Detection of optical dips during the 2019 outburst of Swift J1357.2-0933

ATel #12867; F. Jimenez-Ibarra, T. Munoz-Darias, J. Casares, M. Armas Padilla (IAC-ULL), J. M. Corral-Santana (ESO)
on 13 Jun 2019; 09:43 UT
Credential Certification: Teo Muñoz-Darias (teo.munoz-darias@iac.es)

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We report on time resolved optical photometry of the black hole candidate Swift J1357.2-0933, which is currently in outburst [ATels #12796 and #12801]. Observations were carried out with the instrument RISE attached to the Liverpool Telescope at the Observatorio del Roque de los Muchachos (La Palma). We performed 6 x 1 hour observations within May 26--June 9 (2019) with a time resolution of 10s and using the ~ V+R filter. The six light-curves have nearly the same average magnitude (V+R ~ 17.4 calibrated against R band) and show clear dips up to 0.4 mag deep. The dip recurrence period determined via a Lomb-Scargle analysis is ~11 min. Swift J1357.2-0933 also displayed optical dips during its two previous outbursts (2011 and 2017). In both cases the recurrence period was observed to increase throughout the outburst decay, from ~2 min at outburst peak, to ~8 min a few months later (Corral-Santana et al. 2013, Paice et al. 2019, Jimenez-Ibarra et al. 2019). Therefore, assuming a similar behaviour for the current episode, a 11 min recurrence period would correspond to a late phase of the outburst decay. This is consistent with ATel #12803 , which showed that the 2019 outburst started before the 21th March.

References:
Corral-Santana J. M. et al. 2013, Science, 339, 1048
Paice J. A., et al., 2019, arXiv, 1905.09784.
Jimenez-Ibarra F., et al., 2019, MNRAS, submitted.