We experienced a failed balloon launch in 2011, a cancelled launch due to bad weather in 2012, and technical problems with the telescope in 2013 (moreover Cygnus X-1 was in an unfavourable spectral state, although we did manage to observe the Crab - but, that’s another story). Progress was not as straight-forward as we had hoped for. After spending a number of years working with telescope prototypes, and then building and calibrating the flight version, we turned our attention to balloon flights. This reveals that the accretion corona is an extended structure or lies far from the black hole - providing important new insights into black-hole binary accretion physics.Īrriving at this new view of Cygnus X-1 has been a long and, at times, frustrating journey - as experimental work often is. We interpret this as the X-ray emission not being influenced by the strong gravity of the black hole. PoGO+ discovered that only a small fraction of X-rays are polarised (<8.6% at 90% confidence level) and for these X-rays that the polarisation angle is aligned with the disk rotation axis. The PoGO+ energy band is well matched to that of the flux reflected from the corona. X-rays become polarised when they scatter off the accretion disk with the details depending on the disk-corona geometry. The PoGO+ telescope has no imaging capability but, uniquely, it can determine the polarisation of incident X-rays, described by the polarisation fraction (%) and polarisation angle (degrees). Close to the black hole lies the corona - a hot, optically thin region where X-rays undergo Compton scattering on energetic electrons.Ĭurrent imaging instruments cannot resolve details of the binary system. The disk is heated by friction and produces intense X-ray emission. The intense gravitational field of the black hole rips matter from the companion star onto a thin circulating accretion disk around the black hole. Credit: SSC.Ĭomprising the first generally accepted black hole and a massive supergiant companion star, Cygnus X-1 is one of the brightest persistent sources of X-rays in the galaxy. The PoGO+ balloon-flight in July 2016 - from launch to landing. The data which appears in our paper was collected each day during the following week as the balloon is carried on the stratospheric winds from Sweden to Victoria Island, Northern Canada. The atmosphere is now sufficiently thin to allow us to observe the X-ray photons which started their journey 6000 light-years away at the black-hole binary Cygnus X-1. fast-forward to later that day and the balloon has reached 40 km altitude.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |