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K. Xilouris (NAIC), D.R. Lorimer (Cornell University), C. Kouveliotou (USRA at NASA/MSFC), R. Ramachandran (University of Amsterdam), J. van Paradijs (University of Amsterdam \& University of Alabama , Huntsville), M. Goss (NRAO)
We have observed the soft gamma-ray repeater SGR~1900+14 with the Arecibo telescope for seven days after the source became active again in June 1998. A search for pulsed radio emission at 0.43 and 1.4 GHz did not reveal the 5.16 s period reported for SGR~1900+14. Based on our original and follow up observations we place an upper flux density limit of 150 \mu Jy. We are presently trying to improve this limit by incoherently stacking power spectra.
During our search we have discovered a 226-ms radio pulsar, PSR~J1907+0918. Deep imaging with the VLA lead to the identification of the pulsar with a 0.2 mJy source at R.A.=19h07m22s.37, Decl =+9\circ18\prime27\prime\prime.03 (equinox 2000.0). The Arecibo observations of PSR~J1907+0918 show that it has a relatively flat spectrum with a spectral index of > -1. At 1.4 GHz the mean flux density is ~ 0.3 mJy. The pulsar appears to scintillate showing a flux variability of about 17% in time-scales of one hour. The pulse profile at high frequencies has a duty cycle of 2.0% - somewhat narrower than most pulsars of this type. Measurements of the pulse period over a 120-day baseline give a period derivative of (1±2) \times 10-13 s/s (3\sigma upper limit). Preliminary timing observations at L and S-band suggest a dispersion measure of 400± pc cm-3 indicating a distance ~8 kpc. This is the first pulsar to be discovered with the recently upgraded Arecibo telescope at L-band. This serendipitous discovery suggests that high frequency observations can potentially reveal many more flat spectrum low luminosity objects, along highly dispersive areas such as the spiral arms of our Galaxy.