A 32-day Quasi-periodic Modulation in the Post-peak Light Curve of the Superluminous Supernova SN 2018bsz

Aiswarya Sankar. K; Ting-Wan Chen; Seán J. Brennan; Morgan Fraser; Keiichi Maeda; Thomas Moore; Sheng Yang; Amar Aryan; Dietrich Baade; Ping Chen; Chow-Choong Ngeow

arXiv · 2609.19984

A 32-day Quasi-periodic Modulation in the Post-peak Light Curve of the Superluminous Supernova SN 2018bsz

Aiswarya Sankar. K·Ting-Wan Chen·Seán J. Brennan·Morgan Fraser·Keiichi Maeda·Thomas Moore·Sheng Yang·Amar Aryan·Dietrich Baade·Ping Chen·Chow-Choong Ngeow

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Abstract

Recurrent structure in supernova (SN) light curves may reveal physical clocks associated with central-engine dynamics, binary orbital motion, or interaction with structured circumstellar material (CSM). We present a multiband photometric reanalysis of the nearby hydrogen-poor superluminous SN (SLSN-I) 2018bsz (z=0.0267), using Swift/UVOT and GROND observations spanning approximately 110 rest-frame days after maximum light. After independently modelling and subtracting the smooth decline in each band, Generalized Lomb-Scargle periodograms reveal recurrent residual variations at broadly consistent phases across ten bands from u to Ks. The strongest individual-band detections, in the g, r, i, z, and J bands, yield periods of 31.5-31.8 days, while the joint multiband analysis gives a rest-frame period of P=31.61 (+/-0.03) days. The modulation is traced over approximately three cycles and is therefore described as quasi-periodic. The signal is robust to the adopted detrending procedure, while comparison-star and lunar-cycle tests disfavour an observational systematic. The modulation is broadly phase-coherent from the optical to the near-infrared, but its amplitude increases towards shorter wavelengths; lower-significance bands also show possible wavelength-dependent shifts in the best-fitting period. The present observations do not uniquely determine the physical origin. Lense-Thirring precession, interaction with CSM structured before the explosion, and post-SN interaction with a surviving companion remain possible. SN 2018bsz provides one of the clearest examples of coherent, month-scale photometric modulation in an SLSN-I.

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Aiswarya Sankar. K, Ting-Wan Chen, Seán J. Brennan, Morgan Fraser, Keiichi Maeda, Thomas Moore, Sheng Yang, Amar Aryan, Dietrich Baade, Ping Chen, Chow-Choong Ngeow. 2026-09-17. A 32-day Quasi-periodic Modulation in the Post-peak Light Curve of the Superluminous Supernova SN 2018bsz. https://arxiv.org/abs/2609.19984

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