Chandra Observations of IGR J17511-3057: A Revised Source Position
ATel #2215; M. A. Nowak (MIT-CXC), A. Paizis (INAF-Milano), J. Wilms (Remeis-Observatory & ECAP), J. Rodriguez (CEA), S. Chaty (CEA),K. Ebisawa (ISAS), M. Del Santo (IASF-Roma), R. Farinelli (U. Ferrara), P. Ubertini (IASF-Roma), T. Courvoisier (ISDC)
on 25 Sep 2009; 16:08 UT
Credential Certification: Joern Wilms (firstname.lastname@example.org)
Subjects: X-ray, Binary, Neutron Star, Pulsar
Chandra-HETG observations were performed on the bursting accreting
milli-second X-ray pulsar IGR J17511-3057 (Baldovin et al. ATEL #2196,
and further reported upon in ATEL #2197, #2198, #2199). We have used
these observations to refine the X-ray position. By intersecting the
image of the Medium Energy Grating (MEG) dispersed spectra with the
CCD readout streak from the 0th order image, we find a J2000.0
RA: 17 51 08.66
Dec: -30 57 41.0
We estimate that the 1sigma statistical error on the position is 0.1
arcsec, while the 1sigma systematic error on the position is 0.6
arcsec. As there are no other X-ray sources observed within the field
of view, the latter is determined by the absolute accuracy with which
the Chandra aspect solution is typically known.
Note that this position is slightly more than 5 arcsec away from the
position reported by Bozzo et al. (ATEL #2198), which was determined
from a Swift observation. We have reexamined the Swift data and find
that the Chandra error circle lies within the Swift source image, and
furthermore that due to pileup effects, the Swift error circle was
considerably larger than the originally reported 3.5 arcsec.
The Chandra-HETG observations began on 2009 Sept. 22 7:40 UT and
lasted for 20 ksec. We have performed simple phenomenological
(absorbed disk plus powerlaw) fits to the gratings spectra. The
spectra are consistent with being absorbed by a column of
approximately 1.3x1022 cm-2. The absorbed 0.5-5 keV flux is 1.9x10-10
ergs cm2 sec-1 (6 mCrab), and the absorbed 2-10 keV flux is 3.2x10-10 ergs cm-2 sec-1 (13 mCrab).
The Chandra lightcurve shows an X-ray burst occurring approximately
17.5 ksec into the observation, rising in less than a few 10s of
seconds and completely decaying in less than 200 seconds. (These data
have been excluded from the above spectral fits.) Owing to the CCD
pileup present during the burst, further details of the burst
properties await a more careful analysis.
We would like to thank the Chandra team for their rapid response in
both scheduling this Target of Opportunity observation and in
delivering the data.