GRO J1008-57: high precision timing and spectral evolution

Presentation duration: 15 minutes

Presenter: Matthias Kühnel

The transient high mass X-ray binary GRO J1008-57 underwent an outburst in December 2007, which was recorded by RXTE, Suzaku and Swift. With ~180 mCrab this outburst was the most luminous since the start of the RXTE ASM monitoring in 1996. The system is only visible in X-rays during outbursts, which repeat mostly on the 249 day orbital period of the system. Due to the relatively short outburst durations of around 15 days, the orbital coverage is quite low. Hence determining the orbit is challenging. By analysing pulse arrival times of the 2007 lightcurves together with data from an outburst in 2005 recorded by RXTE, we were able to improve the existing orbital parameters. Since the discovery of GRO J1008-57 in 1993 a cyclotron absorption feature at 88 keV is claimed, which could not be securely confirmed yet. Focusing on the spectral evolution we also found evidence for this possible cyclotron line. Additionally we discovered an absorption like feature at around 22 keV, which is, however, only seen at high luminosities. RXTE will observe the outburst of GRO J1008-57 in April 2011 to clarify its existence.

Müller, S.
Kreykenbohm, I.
Wilms, J.
Pottschmidt, K.
Fuerst, F.
Suchy, S.
Rothschild, R.
Caballero, I.
Kretschmar, P.
Schoenherr, G.
Klochkov, D.
Santangelo, A.
Staubert, R.