Extremely High energy peaked BL Lac nature of the TeV blazar Mrk 501
  Extremely High energy peaked BL Lac (EHBL) objects are a special class of
blazars with peculiar observational properties at X-ray and $\gamma$--ray
energies. The observations of these sources indicate hard X-ray and
$\gamma$--ray spectra and absence of rapid flux variations in the
multi-wavelength light curves. These observational features challenge the
leptonic models for blazars due to unusually hard particle spectrum in the
emission region of the blazar jet and provide a strong motivation for exploring
alternative scenarios to interpret the broad-band emission from blazars. At
present, only few TeV blazars have been observed as EHBL objects in the
extragalactic Universe. Due to their hard $\gamma$--ray spectra and long term
variability, the observations of EHBL type of blazars at different redshifts
help in probing the cosmic magnetic field and extragalactic background light in
the Universe. Such objects also provide astrophysical sites to explore the
particle acceleration mechanisms like magnetic reconnection and second order
Fermi acceleration. Therefore, it has become important to identify more objects
as EHBL using the observations available in the literature. Recent studies on
the blazar Mrk 501 indicate that this source may exhibit an EHBL behaviour. In
this paper, we use long term observations of Mrk 501 to explore its nature. Two
sets of data, related to low and high/flaring activity states of Mrk 501, have
been presented and compared with the observed features of a few well known EHBL
type of blazars.
