{"ID":23577924,"CreatedAt":"2026-09-18T05:07:30.921092366Z","UpdatedAt":"2026-09-18T05:07:30.921092366Z","DeletedAt":null,"paper_url":"https://arxiv.org/abs/2609.19984","arxiv_id":"2609.19984","title":"A 32-day Quasi-periodic Modulation in the Post-peak Light Curve of the Superluminous Supernova SN 2018bsz","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.","short_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...","url_abs":"https://arxiv.org/abs/2609.19984","url_pdf":"https://arxiv.org/pdf/2609.19984v1","authors":"[\"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\"]","published":"2026-09-17T09:57:27Z","proceeding":"astro-ph.HE","tasks":"[\"astro-ph.HE\"]","methods":"[]","has_code":false}