Browsing by Author "Reshid, Remudin (PhD)"
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Item Construction of the Radiation Curve of Pulsar Corresponding to Emission from Magnetic Dipole Field(Addis Ababa University, 2017-11-04) Kenea, Fekadu; Reshid, Remudin (PhD)In this work we derive the equations for the dipole component of pulsar’s magnetic field and construct its radiation curve. This is done following spinning separated charges as an alternative model for generating dipolar pulsar magnetic field from Kebede, L.W. 2002. We approach the problem by solving Legendre functions, spherical harmonics theorem (i.e, Ylm(θ, ϕ) for l = m = 1) and Maxwell’s equations to find the equations of the magnetic field strength B. The dipolar magnetic field obtained based on this model is proportional to the charge Q and the angular frequency ω of the pulsar (i.e, B ∝ Qω) which has an advantage of accommodating the wide range of neutron stars’s (i.e, both pulsars and magnetars) magnetic field. We have taken data for the parameters such as Q and ω for the seven well studied pulsars to check the magnetic field prediction of the model with the observational values, and our result is in close confirmation with the observed strength of the magnetic field for these seven well known pulsars.Item Coronal Mass Ejections and Problem they Cause on Earth(Addis Ababa University, 2020-10-10) Alemayehu, Debela; Reshid, Remudin (PhD)In this thesis work we study coronal mass ejections (CMEs) and their impact on earth with emphases on solar active regions, geomagnetic storms and geomagnetically induced current densities. Based on present concept, strong southward interplanetary magnetic field and high-speed of interplanetary CMEs are important main drivers of severe geomagnetic storms that lead to geomagnetically induced currents. These can cause powerful effect on the magnetosphere to ground and on the modern technologies, such as power transmissions, satellites and spacecrafts, positioning and navigation systems, oil and gas pipe lines and harmful to astronauts in space. Therefore, primarly understanding for the prime drivers of the above effects in general is important, to predict space-weather and CME impacts on earth. We correlated sunspot cycle, CMEs and geomagnetic storms using yearly sunspot-index number data in the years of 1950–2009 and disturbance storm time index (Dst-index) data obtained from the WDC of Kyoto, Japan on March 12– 14, 1989 and on October 29–31, 2003 to November 19–21, 2003. The results indicates that major CMEs can cause severe geomagnetic storms as on March 13–14, 1989 with Dst-index of _ ��589nT during sunspot cycle 22 (1986–1996) of maximum sunspot number. On the other hand, during October 29–31, 2003 geomagnetic storm of minimum peak Dst-index of _ ��400nT is correlated with the declining phase of sunspot number in cycle 23 (1996–2008). Moreover, we suggested that severe geomagnetic storms which affects modern technologies can be occured during the declining sunspot number (in the way of recovery phase) as well as during the maximum sunspot number (storm main phase). Finally, we computed sample of ground current densities using plane wave method, based on magnetic diffusion equation. We found that maximum amplitudes of this at the ground. Then, they all show an exponentially decrease in the intensity of current density values towards the earth center. Furthermore, we suggested that such east-west current densities during major CMEs can cause problem on power transmissions which are connected to area of high ground resistivity.Item Exploring Different Neutralino Dark Matter Annihilation Channels in Radio Frequency Emission in Simulated Coma Like Galaxy Cluster(Addis Ababa University, 2020-02-02) Regasa, Jemal; Reshid, Remudin (PhD)We studied various dark matter(DM) annihilation channels in radio frequency in order to explore the possibility to interpret the still unknown origin of radio emission in coma like simulated galaxy clusters. We consider three different DM models with light (9 GeV), intermediate (60 GeV), and high (500 GeV) neutralino mass with annihilation cross-section times velocity of 1:0_1026 cm3s1. We predict radio emission from non-thermal scenario whenDMannihilates into different channels such as b_ b, __+ and WW+. The radio emission produced for the three channels in a simulated galaxy cluster is based on the MUSIC-data set. The raw data contain the particle mass and coordinates, which are used to determine the density _i of the DM particle by using Smoothed Particle Hydrodynamics(SPH) kernel. This allows us to easily compute the square of the DM densities integrated in the lineof- sight, revil the observed radio halo morphology showing radio emission both from the centeral regions of the cluster and substructures lying off-center. The radio emission maps and the square of DM density maps were found to be identical proving the fact that higher emission originate from the densest structures. The integrated radio spectrum declines as frequency increases because of the radiative lifetime of the relativistic