X-ray and Optical Studies of Millisecond Pulsars in 47 Tucanae

Our Chandra X-ray observation of the globular cluster 47 Tuc clearly detected most of the 16 MSPs with precise radio positions, and indicates probable X-ray emission from the remainder. The MSPs are soft (BB kT ∼0.2-0.3 keV) and faint (LX ∼ few 10 30 ergs s), and generally consistent with thermal emission from small polar caps. An additional 40 soft X-ray sources are consistent with the known MSPs in X-ray colors, luminosity, and radial distribution within the cluster (and thus mass). We note that these MSPs display a flatter LX to Ė relation than pulsars and MSPs in the field, consistent with polar cap heating models for younger MSPs and may suggest the surface magnetic field has been modified by repeated accretion episodes to include multipole components. Correlating HST images, radio timing positions, and the Chandra dataset has allowed optical searches for MSP binary companions. The MSP 47 Tuc-U is coincident with a blue star exhibiting sinusoidal variations that agree in period and phase with the heated face of the WD companion. Another blue variable star (and X-ray source) agrees in period and phase with the companion to 47 Tuc-W (which lacks an accurate timing position); this companion is probably a main sequence star. X-ray and optical studies of the millisecond pulsars (MSPs) in 47 Tuc (Freire et al. 2001a; Lorimer, these proceedings) allow us to probe the physics of the polar caps, the evolutionary state of the binary systems in which many reside, and the complete population of millisecond pulsars, many of which have not yet been discovered in the radio. Chandra is the only X-ray telescope capable of resolving the faint MSPs from the quiescent LMXBs, cataclysmic variables (CVs), and active (flaring) main-sequence binaries in the crowded central regions of globular clusters, and Hubble Space Telescope (HST ) archival data allows deep searches for the intrinsically faint white dwarf (WD) binary companions expected for the MSPs.