The discovery of \gamma -ray emission from radio-loud narrow-line Seyfert 1 ( NLSy1 ) galaxies has questioned the need for large black hole masses ( \ga 10 ^ { 8 } M _ { \odot } ) to launch relativistic jets .
We present near-infrared data of the \gamma -ray-emitting NLSy1 FBQS J1644 + 2619 that were collected using the camera CIRCE ( Canarias InfraRed Camera Experiment ) at the 10.4-m Gran Telescopio Canarias to investigate the structural properties of its host galaxy and to infer the black hole mass .
The 2D surface brightness profile is modelled by the combination of a nuclear and a bulge component with a Sérsic profile with index n = 3.7 , indicative of an elliptical galaxy .
The structural parameters of the host are consistent with the correlations of effective radius and surface brightness against absolute magnitude measured for elliptical galaxies .
From the bulge luminosity , we estimated a black hole mass of ( 2.1 \pm 0.2 ) \times 10 ^ { 8 } M _ { \odot } , consistent with the values characterizing radio-loud active galactic nuclei .