X‐Ray Sources with Periodic Variability in a DeepChandraImage of the Galactic Center

Abstract

We report the discovery of eight X-ray sources with periodic variability in 487 ks of observations of the Galactic center with Chandra. The sources are identified from a sample of 285 objects detected with 100-4200 net counts. Their periods range from 300 s to 4.5 hr, with amplitudes between 40% and 70% rms. They have luminosities of (1-5) × 1032 ergs s-1 (2-8 keV at 8 kpc). The spectra of seven of the eight sources are consistent with Γ ≈ 0 power laws absorbed by gas and dust with a column density equal to or higher than that toward the Galactic center (6 × 1022 cm-2). Four of these sources also exhibit emission lines near 6.7 keV from He-like Fe, with equivalent widths of 600-1000 eV. These properties are consistent with both magnetically accreting cataclysmic variables and wind-accreting neutron stars in high-mass X-ray binaries. The eighth source has an absorbing column of 5 × 1021 cm-2 that places it in the foreground. Its spectrum is consistent with either a Γ = 1.4 power law or kT = 25 keV bremsstrahlung emission. Its period-folded flux profile clearly identifies it as an eclipsing polar. We place an approximate upper limit of i' > 23 mag on the optical counterpart to this source using a 5 minute exposure obtained with the Magellan Instant Camera on the Clay telescope (Magellan II) at Las Campanas.