A ~4.6 h quasi-periodic oscillation in the BL Lacertae
PKS 2155-304?

Lachowicz, Pawel; Gupta, Alok C.; Gaur, Haritma; Wiita, Paul J.

doi:10.1051/0004-6361/200913161

Cited by 97 publications

(102 citation statements)

References 44 publications

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“…6)? And indeed in most blazars QPOs have not been detected, but in few QPO was found (Lachowicz et al 2009). This issue need further in- vestigation.…”

Section: Discussion and Concluding Remarksmentioning

confidence: 99%

Periodic mass loss from viscous accretion flows around black holes

Das

Chattopadhyay

Nandi

et al. 2014

Monthly Notices of the Royal Astronomical Society

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We investigate the behaviour of low angular momentum viscous accretion flows around black holes using Smooth Particle Hydrodynamics (SPH) method. Earlier, it has been observed that in a significant part of the energy and angular momentum parameter space, rotating transonic accretion flow undergoes shock transition before entering in to the black hole and a part of the post-shock matter is ejected as bipolar outflows, which are supposed to be the precursor of relativistic jets. In this work, we simulate accretion flows having injection parameters from the inviscid shock parameter space, and study the response of viscosity on them. With the increase of viscosity, shock becomes time dependent and starts to oscillate when the viscosity parameter crosses its critical value. As a result, the in falling matter inside the post-shock region exhibits quasi-periodic variations and causes periodic ejection of matter from the inner disc as outflows. In addition, the same hot and dense post-shock matter emits high energy radiation and the emanating photon flux also modulates quasi-periodically. Assuming a ten solar mass black hole, the corresponding power density spectrum peaks at the fundamental frequency of few Hz followed by multiple harmonics. This feature is very common in several outbursting black hole candidates. We discuss the implications of such periodic variations.

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“…6)? And indeed in most blazars QPOs have not been detected, but in few QPO was found (Lachowicz et al 2009). This issue need further in- vestigation.…”

Section: Discussion and Concluding Remarksmentioning

confidence: 99%

Periodic mass loss from viscous accretion flows around black holes

Das

Chattopadhyay

Nandi

et al. 2014

Monthly Notices of the Royal Astronomical Society

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“…Another case of QPO reported in the literature is the blazar PKS 2155-304. Lachowicz et al (2009) reported a 4.6 h QPO in the 0.3−10 keV data (from ObsID 158961401). We have analyzed 8 observations of this source, including this one; none showed indications of a QPO.…”

Section: Qpo Detectionmentioning

confidence: 99%

X-ray variability of 104 active galactic nuclei

González‐Martín

Vaughan

2012

A&A

198

204

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Context. Active galactic nuclei (AGN), powered by accretion onto supermassive black holes (SMBHs), are thought to be scaled up versions of Galactic black hole X-ray binaries (BH-XRBs). In the past few years evidence of such correspondence include similarities in the broadband shape of the X-ray variability power spectra, with characteristic bend times-scales scaling with mass. Aims. The aim of this project is to characterize the X-ray temporal properties of a sample of AGN to study the connection among different classes of AGN and their connection with BH-XRBs. Methods. We have performed a uniform analysis of the power spectrum densities (PSDs) of 104 nearby (z < 0.4) AGN using 209 XMM-Newton/pn observations. These PSDs span 3 decades in temporal frequencies, ranging from minutes to days. The PSDs have been estimated in three energy bands: 0.2−10 (total), 0.2−2 (soft), and 2−10 keV (hard). The sample comprises 61 Type-1 AGN, 21 Type-2 AGN, 15 NLSy1, and 7 BLLACS. We have fitted each PSD to two models: (1) a single power-law model and (2) a bending power-law model. Results. Among the entire sample, 72% show significant variability in at least one of the three bands tested. A high percentage of low-luminosity AGN do not show any significant variability (86% of LINERs). The PSD of the majority of the variable AGN was well described by a simple power-law with a mean index of α = 2.01 ± 0.01. In 15 sources we found that the bending power law model was preferred with a mean slope of α = 3.08 ± 0.04 and a mean bend frequency of ν b 2 × 10 −4 Hz. Only KUG 1031+398 (RE J1034+396) shows evidence for quasi-periodic oscillations. The "fundamental plane" relating variability timescale, black hole mass, and luminosity is demonstrated using the new X-ray timing results presented here together with a compilation of the previously detected timescales from the literature. Conclusions. Both quantitative (i.e. scaling with BH mass) and qualitative (overall PSD shapes) found in this sample of AGN are in agreement with the expectations for the SMBHs and BH-XRBs being the same phenomenon scaled-up with the size of the BH. The steep PSD slopes above the high frequency bend bear a closer resemblance to those of the "soft/thermal dominated" BH-XRB states than other states.

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“…Groth 1975;Deeter & Boynton 1982;Israel & Stella 1996;Vaughan 2005). When determining the significance of possible periodicities in the PSD, the red-noise has to be accounted for in order not to severely overestimate the significance of identified frequencies (Lachowicz et al 2009). In this paper, we account for the red-noise properties when performing a periodogram analysis.…”

Section: Introductionmentioning

confidence: 99%

Quasi-periodic pulsations in solar flares: new clues from theFermi Gamma-Ray Burst Monitor

Gruber

Lachowicz

Bissaldi

et al. 2011

A&A

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Aims. In the past four decades, it has been observed that solar flares display quasi-periodic pulsations (QPPs) from the lowest, i.e. radio, to the highest, i.e. gamma-ray, frequencies in the electromagnetic spectrum. It remains unclear which mechanism creates these QPPs. In this paper, we analyze four bright solar flares that display compelling signatures of quasi-periodic behavior and were observed with the Gamma-Ray Burst Monitor (GBM) onboard the Fermi satellite. Because GBM covers over three decades in energy (8 keV to 40 MeV), it is regarded as a key instrument in our attempt to understand the physical processes that drive solar flares. Methods. We tested for periodicity in the time series of the solar flares observed by GBM by applying a classical periodogram analysis. However, in contrast to previous authors, we did not detrend the raw light curve before creating the power spectral density (PSD) spectrum. To assess the significance of the frequencies, we used a method that is commonly applied to X-ray binaries and Seyfert galaxies. This technique takes into account the underlying continuum of the PSD, which for all of these sources has a P( f ) ∼ f −α dependence and is typically labeled red-noise. Results. We checked the reliability of this technique by applying it to observations of a solar flare that had been observed by the Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI ). These data contain, besides any potential periodicity from the Sun, a 4 s rotational period caused by the rotation of the spacecraft about its axis. We were unable to identify any intrinsic solar quasi-periodic pulsation but we did manage to reproduce the instrumental periodicity. Moreover, with the method adopted here, we do not detect significant QPPs in the four bright solar flares observed by GBM. We stress that for this kind of analyses it is of utmost importance to account appropriately for the red-noise component in the PSD of these astrophysical sources.

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A ~4.6 h quasi-periodic oscillation in the BL Lacertae PKS 2155-304?

Cited by 97 publications

References 44 publications

Periodic mass loss from viscous accretion flows around black holes

Periodic mass loss from viscous accretion flows around black holes

X-ray variability of 104 active galactic nuclei

Quasi-periodic pulsations in solar flares: new clues from theFermi Gamma-Ray Burst Monitor

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