Steven H. Pravdo et al. 2009 ApJ 690 850 doi:10.1088/0004-637X/690/1/850
Steven H. Pravdo1, Yohko Tsuboi2, Yuichiro Suzuki2, Timothy J. Thompson3 and Luisa Rebull4
Show affiliationsWe report the discovery of a cluster of Class I protostars in GGD 27. One of these protostars is the previously known, centrally located, GGD 27-ILL, which powers a massive bipolar outflow. We show that GGD 27-ILL, which is known to be the bright infrared (IR) source, IRAS 18162-2048, and a compact radio continuum source, is also the newly discovered hard X-ray source, GGD 27-X. The observations were made with the ACIS instrument on the Chandra X-ray Observatory. The X-rays from GGD 27-X are variable when compared with 4 years earlier, with an unabsorbed 2-10 keV X-ray luminosity in this observation of 1.5-12 × 1031 erg s–1 and a plasma temperature of ≥ 107 K. The X-rays are probably associated with the underlying B0 star (rather than outflowing material), providing a rare glimpse in hard X-rays of an optically obscured massive protostar with an outflow. The X-ray luminosity and spectrum appear to be consistent with stars of its type in other star formation regions. Several other variable X-ray sources are also detected in the IR cluster that contains GGD 27-X. We also discuss another nearby cluster. In each of the clusters there is an object that is X-ray hard, highly absorbed at low energies, in a blank optical/IR/radio field, and variable in X-ray intensity by a factor of ≥ 10 on a timescale of 4 years. These latter objects may arise from more recent episodes of star formation or may be "hidden" Class III sources.
Issue 1 (2009 January 1)
Received 2008 March 17, accepted for publication 2008 September 9
Published 2008 December 1
Steven H. Pravdo et al. 2009 ApJ 690 850
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