Swift Observations Confirm XTE J1824-141 = IGR J18246-1425
ATel #1686; C. B. Markwardt (CRESST/U. Md./NASA/GSFC)
on 30 Aug 2008; 00:15 UT
Credential Certification: Craig B. Markwardt (craigm@lheamail.gsfc.nasa.gov)
Subjects: X-ray, Binary, Neutron Star, Transient, Pulsar
After the report of a 120 second pulsar, XTE J1824-141 (ATEL #1679),
and of a possible INTEGRAL counterpart (IGR J18246-1425; Stephen et
al., ATEL #1680), we obtained preliminary Swift XRT observations of a
small part of the RXTE PCA error circle (ATEL #1681). In that observation,
only a single source was found, consistent with the IGR source position.
We obtained further Swift XRT observations which almost completely
cover the PCA error circle (observed mostly on 2008-08-28). We can
now confirm that the previously reported Swift/IGR source is the only
reasonable counterpart in the entire PCA error circle. The next brightest
XRT source is a factor of 10 fainter, completely inconsistent with the
PCA flux. We also obtained RXTE PCA observations on 2008-08-28 at
11:20 UT which confirmed that the RXTE pulsar was still active at
approximately the same flux level, ~1 mCrab, i.e. it has not become
quiescent.
We re-examined the XRT data for pulsations. We do detect a
periodic modulation at the expected pulse period of 120.0 seconds,
with 99% confidence. We had disregarded this signal previously because
of a processing error related to the CCD frame read-out time, which
had produced some spurious aliases.
Given the detection of pulsations, we are convinced that XTE J1824-141
and IGR J18246-1425 are the same source. We note that a slightly
revised position based on the 'xrtcentroid' software is RA,Dec =
276.0990, -14.4154 (J2000) with a systematic error radius of 4.3
arcsec. (We thank A. Kong, priv. comm., for his comment on this.)
I would like to thank the Swift planners for their assistance in
planning this observation and their help afterward, especially
J. Kennea and M. Stroh.
