THE PERSISTENT X-RAY PULSAR AND CYCLOTRON LINE SOURCE 4U 1907+09 HAS NOT BEEN OBSERVED IN SEVERAL YEARS. RECENTLY SEVERAL X-RAY PULSARS HAVE BEEN SHOWN TO EXHIBIT A SECULAR DECAY IN THEIR CYCLOTRON LINE ENERGY ON TIMESCALES OF MONTHS TO YEARS. 4U 1907+09 IS A PRIME CANDIDATE TO SEARCH FOR THIS KIND OF BEHAVIOR DUE TO ITS PERSISTENT FLUX LEVEL AND ITS TWO CYCLOTRON LINES WELL WITHIN THE NUSTAR BAND. IT IS ADDITIONALLY OF INTEREST DUE TO ITS MODERATE X-RAY FLUX WHICH LIKELY PLACES IT IN THE "LOW SUB-CRITICAL" ACCRETION REGIME A PRIME AREA FOR TESTING NEW DEVELOPMENTS IN THE MODELING OF X-RAY SPECTRA FROM ACCRETING PULSARS.

Massachusetts Institute Of Technology, Cambridge MA

Investigators