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Improved orbital ephemeris of GRO J1008-57

ATel #4564; M. Kuehnel, S. Mueller, I. Kreykenbohm, J. Wilms (Remeis-Observatory Bamberg), K. Pottschmidt (CRESST-UMBC/NASA-GSFC), F. Fuerst (Caltech-SRL), R. E. Rothschild (UC San Diego), I. Caballero (CEA Saclay), D. Klochkov, R. Staubert, S. Suchy (IAA Tuebingen), P. Kretschmar (ESAC/ESA), C. Ferrigno (ISDC, University of Geneva), J. M. Torrejon and S. Martinez-Nunez (U Alicante)
on 10 Nov 2012; 10:35 UT
Credential Certification: Ingo Kreykenbohm (ingo.ik.kreykenbohm@fau.de)

Subjects: X-ray, Binary, Neutron Star, Transient, Pulsar

Referred to by ATel #: 4573, 4577, 4759, 5004, 6465, 6656, 6917, 8547

The recurrent transient GRO J1008-57 is currently undergoing an unusal long outburst (ATELs #4561, #4355, #4319). Typically, outbursts of this system are associated with the periastron passage of the neutron star. We have triggered Swift observations of the current outburst (MJD 56197) and furthermore analyzed all available RXTE, Swift, and Suzaku data of previous outbursts of the system. Using pulse arrival times we derived an updated solution for the orbital period and the time of the periastron passage with significantly increased accuracy compared to the previous solutions of Coe et al. (2007) based on BATSE data and Levine & Corbet (2006) based on ASM data. We obtain the following ephemeris: Porb = 249.46(10) d; T0 = MJD 54424.6(4) where T0 is the time of periastron passage; asini = 530(60) lt-sec (Coe et al. 2007); omega = -26(8) deg (Coe et al. 2007) ; e = 0.68(2) (Coe et al. 2007). This new ephemeris allowed us to predict the outburst in April 2011 and this outburst with a precision of 5 days. Using this updated ephemeris we obtain an orbital phase for the current re-brightening of GRO J1008-57 of phi = 0.278(4) consistent with the value of 0.3 found by Nakajima et al. 2012 (ATEL #4561).