Exploring the hadronic origin of LHAASO J1908+0621

Abstract

Recent observations by the Large High Altitude Air Shower Observatory (LHAASO) have paved the way for the observational detection of PeVatrons in the Milky Way Galaxy, thus revolutionizing the field of $\gamma$-ray astrophysics. In this paper, we study one such detected source, LHAASO J1908+0621, and explore the origin of multi-TeV $\gamma$-ray emission from this source. A middle-aged radio supernova remnant SNR G40.5-0.5 and a GeV pulsar PSR J1907+0602 are co-spatial with LHAASO J1908+0621. Dense molecular clouds are also found to be associated with SNR G40.5-0.5. We explain the multi-TeV $\gamma$-ray emission observed from the direction of LHAASO J1908+0621, by the hadronic interaction between accelerated protons that escaped from the SNR shock front and cold protons present inside the dense molecular clouds, and the leptonic emission from the pulsar wind nebula (PWN) associated with the pulsar J1907+0602. Moreover, we explain lower energy $\gamma$-ray emission by considering the radiative cooling of the electrons that escaped from SNR G40.5-0.5. Finally, the combined lepto-hadronic scenario was used to explain the multi-wavelength spectral energy distribution (SED) of LHAASO J1908+0621. Although not yet significant, an ICECUBE hotspot of neutrino emission is spatially associated with LHAASO J1908+0621, indicating a possible hadronic contribution. In this paper, we show that if a hadronic component is present in LHAASO J1908+0621, then the second generation ICECUBE observatory will detect neutrino from this source.