Detection of IR enhancement and evidence of disk formation around the Be star from SAX J2103.5+4545/ CGS 03588-00834
A. Camero-Arranz (IEEC/ICE), E. Nespoli (University of Valencia - ESA/ESAC), J. Gutierrez-Soto (Valencian International University, IAA/CSIC) and  C. Zurita (Instituto de Astrofisica de Canarias)
We report on recent IR observations of the Be/X-ray binary system SAX J2103.5+4545/ CGS 03588-00834, obtained with the 1.52 m Carlos Sánchez Telescope (Observatorio de Izaña, Tenerife, Spain), and on the evolution of the H-alpha equivalent width for this system measured with the spectrograph Albireo, at the 1.5 m telescope of the Observatorio de Sierra Nevada (Granada, Spain). Observations from 2011 December 26 up to 2012 June 10 showed and IR enhancement of the optical counterpart CGS 03588-00834, with the brightness varying from J = 11.90 +/- 0.05 mag, H = 11.51 +/- 0.06 mag and Ks = 11.33 +/- 0.08 mag (MJD 55921.0), to J = 11.02 +/- 0.06 mag, H = 10.61 +/- 0.03 mag and Ks = 10.3 +/- 0.1 mag (MJD 56088.0).

In addition, using our spectra of CGS 03588-00834 from 2011 December 22 up to 2012 May 23, we observed the equivalent width of the H-alpha line changing from being in absorption with a value of 1.6 +/- 0.2 (MJD 55856.007), to being in emission with values of -1.1 +/- 0.2 (MJD 56014.13), -1.4 +/- 0.2 (MJD 56069.17) and -1.0 +/- 0.2 (MJD 56070.17). The IR brightening of the system and H-alpha line emission are evidences of a new disk formation around the Be star.

INTEGRAL IBIS/ISGRI detected renewed X-ray activity from this source starting on 2012 June 12 (ATel #4168), as predicted by the detection of increased optical activity of SAX J2103.5+4545 reported on 2012 April 25 (ATel #4068). The Swift/BAT Hard X-ray Transient Monitor initially detected this source during a short X-ray episode in 2012 June 9 (MJD 56087.0), peaking at a flux of about 56 mCrabs in the 15-50 keV band. We note that pre-outbursts peaks have been a common feature for this source (Camero-Arranz et al. 2007, Reig et al. 2010).

Disk appearance, IR and optical brightening and a pre-outburst peak in the X-rays give us opportunity to predict a new possible major X-ray outburst of SAX J2103.5+4545 in the nearest future. More observations are encouraged in order to cover this possible new event.

We thank the Swift/BAT Hard X-ray Transient Monitor team for all the available data found for this source.
infra-red,optical,x-ray,binary,neutron star,pulsar,star,transient