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The $\gamma$-ray loud narrow line Seyfert 1 ($\gamma$-NLSy1) galaxy PKS1502+036 ($z=0.409$) exhibited its first $\gamma$-ray outburst on 2015 December20. In the energy range of 0.1-300 GeV, the highest flux measured by {\itFermi}-Large Area Telescope is (3.90 $\pm$ 1.52) $\times$ 10$^{-6}$ phcm$^{-2}$ s$^{-1}$, which is the highest $\gamma$-ray flux ever detected fromthis object. The associated spectral shape is soft ($\Gamma_{0.1-300~{\rmGeV}}=2.57\pm0.17$) and this corresponds to an isotropic $\gamma$-rayluminosity of (1.2 $\pm$ 0.6) $\times$ 10$^{48}$ erg s$^{-1}$. We generate thebroadband spectral energy distribution (SED) during the GeV flare and reproduceit using a one zone leptonic emission model. The optical-UV spectrum can beexplained by a combination of synchrotron and the accretion disk emission,whereas, the X-ray to $\gamma$-ray SED can be satisfactorily reproduced byinverse-Compton scattering of thermal photons originated from the torus. Thederived SED parameters hint for the increase in the bulk Lorentz factor as amajor cause of the flare and the location of the emission region is estimatedas outside the broad line region but still inside torus. A comparison of theGeV flaring SED of PKS 1502+036 with that of two other $\gamma$-NLSy1 galaxies,namely, 1H 0323+342 ($z=0.061$) and PMN J0948+0022 ($z=0.585$), and also withFSRQ 3C 279 ($z=0.536$) has led to the conclusion that the GeV flaring SEDs of$\gamma$-NLSy1 galaxies resemble with FSRQs and a major fraction of theirbolometric luminosity is emitted at $\gamma$-ray energies.

The First GeV Outburst of the Radio-loud Narrow Line Seyfert 1 galaxy PKS 1502+036