Temporary EHBL-like behavior of Markarian 501 during July 2014 VHE flaring

Abstract Markarian 501, a BL Lac object well-known as a high energy gamma-ray source, has exhibited several epochs of very high energy (VHE) gamma-ray flaring events when its synchrotron peak frequency shifted above $$10^{17}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mn>10</mml:mn> <mml:mn>17</mml:mn> </mml:msup> </mml:math> Hz, a signature of extreme behavior. From July 16 to July 31, 2014 such flaring events were observed for 15 days by various telescopes. On July 19 (MJD 56857.98), the X-ray outburst from the source was at its highest and on the same day an intriguing narrow peak-like feature around 3 TeV was observed by the MAGIC telescopes, a feature inconsistent with standard interpretations. Using the well-known two-zone photohadronic model, we study these VHE gamma-ray spectra on a day-by-day basis and offer explanation. Our two-zone photohadronic scenario shows that, on MJD 56857.98, the peak-like feature appears at a cutoff energy of $$E^c_{\gamma }=3.18$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msubsup> <mml:mi>E</mml:mi> <mml:mi>γ</mml:mi> <mml:mi>c</mml:mi> </mml:msubsup> <mml:mo>=</mml:mo> <mml:mn>3.18</mml:mn> </mml:mrow> </mml:math> TeV. Below this energy the VHE spectrum increases slowly and is in high emission state. However, for $$E^c_{\gamma }\, &gt; 3.18$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msubsup> <mml:mi>E</mml:mi> <mml:mi>γ</mml:mi> <mml:mi>c</mml:mi> </mml:msubsup> <mml:mspace/> <mml:mo>&gt;</mml:mo> <mml:mn>3.18</mml:mn> </mml:mrow> </mml:math> TeV, the spectrum falls faster, resulting in a mild peak-like feature, not prominent enough as claimed by the MAGIC collaboration.