Detection of quasi‐periodic oscillations in γ ‐ray and optical light curves of the BL Lac 4FGL J0650 .7 + 2503

2021 ◽  
Author(s):  
Yunlu Gong ◽  
Tingfeng Yi ◽  
Xing Yang ◽  
Xin Chang
Keyword(s):  
Light Curves ◽  
Periodic Oscillations ◽  
Bl Lac ◽  
Γ Ray

Quasi-Periodic Oscillations in Dwarf Novae

1979 ◽  
Vol 46 ◽  
pp. 77-88
Author(s):  
Edward L. Robinson
Keyword(s):  
Binary Systems ◽  
Outer Edge ◽  
Light Curves ◽  
Close Binary ◽  
Bright Spot ◽  
Dwarf Novae ◽  
Periodic Oscillations ◽  
High Frequencies ◽  
Short Period ◽  
Typical Time

Three distinct kinds of rapid variations have been detected in the light curves of dwarf novae: rapid flickering, short period coherent oscillations, and quasi-periodic oscillations. The rapid flickering is seen in the light curves of most, if not all, dwarf novae, and is especially apparent during minimum light between eruptions. The flickering has a typical time scale of a few minutes or less and a typical amplitude of about .1 mag. The flickering is completely random and unpredictable; the power spectrum of flickering shows only a slow decrease from low to high frequencies. The observations of U Gem by Warner and Nather (1971) showed conclusively that most of the flickering is produced by variations in the luminosity of the bright spot near the outer edge of the accretion disk around the white dwarf in these close binary systems.

Multi-wavelength search for quasi-periodic oscillations in BL Lac 4FGL J0112.1+2245

2022 ◽  
Vol 367 (1) ◽  
Author(s):  
Y. L. Gong ◽  
T. F. Yi ◽  
X. Yang ◽  
H. Z. Li ◽  
X. Chang ◽  
...  
Keyword(s):  
Periodic Oscillations ◽  
Bl Lac ◽  
Multi Wavelength

scholarly journals Gamma-ray counterparts of 2WHSP high-synchrotron-peaked BL Lac objects as possible signatures of ultra-high-energy cosmic ray emission

2020 ◽  
Vol 497 (2) ◽  
pp. 2455-2468
Author(s):  
Michael W Toomey ◽  
Foteini Oikonomou ◽  
Kohta Murase
Keyword(s):  
Energy Range ◽  
Gamma Ray ◽  
Cosmic Ray ◽  
High Energy ◽  
Potential Candidate ◽  
Ultra High Energy ◽  
Bl Lac Objects ◽  
Cherenkov Telescopes ◽  
Bl Lac ◽  
Γ Ray

ABSTRACT We present a search for high-energy γ-ray emission from 566 Active Galactic Nuclei at redshift z > 0.2, from the 2WHSP catalogue of high-synchrotron peaked BL Lac objects with 8 yr of Fermi-LAT data. We focus on a redshift range where electromagnetic cascade emission induced by ultra-high-energy cosmic rays can be distinguished from leptonic emission based on the spectral properties of the sources. Our analysis leads to the detection of 160 sources above ≈5σ (TS ≥25) in the 1–300 GeV energy range. By discriminating significant sources based on their γ-ray fluxes, variability properties, and photon index in the Fermi-LAT energy range, and modelling the expected hadronic signal in the TeV regime, we select a list of promising sources as potential candidate ultra-high-energy cosmic ray emitters for follow-up observations by Imaging Atmospheric Cherenkov Telescopes.

scholarly journals Broad-band study of high-synchrotron-peaked BL Lac object 1ES 1218+304

2020 ◽  
Vol 496 (4) ◽  
pp. 5518-5527
Author(s):  
N Sahakyan
Keyword(s):  
Energy Distribution ◽  
Electron Energy ◽  
Power Law ◽  
Spectral Energy Distribution ◽  
Broad Band ◽  
Energy Distributions ◽  
X Ray ◽  
Bl Lac ◽  
Photon Index ◽  
Γ Ray

