Multi-band optical variability of the blazar OP 313 in the outburst state during 2024-2025

Abstract

We present the analysis results of flux and spectral variability of the blazar OP 313 across intra-night to short-term timescales using BVRI photometric data, gathered over 25 nights from Nov 2024 to May 2025, using two optical telescopes in ARIES, India. The source was in an outburst state during this period. We searched for intraday variations (IDV), using two powerful statistical tests: the Power Enhanced F-test and the Nested ANOVA test. The source displayed IDV in the R band for five of the ten nights, yielding a duty cycle of 34$\%$. During the entire monitoring of the source, it showed variations of over two mag in all B, V, R, and I data bands. We obtained a variability timescale for a variable light curve, giving us an upper limit for the size of the emission region. We generated optical SEDs of the blazar for these 25 nights, fitted a power law of form $(F_{\nu }\propto {\nu }^{-{\alpha }_o})$ and found the weighted mean spectral index to be 1.471$\pm$0.004. An analysis of the color-magnitude diagram shows that, contrary to the redder-when-brighter (RWB) trend typically observed in FSRQs, this source exhibits a bluer-when-brighter (BWB) trend on short-term variability (STV) timescales - a behavior more commonly associated with BL Lac object. We explore potential physical mechanisms responsible for the observed spectral variability.

arXiv comment19 pages, 4 Figures, 4 Tables Accepted for publication in The Astrophysical Journal

References in corpus (44)

• Unified Schemes for Radio-Loud Active Galactic Nuclei
• A Unifying View of the Spectral Energy Distributions of Blazars
• The Spectral Energy Distribution of Fermi bright blazars
• BL Lac Objects in the Synchrotron Proton Blazar Model
• Internal shocks in the jets of radio-loud quasars
• Modeling the Emission Processes in Blazars
• Generating artificial light curves: Revisited and updated
• Improved redshifts for SDSS quasar spectra
• Blazar spectral variability as explained by a twisting inhomogeneous jet
• The unprecedented optical outburst of the quasar 3C 454.3. The WEBT campaign of 2004-2005
• Multi-colour optical monitoring of eight red blazars
• Testing tests on AGN microvariability
• Near Infrared Intraday Variability of Mrk 421
• The optical microvariability and spectral changes of the BL Lacertae object S5 0716+714
• Intranight optical variability of radio-quiet and radio lobe dominated quasars
• Multi-band optical variability studies of BL Lacertae
• Longterm Optical Monitoring of Bright BL Lacertae Objects with ATOM: Spectral Variability and Multiwavelength Correlations
• Quasi-simultaneous two band optical variability of the blazars 1ES 1959+650 and 1ES 2344+514
• X-ray Intraday Variability of Five TeV Blazars with NuSTAR
• Multiwavelength Variability of the Blazars Mrk 421 and 3C 454.3 in the High-State
• Multi-band optical variability of three TeV Blazars on Diverse Timescales
• On the reliability of microvariability tests in quasars
• Nature of Intra-night Optical Variability of BL Lacertae
• The WEBT Campaign on the Intermediate BL Lac Object 3C66A in 2007-2008
• A Consolidated Framework of the Color Variability in Blazars: Long-Term Optical/Near-Infrared Observations of 3C 279
• Multi-band optical variability of the Blazar S5 0716+714 in outburst state during 2014-2015
• Optical Intraday Variability Studies of Ten Low Energy Peaked Blazars
• A peculiar multi-wavelength flare in the Blazar 3C 454.3
• Testing microvariability in quasar differential light curves using several field stars
• The optical spectral slope variability of 17 blazars
• Long-term monitoring of PKS 2155$-$304 with ATOM and H.E.S.S.: investigation of optical/$\gamma$-ray correlations in different spectral states
• 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
• Intra-night optical flux and polarization variability of BL~Lacertae during its 2020 $-$ 2021 high state
• Detection of Quasi-Periodic Oscillations in the Blazar S4 0954+658 with TESS
• X-ray intraday variability of the TeV blazar Mrk 421 with {\it XMM-Newton}
• Quasi-simultaneous Optical Flux and Polarization Variability of the Binary Super Massive Black Hole Blazar OJ 287 from 2015 to 2023: Detection of an Anticorrelation in Flux and Polarization Variability
• Relativistic Doppler beaming and misalignments in AGN jets
• Detecting microvariability in type 2 quasars using enhanced F-test
• Optical Variability of Three Extreme TeV Blazars
• Optical flux and spectral variability of BL Lacertae during its historical high outburst in 2020
• The variability patterns of the TeV blazar PG 1553+113 from a decade of MAGIC and multi-band observations
• Multi-band Optical Variability of the TeV Blazar PG 1553+113 in 2019
• Multiband Optical Variability of the Blazar 3C 454.3 on Diverse Timescales