2009A&A...506..281R

The CoRoT space mission continues to photometrically monitor about 12000 stars in its field-of-view for a series of target fields to search for transiting extrasolar planets ever since 2007. Deep transit signals can be detected quickly in the ``alarm-mode'' in parallel to the ongoing target field monitoring. CoRoT's first planets have been detected in this mode. The CoRoT raw lightcurves are filtered for orbital residuals, outliers, and low-frequency stellar signals. The phase folded lightcurve is used to fit the transit signal and derive the main planetary parameters. Radial velocity follow-up observations were initiated to secure the detection and to derive the planet mass. We report the detection of CoRoT-5b, detected during observations of the LRa01 field, the first long-duration field in the galactic anti-center direction. CoRoT-5b is a ``hot Jupiter-type'' planet with a radius of 1.388^+0.046_–0.047R_Jup, a mass of 0.467^+0.047_–0.024 M_Jup, and therefore, a mean density of 0.217^+0.031_–0.025g/cm³. The planet orbits an F9V star of 14.0mag in 4.0378962 ±0.0000019-days at an orbital distance of 0.04947^+0.00026_–0.00029AU.