Magnetically gated accretion model: Application to short bursts in the intermediate polar V1223 Sgr

Abstract

Context. Some intermediate polars (IPs) show outbursts that are much shorter than those observed in normal dwarf novae, and their origin remains unclear. Aims. We examine the case of V1223 Sgr, an intermediate polar that showed a short outburst in 1984, and compare the outburst characteristics with the predictions of the magnetospheric gating model. Methods. We extracted outburst profiles from the American Association of Variable Star Observers (AAVSO) archival data. We used our code to compute the time-dependent evolution of an accretion disc truncated by the white dwarf magnetic field, using a simple description of the interaction between the disc and the magnetic field, as in D’Angelo & Spruit (2010, MNRAS, 406, 1208). Results. We find that V1223 Sgr underwent a series of short outbursts, with a rise lasting for typically two to three hours, and a slightly longer decay. When applied to IPs, the model by D’Angelo & Spruit (2010, MNRAS, 406, 1208) accounts well for the observed outburst duration and intensity. However, we confirm that the model outcome depends sensitively on the assumptions of the rather poorly constrained model. We also searched the AAVSO database for short outbursts in other IPs, identifying individual short outbursts in FO Aqr, TV Col, NY Lup, and EI UMa, but no series such as those observed in V1223 Sgr. We also found a superoutburst, followed by a reflare in CTCV J2056−3014. Conclusions. Although the magnetic–gating accretion instability model is clearly responsible for the series of V1223 Sgr short outbursts and most probably for similar events in other IPs, the model describing this process needs improvement, in particular concerning the interaction between the magnetic field of the white dwarf and the accretion disc. This difficult task might benefit from further comparison of the model outcome with additional observations that show good time coverage and time resolution.