ABSTRACT The origin of the multiwavelength emission from the high-synchrotron-peaked BL Lac 1ES 1218+304 is studied using the data from SwiftUVOT/XRT, NuSTAR, and Fermi-LAT. A detailed temporal and spectral analysis of the data observed during 2008–2020 in the  γ-ray (>100 MeV), X-ray (0.3–70 keV), and optical/UV bands is performed. The γ-ray spectrum is hard with a photon index of 1.71 ± 0.02 above 100 MeV. The SwiftUVOT/XRT data show a flux increase in the UV/optical and X-ray bands; the highest 0.3–3 keV X-ray flux was (1.13 ± 0.02) × 10−10 erg cm−2 s−1. In the 0.3–10 keV range, the averaged X-ray photon index is >2.0 which softens to 2.56 ± 0.028 in the 3–50 keV band. However, in some periods, the X-ray photon index became extremely hard (<1.8), indicating that the peak of the synchrotron component was above 1 keV, and so 1ES 1218+304 behaved like an extreme synchrotron BL Lac. The hardest X-ray photon index of 1ES 1218+304 was 1.60 ± 0.05 on MJD 58489. The time-averaged multiwavelength spectral energy distribution is modelled within a one-zone synchrotron self-Compton leptonic model using a broken power law and power law with an exponential cutoff electron energy distributions. The data are well explained when the electron energy distribution is $E_{\rm e}^{-2.1}$ extending up to γbr/cut ≃ (1.7 − 4.3) × 105, and the magnetic field is weak (B ∼ 1.5 × 10−2 G). By solving the kinetic equation for electron evolution in the emitting region, the obtained electron energy distributions are discussed considering particle injection, cooling, and escape.

scholarly journals Optical Short-Term Variability in the X-Ray-Selected BL Lac Object IE 0317+186 and the Radio-Selected BL Lac Object ON231

1989 ◽  
Vol 134 ◽  
pp. 108-109
Author(s):  
F.Z. Cheng ◽  
J.F. Lu ◽  
G.Z. Xie ◽  
K.H. Li ◽  
Z.L. Li ◽  
...  
Keyword(s):  
Light Curves ◽  
Optical Monitoring ◽  
National Observatory ◽  
Image System ◽  
Short Term ◽  
Bl Lac Objects ◽  
X Ray ◽  
Bl Lac ◽  
Ccd Image ◽  
Short Term Variability

In order to compare X-ray-selected BL Lac objects with radio-selected BL Lac objects, we have carried out optical monitoring of some of these objects for about three years at Yunnan Observatory in China. All observations have been made with a CCD-image system at the f/13.3 Cassegrain focus of the 102-cm RCC telescope. The CCD-image system was developed by Ye et al. in Kitt Peak National Observatory of USA (Ye et al., 1985). The filters used were as follows: B-GG385(2mm)+BG12(1mm)+BG18(1mm), V-GG495(2mm)+BG18(2mm). After observing many times, more complete light curves have obtained for the X-ray-selected BL Lac object IE 0317+186 and the radio-selected BL Lac object ON 231, respectively(Fig 1 and Fig 2). Fig 1 shows that IE 0317+186 has a characteristic timescale of about 4.5hours with an amplitudes of ΔV≃0.65 mag. Fig 2 indicates that a timescale of short-term variability in ON 231 is about 70 min with an amplitudes of ΔB≃0.8 mag.

scholarly journals An intermittent extreme BL Lac: MWL study of 1ES 2344+514 in an enhanced state

2020 ◽  
Vol 496 (3) ◽  
pp. 3912-3928
Author(s):  
MAGIC Collaboration: V A Acciari ◽  
S Ansoldi ◽  
L A Antonelli ◽  
A Arbet Engels ◽  
A Babić ◽  
...  
Keyword(s):  
Crab Nebula ◽  
Spectral Energy Distribution ◽  
Broad Band ◽  
High Energy ◽  
Spectral Energy ◽  
Bl Lac ◽  
Very High Energy ◽  
Γ Ray ◽  
Using Data ◽  
The Crab Nebula

