PoGO is a balloon borne X-ray telescope that was developed at KTH. In 2016 it flew from Esrange, Kiruna to Victoria Island, Canada on stratospheric winds, 40 km up. To be able to lift the instrument an enormous balloon containing more than 1 million cubic meter Helium was used!
During the six days long flight PoGO+ studied polarised X-rays from two objects – the Crab and Cygnus X-1.
What are X-rays?
X-rays are electromagnetic radiation, just like light and radio waves, but with higher energies. Since the earth’s atmosphere is shielding us from X-rays from space, we need to lift up our instruments above it.
What is polarisation?
The polarisation of an electromagnetic wave describes the direction of the electric field. If the electric field is randomly oriented, the wave is said to be unpolarised. On the other hand, if the wave is oscillating in one direction it is polarised.
Why measure polarisation?
Instrument that measure X-rays from astronomical objects already exists but ordinary X-ray instruments can’t tell us so much about the environment where the radiation originates. This, on the other hand, is something that polarimeters can do! For example they can help us learn more about the magnetic fields around an object. Polarisation measurements are therefore important tools to learn more about the environment in extreme objects like pulsars and X-ray binaries.
The Crab, containing a nebula and a pulsar, is the name of a system that was form in a Supernova in the year 1054.
Pulsars are fast rotating neutron rich stars that are about 15 km in diameter but have roughly the same mass as our sun (1.4 million km in diameter). They are called pulsars because they emit radiation in short pulses, a bit like lighthouses that light up the sea.
Cygnus X-1 is the name of the X-ray component in a so called X-ray binary containing a black hole and a blue supergiant. X-ray binaries are double stars that are radiating a lot of X-ray. The strong gravitational force from the black hole drags gas and dust from the star toward it and it is in that process the radiation is formed.
Who are involved in the PoGO-project?
PoGO+ has mainly been built by the Particle and astroparticle physics group here at KTH but in collaboration with Hiroshima University in Japan and Stockholm University. The attitude control system was developed by DST control (www.dst.se) that also developed the Sun tracker. SSC (www.sscspace.com) developed the gondola, power and communication system.
Who funded the project?
Besides faculty research funding from KTH, the PoGO-project was made possible thanks to the Knut and Alice Wallenberg foundation, The Swedish National Space Board, The Swedish Research Council and The Göran Gustafsson Foundation.
Video showing the PoGO+ flight