Renewed activity in recurrent transient A0535-66

ATel #15781; Rod Stubbings (Tetoora Road Observatory, Victoria, Australia and AAVSO), Gerry Skinner (University of Birmingham, UK)
on 29 Nov 2022; 14:32 UT
Credential Certification: G. Skinner (gerald.k.skinner@gmail.com)

Tweet

We report signs of a new period of activity in A0535-66 (=LMC V3434), a recurrent X-ray and optical transient with a period of 16.64 days. In the past, it has shown evidence of 69 ms X-ray pulsations and various super-orbital periods. On 2022 Nov 17 at 12.5-17.5 h UT visual observations from Tetoora Road Observatory found A0538-66 to have a magnitude of 14.6 compared with 15.3 in most recent data. The Nov 17 observations were close to phase 0, cycle n=254, on the extrapolated ephemeris of Rajoelimanana et al. (2016) and about 12h after phase zero on that of Ducci et al (2022). NICER x-ray observations were commenced at 22.4h UT and monitoring has continued. Examination of publicly available A0538-66 data from OGLE-IV shows relatively bright I-band magnitudes (15.0-15.2m) close to the times corresponding to cycles n=249-252, but the increases in brightness were smaller (0.2-0.45m). At the time of the n=252 brightening, Tetoora Road Observatory visual observations also indicated an optical brightening to (15.0m). A summary is of the times of observations and of the optical results is provided at the link below. The next phase zero is due to occur at 2022 Dec 03 at 22.0h +/- 2.0h UT according to the ephemeris of Ducci et al., or at 2022 Dec 04 at 09.8h +/- 2.0h UT according to that of Rajoelimanana et al. Multiband observations around these times are encouraged to elucidate the nature of this quixotic system. We acknowledge the use of OGLE data (Udalski, Acta Astron. 58 p187, 2008) available at http://ogle.astrouw.edu.pl/ogle4/xrom/1a0538-66.html. We wish to thank Keith Gendreau and the NICER team at NASA-GSFC for the rapid organisation of the NICER observations which will be continued with high cadence through the time of the next expected brightening. References : Ducci, L. et al. A&A 661, A22, 2022 Rajoelimanana, A.F., MNRAS 464, 4133, 2017

Plots