NuSTAR and XMM-Newton observations of the binary 4FGL J1405.1-6119. A $\gamma$-ray emitting microquasar?

Abstract

4FGL J1405.1-6119 is a high-mass $\gamma$-ray emitting binary that has been studied at several wavelengths. The nature of this type of binary is still under debate, with three possible scenarios usually invoked to explain the origin of the $\gamma$-ray emission: collisions between the winds of a rapidly rotating neutron star and its companion, collisions between the winds of two massive stars, and non-thermal emission from the jet of a microquasar. We analyze two pairs of simultaneous NuSTAR and XMM-Newton observations to investigate the origin of the radio, X-ray, and $\gamma$-ray emissions. We extracted light curves between 0.5-78 keV from two different epochs, named Epoch 1 and Epoch 2, respectively. We propose a scenario to explain the observations involving a parabolic, mildly relativistic, lepto-hadronic jet. This jet has a compact acceleration region that injects a hard spectrum of relativistic particles. The dominant non-thermal emission processes include synchrotron radiation of electrons, inverse Compton scattering of photons from the stellar radiation field, and the decay of neutral pions resulting from inelastic proton-proton collisions within the bulk matter of the jet. These estimates are in accordance with the values of a super-Eddington lepto-hadronic jet scenario. The compact object could be either a black hole or a neutron star with a low magnetic field. Most of the X-ray emission from the disk could be absorbed by the dense wind that is ejected from the same disk. We conclude that it is possible that the binary 4FGL J1405.1-6119 could be a supercritical microquasar like SS433.