Norway half penning Olaf Magnusson 1103-1115

https://static-numista.com/forum/images/613c310553ebb.jpg
Does anybody have any knowledge of this coin from Norway
looking to find out how to determine its authenticity and maybe then looking to sell
please let me know if you know anything or have knowledge of where I can find out more about this point
thank you.

I rotated and cropped your one image.
What is on the other side?
What is the diameter?

Same thing on the reverse ,it's approx 3/4 "x1"and it does not stick to a magnet