It could be a Magnetar
No, not the Pokemon. That's Magneton. Magnetars are incredibly dense Neutron Stars that have such a strong magnetic force, any within 1 million light years of Earth would completely wipe out our communications systems, and possibly destroy the planet. Luckily for us, they seem to be too far away to be any real threat.
It could be Aliens
It could be a Black Hole
Supermassive Black Holes sit in the centre of Galaxies. Other Black Holes roam freely through space. One could be orbiting a Magnetar, which causes the strong radio pulse as two powerful energies collide.
What do you think it is?