Further Swift observations of XTE J1810-189
ATel #1441; R. Starling (U. Leicester), J. Kennea (PSU), H. Krimm (CRESST/GSFC/USRA)
on 25 Mar 2008; 23:48 UT
Credential Certification: Rhaana Starling (firstname.lastname@example.org)
Subjects: Infra-Red, Optical, Ultra-Violet, X-ray, Binary, Transient
Swift re-observed the possible high mass X-ray binary XTE J1810-189
(Krimm, Kennea and Tueller, ATEL#1432; Markwardt and Swank, ATEL#1424)
at 16:55 UT on March 18, 2008.
Here we report an improved position based on 1.3 ks of XRT Photon Counting
mode data from these observations of RA,Dec = 272.58535, -19.07026
deg, equivalent to:
RA (J2000) = 18h 10m 20.48s
Dec (J2000) = -19d 04' 12.9"
with an uncertainty of 3.5 arcseconds (radius, 90% containment). This is
within the previously reported error circle, 3.7 arcseconds from its
We note that this observation is not affected by the hot columns.
The X-ray spectrum is consistent with that observed previously
(ATEL#1432), well fitted with an absorbed power law of photon index
Gamma = 2.0+/-0.3 and total absorption (at z=0) N_H = (3.8+/-0.6)e22 cm^-2
(including the Galactic contribution of approximately 1.3e22 cm^-2). A
correction for pile-up has been applied.
We measure an observed (unabsorbed) 0.3-10 keV flux of 4.3e-10 (5.6e-10)
erg cm^-2 s^-1, somewhat higher than previously measured.
This new position is inconsistent (using the 90% error circle) with the
proposed IR counterpart 2MASS 18102072-1904093 (ATEL#1432),
lying 5 arcseconds away, but is consistent with another IR source: 2MASS
1810233-1904136 which has 2MASS reported magnitudes of J=14.68+/-0.05,
H=13.01+/-0.06, K=12.32+/-0.05. We propose that 2MASS 1810233-1904136 is
the more likely IR counterpart of XTE J1810-189.
Swift UVOT observed the field beginning with a long exposure in v band, thereafter
cycling through all six lenticular filters. The source was
not detected in any filter, though we note the very high Galactic
extinction in this direction of E(B-V) = 18.3, and we derive the following
3-sigma upper limits on the magnitudes:
|filter||Texp (s)||mag limit