Houston, TX 77005
12:00 p.m. Wednesday, Oct. 30, 2013
On Campus | Alumni
1) The widely accepted magnetospheric accretion model for classic T Tauri Stars asserts that magnetic field controls the interaction between central star and its circumstellar disk, thus It is of great importance to study the properties of magnetic fields on stellar surface: their magnitudes, geometries and their origin. Spectropolarimetric studies have been carried out a couple of times on TW Hya. Different authors gave quite different results. It may result from intrinsic variations since observations are several years apart. It can also be due to the different methods used. To investigate the discrepancy, we have revisited these data. We also have our own observations on this object obtained in Feb 2013. Combining all these data, analyzing them in the exact same way and comparing the results enables us to identify if the magnetic variations are real. Moreover, the field strengths we measured from the 2013 data set almost doubled compared to the results from earlier data sets, which supports the dynamo generated origin of these fields.2) Hard, non-thermal and pulsed persistent X-ray emission extending between 10 keV and 230 keV has been seen in a number of magnetars by RXTE, INTEGRAL, Suzaku and Fermi-GBM. For inner magnetospheric models of such hard X-ray emission, resonant Compton upscattering of soft thermal photons is anticipated to be the most efficient radiative process. This is due to the relative close proximity of the surface thermal photons, and because the scattering becomes resonant at the cyclotron frequency with the effective cross section exceeding the classical Thomson one by over two orders of magnitude, thereby enhancing the efficiency of continuum production and cooling of relativistic electrons. I present angle-dependent upscattering model spectra for uncooled monoenergetic relativistic electrons injected in inner regions of pulsar magnetospheres, calculated using collisional integrals. These spectra are integrated over closed field lines and obtained for different observing perspectives. The spectral cut-off energies are critically dependent on the observer viewing angles and electron Lorentz factor. I will discuss the implications of these calculations, and what future work must be done.