Refined position and spectrum for XTE J1720-318

ATel #115; C. B. Markwardt (U. Maryland and GSFC)
on 16 Jan 2003; 00:24 UT
Credential Certification: Craig B. Markwardt (craigm@lheamail.gsfc.nasa.gov)

Tweet

I report further information on RXTE PCA observations of the new transient XTE J1720-318. Observations from 2002 Jan 15.06-15.10 were analyzed, the first 1500 ks of which contained a raster scan pattern, and remainder was pointed near the source position. From the raster scan portion of the data, I determine a best-fit position to be R.A.(J2000) = 17h20m00s, Decl.(J2000) = -31d44.8m. The estimated position error is likely to be dominated by systematic errors in the modeling process, with error radius in the 0.5 to 1 arcminute range. Based on the pointed data, the flux was determined to be 410 +/- 20 mCrab (2-10 keV). A very good spectral fit was achieved using an absorbed blackbody plus power law continuum model, with a temperature of 0.6 keV and photon index of 2.0 for each component respectively. The ratio of black body to power law fluxes in the 2-10 keV band was about 10 to 1. An iron line was present in the spectrum with an equivalent width of about 95 eV. The centroid energy was 6.2 keV, however the line is significantly broadened with a FWHM of 2.5 keV. Since no evidence of reflection or edges was seen, it is possible that the broadening is due to relativistic effects. Some variability on time scales < 1 Hz were detected, but no low or high frequency oscillations were found. XTE J1720-318 is approximately 6 degrees from the galactic center. If placed at the same distance, the 2-10 keV luminosity would be of order 10^{39} erg/s. This consideration, along with the spectral and timing properties, suggests that the sources is a black hole candidate in the so-called "high" state. RXTE will continue to observe the source.