Morphology-aware periodicity searches in Fermi-LAT blazars
Abstract
Standard periodicity searches in active galactic nuclei assume sinusoidal modulation, whereas gamma-ray blazar emission often features asymmetric flares and localized bursts. We investigate how periodicity significance in Fermi-LAT light curves depends on intra-cycle morphology and data-quality cuts. We analyze 101 seven-day binned light curves from the Fermi-LAT Light Curve Repository (LCR) using the Fast Template Periodogram with sinusoidal, Gaussian burst, and empirical asymmetric templates. Significances are calibrated with red-noise simulations including a Poisson noise floor. A Random Forest classifier scores sources using periodogram, phase-coherence, and period-stability features. Unconstrained likelihood fits in a few bins flatten the periodogram and make the simulated null effectively white. After quality cuts, three sources exceed a per-source significance of 3 sigma, versus 0.14 expected by chance. One is the established candidate PG 1553+113, but none reaches 3 sigma after correcting for the 101 light curves searched. Template choice substantially affects significance: for 4FGL J0102.8+5824, it is 0.24 sigma with a sinusoid and 3.85 sigma with a Gaussian burst. Such a gain is expected for about one source in simulated noise, while about 40 percent of sources favor a sinusoid. The significance distribution has a heavier upper tail than the Gaussian null predicts, consistent with flares. We report no new periodicity detection. Non-sinusoidal templates complement sinusoidal searches, but a large significance gain alone does not establish periodicity. The classifier also responds to isolated flares, indicating that the null does not fully capture flare behavior. Our results agree with recent systematic searches. Applying the LCR convergence criterion, supplemented by a consistency check, is important for periodicity searches, especially with seven-day bins.
Related
- FALCON (FERMI-ALMA Calibrator ObservatioN): Cross-matching ALMA Calibrators with Fermi-LAT Blazars
- Validating an X-ray-based method for identifying Fermi blazars
- Estimating redshift distributions of Fermi blazars with multiple machine-learning models
- Detection Forecasting for Blazars at MeV Energies with Fermi-LAT Swift-BAT Cross Match
- Classification of Fermi Blazars of Uncertain Type Using Positive-Unlabelled Machine Learning
BibTeX
@misc{maldonado2026morphologyaware,
title = {{Morphology-aware periodicity searches in Fermi-LAT blazars}},
author = {Aaron A. Maldonado and Alberto Domínguez and Adithiya Dinesh and Alba Rico and Pablo Peñil and Sara Buson and Marco Ajello},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2608.00664},
eprint = {2608.00664},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2608.00664},
}
RIS
TY - UNPB
TI - Morphology-aware periodicity searches in Fermi-LAT blazars
AU - Aaron A. Maldonado
AU - Alberto Domínguez
AU - Adithiya Dinesh
AU - Alba Rico
AU - Pablo Peñil
AU - Sara Buson
AU - Marco Ajello
PY - 2026
DA - 2026/10/12
PB - arXiv
DO - 10.48550/arxiv.2608.00664
UR - https://arxiv.org/abs/2608.00664
AB - Standard periodicity searches in active galactic nuclei assume sinusoidal modulation, whereas gamma-ray blazar emission often features asymmetric flares and localized bursts. We investigate how periodicity significance in Fermi-LAT light curves depends on intra-cycle morphology and data-quality cuts. We analyze 101 seven-day binned light curves from the Fermi-LAT Light Curve Repository (LCR) using the Fast Template Periodogram with sinusoidal, Gaussian burst, and empirical asymmetric templates. Significances are calibrated with red-noise simulations including a Poisson noise floor. A Random Forest classifier scores sources using periodogram, phase-coherence, and period-stability features. Unconstrained likelihood fits in a few bins flatten the periodogram and make the simulated null effectively white. After quality cuts, three sources exceed a per-source significance of 3 sigma, versus 0.14 expected by chance. One is the established candidate PG 1553+113, but none reaches 3 sigma after correcting for the 101 light curves searched. Template choice substantially affects significance: for 4FGL J0102.8+5824, it is 0.24 sigma with a sinusoid and 3.85 sigma with a Gaussian burst. Such a gain is expected for about one source in simulated noise, while about 40 percent of sources favor a sinusoid. The significance distribution has a heavier upper tail than the Gaussian null predicts, consistent with flares. We report no new periodicity detection. Non-sinusoidal templates complement sinusoidal searches, but a large significance gain alone does not establish periodicity. The classifier also responds to isolated flares, indicating that the null does not fully capture flare behavior. Our results agree with recent systematic searches. Applying the LCR convergence criterion, supplemented by a consistency check, is important for periodicity searches, especially with seven-day bins.
ER -