On the first episode of To Aru Majutsu No Index, Touma said
Magic is impossible, psychic powers aren't even rare at this city school. Anyone can invent it with the powers of science.
And Touma himself said that he got his power since he was born.
So, is there anyone in Index and Railgun who become an esper using science?
Note: I haven't finished watching Index, but I've watch Railgun, and I don't think there's anyone able to do this.