scholarly journals DISTINGUISHING BETWEEN SPOT AND TORUS MODELS OF HIGH-FREQUENCY QUASIPERIODIC OSCILLATIONS

2014 ◽  
Vol 54 (3) ◽  
pp. 191-196 ◽  
Author(s):  
Vladimír Karas ◽  
Pavel Bakala ◽  
Gabriel Török ◽  
Michal Dovčiak ◽  
Martin Wildner ◽  
...  
Keyword(s):  
High Frequency ◽  
Periodic Oscillation ◽  
Quasi Periodic Oscillation ◽  
X Ray ◽  
Bright Spots ◽  
Power Spectral ◽  
Stable Circular Orbit ◽  
Innermost Stable Circular Orbit ◽  
Competing Models ◽  
Quasiperiodic Oscillations

In the context of high-frequency quasi-periodic oscillation (HF QPOs) we further explore the appearance of an observable signal generated by hot spots moving along quasi-elliptic trajectories close to the innermost stable circular orbit in the Schwarzschild spacetime. The aim of our investigation is to reveal whether observable characteristics of the Fourier power-spectral density can help us to distinguish between the two competing models, namely, the idea of bright spots orbiting on the surface of an accretion torus versus the scenario of intrinsic oscillations of the torus itself. We take the capabilities of the present observatories (represented by the Rossi X-ray Timing Explorer, RXTE) into account, and we also consider the proposed future instruments (represented here by the Large Observatory for X-ray Timing, LOFT).

scholarly journals Reobserving the NLS1 galaxy RE J1034+396 – I. The long-term, recurrent X-ray QPO with a high significance

2020 ◽  
Vol 495 (4) ◽  
pp. 3538-3550 ◽  
Author(s):  
Chichuan Jin ◽  
Chris Done ◽  
Martin Ward
Keyword(s):  
High Frequency ◽  
Active Galactic Nucleus ◽  
Periodic Oscillation ◽  
Interesting Phenomenon ◽  
Quasi Periodic Oscillation ◽  
X Ray ◽  
Black Hole Binary ◽  
High Coherence ◽  
Spectral State

ABSTRACT RE J1034+396 is a narrow-line Seyfert 1 galaxy (NLS1) in which the first significant X-ray quasi-periodic oscillation (QPO) in an active galactic nucleus (AGN) was observed in 2007. We report the detection of this QPO in a recent XMM–Newton observation in 2018 with an even higher significance. The quality factor of this QPO is 20, and its period is 3550 ± 80 s, which is 250 ± 100 s shorter than in 2007. While the QPO’s period has no significant energy dependence, its fractional root mean square variability increases from 4 per cent in 0.3–1 keV to 12 per cent in 1–4 keV bands. An interesting phenomenon is that the QPO in 0.3–1 keV leads that in the 1–4 keV bands by 430 ± 50 s with a high coherence, opposite to the soft X-ray lag reported for the observation in 2007. We speculate that the QPO has an intrinsic hard lag, while the previous reported soft lag is caused by the interference of stochastic variability. This soft X-ray lead in the new data supports the idea that the QPO of RE J1034+396 is a possible AGN counterpart of the 67 Hz high-frequency QPO seen in the black hole binary GRS 1915+105. We also search for QPO harmonics, but do not find any significant signals. Our new data reinforce previous results that the QPO is seen in a specific spectral state, as the only two observations showing no significant QPO signal exhibit an even stronger soft X-ray excess than the other six observations that display the QPO. Therefore, our results imply that the QPO in RE J1034+396 is physically linked to a soft X-ray component.

scholarly journals A Possible Quasi-Periodic Oscillation in the X-ray Emission of 3C 120

Galaxies ◽  
2021 ◽  
Vol 9 (2) ◽  
pp. 20
Author(s):  
Aditi Agarwal ◽  
Priyanka Rani ◽  
Raj Prince ◽  
C. S. Stalin ◽  
G. C. Anupama ◽  
...  
Keyword(s):  
Black Hole ◽  
Kerr Black Hole ◽  
Periodic Oscillation ◽  
Black Hole Mass ◽  
Telescope Array ◽  
Quasi Periodic Oscillation ◽  
X Ray ◽  
Reverberation Mapping ◽  
Power Spectral ◽  
3C 120

We present here the detection of a possible quasi-periodic oscillation (QPO) signal in the X-ray light curve of the active galactic nucleus 3C 120, a broad line radio galaxy at z = 0.033. The hint of a QPO at the 3σ level at 7.1 × 10−6 Hz (∼1.65 days) was detected based on the analysis of X-ray data acquired in the 3–79 keV band by the Nuclear Spectroscopic Telescope Array (NuSTAR). The data, when processed separately in the soft (3–10 keV), hard (10–79 keV) and the total (3–79 keV) bands using four different techniques, namely discrete correlation function, Lomb Scargle periodogram, structure–function, and power spectral density indicated the presence of a QPO. 3C 120 very well fits in the negative correlation in the frequency of the QPO versus the black hole mass (FQPO versus MBH) diagram known for stellar-mass and supermassive black hole sources. Considering the observed signs of QPO to represent the innermost stable orbit of the accretion disk, we found a black hole mass of 1.9×109 M⊙ for a Kerr black hole and 3.04×108 M⊙ for a Schwarzschild black hole. This deduced black hole mass from QPO measurement is a few times larger than the black hole mass obtained from reverberation mapping observations.

