  The high energy blazar, Markarian 501 was observed as a part of
multi-instrument and multiwavelength campaign spanning the whole
electromagnetic spectrum for 4.5 months during March 15 to August 1, 2009. On
May 1, Whipple 10m telescope observed a very strong $\gamma$-ray flare in a
time interval of about 0.5 h. Apart from this flare, high state and low state
emissions were also observed by Whipple, VERITAS and MAGIC telescopes. Using
the photohadronic model and accounting for the absorption of the extragalactic
background light (EBL) to these very high energy $\gamma$-rays, excellent fits
are obtained for the observed spectra. We have shown that the intrinsic
spectrum for low state emission is flat, however, for high and very high states
this is a power-law with slowly increasing exponent.
