Detection of Formaldehyde Maser Emission near the Ultracompact H II Region G29.96-0.02

Using the Very Large Array (VLA) we have discovered the third Galactic source showing maser emission in the 6 cm transition of H2CO toward the molecular environment of the cometary ultracompact H ll region G29.96-0.02. The maser appears projected against a dense, hot core traced by high-excitation ammonia emission that also has associated water masers. The luminosity of the new maser is comparable to the values found for the H2CO masers in the Sgr B2 region. High-sensitivity observations toward seven other star-forming regions did not reveal any additional maser, confirming that H2CO maser emission is indeed a rare phenomenon.