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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
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
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 ( that also developed the Sun tracker. SSC ( 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.

A sketch over the polarimeter: The copper collimators, neutron and anticoincidence shields reduce the radiation from among others the atmosphere. The heart of the instrument – where the radiation is detected – is the 61 plastic scintillators with associated photomultiplier tubes (PMTs). Further down in the instrument you find the electronics.

Video showing the PoGO+ flight

PoGO+ and the team before the launch from Esrange. On the exhibition PoGO is assembled in the GUA. The Sun tracker is placed directly on the GUA even if it on this photo might look like it is situated on the gondola. Therefore you can see the Sun tracker holder on the exhibition if you look closely! You can clearly see that the landing was rough, since the previously straight holder is bent. (Photo: M. Pearce)
Left: The Crab according to the Hubble and Chandra telescopes. In the figure optical data (red) and X-ray data (blue) has been superimposed. As you can see the blue and red areas does not overlap completely, which shows how importance of multi wavelength studies. Right: The Crab nebula photographed by the Hubble telescope in 2005.
This is what it looked like when PoGO+ launched from Esrange the 12th July 2016 for its six days long journey to Canada. (Photo: M. Pearce)


Page responsible:Jahangir Jazayeri
Belongs to: KTH Space Center
Last changed: Apr 19, 2018