Studies of the microwave emission of extensive air showers with GIGAS and MIDAS at the Pierre Auger Observatory

In 2008, a radio signal interpreted as Molecular Bremsstrahlung Radiation (MBR) was detected at SLAC at microwave frequencies from electromagnetic showers produced in beam test exper- iments. Due to the isotropic nature of MBR and its insensitivity to atmospheric attenuation and light conditions, it would allow the measurement of the shower longitudinal profile with an al- most 100% duty cycle compared to 15% at most with the fluorescence technique today. Several experiments either in the laboratory or in situ within cosmic-ray observatories have been set up aiming at the detection of the MBR flux. The Pierre Auger Observatory has been used as the base for two experiments pursuing the detection of the MBR at GHz frequencies. MIDAS is a radio telescope instrumented with a parabolic dish focusing the radio signal on an array of 53 horn antennas and has taken data for 2 years. GIGAS on the other hand is a single antenna detector embedded in a surface detector. It was implemented in three different versions with a gradually improved sensitivity to comply with the evolution in the expected MBR intensity. We review these two experimental efforts undertaken at the Pierre Auger Observatory attempting at MBR detection and present their latest results.