scholarly journals Multiwaveband quasi-periodic oscillation in the blazar 3C 454.3

2020 ◽  
Vol 501 (1) ◽  
pp. 50-61
Author(s):  
Arkadipta Sarkar ◽  
Alok C Gupta ◽  
Varsha R Chitnis ◽  
Paul J Wiita
Keyword(s):  
Black Hole ◽  
Light Curve ◽  
Gamma Ray ◽  
Moving Average ◽  
Periodic Oscillation ◽  
Physical Models ◽  
Quasi Periodic Oscillation ◽  
Stable Circular Orbit ◽  
Optical Light Curve ◽  
Innermost Stable Circular Orbit

ABSTRACT We report the detection (>4σ) of a quasi-periodic oscillation (QPO) in the gamma-ray light curve of 3C 454.3 along with a simultaneous marginal QPO detection (>2.4σ) in the optical light curves. Periodic flux modulations were detected in both of these wavebands with a dominant period of ∼47 d. The gamma-ray QPO lasted for over 450 d (from MJD 56800 to 57250), resulting in over nine observed cycles which is among the highest number of periods ever detected in a blazar light curve. The optical light curve was not well sampled for almost half of the gamma-ray QPO span due to the daytime transit of the source, which could explain the lower significance of the optical QPO. Autoregressive Integrated Moving Average (ARIMA) modelling of the light curve revealed a significant, exponentially decaying, trend in the light curve during the QPO, along with the 47 d periodicity. We explore several physical models to explain the origin of this transient quasi-periodic modulation and the overall trend in the observed flux with a month-like period. These scenarios include a binary black hole system, a hotspot orbiting close to the innermost stable circular orbit of the supermassive black hole, and precessing jets. We conclude that the most likely scenario involves a region of enhanced emission moving helically inside a curved jet. The helical motion gives rise to the QPO and the curvature (∼0.05○ pc−1) of the jet is responsible for the observed trend in the light curve.

Discovery of an ∼7 H[CLC]z[/CLC] Quasi-periodic Oscillation in the Low-Luminosity Low-Mass X-Ray Binary 4U 1820−30

1999 ◽  
Vol 512 (1) ◽  
pp. L39-L42 ◽  
Author(s):  
Rudy Wijnands ◽  
Michiel van der Klis ◽  
Erik-Jan Rijkhorst
Keyword(s):  
Periodic Oscillation ◽  
Quasi Periodic Oscillation ◽  
X Ray ◽  
Low Mass

scholarly journals The soft state of the black hole transient source MAXI J1820+070: emission from the edge of the plunge region?

2020 ◽  
Vol 493 (4) ◽  
pp. 5389-5396 ◽  
Author(s):  
A C Fabian ◽  
D J Buisson ◽  
P Kosec ◽  
C S Reynolds ◽  
D R Wilkins ◽  
...  
Keyword(s):  
Black Hole ◽  
Photon Counting ◽  
Black Hole Mass ◽  
X Ray ◽  
Excess Emission ◽  
Transient Source ◽  
Stable Circular Orbit ◽  
Soft State ◽  
Galactic Black Hole ◽  
Innermost Stable Circular Orbit

ABSTRACT The Galactic black hole X-ray binary MAXI J1820+070 had a bright outburst in 2018 when it became the second brightest X-ray source in the sky. It was too bright for X-ray CCD instruments such as XMM–Newton and Chandra, but was well observed by photon-counting instruments such as Neutron star Inner Composition Explorer (NICER) and Nuclear Spectroscopic Telescope Array(NuSTAR). We report here on the discovery of an excess-emission component during the soft state. It is best modelled with a blackbody spectrum in addition to the regular disc emission, modelled as either diskbb or kerrbb. Its temperature varies from about 0.9 to 1.1 keV, which is about 30–80 per cent higher than the inner disc temperature of diskbb. Its flux varies between 4 and 12 per cent of the disc flux. Simulations of magnetized accretion discs have predicted the possibility of excess emission associated with a non-zero torque at the innermost stable circular orbit (ISCO) about the black hole, which, from other NuSTAR studies, lies at about 5 gravitational radii or about 60 km (for a black hole, mass is $8\, {\rm M}_{\odot }$). In this case, the emitting region at the ISCO has a width varying between 1.3 and 4.6 km and would encompass the start of the plunge region where matter begins to fall freely into the black hole.

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