Strong gravitational lensing in hairy Schwarzschild background

We consider the hairy Schwarzschild black hole that evades the no-hair theorem. The hair is induced by additional sources from the surroundings, namely dark matter, that has a constant energy-momentum tensor (EMT). Hair parameter was designated by l(0). We study the strong gravitational lensing of light in the background of the hairy Schwarzschild black hole. We observe that the lensing coefficient a increases with deviation parameter alpha, but decreases with primary hair l(0). The opposite effect is observed for the lensing coefficient b and the impact parameter bm. We also notice that the angular position theta(infinity) decreases with alpha but increases with l(0), whereas the angular separation s increases with alpha and decreases with l(0). For all parameters mentioned, we regain their values for the Schwarzschild black hole whenever we put either alpha = 0 or take the limit l(0) -> 2M. With the help of the Gauss-Bonnet theorem, we briefly describe the weak gravitational lensing in the background of the hairy Schwarzschild black hole.