XTE J1908+094
Abstract
P. M. Woods, C. Kouveliotou, M. H. Finger, and E. Gogus, National Space Science and Technology Center; and J. Swank, C. Markwardt, and T. Strohmayer, Goddard Space Flight Center, report the serendipitous discovery of a new x-ray transient, XTE J1908+094, in RXTE PCA observations of the soft-gamma-ray repeater SGR 1900+14, triggered following the burst activity on Feb. 17-18 (GCN 1253). These observations failed to detect the 5.2-s SGR pulsations, pointing towards a possible new source as the origin of the high x-ray flux. An RXTE PCA scan of the region around SGR 1900+14 on Feb. 21 was consistent with emission only from known sources (and no new sources). However, the scans required SGR 1900+14 to be 20 times brighter than its quiescent flux level (GCN 1256). A Director's Discretionary Time Chandra observation on Mar. 11 showed that the SGR was quiescent and did not reveal any new source within the Chandra ACIS field-of-view. A subsequent RXTE PCA scan on Mar. 17, taken in combination with the first scan, required that a new source be included in the fit. The best-fit position is R.A. = 19h08m50s, Decl. = +9 22'.5 (equinox J2000.0; estimated 2' systematic error radius), or approximately 24' away from the SGR source. The source spectrum (2-30 keV) can be best fit with a power-law function including photoelectric absorption (column density N_h = 2.3 x 10**22, photon index = 1.55). Iron line emission is present, but may be due to the Galactic ridge. Between Feb. 19 and Mar. 17, the source flux (2-10 keV) has risen from 26 to 64 mCrab. The power spectrum is flat between 1 mHz and 0.1 Hz, falling approximately as 1/f**0.5 up to 1 Hz. At 1 Hz is seen a broad quasiperiodic oscillation peak and a break to a 1/f**2 power law, which continues to 4 Hz. The fractional rms amplitude from 1 mHz to 4 Hz is 43 percent. No coherent pulsations are seen between 0.001 and 1024 Hz. The authors conclude that XTE J1908+094 is a new blackhole candidate.
- Publication:
-
International Astronomical Union Circular
- Pub Date:
- March 2002
- Bibcode:
- 2002IAUC.7856....1W