ABSTRACT Extreme high-frequency BL Lacs (EHBL) feature their synchrotron peak of the broad-band spectral energy distribution (SED) at νs ≥ 1017 Hz. The BL Lac object 1ES 2344+514 was included in the EHBL family because of its impressive shift of the synchrotron peak in 1996. During the following years, the source appeared to be in a low state without showing any extreme behaviours. In 2016 August, 1ES 2344+514 was detected with the ground-based γ-ray telescope FACT during a high γ-ray state, triggering multiwavelength (MWL) observations. We studied the MWL light curves of 1ES 2344+514 during the 2016 flaring state, using data from radio to very-high-energy (VHE) γ-rays taken with OVRO, KAIT, KVA, NOT, some telescopes of the GASP-WEBT collaboration at the Teide, Crimean, and St. Petersburg observatories, Swift-UVOT, Swift-XRT, Fermi-LAT, FACT, and MAGIC. With simultaneous observations of the flare, we built the broad-band SED and studied it in the framework of a leptonic and a hadronic model. The VHE γ-ray observations show a flux level of 55 per cent of the Crab Nebula flux above 300 GeV, similar to the historical maximum of 1995. The combination of MAGIC and Fermi-LAT spectra provides an unprecedented characterization of the inverse-Compton peak for this object during a flaring episode. The Γ index of the intrinsic spectrum in the VHE γ-ray band is 2.04 ± 0.12stat ± 0.15sys. We find the source in an extreme state with a shift of the position of the synchrotron peak to frequencies above or equal to 1018 Hz.

scholarly journals A non-linear mathematical model for the X-ray variability classes of the microquasar GRS 1915+105 – I. Quiescent, spiking states, and quasi-periodic oscillations

2020 ◽  
Vol 495 (1) ◽  
pp. 1110-1121 ◽  
Author(s):  
E Massaro ◽  
F Capitanio ◽  
M Feroci ◽  
T Mineo ◽  
A Ardito ◽  
...  
Keyword(s):  
Differential Equations ◽  
Equilibrium Points ◽  
Low Frequency ◽  
Input Function ◽  
Light Curves ◽  
Stable Region ◽  
Periodic Oscillations ◽  
X Ray ◽  
Unstable Solutions ◽  
Unified View

ABSTRACT The microquasar GRS 1915+105 is known to exhibit a very variable X-ray emission on different time-scales and patterns. We propose a system of two ordinary differential equations, adapted from the Hindmarsh–Rose model, with two dynamical variables x(t), y(t), and an input constant parameter J0, to which we added a random white noise, whose solutions for the x(t) variable reproduce consistently the X-ray light curves of several variability classes as well as the development of low-frequency quasi-periodic oscillations (QPO). We show that changing only the value of J0, the system moves from stable to unstable solutions and the resulting light curves reproduce those of the quiescent classes like ϕ and χ, the δ class and the spiking ρ class. Moreover, we found that increasing the values of J0 the system induces high-frequency oscillations that evolve into QPO when it moves into another stable region. This system of differential equations gives then a unified view of the variability of GRS 1915+105 in term of transitions between stable and unstable states driven by a single input function J0. We also present the results of a stability analysis of the equilibrium points and some considerations on the existence of periodic solutions.

scholarly journals Radio-to-γ-Ray, Broadband Variability Study of the Classical BL Lac Object PKS 0735+178

Galaxies ◽  
2016 ◽  
Vol 4 (4) ◽  
pp. 42 ◽  
Author(s):  
Arti Goyal ◽  
Łukasz Stawarz ◽  
Michal Ostrowski ◽  
Valeri Larionov
Keyword(s):  
Bl Lac ◽  
Γ Ray ◽  
Variability Study

scholarly journals Wave modes from the magnetorotational instability in accretion discs

2012 ◽  
Vol 8 (S290) ◽  
pp. 201-202
Author(s):  
Giuseppe Di Bernardo ◽  
Ulf Torkelsson
Keyword(s):  
Three Dimensional ◽  
Accretion Disc ◽  
Light Curves ◽  
Accretion Discs ◽  
Magnetorotational Instability ◽  
Periodic Oscillations ◽  
X Ray ◽  
Black Hole Binaries ◽  
Angular Momentum Transport ◽  
Magnetohydrodynamic Simulations

AbstractThe magnetorotational instability (MRI) is widely believed to be the source of turbulence in accretion discs. This turbulence is responsible for the anomalous angular momentum transport in accretion discs. The turbulence will affect other aspects of the dynamics of the disc as well, and we will concentrate on two such issues: a) what kind of oscillations can be excited by the turbulence itself, and b) how the turbulence is interacting with modes that have been excited by some other agent. This is of interest in understanding the quasi-periodic oscillations (QPOs) that have been observed in the X-ray light curves of accreting neutron star and black hole binaries. We carry out local three dimensional (3D) magnetohydrodynamic simulations of a keplerian differentially rotating accretion disc, using a shearing box configuration taking in account the effects of the vertical stratification.

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