Recurrent double-peaked γ-ray sub-flares in PKS 1424-418
Abstract
We report a hint of recurrent double-peaked γ-ray sub-flares in PKS~1424--418 during two similar major active epochs, MJD 56117--56498 and MJD 59669--59978. The candidate double-peaked sub-flares show a characteristic intra-subflare peak separation of ∼ 11.8 d and a neighbouring-subflare spacing of ∼ 67 d. Red-noise Monte Carlo tests indicate that the candidate recurrent double-peaked morphology is not easily reproduced by stochastic variability alone, with false-alarm probabilities of pa=0.0216 and pb=0.0006 for the two active epochs, respectively. In the simulations of the entire \textit{Fermi} Large Area Telescope (LAT) light curve, no red-noise realisation reproduces both epoch-like structures. The spectral energy distribution (SED) modelling shows similar radiative properties for the two peaks of one double-peaked candidate, while changes in the Doppler factor appear to play an important role in the flaring activity. Together with the previously reported near-zero lag between the millimetre and γ-ray emission, these results suggest that the recurrent activity may be associated with the compact mm/sub-mm core region. We discuss a possible structured-jet scenario in which a single disturbance propagates through a chain of quasi-stationary recollimation shocks. In this picture, repeated interactions between the disturbance and the shock structure may qualitatively account for both the double-peaked sub-flare profiles and the observed ∼ 11.8 d and ∼ 67 d time-scales. Further active epochs are required to determine whether this similarity represents a recurrent long-term behaviour.
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BibTeX
@misc{wang2026recurrent,
title = {{Recurrent double-peaked $γ$-ray sub-flares in PKS 1424-418}},
author = {Na Wang and Tong Liu and Jingran Xu},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.28932},
eprint = {2609.28932},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.28932},
note = {CC0},
}
RIS
TY - UNPB
TI - Recurrent double-peaked γ-ray sub-flares in PKS 1424-418
AU - Na Wang
AU - Tong Liu
AU - Jingran Xu
PY - 2026
DA - 2026/09/24
PB - arXiv
DO - 10.48550/arxiv.2609.28932
UR - https://arxiv.org/abs/2609.28932
AB - We report a hint of recurrent double-peaked γ-ray sub-flares in PKS~1424--418 during two similar major active epochs, MJD 56117--56498 and MJD 59669--59978. The candidate double-peaked sub-flares show a characteristic intra-subflare peak separation of ∼ 11.8 d and a neighbouring-subflare spacing of ∼ 67 d. Red-noise Monte Carlo tests indicate that the candidate recurrent double-peaked morphology is not easily reproduced by stochastic variability alone, with false-alarm probabilities of p_a=0.0216 and p_b=0.0006 for the two active epochs, respectively. In the simulations of the entire \textit{Fermi} Large Area Telescope (LAT) light curve, no red-noise realisation reproduces both epoch-like structures. The spectral energy distribution (SED) modelling shows similar radiative properties for the two peaks of one double-peaked candidate, while changes in the Doppler factor appear to play an important role in the flaring activity. Together with the previously reported near-zero lag between the millimetre and γ-ray emission, these results suggest that the recurrent activity may be associated with the compact mm/sub-mm core region. We discuss a possible structured-jet scenario in which a single disturbance propagates through a chain of quasi-stationary recollimation shocks. In this picture, repeated interactions between the disturbance and the shock structure may qualitatively account for both the double-peaked sub-flare profiles and the observed ∼ 11.8 d and ∼ 67 d time-scales. Further active epochs are required to determine whether this similarity represents a recurrent long-term behaviour.
ER -