2012ApJ...748...86O

The transient 500 s X-ray pulsar MAXI J1409-619 was discovered by the slit cameras aboard Monitor of All-sky X-ray Image (MAXI) on 2010 October 17, and soon after accurately localized by Swift. We found that the source position was serendipitously observed in 2000 during BeppoSAX observations of the Galactic plane. Two sources are clearly detected in the Medium-Energy Concentrator Spectrometer (MECS): one is consistent with the position of IGR J14043-6148 and the other one with that of MAXI J1409-619. We report on the analysis of this archival BeppoSAX/MECS observation integrated with newly analyzed observation from ASCA and a set of high-energy observations obtained from the offset fields of the BeppoSAX/PDS instrument. For the ON-source observation, the 1.8-100 keV spectrum is fit by an absorbed power law with a photon index Γ = 0.87^+0.29_–0.19, corresponding to 2-10 and 15-100 keV unabsorbed fluxes of 2.7x10^–12 and 4x10^–11 erg/cm2/s, respectively, and a 2-10 keV luminosity of 7x10³⁴ erg/s for a 15 kpc distance. For a PDS offset field observation, performed about one year later and showing a 15-100 keV flux of 7x10^–11 erg/cm2/s, we clearly pinpoint three spectral absorption features at 44, 73, and 128 keV, resolved both in the spectral fit and in the Crab ratio. We interpret these not harmonically spaced features as due to cyclotron resonances. The fundamental energy of 44±3 keV corresponds to a magnetic field strength at the neutron star surface of 3.8 x10¹²(1 + z) G, where z is the gravitational redshift. We discuss the nature of the source in the light of its possible counterpart.