Proposal Details - 1120030
Hunting the claimed high energy cyclotron line of GRO J1008-57 (Kühnel)

Proposal Abstract

It is proposed to monitor the recurrent neutron star transient GRO J1008-57 during the predicted outburst of the source within INTEGRAL-AO11 in 2014 January during 3 INTEGRAL revolutions, with one 50 ks observation per revolution, resulting in a total exposure time of 150 ks. Several type I outbursts of GRO J1008-57 have been observed in the past as ToOs by Swift, RXTE, and also Suzaku, showing that the spectral shape remains constant between regular outbursts. No cyclotron absorption feature has been detected significantly in the spectrum. Since we were able to improve the orbital ephemeris (Kuehnel et al., ATel #4564) it is now possible to predict the onset and maximum of future outbursts of the source to better than 5 days. The source underwent an irregular giant type II outburst in 2012 November (Nakajima et al., ATel #4561; Krimm et al., ATel #4573) during which a cyclotron absorption feature was claimed between 74 and 78 keV (Yamamoto et al., ATel #4759). It is, therefore, proposed to observe the system again after the giant outburst to confirm the claimed cyclotron line. In addition, one will check on any changes of the spectral and temporal behavior during known type I outbursts.

Observation Strategy (Recommended by TAC)

Total of 150 ks split in 3 times 50 ks INTEGRAL observations, using a standard Hex dither pattern centered at RA, Dec (J2000.0, in degrees) = 152.442, -58.292 (l,b = 282.998, -1.822 degrees). The observations start early 2014 January, and are to be done during 3 consecutive INTEGRAL revolutions, with one 50 ks observation per revolution.

Proposal grade: A

Data Rights (Recommended by TAC)

Data rights were granted for GRO J1008-57 only.

Exposure Map

The exposure maps are in galactic coordinates using the Aitoff projection and units of seconds, and the colour scale is indicated at the bottom. The green lines provide the 100, 300 and 500 ksec contour.