A New 626 s periodic X-ray source in the direction of the Galactic center
Université de Toulouse, UPS, CESR, 9 Avenue du Colonel Roche, 31028
Toulouse Cedex 9,
2 Department of Physics and Astronomy, University of Leicester, University Road, Leicester, LE1 7RH, UK
3 Astronomy Division, Department of Physical Sciences, PO Box 3000, 90014 University of Oulu, Finland
4 Department of Astrophysics, University of Oxford, Keble Road, Oxford, OX1 3RH, UK
Received: 15 January 2010
Accepted: 19 August 2010
Aims. Here we report the detection of a 626 s periodic modulation from the X-ray source 2XMM J174016.0−290337 located in the direction of the Galactic center.
Methods. We present temporal and spectral analyses of archival XMM-Newton data and photometry of archived near-infrared data in order to investigate the nature of this source.
Results. We find that the X-ray light curve shows a strong modulation at 626 ± 2 s with a confidence level >99.9% and a pulsed fraction of 54%. Spectral fitting demonstrates that the spectrum is consistent with an absorbed power law. No significant spectral variability was observed over the 626 s period. We have investigated the possibility that the 626 s period is orbital in nature (either that of an ultra-compact X-ray binary or an AM CVn) or related to the spin of a compact object (either an accretion powered pulsar or an intermediate polar).
Conclusions. The X-ray properties of the source and the photometry of the candidate near-infrared counterparts are consistent with an accreting neutron star X-ray binary on the near-side of the Galactic bulge, where the 626 s period is most likely indicative of the pulsar spin period. However, we cannot rule out an ultra-compact X-ray binary or an intermediate polar with the data at hand. In the former case, if the 626 s modulation is the orbital period of an X-ray binary, it would be the shortest period system known. In the latter case, the modulation would be the spin period of a magnetic white dwarf. However, we find no evidence for absorption dips over the 626 s period, a low temperature black body spectral component, or Fe Kα emission lines. These features are commonly observed in intermediate polars, making 2XMM J174016.0−290337 a rather unusual member of this class if confirmed. Based on the slow period and the photometry of the near-infrared counterparts, we instead suggest that 2XMM J174016.0−290337 could be a new addition to the emerging class of symbiotic X-ray binaries.
Key words: accretion, accretion disks / binaries: general / pulsars: individual: 2XMM J174016.0 − 290337 / X-rays: binaries
© ESO, 2010