1. Department of Physics, University of North Bengal, Siliguri, Darjeeling 734 013, West Bengal, India
2. Astrophysics and Cosmology Research Unit, School of Mathematics, Statistics and Computer Science, University of KwaZulu-Natal, Private Bag X54001, Durban 4000, South Africa
3. Department of Mathematical Sciences, University of Zululand, Private Bag X1001, Kwa-Dlangezwa 3886, South Africa
4. Faculty of Natural Sciences, Mangosuthu University of Technology, P.O. Box 12363, Jacobs 4026, South Africa