XTE J1811-197: Position and Fluxes of A New 5.54 s pulsar
ATel #167; C. B. Markwardt (U. Md. & GSFC), A. I. Ibrahim (GWU), J. H. Swank (GSFC)
on 23 Jul 2003; 14:49 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Craig B. Markwardt (craigm@lheamail.gsfc.nasa.gov)
Subjects: X-ray, Request for Observations, Neutron Star, Soft Gamma-ray Repeater, Transient, Pulsar
Referred to by ATel #: 188
In Ibrahim et al. (GCN #2306), we reported the presence of a 5.54 s
pulsar, detected in the RXTE PCA field of an observation of SGR
1806-20. At the time, we speculated that the pulsar could either be
the source of soft gamma repeater bursts seen by the IPN (GCN #2297);
or, a previously unknown pulsar simultaneously active with the known
SGR 1806-20. Since then, Hurley et al. (GCN #2308) have concluded
that HETE data agree with the IPN that SGR 1806-20 is the likely
source of the bursts.
An RXTE PCA scanning observation was performed on Jul 18.23-18.27
(UT). A new source was detected, whose position is, R.A. = 18h10.9m,
Decl. = -19o42' (equinox 2000.0), with estimated 99% confidence
semi-major axes of 5' in R.A. and 7' in Decl. This confidence region
is not consistent with either the IPN burst annuli (GCN #2297) or the
HETE burst error region (GCN #2308), or with any other known pulsar of
that period. Thus, we designate this new source as XTE J1811-197.
The best fit position is 21' from the galactic plane. See the
following web
page for more details.
The fitted flux of XTE J1811-197 was 2.5 +/- 0.2 mCrab (2-10 keV),
which is comparable to flux of SGR 1806-20 (1.1 +/- 0.1 mCrab) and the
galactic diffuse emission (2.9 mCrab), which are also in the field of
view. Assuming a distance of 8.5 kpc, the luminosity is approximately
10^{36} erg/s.
In retrospect, the source has been present in the RXTE PCA galactic
bulge monitoring program at the very edge of the scan region since Feb
7, and has declined steadily from an initial flux of 3.6 mCrab (2-10
keV).
The spectra of the sources were deconvolved by selecting light curves
of different energy bands and fitting the source intensities while
holding the positions constant. The resulting spectrum of XTE
J1811-197 is consistent with a power law of photon index ~4. Such a
soft spectrum is not typical of high mass X-ray binaries, and based on
the pulse period, one might speculate that it is an anomalous X-ray
pulsar. On the other hand, the long term light curve is more typical
of a transient pulsar in an X-ray binary.
Position of XTE J1811-197
