The most powerful flaring activity from the NLSy1 PMN J0948+0022

TL;DR

This paper reports the most powerful gamma-ray flare observed from the NLSy1 galaxy PMN J0948+0022, including multiwavelength data and modeling of its spectral energy distribution during the flare.

Contribution

It presents the first detailed multiwavelength observation of a powerful gamma-ray flare from a narrow-line Seyfert 1 galaxy and models the emission mechanisms involved.

Findings

Gamma-ray peak flux of (155 ± 31) × 10^{-8} ph cm^{-2} s^{-1} on Jan 1, 2013

Record optical to gamma-ray flux during the flare

SED can be modeled with synchrotron and external Compton processes

Abstract

We report on multifrequency observations performed during 2012 December-2013 August of the first narrow-line Seyfert 1 galaxy detected in gamma rays, PMN J0948+0022 ($z$ = 0.5846). A gamma-ray flare was observed by the Large Area Telescope on board Fermi during 2012 December-2013 January, reaching a daily peak flux in the 0.1-100 GeV energy range of (155 $\pm$ 31) $\times$10$^{-8}$ ph cm$^{-2}$ s$^{-1}$ on 2013 January 1, corresponding to an apparent isotropic luminosity of about 1.5$\times$10$^{48}$ erg s$^{-1}$. The gamma-ray flaring period triggered Swift and VERITAS observations in addition to radio and optical monitoring by OVRO, MOJAVE, and CRTS. A strong flare was observed in optical, UV, and X-rays on 2012 December 30, quasi-simultaneously to the gamma-ray flare, reaching a record flux for this source from optical to gamma rays. VERITAS observations at very high energy (E > 100 GeV) during 2013 January 6-17 resulted in an upper limit of F (> 0.2 TeV) < 4.0$\times$10$^{-12}$ ph cm$^{-2}$ s$^{-1}$. We compared the spectral energy distribution (SED) of the flaring state in 2013 January with that of an intermediate state observed in 2011. The two SEDs, modelled as synchrotron emission and an external Compton scattering of seed photons from a dust torus, can be modelled by changing both the electron distribution parameters and the magnetic field.