A systematic search for optical outbursts in IPs using ASAS-SN

Journal article

Cataclysmic variables can show rapid increases in optical flux. Intermediate polars (IPs), a subset with strong magnetic fields that disrupt the inner accretion disc, have been thought to possess truncated discs that rarely undergo the disc-instability outbursts seen in dwarf novae. However, the discovery of micronovae and magnetic-gating bursts suggests that such events may occur even without a fully developed disc. Using data from the All-Sky Automated Survey for Supernovae (ASAS-SN), we identify a previously unrecognized population of short-time-scale optical outbursts in IPs. Initial energy estimates indicate that at least half of these bursts may be consistent with micronovae, though limited cadence reduces our ability to classify each event with high confidence. These detections should therefore be regarded as evidence of short outbursts in IPs rather than definitive micronova identifications. Our results show that such bursts are more common in IPs than assumed and may include a substantial fraction of micronovae. Simulations reveal that if micronovae occur once per year at regular intervals, up to 30 per cent of the shortest bursts could be missed over a 10-yr observing baseline. Under the same assumptions, and assuming all IPs display micronovae, we would expect 50–70 per cent of IPs to show these bursts, yet only 14 per cent of known IPs in our sample do so. This discrepancy suggests that not all IPs undergo micronovae. Overall, this work establishes the first comprehensive set of short burst detections in IPs, providing a foundation for future investigations and a list of candidate micronova systems for follow-up analysis.

Authors: Mendelsohn, JM; Scaringi, S; Veresvarska, M; Iłkiewicz, K

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Oxford University Press
• Journal: Monthly Notices of the Royal Astronomical Society
• Volume: 549
• Issue: 1
• Article number: stag822
• Publication date: 2026-04-30
• Acceptance date: 2026-04-28
• DOI: 10.1093/mnras/stag822
• EISSN: 1365-2966
• ISSN: 0035-8711
• Language: English
• Keywords: cataclysmic variables; accretion, accretion discs; magnetic fields