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Chandra Localization of the Neutron Star X-Ray Transients XTE J1739-285 and XTE J1701-462

ATel #777; Miriam I. Krauss (MIT), Adrienne M. Juett (U. Virginia), Deepto Chakrabarty (MIT), Peter G. Jonker (CfA/SRON), and Craig B. Markwardt (GSFC/U. Maryland)
on 28 Mar 2006; 21:39 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Deepto Chakrabarty (deepto@space.mit.edu)

Subjects: X-ray, Binary, Neutron Star, Transient

Referred to by ATel #: 780, 781, 784

We observed the neutron star soft X-ray transients XTE J1701-362 and XTE J1739-285 on 2006 March 27 with the Chandra X-Ray Observatory's High-Resolution Camera (HRC-S) in timing mode, as part of an existing program for the precise localization of neutron star/soft X-ray transients.

The transient Z source XTE J1701-462 has been active since its discovery in 2006 January (ATels #696, #725, #748). We observed the source with Chandra on March 27 for 1140 s beginning at 03:40 UT. The mean count rate was 64.1(2) ct/s. For the spectral shape previously measured by Swift/XRT (ATel #704), this corresponds a flux of 7.6e-9 erg/cm^2/s (0.5-10 keV). The best-fit source coordinates are: R.A. 17:00:58.46, Decl. -46:11:08.6, equinox J2000.0, with an error radius of 0.6 arcsec (90-percent confidence). This position is coincident with the proposed optical (ATel #706), infrared (ATel #712), and radio (ATel #710) counterparts for this source. However, it is inconsistent with the 5.8-arcsec Swift/XRT position error circle (ATel #702), lying 15.4 arcsec from its center.

The transient X-ray burster XTE J1739-285 (IAUC # 7300 ; ATel #622) was discovered in 1999, and the most recent new outburst was reported in 2005 August (ATel #592). We observed the source with Chandra on March 27 for 1156 s beginning at 03:04 UT. The mean count rate was 2.65(5) ct/s. Assuming an absorbed power-law spectrum with photon index 2 and a Galactic absorption column density of 7.8e21 cm^-2, this corresponds to a flux of 1.2e-10 erg/cm^2/s (0.5-10 keV). The best-fit source coordinates are: R.A. 17:39:53.95, Decl. -28:29:46.8, equinox J2000.0, with an error radius of 0.6 arcsec (90-percent confidence). This is consistent with the 6-arcsec Swift/XRT position error circle (ATel #602).