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Renewed activity from the Be/X-ray binary GRO J1008-57

ATel #3254; M. Kuehnel, I. Kreykenbohm, S. Mueller, F. Fuerst, J. Wilms (ECAP & Remeis Observatory Bamberg), K. Pottschmidt (CRESST-UMBC/NASA-GSFC), S. Suchy, R. E. Rothschild (UC San Diego), I. Caballero (CEA Saclay), P. Kretschmar (ESAC), G. Schoenherr (AIP), D. Klochkov, A. Santangelo and R. Staubert (Institut fuer Astronomie und Astrophysik Tuebingen)
on 2 Apr 2011; 22:08 UT
Credential Certification: Joern Wilms (j.wilms@sternwarte.uni-erlangen.de)

Subjects: X-ray, Binary, Transient

Referred to by ATel #: 3796, 3805, 4759, 5004, 7490

We report on the onset of activity of the transient Be/X-ray binary GRO 1008-57 as detected by short RXTE/PCA observations. The flux in PCA (2 to 60 keV) increased from 7+-1 mCrab on 27 March 2011 (MJD 55647.3) to 12+-1 mCrab on 01 April 2011 (MJD 55652.5). Although the luminosity is too low to obtain spectral parameters, the lightcurve already shows weak pulsations with a period of around 93(2) s. This value is in agreement with the pulse period of 93.74 s (GBM Pulsar Project) for the last outburst in the beginning of August 2010 (ATel #2769).

The recurrence of activity is in agreement with the orbital period of about 247.8 d as found by Coe et al. (2007), indicating a further outburst. From lightcurves of previous outbursts we expect the source to be most luminous around April 9th. RXTE follow up observations of GRO J1008-57 have been scheduled and further multi wavelength observations are encouraged.

We thank the RXTE team, especially Evan Smith, for his help working out the final monitoring schedule and for implementing it.