Swift Observations Near XTE J1824-141
ATel #1681; C. B. Markwardt (CRESST/U. Md./NASA/GSFC)
on 27 Aug 2008; 02:40 UT
Credential Certification: Craig B. Markwardt (craigm@lheamail.gsfc.nasa.gov)
Subjects: Infra-Red, X-ray, Binary, Neutron Star, Transient, Pulsar
Referred to by ATel #: 1686
Regarding the 120 sec X-ray pulsar XTE J1824-141 (Markwardt et al., ATEL
#1679), we requested follow-up observations with the Swift
observatory. The Swift planners concentrated on the INTEGRAL
candidate position, IGR J18246-1425 (Stephen, ATEL #1680). The
observation started on 2008-08-26 at 15:40 UT, for an exposure of 1
ks. The Swift pointing direction was RA, Dec = 276.1536, -14.39392
(J2000), and the XRT field of view is 24 x 24 arcmin^2.
In the XRT image, only one significant source appears in the image, at
position RA, Dec = 276.09833, -14.415778 (J2000), with a position
error of < 6 arcsec. The XRT candidate position is consistent with
the IGR and XTE source positions. The XRT source has a 2-10 keV flux
of about 1.4e-11 erg/cm^2/s, or ~0.6 mCrab, which is quite a bit
fainter than the recent PCA fluxes (ATEL #1679). Also, no significant
pulsations were present at the expected period of 120 seconds. The
spectrum is highly absorbed, with a neutral column density of about
8e22 cm^2 (for a power law continuum, with photon index 1.15). There
is also a rather bright infrared 2MASS catalog source within about 6
arcsec of the XRT position (K=10), designated 2MASS J18242381-1424509,
which may be a plausible X-ray binary counterpart. (Thanks to
J. Halpern for noting this; priv. comm.)
Given the lack of pulsations, the correspondence between the XTE and
IGR candidates is suggestive, but we cannot directly confirm the
association yet. The source flux is already known to be variable
based on PCA data (ATEL #1679), so the low flux observed in the XRT
source may be consistent with the PCA behavior.
