* Astronomy

Title: X-ray follow-ups of the mysterious source XSSJ12270-4859: a LMXB with high energy Gamma ray FERMI/LAT association
Authors: D. de Martino, T. Belloni, M. Falanga, A. Papitto, S. Motta, A. Pellizzoni, Y. Evangelista, G. Piano, N. Masetti, J.-M. Bonnet-Bidaud, M. Mouchet, K. Mukai, A. Possenti

XSSJ1227.0-4859 is a peculiar hard X-ray source recently positionally associated to the Fermi/LAT source 1FGLJ1227.9-4852/2FGLJ1227.7-4853. Multi-wavelength observations have added information on this source indicating a low-luminosity low mass X-ray binary (LMXB) but its nature is still unclear. To progress in our understanding, we present new X-ray data from a monitoring campaign performed in 2011 with the XMM-Newton, RXTE and Swift satellites and combine them with new Gamma-ray data from the Fermi and AGILE satellites. We complement the study with simultaneous near-UV photometry from XMM-Newton and with previous UV/optical and near-IR data. The X-ray history of XSSJ1227.0-4859 over 7yr shows a persistent and rather stable low luminosity (~6x10^33 d_{1 kpc}^2 erg/s) source, with flares and dips being a peculiar and permanent characteristics. The associated Fermi/LAT source 2FGLJ1227.7-4853 is also stable over an overlapping period of 4.7 yr. Searches for fast pulsations down to msec give upper limits to pulse fractional amplitudes of 15-25% that do not rule out a fast spinning pulsar. The combined UV/optical/near-IR spectrum reveals a hot component at ~13 kK and a cool one at ~4.6 kK. The latter would suggest a late type K2-K5 companion star, a distance range of1.4--3.6kpc and an orbital period of 7--9 h. A near-UV variability (>6 h) also suggests a longer orbital period than previously estimated. The analysis shows that the X-ray and UV/optical/near-IR emissions are more compatible with an accretion powered compact object rather than a rotational powered pulsar. The X-ray to UV bolometric luminosity ratio could be consistent with a binary hosting a neutron star, but the uncertainties in the radio data may also allow a LMXB black hole with a compact jet. In this case it would be the first associated with a high energy Gamma-ray source.

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