RADIO AND γ-RAY CONSTRAINTS ON THE EMISSION GEOMETRY AND BIRTHPLACE OF PSR J2043+2740

We report on the first year of Fermi gamma-ray observations of pulsed high-energy emission from the old PSR J2043 + 2740. The study of the gamma-ray efficiency of such old pulsars gives us an insight into the evolution of pulsars' ability to emit in gamma rays as they age. The gamma-ray light curve of this pulsar above 0.1 GeV is clearly defined by two sharp peaks, 0.353 +/- 0.035 periods apart. We have combined the gamma-ray profile characteristics of PSR J2043 + 2740 with the geometrical properties of the pulsar's radio emission, derived from radio-polarization data, and constrained the pulsar-beam geometry in the framework of a two-pole caustic (TPC) and an outer gap (OG) model. The ranges of magnetic inclination and viewing angle were determined to be {alpha, zeta} similar to {52 degrees-57 degrees, 61 degrees-68 degrees} for the TPC model, and {alpha, zeta} similar to {62 degrees-73 degrees, 74 degrees-81 degrees} and {alpha, zeta} similar to {72 degrees-83 degrees, 60 degrees-75 degrees} for the OG model. Based on this geometry, we assess possible birth locations for this pulsar and derive a likely proper motion, sufficiently high to be measurable with VLBI. At a characteristic age of 1.2 Myr, PSR J2043 + 2740 is the third oldest of all discovered, non-recycled, gamma-ray pulsars: it is twice as old as the next oldest, PSR J0357 + 32, and younger only than the recently discovered PSR J1836 + 5925 and PSR J2055 + 25, both of which are at least five and ten times less energetic, respectively.