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RXTE PCA detects a new transient, XTE J1810-189

ATel #1424; C. B. Markwardt (CRESST/U. Md/NASA GSFC), J. H. Swank (NASA GSFC)
on 14 Mar 2008; 19:45 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Craig B. Markwardt (craigm@lheamail.gsfc.nasa.gov)

Subjects: X-ray, Binary, Transient, Pulsar

Referred to by ATel #: 1430, 1432, 1441, 1443, 1446, 1633, 4752

During recent monitoring scans of the galactic ridge region, the RXTE PCA detected a new source, designated XTE J1810-189. A dedicated cross scan yielded a position (RA,Dec) = (272.646,-18.924) (J2000), with a 95% error radius of about 3.2 arcmin.

A pointed observation on 2008-03-10 21:05 UTC detected a variable source (30% r.m.s. fluctuations). There is an indication of a QPO, or possibly weak pulsations, at a period of 110 sec. The spectrum is consistent with an absorbed power law (N_H = 1e22 cm-2, photon index 1.9). An iron line at 6.4 keV was present, but there may be contamination by diffuse galactic ridge emission. X-ray fluxes in the 2-10 keV, 10-20 keV and 20-40 keV bands were 2.5e-10, 1.3e-10, 1.4e-10, respectively (in units of erg s-1 cm-2, uncorrected for diffuse contamination). The cross-scan detection was on 2008-03-13 18:13 UTC.

Based on the PCA scans, the flux history suggests a gradual rise starting on Mar 5. The fluxes on Mar 3.99, 9.01 and 12.27 were 3.1, 2.8 and 15.1 mCrab, respectively. There were no previous detections in 2008 (< 1.6 mCrab, 95% confidence).