First Detection of the X-ray Burster 2S 1711-339 in Quiescence and a Suggested Optical Counterpart.

ATel #233; M. A.P. Torres (CfA), J. E. McClintock (CfA), M. R. Garcia (CfA), S. S. Murray (CfA)
on 13 Feb 2004; 18:16 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Jeffrey McClintock (jem@cfa.harvard.edu)

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We report on a Chandra observation of the transient low-mass X-ray binary and type-I X-ray burst source 2S 1711-339 (Carpenter et al. 1977,MNRAS,179,270; Wilson et al. 2003,ApJ,596,1220). The 2S 1711-339 region was observed with the Chandra ACIS-S3 CCD array for 25 ks on 2003 February 07. A total of 64 counts were detected from a source at R.A. = 17h:14m:19s.73, decl. = -34:02:46.9 (J2000), a position consistent with the precise position of 2S 1711-339 obtained earlier during outburst (Cornelisse et al. 2002,A&A,392,885). We fitted the Chandra spectrum using a blackbody model with the column density fixed at 1.5e22 cm-2 (Cornelisse et al. 2002) to derive an X-ray flux of 2e-15 ergs cm-2 s-1 (0.3-7.0 keV). This flux is a factor of 50 below the limit on the quiescent flux obtained by Wilson et al. (2003) and represents a definitive detection of 2S 1711-339 during quiescence.

We determined the position of the probable optical counterpart of 2S 1711-339 by matching USNO-B1.0 stars against six 5-min R-band images of the field that we acquired at the 6.5-m Magellan telescope with the MagIc camara at the Las Campanas Observatory. The frames were obtained with a seeing of 0.7 arcsec and a projected pixel size of 0.069 arcsec. The plate solution has an rms position uncertainty of 0.3 arcsec and shows a R=19.4 +/- 0.1 star located at R.A. = 17h14m19s.68, decl = -34:02:46.5. The offset from the X-ray position is 0.8 +/- 0.7 arcsec; thus, the position of the optical source is consistent with the position for 2S 1711-339. Two unresolved stars located 1.4 +/- 0.7 arcsec SE from the Chandra position are probably not related to the X-ray source.