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Bright apastron outburst of GRO J1008-57

ATel #6917; P. Kretschmar, E. Salazar (ESA/ESAC), E. Laplace (IAA Tuebingen), C. A. Wilson-Hodge (NASA-MSFC), R. E. Rothschild (UC San Diego), I. Kreykenbohm, M. Kuehnel (Remeis-Observatory & ECAP/Univ. Erlangen) T. Mihara (RIKEN) and M. Nakajima (Nihon U.) for MAXI
on 14 Jan 2015; 14:22 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Peter Kretschmar (Peter.Kretschmar@obs.unige.ch)

Subjects: X-ray, Binary, Transient

Referred to by ATel #: 7490, 8547, 10529, 10902

GRO J1008-57 is rising again steeply in brightness. Daily averaged flux levels were ~200mCrab (~0.7 counts/sec/cm^2, 2-20 keV) in MAXI and ~400 mCrab (~0.086 count/cm^2/s) in the Swift BAT band at the time of writing. This is the second highest flux in the last decade, only superseded by the giant outburst of end 2012 (ATEL #4561, #4564, #4573, #4577) which was also connected with complex activity after a normal outburst around periastron.

This is the third major peak of an activity that has been ongoing since the last periastron passage in September 2014 (ATEL #6465, #6630, #6656, #6664, #6819, #6823). Note that the third peak referred to in ATEL #6819 and #6823 in retrospect turned out to be a minor peak on a longer interval of moderate activity. The current rise is at nearly half an orbital phase from periastron; the steeper rise starting at orbital phase ~0.446(5) according to the ephemeris of Kuehnel et al. (ATel #4564).

Monitoring of the period evolution by the Fermi/GBM shows a behaviour reminiscent of a giant or type II outburst, see http://gammaray.nsstc.nasa.gov/gbm/science/pulsars/lightcurves/groj1008_fig1.png

Multiwavelength observations of the source during this very peculiar outburst are encouraged to shed light on the similarities and differences to the previously observed events.

The further evolution of the outburst can be followed at the BeXRB monitor page http://integral.esac.esa.int/bexrbmonitor/webpage_oneplot.php or the specific page http://integral.esac.esa.int/bexrbmonitor/Plots/sim_plot_GROJ1008-57.html combining data from MAXI (http://maxi.riken.jp/top/index.php?cid=1&jname=J1009-582), Swift/BAT (http://swift.gsfc.nasa.gov/results/transients/GROJ1008-57/), and Fermi/GBM (http://gammaray.msfc.nasa.gov/gbm/science/pulsars/lightcurves/groj1008.html)