H1722 + 119 - A highly polarized X-ray-selected BL Lacertae object

A 15th-mag, X-ray-selected BL Lac object, H1722 + 119, has been discovered to possess a steep X-ray spectrum with power-law energy index near 1.3; radio measurements indicate a variable, compact source with 1.4-4.9 GHz power-law energy index of 0.04. The optical-IR polarization of H1722 + 119 reaches a maximum of 17 percent, which is much higher than other X-ray-selected BL Lac objects. The degree of polarization is found to be wavelength-dependent, decreasing monotonically toward the IR.