Astronomy and Astrophysics, volume 550A, 89-89 (2013/2-1)
X-ray follow-ups of XSS J12270-4859: a low-mass X-ray binary with gamma-ray Fermi-LAT association.
DE MARTINO D., BELLONI T., FALANGA M., PAPITTO A., MOTTA S., PELLIZZONI A., EVANGELISTA Y., PIANO G., MASETTI N., BONNET-BIDAUD J.-M., MOUCHET M., MUKAI K. and POSSENTI A.
Abstract (from CDS):
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. We analysed the temporal characteristics in the X-rays, near-UV, and gamma rays and studied the broad-band spectral energy distribution from radio to gamma rays. The X-ray history of XSSJ1227 over 7yr shows a persistent and rather stable low-luminosity (6x1033d1kpc2erg/s) source, with flares and dips being peculiar and permanent characteristics. The associated Fermi-LAT source 2FGLJ1227.7-4853 is also stable over an overlapping period of 4.7yr. Searches for X-ray 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 ∼13kK and a cool one at ∼4.6kK. The latter would suggest a late-type K2-K5 companion star, a distance range of 1.4-3.6kpc, and an orbital period of 7-9h. A near-UV variability (>6h) 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 than with 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 an LMXB black hole with a compact jet. In this case, it would be the first associated with a high-energy gamma-ray source.
accretion, accretion disks - X-rays: binaries - gamma rays: stars - binaries: close
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