A New 626 s periodic X-ray source in the direction of the Galactic center

Abstract

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.

Optical and X-Ray Studies of 10 X-Ray-Selected Cataclysmic Binaries

“…A Monte Carlo test gives a discriminatory power (Thorstensen & Freed 1985) of around 0.98 for our time series, so the period determination is reasonably secure. The results presented here, especially the short orbital period, rule out the hypothesis of Farrell et al (2010) that AX J1740.2−2903 is symbiotic binary. Masetti et al (2009) identified the counterpart using a Swift follow-up observation reported by Landi et al (2008) and obtained a spectrum.…”

The XMM-Newton serendipitous survey

“…7. (Vogel et al 2007); g) highly variable AND periodic object, likely to be a cataclysmic or X-ray binary (Farrell et al 2008) -the binning results in poor sampling of the intrinsic periodic behaviour; h) source showing clear variability but not flagged as variable in the catalogue (the probability of variability falls below the threshold of 10 −5 ). These last two cases highlight the sensitivity of the variability characterisation on the time bin size.…”

Unveiling the nature of INTEGRAL objects through optical spectroscopy

“…Using the same approach we applied in our previous Papers I-VIII, we considered the IBIS surveys of Bird et al ( , 2010 and Krivonos et al (2010), and we selected unidentified or unclassified hard X-ray sources that contain, within the IBIS 90% confidence level error box, a single bright soft X-ray object detected either in the ROSAT all-sky surveys (Voges et al 1999(Voges et al , 2000, or with Swift/XRT (from Page et al 2007;Lutovinov et al 2010;Rodriguez et al 2010a,b;Landi et al 2010a,b,c;2011;Krivonos et al 2011, as well as from the XRT archive 4 ), or in the Slew Survey (Saxton et al 2008) or Serendipitous Source Catalog (Watson et al 2009) of XMM-Newton, or with pointed Chandra (Fiocchi et al 2010) and XMM-Newton (Halpern & Gotthelf 2010;Farrell et al 2010) observations. This approach was proven by Stephen et al (2006) to be very effective in associating, with a high degree of probability, IBIS sources with a softer X-ray counterpart and in turn drastically reducing their positional error circles to better than a few arcsec in radius, making the search area smaller by a factor of ∼10 4 .…”

“…The main spectral diagnostic lines of these objects, as well as the main astrophysical parameters which can be inferred from the available optical and X-ray observational data, are given in Table 6. The X-ray luminosities listed in this table for the various objects were computed using the fluxes reported in Voges et al (1999) Farrell et al (2010) and Malizia et al (2010).…”