We used the Magellan adaptive optics ( MagAO ) system and its VisAO CCD camera to image the young low mass brown dwarf companion CT Chamaeleontis B for the first time at visible wavelengths .
We detect it at r ^ { \prime } , i ^ { \prime } , z ^ { \prime } , and Y _ { S } .
With our new photometry and T _ { eff } \sim 2500 K derived from the shape its K - band spectrum , we find that CT Cha B has A _ { V } = 3.4 \pm 1.1 mag , and a mass of 14 - 24 M _ { J } according to the DUSTY evolutionary tracks and its 1 - 5 Myr age .
The overluminosity of our r ^ { \prime } detection indicates that the companion has significant H \alpha emission and a mass accretion rate \sim 6 \times 10 ^ { -10 } \mbox { $M _ { \odot } $ } / \mbox { yr } , similar to some substellar companions .
Proper motion analysis shows that another point source within 2 \arcsec of CT Cha A is not physical .
This paper demonstrates how visible wavelength AO photometry ( r ^ { \prime } , i ^ { \prime } , z ^ { \prime } , Y _ { S } ) allows for a better estimate of extinction , luminosity , and mass accretion rate of young substellar companions .