2003IAUC.8109....2K

C. Kouveliotou, Marshall Space Flight Center (MSFC) and Universities Space Research Association (USRA); S. Patel, National Research Council; A. Tennant, MSFC; P. Woods and M. Finger, USRA; and S. Wachter, SIRTF Science Center, California Institute of Technology, report that IGR J16358-4726 (cf. IAUC 8097) was observed for 25700 s serendipitously with the Chandra X-ray Observatory during a scheduled observation of SGR 1627-41 starting on Mar. 24.17 UT. The source was approximately 9'.7 off axis. A fit to the off-axis image was found to be consistent with the point-spread function and put the transient at R.A. = 16h35m53s.8, Decl. = -47o25'41".1 (equinox 2000.0; error radius 0".6). The spectrum of the source is hard and highly absorbed, consistent with a power law of index 0.5(1) plus a line feature at 6.4 keV and a column density of N_H = 3.3 x 10**23 cm**-2. The source flux (unabsorbed) is 1.7 x 10**-10 (2-10 keV). Pulsations with a period of 5850(50) s are directly visible in the x-ray light curve with an energy-dependent amplitude; the pulse fraction between 2 and 10 keV is 63(6) percent, peak-to-peak. It is unclear whether these pulsations reflect a spin or orbital period, or a high-coherence quasiperiodic oscillation. A search for an infrared counterpart in the 2MASS All Sky Catalog reveals a relatively bright source 1".7 from the Chandra position of IGR J16358-4726 (2MASS J16355369-4725398, with J = 15.41, H = 13.44, K = 12.59). Further observations are encouraged.