Doctor of Philosophy, The Ohio State University, 1984, Graduate School

Committee: Not Provided (Other) Subjects: Physics

Master of Science (MS), Ohio University, 2016, Physics and Astronomy (Arts and Sciences)

Weak lensing is one of the powerful tools for measuring mass energy content of galaxies and galaxy cluster. Light is deflected by gravity when passing by massive objects(galaxy,galaxy cluster). Shear measurement due to distortion of light depends upon the Point spread Function(PSF) which is caused by telescope optics and atmosphere. Previous work had been done on how monochromatic PSF affects shear measurements. But each star has different spectral energy distribution and galaxy has internal colour gradient. We have taken these two effects into consideration in our study. To find the dependence upon wavelength of PSF we took different stellar spectra. The AB magnitude was calculated using two infrared regions(1.24-1.57)µm and (1.57-2.00)µm. We found that the size of PSf does not vary linearly with wavelength. This implies that based upon stellar spectra we can not estimate the PSF for a galaxy. In the simulation we considered one wavelength range in the infrared region(1.57-2.00)µm and divided the region into 21 parts . We took galaxies which have internal colour gradients.The convolution was done with wavelength dependent PSF. We found that the ratio of monochromatic and chromatic shear vs radius from the center of lens, the ratio varies around 0.1 but needs to be below 0.001. This implies that the colour dependence of PSF and galaxy internal colour gradients needs to be studied more.

Committee: Douglas Clowe (Advisor) Subjects: Physics

Doctor of Philosophy (PhD), Ohio University, 2012, Physics and Astronomy (Arts and Sciences)

Recently some intermediate BL Lac objects (IBL), low frequency peak BL Lac objects (LBL) and flat spectrum radio quasars (FSRQs) were detected as very high energy gamma-ray sources (VHE; E > 100 GeV) by the Major Atmospheric Gamma-ray Imaging Cherenkov Telescope (MAGIC), the High Energy Stereoscopic System (H.E.S.S) and the Very Energetic Radiation Imaging Telescope Array System (VERITAS). These discoveries suggest that VHE gamma-rays may be produced in all types of active galactic nuclei (AGN) and that this is not only a common property of high frequency peaked BL Lac objects (HBL). The detection of the radio galaxies M87, Cen A and NGC 1275 supports this idea. In those AGN, VHE photons may interact with low energy photons from the broad line region (BLR), accretion disk around the black hole or thermal infrared photons form a dust torus by photon-photon pair production if the total center-of-momentum frame energy is above threshold to produce an electron-positron pair. These particles can produce new high energy photons by Compton up-scattering, and again these high energy photons can interact with soft photons to produce a pair of particles. This process will continue, leading to a shower (cascade) of particles and radiation. As the shower develops, it will expand laterally. This may explain the detection of the radio galaxies as VHE gamma-ray sources. The central part of my Ph.D. research work deals with the theoretical simulation of very high energy gamma-ray induced pair cascades in blazars and radio galaxies. Gamma-rays from the core of the AGN interact with low energy photons from the AGN environment and produce pairs of electrons and positrons resulting in Compton supported pair cascades. I developed a Monte Carlo code which treats the processes of gamma-gamma absorption and pair production, gamma-ray and electron/positron propagation, and Compton scattering, tracking particle trajectories in full 3-dimensional geometry. I showed that even for a very weak m (open full item for complete abstract)

Committee: Markus Boettcher Prof. (Advisor); Joseph Shields Prof. (Committee Member); Douglas Clowe Prof. (Committee Member); Jeffrey Rack Prof. (Committee Chair) Subjects: Physics

Master of Science (MS), Ohio University, 2010, Physics and Astronomy (Arts and Sciences)

We present multiwavelength observations of the ultraluminous blazar-type radio loud quasar PKS 0528+134 obtained in September 2009. Our main goal was to characterize this blazar in a quiescence state. We performed optical observations at the 1.3-m McGraw-Hill telescope of the MDM Observatory and also collected radio and optical data from the GASP. In the X-ray regime we collected data from the XMM-Newton Satellite in the 0.2 – 10 keV range. We also obtained gamma-ray data from the Fermi Large Area Telescope (LAT) in the 100 MeV – 300 GeV range. We found no evidence of significant flux or spectral variability in the radio, X-ray and gamma-ray regime. However, significant flux variability was found in the optical region, especially in the R and B bands, and we also found a spectral softening trend. We produced four SEDs with the data we were able to gather, and for the Leptonic combined SSC+ERC jet model that we used, acceptable fits were produced.

Committee: Markus Boettcher Dr. (Advisor); David Drabold Dr. (Committee Co-Chair); Justin Frantz Dr. (Committee Member) Subjects: Astronomy; Astrophysics; Physics

Master of Science (MS), Ohio University, 2012, Physics and Astronomy (Arts and Sciences)

BL-Lacertae is the prototype of BL Lac objects. It has been observed during the months of May, October and December 2011 with the aim of studying the intranight color variations on short timescales using the method of Color-Magnitude Diagram analysis and to look for the time-lag between the variations at different optical wavelengths using the method of Discrete Correlation Function analysis. Quasi-simultaneous measurements in the UBVRI bands have been performed using the 1.3 m optical telescope at MDM observatory at Kitt-Peak, AZ. A flare is observed during May 2011 in optical data that is also seen in the same time period in the gamma ray data, which is taken directly from the Fermi LAT website. BL Lacertae showed the trend Redder when Brighter and the transition to Bluer when brighter in the higher flux states, i.e. when the magnitude of R band is less than 13.5. A time-lag between the variations at optical wavelength band B and R is found to be (0.01 +/- 0.0056) day (less than 2ς). Using the value of time-lag, the lower limit on the magnetic field in the jet is found to be B > 1.24 G.

Committee: Charlotte Elster (Committee Chair); david Drabold (Committee Member); Markus Boettcher (Advisor); Joseph Shields (Committee Member) Subjects: Physics