The X-ray Outburst of H1743–322: High-Frequency QPOs with a 3:2 Frequency Ratio

The 2003 X-ray outburst of the candidate black-hole binary, H1743–322, was investigated in frequent pointed observations (2–250 keV) with the Rossi X-ray Timing Explorer. We consider one particular program of 130 observations. We organized these data into 111 time intervals and conducted a search for the presence of high-frequency quasiperiodic oscillations (HFQPOs) in the range 50–2000 Hz. Only a single observation (2003 June 13) yielded a detection above 4σ; the central frequency of 239± 4 Hz is consistent with the 240 Hz QPO reported for this source on 2003 May 28 (Homan et al. 2003). We next grouped the observations in several different ways and computed the average power-density spectra (PDS) in a search for further evidence of HFQPOs. This effort yielded two significant results for those observations defined by the presence of low-frequency QPOs (0.1-20 Hz) and an absence of “band-limited” power continua: (1) The 9 time intervals with the highest X-ray flux yielded an average PDS with a QPO at 166± 5 Hz. (4.1σ; 3–35 keV); and (2) a second group with lower X-ray flux (24 time intervals) produced an average PDS with a QPO at 242± 3 Hz (6.0σ; 7–35 keV). The ratio of these two frequencies is 1.46 ± 0.05. This finding is consistent with results obtained for three other black hole systems that exhibit commensurate HFQPOs in a 3:2 ratio. Furthermore, the occurrence of H1743-322’s slower HFQPO at times of higher X-ray luminosity closely resembles the behavior of XTE J1550-564 and GRO J1655-40. We discuss our results in terms of a resonance model that invokes frequencies set by general relativity for orbital motions near a black-hole event horizon. Subject headings: black hole physics — general relativity — stars: individual (H1743–322) — stars: oscillations — X-rays: stars 1