On the frequency-dependent time lags of the intermediate polar V709 Cas
10 affiliations
- 1School of Physics and Astronomy, University of Southampton , University Road, Southampton SO17 1BJ ,
- 2Department of Physics, University of Warwick , Gibbet Hill Road, Coventry CV4 7AL ,
- 3Institute of Space Sciences (ICE, CSIC) , Campus UAB, Carrer de Can Magrans s/n, E-08193 Barcelona ,
- 4Institut d’Estudis Espacials de Catalunya (IEEC) , E-08860 Castelldefels (Barcelona) ,
- 5Kapteyn Astronomical Institute, University of Groningen , PO Box 800, NL-9700 AV Groningen ,
- 6Instituto Argentino de Radioastronoía (CCT La Plata, CONICET; CICPBA; UNLP) , C.C.5, (1894) Villa Elisa, Buenos Aires ,
- 7INAF – Osservatorio Astronomico di Capodimonte , Salita Moiariello 16, I-80131 Napoli ,
- 8Centre for Extragalactic Astronomy, Department of Physics, Durham University , South Road, Durham DH1 3LE ,
- 9Fluid and Complex Systems Centre, Coventry University , Coventry CV1 5FB ,
- 10Instituto de Astronomía, Universidad Nacional Autónoma de México , AP 106, Ensenada 22800, BC ,
Abstract
Cataclysmic variables (CVs) are binary systems in which a white dwarf (WD) primary accretes material from a late-type secondary, typically via a disc. To date, only six CVs, all of which are non-magnetic, have been found to exhibit lags (delayed variability in one band with respect to another). In all six cases, these lags are ‘red’ (i.e. red lags blue) with a time lag of order seconds. While there is no generally accepted mechanism for producing red lags in CVs, current theories suggest reprocessing in the disc, either on the thermal or recombination time-scales, or inside-out shocks propagating through the disc. Using g-, r-, and i-band data from the OPTICAM (OPtical TIming CAMera), we report the discovery of frequency-dependent red lags from V709 Cas: a magnetic CV of the intermediate polar (IP) subclass. These red lags reach a maximum of ∼4–6 s on time-scales of 7.4–13.0 min, similar to previously reported lags in non-magnetic CVs. The detection of lags in an IP is significant as the WD’s magnetic field truncates the accretion disc, limiting disc-based lag mechanisms to large radii; as a result, characteristic accretion disc time-scales cannot explain the observed lags. However, recombination can occur on second time-scales, even in systems with truncated discs. For example, we show that recombination in the disc’s bright spot, where overflowing material from the secondary meets the outer edge of the disc, plausibly explains V709 Cas’s optical spectrum, the prominence of optical spin-orbit beat pulsations, and the red lags found in this work.
Versions
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BibTeX
@article{irving2026frequencydependent,
title = {{On the frequency-dependent time lags of the intermediate polar V709 Cas}},
author = {Zackery A Irving and Noel Castro Segura and Diego Altamirano and Martina Veresvarska and Mariano Méndez and Federico García and Domitilla de Martino and Simone Scaringi and Federico Vincentelli and Angel Castro and Federico Soto and Raul Michel},
journal = {Monthly Notices of the Royal Astronomical Society},
year = {2026},
month = oct,
doi = {10.1093/mnras/stag1875},
url = {https://academic.oup.com/mnras/article/doi/10.1093/mnras/stag1875/8869233},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - On the frequency-dependent time lags of the intermediate polar V709 Cas
AU - Zackery A Irving
AU - Noel Castro Segura
AU - Diego Altamirano
AU - Martina Veresvarska
AU - Mariano Méndez
AU - Federico García
AU - Domitilla de Martino
AU - Simone Scaringi
AU - Federico Vincentelli
AU - Angel Castro
AU - Federico Soto
AU - Raul Michel
PY - 2026
DA - 2026/10/06
JO - Monthly Notices of the Royal Astronomical Society
DO - 10.1093/mnras/stag1875
UR - https://academic.oup.com/mnras/article/doi/10.1093/mnras/stag1875/8869233
AB - Cataclysmic variables (CVs) are binary systems in which a white dwarf (WD) primary accretes material from a late-type secondary, typically via a disc. To date, only six CVs, all of which are non-magnetic, have been found to exhibit lags (delayed variability in one band with respect to another). In all six cases, these lags are ‘red’ (i.e. red lags blue) with a time lag of order seconds. While there is no generally accepted mechanism for producing red lags in CVs, current theories suggest reprocessing in the disc, either on the thermal or recombination time-scales, or inside-out shocks propagating through the disc. Using g-, r-, and i-band data from the OPTICAM (OPtical TIming CAMera), we report the discovery of frequency-dependent red lags from V709 Cas: a magnetic CV of the intermediate polar (IP) subclass. These red lags reach a maximum of ∼4–6 s on time-scales of 7.4–13.0 min, similar to previously reported lags in non-magnetic CVs. The detection of lags in an IP is significant as the WD’s magnetic field truncates the accretion disc, limiting disc-based lag mechanisms to large radii; as a result, characteristic accretion disc time-scales cannot explain the observed lags. However, recombination can occur on second time-scales, even in systems with truncated discs. For example, we show that recombination in the disc’s bright spot, where overflowing material from the secondary meets the outer edge of the disc, plausibly explains V709 Cas’s optical spectrum, the prominence of optical spin-orbit beat pulsations, and the red lags found in this work.
SN - 0035-8711
SN - 1365-2966
ER -