Quasi-periodic oscillation detected in γ-rays in blazar PKS 0346−27

¹ Center for Theoretical Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02-668 Warsaw, Poland
e-mail: raj@cft.edu.pl
² S. N. Bose National Centre for Basic Sciences, Block JD, Salt Lake, Kolkata 700106, India
³ Department of Physical Sciences, Indian Institute of Science Education and Research Mohali, Knowledge City, Sector 81, SAS Nagar, Punjab 140306, India
⁴ Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 200030, PR China
⁵ Aryabhatta Research Institute of Observational Sciences (ARIES), Manora Peak, Nainital, 263001 Uttarakhand, India
⁶ School of Astrophysics, Presidency University, 86/1 College Street, Kolkata, 700073 West Bengal, India

Received: 13 March 2023
Accepted: 20 August 2023

Abstract

Aims. We present a variability study of the blazar PKS 0346−27 conducted between December 2018 and January 2022 using archival γ-ray observations from Fermi-LAT.

Methods. We used Lomb–Scargle periodogram and weighted wavelet transform methods to detect the presence of periodicity or quasi-periodicity and localize this feature in time and frequency space. We estimated the significance of the periodicity feature using a Monte Carlo simulation approach. We also determined the global significance of the periodicity to test the robustness of our claim. To explore the most probable scenario, we modeled the light curve with both a straight-jet and a curved-jet model.

Results. We detect a periodicity feature of ∼100 days in the entire period of observation with a statistical significance of 3σ, which amounts to a 99.7% confidence level. The global significance of this feature is found to be 96.96%. Based on the Akaike information criterion, the most probable explanation is that the observed emission is enhanced due to the helical motion of a blob within a curved jet.

Conclusions. The origin of this quasi-periodic oscillation is very likely a region of enhanced emission moving helically inside a curved jet. This work presents strong evidence for jet curvature in the source and an independent (albeit a little serendipitous) procedure to estimate the curvature in blazar jets.