We present the low-resolution transmission spectra of the puffy hot Jupiter HAT-P-65b (0.53 MJup, 1.89 RJup, Teq = 1930 K), based on two transits observed using the OSIRIS spectrograph on the 10.4 m Gran Telescopio CANARIAS. The transmission spectra of the two nights are consistent, covering the wavelength range 517–938 nm and consisting of mostly 5 nm spectral bins. We perform equilibrium-chemistry spectral retrieval analyses on the jointly fitted transmission spectrum and obtain an equilibrium temperature of 1645 (-244+255) K and a cloud coverage of 36 (-17+23) %, revealing a relatively

The most extreme electromagnetic radiation that can be observed is known as very high energy gamma rays (VHE, E>100 GeV). It is the last window open to the Universe, thanks to the development of the Cherenkov telescopes. The extragalactic VHE sky is still nowadays vastly unexplored, only composed of around 80 known sources. The great majority of them are classified as blazars, a type of Active Galactic Nuclei (AGN) whose relativistic jets point in the direction of the Earth boosting their emission. While the observation of the gamma-ray emission is crucial to understand the extreme physical

Blazars, Active Galactic Nuclei (AGN) whose relativistic jets point in the direction of the Earth, dominate the VHE (VHE, E>100 GeV) gamma-ray extragalactic sky. One of the most famous archetypical VHE gamma-ray emitters is the blazar Markarian 501 (Mrk 501). During July 2014, the source displayed a strong flare detected across all wavelengths from VHE to the optical band. In particular, it is especially interesting that the source reached the maximum flux and harder spectrum measured in the X-ray band, compatible with the most extreme historical flare from this source. On 2014 July 19