Chandra observation of the unidentified TeV gamma-ray source HESS J1303-631 in the galactic plane

The imaging atmospheric Cerenkov array HESS recently discovered an extended source in the 0.4 - 10 TeV energy range, HESS J1303 - 631. We obtained a 5 ks observation with the ACIS-I array on the Chandra X-Ray Observatory that does not reveal an obvious compact or diffuse X-ray counterpart. Archival ROSAT images are also blank in this region. Although there are several radio pulsars within the field of HESS J1303 - 631, none is detected in X- rays to a flux limit of < 5 x 10(-14) ergs cm(-2) s(-1), and none is a likely counterpart on energetic grounds. Over the entire 17' x 17' ACIS- I field, we place an upper limit of < 5.4 x 10(-12) ergs cm (-2) s (-1) on the excess diffuse flux in the 2 - 10 keV band. One hard point source with flux approximate to 4 x 10(-14) ergs cm(-2) s(-1) lies within 0.'5 of the centroid of the TeVemission. These exploratory observations suggest that deeper pointings with Chandra and XMM- Newton are needed before we can learn more about the nature of HESS J1303 - 631. Its similarity to the unidentified source TeV J2032+ 4130 indicates the probable existence of a new class of high-energy source in the Galactic plane that originates from young, massive stars or their supernova remnants.