We report on the identification of a new \gamma -ray-emitting narrow-line Seyfert 1 ( NLS1 ) galaxy , SDSS J211852.96 - 073227.5 ( hereinafter J2118 - 0732 ) .
The galaxy , at a redshift of 0.26 , is associated with a radio source of flat/inverted spectrum at high radio frequencies .
The analysis of its optical spectrum obtained in the Sloan Digital Sky Survey ( SDSS ) revealed a small linewidth of the broad component of the H \beta line ( full width at half-maximum = 1585 km s ^ { -1 } ) , making it a radio-loud NLS1 galaxy – an intriguing class of active galactic nuclei with exceptional multiwavelength properties .
A new \gamma -ray source centred at J2118 - 0732 was sporadically detected during 2009–2013 in form of flares by the Fermi -LAT .
Our XMM-Newton observations revealed a flat X-ray spectrum described by a simple power law , and a flux variation by a factor of \sim 2.5 in five months .
The source also shows intraday variability in the infrared band .
Its broad-band spectral energy distribution can be modelled by emission from a simple one-zone leptonic jet model , and the flux drop from infrared to X-rays in five months can be explained by changes of the jet parameters , though the exact values may be subject to relatively large uncertainties .
With the NLS1-blazar composite nucleus , the clear detection of the host galaxy , and the synchronous variations in the multiwavelength fluxes , J2118 - 0732 provides a new perspective on the formation and evolution of relativistic jets under the regime of relatively small black hole masses and high accretion rates .