SIMBAD references

As part of an ongoing Chandra X-ray Observatory program for precise localization of X-ray transients in low-mass X-ray binaries, we obtained a short Chandra/ACIS-S observation of the neutron star transient/X-ray burster SAX J1806.5-2215 during its current outburst (ATEL #3193, #3202, #3210). Our observation was made on 2011 March 7, 23:59 TT with an exposure time of 916 s. We used a (1/8)-subarray of the S3 chip with 0.4 s readout time in order to minimize photon pileup.

The source was detected with a measured source intensity of 1.61(4) count/s or 0.64(4) count/frame, uncorrected for pileup. We estimate a pileup fraction of less than 30 percent. The best-fit X-ray source position is:

RA(J2000) = 18h 06m 32.177s

Dec(J2000) = -22d 14' 17.20"

with an uncertainty radius of 0.6 arcsec (90% confidence). We note that this is somewhat outside the recently reported 2.0 arcsec (90% confidence) Swift X-ray error circle (ATEL #3202), lying 5.4 arcsec from its center. No other sources were detected in the 1x8 arcmin ACIS subarray field. Our measured source position is not consistent with any of the sources detected in a 2001 archival Chandra image taken during the quiescent state of SAX J1806.5-2215 (Cornelisse et al. 2002, A&A, 392, 931).