Status of the new Sum-Trigger system for the MAGIC telescopes

MAGIC is a stereoscopic system of two 17m diameter Imaging Air Cherenckov Telescopes (IACTs) for $\gamma$-ray astronomy. Lowering the energy threshold of IACTs is crucial for the observation of Pulsars, high redshift AGNs and GRBs. A lower threshold compared to conventional digital trigger can be achieved by means of a novel concept, the so called Sum-Trigger, based on the analogue sum of a patch of pixels. The Sum-Trigger principle has been proven experimentally in 2007 by decreasing the energy threshold of the first MAGIC telescope from 55GeV down to 25GeV. The first VHE detection of the Crab Pulsar was achieved due to this low threshold. After the upgrade of the MAGIC I and MAGIC II, a new Sum-Trigger system will be installed in both telescopes in Summer 2013. The expected trigger threshold in stereo mode is about 25$\div$30GeV. It is a an improvement over the existing threshold (about 50GeV) of the digital trigger. We will report about the current status of the project.