Chandra Localization of IGR J17494-3030
ATel #14146; Deepto Chakrabarty (MIT), Peter G. Jonker (SRON)
on 4 Nov 2020; 02:06 UT
Credential Certification: Deepto Chakrabarty (deepto@space.mit.edu)
Subjects: X-ray, Binary, Neutron Star, Transient, Pulsar
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 Swift J17494-3030, following a report that it was in outburst (ATel #14119, #14126). The source was recently identified as a 376 Hz accreting millisecond X-ray pulsar in an ultracompact 75-min binary (ATel #14124).
Our 1069.2 s observation was made on 2020 November 3, 08:03 TT (MJD 59156.34), which was 11 days after the new outburst was
detected by INTEGRAL/IBIS/ISGRI (ATel #14119). We used a (1/8)-subarray of the ACIS S3 chip with 0.4 s frame time, in order to
minimize photon pileup. The source was detected with a measured count rate of 0.41(2) count s-1 or 0.16(1) count frame-1, uncorrected for pileup. We estimate a pileup fraction of less than 10 percent. The time series was consistent with a constant count rate. The pileup-uncorrected data are well fit by an absorbed power-law spectral model with photon index Gamma=2.6(2), where we have assumed an absorption column density of NH=2x1022 cm-2 based on recent NICER measurements (ATel #14124). This corresponds to an absorbed (unabsorbed) X-ray flux of 6.0x10-12 (2.0x10-11) erg cm-2 s-1 in the 0.5-10 keV band.
The best-fit X-ray source position is:
RA(J2000) = 17h 49m 23.62s
Dec(J2000) = -30d 29m 59.0s
with an uncertainty radius of 0.6 arcsec (90-percent confidence). This is consistent with the 2.2 arcsec Swift/XRT error circle (ATel #3989), lying 2.1 arcsec from its center. It is also consistent with the proposed VLA radio counterpart (ATel #14129), lying 0.2 arcsec away.
