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تسجيل مستخدم جديدEvidence for High-Frequency QPOs with a 3:2 Frequency Ratio from a 5000 Solar Mass Black Hole
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Following the discovery of 3:2 resonance quasi-periodic oscillations (QPOs) in M82X-1 (Pasham et al. 2014), we have constructed power density spectra (PDS) of all 15 (sufficiently long) {it XMM-Newton} observations of the ultraluminous X-ray source NGC1313X-1 ($L_{X}$ $approx$ 2$times$10$^{40}$ erg/sec). We detect a strong QPO at a frequency of 0.29$pm$0.01 Hz in data obtained on 2012 December 16. Subsequent searching of all the remaining observations for a 3:2/2:3 frequency pair revealed a feature at 0.46$pm$0.02 Hz on 2003 Dec 13 (frequency ratio of 1.59$pm$0.09). The global significance of the 0.29 Hz feature considering all frequencies between 0.1 and 4 Hz is $>$ 3.5 $sigma$. The significance of the 0.46$pm$0.02 Hz QPO is $>$ 3.5$sigma$ for a search at 2/3 and 3/2 of 0.29 Hz. We also detect lower frequency QPOs (32.9$pm$2.6 and 79.7$pm$1.2 mHz). All the QPOs are super-imposed on a continuum consisting of flat-topped, band-limited noise, breaking into a power-law at a frequency of 16$pm$3 mHz and white noise at $gtrsim$ 0.1 Hz. NGC1313X-1s PDS is analogous to stellar-mass black holes (StMBHs) PDS in the so-called steep power-law state, but with the respective frequencies (both QPOs and break frequencies) scaled down by a factor of $sim$ 1000. Using the inverse mass-to-high-frequency QPO scaling of StMBHs, we estimate NGC1313X-1s black hole mass to be 5000$pm$1300 $M_{odot}$, consistent with an inference from the scaling of the break frequency. However, the implied Eddington ratio, L$_{Edd}$ $>$ 0.03$pm$0.01, is significantly lower compared to StMBHs in the steep power-law state (L$_{Edd}$ $gtrsim$ 0.2).
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The black hole mass and spin estimates assuming various specific models of the 3:2 high frequency quasi-periodic oscillations (HF QPOs) have been carried out in Torok et al. (2005, 2011). Here we briefly summarize some current points. Spectral fittin
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ce between axisymmetric epicyclic oscillation modes of an accretion disc around a Kerr black hole has been considered as a model for the observed high-frequency quasi-periodic oscillations (HF QPOs). Estimates of spin predicted by this model have been derived based on the geodesic approximation of the accreted fluid motion. Here we assume accretion flow described by the model of a pressure-supported torus and carry out related corrections to the mass-spin estimates. We find that for dimensionless black hole spin a<0.9, the resonant eigenfrequencies are very close to those calculated for the geodesic motion. Their values slightly grow with increasing torus thickness. These findings agree well with results of a previous study carried out in the pseudo-Newtonian approximation. The situation becomes different for a>0.9, in which case the resonant eigenfrequencies rapidly decrease as the torus thickness increases. We conclude that the assumed non-geodesic effects shift the lower limit of the spin, implied for the three microquasars by the epicyclic model and independently measured masses, from a~0.7 to a~0.6. Their consideration furthermore confirms compatibility of the model with the rapid spin of GRS 1915+105 and provides highly testable predictions of the QPO frequencies. Individual sources with a moderate spin (a<0.9) should exhibit a smaller spread of the measured 3:2 QPO frequencies than sources with a near-extreme spin (a~1). This should be further examined using the large amount of high-resolution data expected to become available with the next generation of X-ray instruments, such as the proposed Large Observatory for X-ray Timing (LOFT).
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