RXTE Discovers XTE J1824-141 - An Intermittent 120 sec Pulsar

ATel #1679; C. B. Markwardt (CRESST/U. Md./NASA/GSFC), D. Pereira (WIS/NASA/GSFC), P. S. Ray (NRL), E. Smith (WIS/NASA/GSFC), J. H. Swank (NASA/GSFC)
on 25 Aug 2008; 22:41 UT
Credential Certification: Craig B. Markwardt (craigm@lheamail.gsfc.nasa.gov)

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During PCA scans of the galactic ridge region on 2008-08-14, RXTE detected a new excess. Follow-up observations revealed a previously unknown pulsar with period 120 seconds. Unfortunately, it is difficult to determine the position of such a variable source with standard PCA scanning techniques.

We performed a set of 9 raster grid observations to try to localize the source further. The strongest pulsations were detected at position (RA,Dec) = 276.02, -14.15 (J2000). We expect the source to be within 30 arcminutes of this position. We designate the source XTE J1824-141.

The position of the source is near the high-mass X-ray binary LS 5039. One of us (P.R.) has serendipitous monitoring observations of LS 5039 which included XTE J1824-141 in the PCA field of view, and the pulsar was detected intermittently in several of them, as far back as June 2008.

The flux of XTE J1824-141 was between 1-3 mCrab (2-10 keV), with the pulsed flux being about 1 mCrab peak to peak. The source has not been detected by BAT monitoring observations (J. Cummings, priv. comm.). This suggests a weak source, possibly with a spectral cut-off at 10-20 keV. The spectrum, period and variability of the source are suggestive of a Be-binary pulsar system.

Because of the intermittent and pulsed nature of the source, we have found it difficult to localize the source further. Additional suggestions or observations would be welcome.