On the reliability of microvariability tests in quasars

Abstract

Microvariations probe the physics and internal structure of quasars. Unpredictability and small flux variations make this phenomenon elusive and difficult to detect. Variance based probes such as the C and F tests, or a combination of both, are popular methods to compare the light-curves of the quasar and a comparison star. Recently, detection claims in some studies depend on the agreement of the results of the C and F tests, or of two instances of the F-test, in rejecting the non-variation null hypothesis. However, the C-test is a non-reliable statistical procedure, the F-test is not robust, and the combination of tests with concurrent results is anything but a straightforward methodology. A priori Power Analysis calculations and post hoc analysis of Monte-Carlo simulations show excellent agreement for the Analysis of Variance test to detect microvariations, as well as the limitations of the F-test. Additionally, combined tests yield correlated probabilities that make the assessment of statistical significance unworkable. However, it is possible to include data from several field stars to enhance the power in a single F-test, increasing the reliability of the statistical analysis. This would be the preferred methodology when several comparison stars are available. An example using two stars and the enhanced F-test is presented. These results show the importance of using adequate methodologies, and avoid inappropriate procedures that can jeopardize microvariability detections. Power analysis and Monte-Carlo simulations are useful tools for research planning, as they can reveal the robustness and reliability of different research approaches.

arXiv commentThe Astronomical Journal, in press. 13 figures. Please request more readable version from the author ([email protected])

References in corpus (13)

• Are the Variations in Quasar Optical Flux Driven by Thermal Fluctuations?
• Testing tests on AGN microvariability
• A comparison of period finding algorithms
• A novel variability-based method for quasar selection: evidence for a rest frame ~54 day characteristic timescale
• Quasi-simultaneous two band optical variability of the blazars 1ES 1959+650 and 1ES 2344+514
• Intranight optical variability of γ-ray loud Narrow Line Seyfert 1 galaxies
• On the reliability of microvariability tests in quasars
• Optical variability of PKS 0736+017
• Improved characterisation of intra-night optical variability of prominent AGN classes
• Optical microvariability properties of BALQSOs
• Multiband Comparative Study of Optical Microvariability in RL vs. RQ Quasars
• Intranight Optical Variability of Radio-Quiet Weak Emission Line Quasars-II
• Intranight optical variability of radio-loud broad absorption line quasars

Cited by in corpus (36)

• On the reliability of microvariability tests in quasars
• Nature of Intra-night Optical Variability of BL Lacertae
• Long-term optical polarization variability and multiwavelength analysis of Blazar Mrk 421
• Multi-wavelength Intra-day Variability and Quasi-periodic Oscillation in Blazars
• Testing microvariability in quasar differential light curves using several field stars
• Intra-night optical variability characteristics of different classes of narrow line Seyfert 1 galaxies
• Optical Flux and Spectral Variability of the TeV blazar PG 1553+113
• Simulated Performance of Timescale Metrics for Aperiodic Light Curves
• The June 2016 Optical and Gamma-Ray Outburst and Optical Micro-Variability of the Blazar 3C454.3
• Intra-night optical flux and polarization variability of BL~Lacertae during its 2020 $-$ 2021 high state
• Intra-Night Optical Variability Monitoring of Fermi Blazars: First Results from 1.3 m J C Bhattacharya Telescope
• Characterization of Variability in Blazar Light curves
• Multiband optical flux density and polarization microvariability study of optically bright blazars
• Optical Variability of the TeV Blazar 1ES 0806+524 on Diverse Timescales
• Comparative intra-night optical variability of X-ray and $\gamma$-ray detected narrow-line Seyfert 1 galaxies
• Optical Variability of Three Extreme TeV Blazars
• Detecting microvariability in type 2 quasars using enhanced F-test
• Characterizing the optical nature of the blazar S5 1803+784 during its 2020 flare
• Optical flux and spectral variability of BL Lacertae during its historical high outburst in 2020
• Microvariability in AGNs: study of different statistical methods II. Light curves from simulated images
• Multi-wavelength Variation Phenomena of PKS 0735+178 on Diverse Timescale
• Optical variability of a newly discovered blazar sample from the BZCAT Catalog
• Multi-Band Intra-Night Optical Variability of BL Lacertae
• Multi-band Optical Variability of the TeV Blazar PG 1553+113 in 2019
• Study of variability in long-term multiwavelength optical lightcurves of blazar AO 0235+164
• Investigating Optical Variability of the Blazar S5 0716+714 On Diverse Time-scales
• Multiband Optical Variability of the Blazar 3C 454.3 on Diverse Timescales
• Investigating the origin of optical flares from the TeV blazar S4 0954+65
• Multi-band optical variability of the blazar OP 313 in the outburst state during 2024-2025
• San Pedro Martir observations of microvariability in obscured quasars
• Intra-night optical variability and radio characteristics of extremely radio-loud narrow-line Seyfert 1 galaxies
• Multi-band optical variability on diverse timescales of blazar 1E 1458.8+2249
• Optical Monitoring and Long-term Optical Spectral Variability of BL Lacertae Object S5 0716+714
• Intra-night optical variability study of a non-jetted narrow-line Seyfert 1 galaxy: SDSS J163401.94+480940.1
• Multi-Band Optical Variability of Blazar 1ES 2344+514 on Diverse Time-Scales
• Evidence of jet induced optical microvariability in radio-loud Narrow Line Seyfert 1 Galaxies