Detection of a Candidate for the Exciting Source of the Expanding Water Maser Bubble in Cepheus A

We report sensitive, high angular resolution VLA 3.6 cm and 7 mm continuum observations toward the star-forming region Cepheus A. Three embedded young stellar objects (YSOs) were found within a projected area of ≃0 6 × 0 6 (400 × 400 AU 2 ). One of the sources is the already known radio continuum jet HW2 (detected at 3.6 cm and 7 mm), while the other two weak sources were not previously known. One of these two new sources is detected only at 7 mm and is located ≃0 15 south from HW2. The other source, detected only at 3.6 cm, is located 0 6 south from HW2 and nearly coincides with the center of the enigmatic expanding bubble of water masers recently detected with the Very Long Baseline Array. We suggest that this radio continuum source is the embedded YSO powering the water maser structure, but its nature is still unknown at present. We also discuss possible scenarios that could explain the surprisingly precise spherical geometry of the water maser bubble.