Detection of Halpha emission from PZ Telescopii B using SPHERE/ZIMPOL

H alpha is a powerful tracer of accretion and chromospheric activity, which has been detected in the case of young brown dwarfs and even recently in planetary mass companions (e.g. PDS70 b and c). H alpha detections and characterisation of brown dwarf and planet companions can further our knowledge of their formation and evolution, and expanding such a sample is therefore our primary goal. We used the Zurich Imaging POLarimeter (ZIMPOL) of the SPHERE instrument at the Very Large Telescope (VLT) to observe the known 38 72 M-J companion orbiting PZ Tel, obtaining simultaneous angular differential imaging observations in both continuum and narrow H alpha band. We detect H alpha emission from the companion, making this only the second H alpha detection of a companion using the SPHERE instrument. We used our newly added astrometric measurements to update the orbital analysis of PZ Tel B, and we used our photometric measurements to evaluate the H alpha line flux. Given the estimated bolometric luminosity, we obtained an H alpha activity (log(L-H alpha= L-bol)) between -4.16 and -4.31. The H alpha activity of PZ Tel B is consistent with known average activity levels for M dwarf of the same spectral type. Given the absence of a known gaseous disk and the relatively old age of the system (24 Myr), we conclude that the H alpha emission around PZ Tel B is likely due to chromospheric activity.