Renewed activity of GRO J1008-57 after its giant outburst

ATel #5004; M. Kuehnel, I. Kreykenbohm, S. Mueller, V. Grinberg, J. Wilms (ECAP & Remeis Observatory Bamberg), K. Pottschmidt (CRESST-UMBC/NASA-GSFC), M. H. Finger (USRA), P. Jenke (UAH), F. Fuerst (Caltech-SLR), R. E. Rothschild (UC San Diego), I. Caballero (CEA Saclay), P. Kretschmar (ESAC/ESA), C. Malacaria, D. Klochkov, A. Santangelo, S. Suchy, and R. Staubert (IAA Tuebingen)
on 23 Apr 2013; 21:38 UT
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Credential Certification: Ingo Kreykenbohm (Ingo.Kreykenbohm@sternwarte.uni-erlangen.de)

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We report on the apparent rise in activity of the Be/X-ray binary GRO J1008-57 as detected by the Swift/BAT Hard X-ray Transient Monitor to ~0.01 cts/s/cm^2. There is also evidence for activity in the MAXI/GSC soft X-ray lightcurves, where the flux has risen to ~0.02 cts/s/cm^2. Pulsations from GRO J1008-57 at a barycentric frequency of 10.6992(10) mHz and r.m.s amplitude of 11(2) mCrab are detected in the Fermi/GBM 12-50 keV data of April 22. GRO J1008-57 is a transient neutron star binary and shows regular type I outbursts close to periastron passage every orbital period of 249.46 days (ATel #4564, ATel #3254). The last type I outburst was around 2012 August 20 (ATel #4319). The source was recently in quiescence since its type II giant outburst in 2012 November (ATel #4561, #4573), which was the first outburst of this type since the discovery of the source in 1993 (Wilson et al. 1994, Stollberg et al. 1993). Using the orbital parameters of the system and the mean orbital phase, at which the outbursts occur (Kuehnel et al. 2013, in press), we predict the peak flux of a possible type I outburst of the system to be on MJD 56412 (2013 April 30th). In combination with the typical outburst duration of 10 to 14 days, the detected activity in Swift/BAT and MAXI/GSC suggests that the source will show a type I outburst in the next two weeks. This indicates that the orbital phase where type I outburst of GRO J1008-57 occurs, is still valid. Further on, there is still a Be-disk present providing matter for accretion, although the source shortly underwent a giant outburst.