XMMSL1 J171900.4-353217 and XTE J1719-356 are Probably the Same Source

ATel #2615; C. B. Markwardt (U. Maryland & NASA/GSFC), T. E. Strohmayer (NASA/GSFC), J. H. Swank (NASA/GSFC)
on 12 May 2010; 19:15 UT
Credential Certification: Craig B. Markwardt (craigm@lheamail.gsfc.nasa.gov)

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Following the report of a new XMM slew transient, XMMSL1 J171900.4-353217 (Read & Saxton, ATEL #2607), we report the likely association to a transient designated XTE J1719-356, a faint transient source discovered in March 2010 by regular RXTE PCA monitoring observations of the galactic center.

The monitoring observations detected enhanced emission from that region in March 2010. Follow-up dedicated PCA scanning and pointed observations 2010-03-10 detected a source. The best fit position was R.A. = 259.97, Decl. = -35.68 (J2000), with formal statistical 3-sigma errors of 8 arcmin. This position is about 13 arcmin from the XMM position. Unfortunately this source is near the galactic ridge, and other diffuse emission, which can confuse the scanning process and contribute difficult-to-quantify systematic errors. It would not be unprecedented for a systematic error of 13 arcmin to be introduced into the scan position.

The sources have comparable fluxes of a few mCrab. Given the proximity in time between the XMM and RXTE detections and the similar fluxes, we suggest the two sources are associated. Another more remote possibility is that two transients were active at the same time, one detected by the PCA scans, and another detected by XMM.

The RXTE PCA scanning light curve is shown at the attached link, in units of ct/s/5PCU (2-10 keV, where 1 mCrab = 2.4e-11 erg/s/cm2 = 10 ct/s/5PCU). It shows that the source had a transient outburst between about 2010-03-05 and 2010-04-15, with a mean 2-10 keV flux of about 2 mCrab, and variations between 0 and ~3 mCrab. There may be other few-day flaring events with amplitudes of a few mCrab. This source is in the overlap region of several scans, and special care has been taken for the linked light curve to subtract scan-dependent biases, that was not done for the automated analysis.

Follow-up pointed observations by the PCA on 2010-03-10 detected enhanced emission. There was no obvious strong periodic or aperiodic modulations. Strong diffuse emission appears in the PCA field of view, so determination of an unambiguous spectrum was not straightforwardly possible with the PCA.

Web Link: Light Curve of XTE J1719-356