Model-independent redshift estimation of BL Lac objects through very-high-energy observations

The very high energy (VHE) gamma-ray spectral indices of blazars show strong correlation with the source redshift. Absence any such in low gamma rays and X-rays indicate presence Extragalactic Background Light (EBL) induced absorption VHE rays. By employing a linear regression analysis, this observational feature is used to constrain redshift BL Lac objects which was unknown/uncertain earlier. Additionally, we also compare observed index-redshift ones predicted from commonly adopted EBL models. Our study highlights deviation model based predictions observation especially at redshifts.