2 (q 10 c  and q 10 c …”