Long-term optical and X-ray variability of the Be/X-ray binary H 1145-619: Discovery of an ongoing retrograde density wave

¹ Centro de Astrobiología – Departamento de Astrofísica (CSIC-INTA), Camino Bajo del Castillo s/n, 28692 Villanueva de la Cañada, Spain
e-mail: julia@cab.inta-csic.es
² Observatorio Astronómico, Universidad de Valencia, Catedrático José Beltrán 2, 46980 Paterna, Spain
³ IESL, Foundation for Research and Technology-Hellas, 71110 Heraklion, Greece
⁴ Physics Department, University of Crete, 71003 Heraklion, Greece
⁵ Finnish Centre for Astronomy with ESO (FINCA), University of Turku, Väisäläntie 20, 21500 Piikkiö, Finland
⁶ European Space Astronomy Centre (ESAC), Camino Bajo del Castillo s/n, 28692 Villanueva de la Cañada, Spain
⁷ Department of Astronomy, University of Cape Town, Private Bag X3, 7701 Rondebosch, South Africa
⁸ South African Astronomical Observatory, Observatory Rd, Observatory, 7935 Cape Town, South Africa
⁹ School of Physics and Astronomy, University of Southampton, Highfield, Southampton SO17 1BJ, UK

Received: 7 December 2016
Accepted: 2 September 2017

Abstract

Context. Multiwavelength monitoring of Be/X-ray binaries is crucial to understand the mechanisms producing their outbursts. H 1145-619 is one of these systems, which has recently displayed X-ray activity.

Aims. We investigate the correlation between the optical emission and X-ray activity to predict the occurrence of new X-ray outbursts from the inferred state of the circumstellar disc.

Methods. We have performed a multiwavelength study of H 1145-619 from 1973 to 2017 and present here a global analysis of its variability over the last 40 yr. We used optical spectra from the SAAO, SMARTS, and SALT telescopes and optical photometry from the Optical Monitoring Camera (OMC) onboard INTEGRAL and from the All Sky Automated Survey (ASAS). We also used X-ray observations from INTEGRAL/JEM-X, and IBIS to generate the light curves and combined them with Swift/XRT to extract the X-ray spectra. In addition, we compiled archival observations and measurements from the literature to complement these data.

Results. Comparing the evolution of the optical continuum emission with the Hα line variability, we identified three different patterns of optical variability: first, global increases and decreases of the optical brightness, observed from 1982 to 1994 and from 2009 to 2017, which can be explained by the dissipation and replenishment of the circumstellar disc; second, superorbital variations with a period of P_superorb ≈ 590 days, observed in 2002–2009, which seems to be related to the circumstellar disc; and third, optical outbursts, observed in 1998–1999 and 2002–2005, which we interpret as mass ejections from the Be star. We discovered the presence of a retrograde one-armed density wave, which appeared in 2016 and is still present in the circumstellar disc.

Conclusions. We carried out the most complete long-term optical study of the Be/X-ray binary H 1145-619 in correlation with its X-ray activity. For the first time, we found the presence of a retrograde density perturbation in the circumstellar disc of a Be/X-ray binary.