A Study of the Extragalactic Gamma-ray Binary LMC P3 using XMM-Newton, NuSTAR and Swift

We report on XMM-Newton, Nuclear Spectroscopic Telescope Array (NuSTAR), Neil Gehrels Swift Observatory (Swift) X-ray Telescope (XRT), and Fermi Large Area Telescope (LAT) observations of LMC P3, the first known High-mass Gamma-ray binary outside of the Milky Way. LMC P3 is four times more luminous than similar HMGBs in the GeV bands is an order of magnitude more luminous in the X-ray and radio bands. The XMM-Newton observations, which were performed at X-ray maximum, X-ray minimum and the inferior conjunction of the 10.301±0.002 day orbit, show that the spectral shape hardens with increasing X-ray flux. We find no evidence of a spectral break in the broadband 3-25 keV XMM-Newton and NuSTAR spectrum. Using the cross-correlation function, we find that the Swift XRT light curve leads the Fermi LAT light curve by a phase of 0.39. The maximum 0.5-9 keV flux was found to be at orbital phase 0.25. This is consistent with a recent orbital solution derived using the Southern African Large Telescope (SALT), where the inferior and superior conjunctions were found to be at phases 0.24 and 0.98, respectively. We compare our observations with archival XMM-Newton and Chandra data and discuss different mechanisms that might drive the particle acceleration in this extreme system.