13 research outputs found
The detection of possible -ray quasi-periodic modulation with 600 days from the blazar S2 0109+22
In this work, we analyzed the long term gamma-ray data by a Fermi Large Area
Telescope (Fermi-LAT) of blazar S2 0109+22, ranging from 2008 to 2023. The
quasi-periodic oscillations (QPOs) of blazars aided in investigating the
physical properties of internal supermassive black holes, the nature of
variability, and the underlying radiation mechanism. We employed four different
methods--Weighted Wavelet Z-transform, Lomb-Scargle periodogram, REDFIT and
phase folded light curve analysis, for searching QPO signals. Our analysis
identified a possible QPO behavior with a periodicity of 600 days in
November 2013 to January 2023 at a significance level of 3.5 . This QPO
signal sustained 9 years, corresponding to 5.6 cycles, which was in good
agreement with the previously observed of periodicity 657 days in radio.
We explained this phenomenon based on the accretion model and the lighthouse
effect, in a binary black hole system.Comment: 12 pages, 8 figures,3 tables,accepted for publication in PAS
The Correlated Multi-color Optical Variations of BL Lac Object S5 0716+714
S5 0716+714 is a well-studied BL Lac object in the sky. Verifying the
existence of correlations among the flux variations in different bands serves
as an important tool to investigate the emission processes. To examine the
possible existence of a lag between variations in different optical bands on
this source, we employ a discrete correlation function (DCF) analysis on the
light curves. In order to obtain statistically meaningful values for the
cross-correlation time lags and their related uncertainties, we perform Monte
Carlo simulations called "flux redistribution/random subset selection"
(FR/RSS). Our analysis confirms that the variations in different optical light
curves are strongly correlated. The time lags show a hint of the variations in
high frequency band leading those in low frequency band of the order of a few
minutes.Comment: 6 pages, 5 figures, 3 tables. This paper has been accepted for
publication in PASA
Search for X-Ray Quasiperiodicity of Six AGNs Using the Gaussian Process Method
The quasiperiodic oscillations (QPOs) found in active galactic nuclei (AGNs) are a very interesting observational phenomenon implying an unknown physical mechanism around supermassive black holes. Several AGNs have been found to have QPO phenomena in the X-ray energy band. Long-duration X-ray observations were collected and reduced for six AGNs with a suspected QPO. The Gaussian process model celerite was used to fit the light curves and to search for the quasiperiodicity behavior. The power spectral density and parameter posterior distributions of each light curve were calculated with the optimal model. Of the six AGNs, only RE J1034+396 was found to have a QPO of about 3600 s. The other five sources do not show QPO modulation behavior. We propose that a hot spot on the accretion disk is a possible physical mechanism resulting in this quasiperiodic behavior of AGNs