A previously unseen maser in the J = 1 - 0 transition of HCO ^ { + } has been detected by the Combined Array for Millimeter-wave Astronomy ( CARMA ) .
A sub-arcsecond map was produced of the 2 arcmin ^ { 2 } region around DR21 ( OH ) , which has had previous detections of OH and methanol masers .
This new object has remained undetected until now due to its extremely compact size .
The object has a brightness temperature of > 2500 K and a FWHM linewidth of 0.497 km s ^ { -1 } , both of which suggest non-thermal line emission consistent with an unsaturated maser .
This object coincides in position and velocity with the methanol maser named DR21 ( OH ) -1 by Plambeck & Menten ( 10 ) .
No compact HCO ^ { + } emission was present in the CARMA data towards the other methanol masers described in that paper .
These new results support the theory introduced in Plambeck & Menten ( 10 ) that these masers likely arise from strong outflows interacting with low mass , high density pockets of molecular gas .
This is further supported by recent observations of a CO outflow by Zapata et al .
( 14 ) that traces the outflow edges and confirms that the maser position lies along the edge of the outflow where interaction with molecular tracers can occur .