electrons. The possibility of interpreting the origin of radio emission in galaxy clusters with DM annihilation scenario requires a low neutralino mass.Item Gamma-Ray Burst In Swift Era: Analysis of Afterglow Light Curves(Addis Ababa University, 2017-10) Endalamaw, Deres; Reshid, Remudin (PhD)We presented the temporal study of all swift/XRT observations of GRB afterglows discovered between January 2005 and July 2005 which they have two or more than two breaks and well known redshift. After constructing and fitting all light curves using MATLAB programming, we have analyzed the temporal and spectral indices for each segments in the canonical X-ray afterglow light curves. The temporal decay index is calculated using log f1−log f2 log t2−log t1 . And the numerical values, resulted from the manipulation, were mostly consistent to the theoretical temporal decay index for each GRBs in each segments. And the spectral index is from closure relation such as = 2 + . In our work, we have used the data of flux decay and time from the Evans et al swift/XRT online repository of United Kingdom solar system data center (UKSSDC). Once we extracted data, we have analyzed the given data to identify the behaviors of the afterglow light curves. The data, we have used, had positive and negative error approximation. Then we have analyzed the data and compared the result and the theoretical value of temporal decay index. Finally the results have been nearly confirmed to 3 . 1 . 5 in early steep decay, the shallow decay with 0.5 . 2 . 1, normal decay with 1.0 < 3 < 1.5 and late steep decay 4. > 2.Item Gamma-ray Emission From Dark Matter Annihilation Process In Simulated Coma Like Galaxy Cluster(Addis Ababa University, 2018-09-03) Woldeyesus, Goshu; Reshid, Remudin (PhD)Galaxy clusters are good targets to search for signals from dark matter (DM) annihilation process as they are dominatly composed of DM. From DM annihilation process neutral and charged pions are beleived to be produced. The neutral pions decay directly into gamma-rays, while the secondary particle e_ produced from the charged pions are expected to emit gamma-rays through inverse compton scattering (ICS) and non-thermal bremsstrahlung processes. Taking energetic particles that are e_ produced from DM annihilation process for the model of the origin of the extended secondary particle observed in radio halos, the corresponding gamma-ray emission in those regions, we have studied both their morphology and the spectral energy distribution using simulated Coma like galaxy clusters. Using raw galaxy cluster data from large set of MUltiDark SImulation of galaxy Clusters (MUSIC- 2) dataset simulation we choose three galaxy clusters for calculating gamma-ray emmission from DM annhilation process. For our calculation we have considered a neutralino annihilation of bb species and mass of DM model of neutralino mass of 35 GeV with annihilation cross-section times velocity of <_v> = 1_ 1026 cm3 s1. Among the three simulated galaxy clusters, simulated galaxy cluster SGC282 showes the densest DM distribution almost in all the regions of the map. The differential gamma-ray flux obtained from neutral pion decay process is on average an order of magnitude higher than that from non-thermal Bremsstrahlung process, for similar photon energy, for all the three simulated galaxy clusters. For all the three gamma-ray emission mechanisims from DM annihilation process, simulated galaxy cluster SGC282 showes dominant differential gamma-ray flux densities. Overall we have observed that the gamma-ray emission flux calculated in these simulated galaxy cluster from the DM annihilation process is higher from regions of denser DM halos in the simulated Coma like galaxy cluster as expected.Item Magnetic Field Decay Due to Gravitational Radiation in Neutron Star(Addis Ababa University, 11/3/2017) Gidey, Tesfay; Reshid, Remudin (PhD)In this thesis, magnetic _eld decay due to gravitational radiation in neutron star (NS) is theoretically studied. By considering the inuence of the \dynamo mechanism"on the generation of a strong magnetic _eld in NS. A NS formed as a large star die in a type II supernova, and their magnetic _elds during formation is 1012 Gauss and 1015 Gauss for both magnetars and pulars, respectively. But their magnetic _eld is decreased. Thus, this study focuses on by how much does the magnetic _eld decay using the mathematical calculation of decay law equation. Based on our _ndings, we have two results. The _rst result shows that, the magnetic _eld of a rotating NS depends only on the decaying time since the moment of inertia is constant. The second result also shows, the magnetic _eld of a rotating NS depends on the decaying time and rotational frequency since moment of inertia varies as a function of rotational frequency. The variation in moment of inertia causes to the variation in braking index as a function of rotational frequency. Thus, the quadrapole magnetic _eld is decaying for positive _ and increased for negative _ , respectively.Item Magnetic Field Decay Due to Gravitational Radiation in Neutron Star(Addis Ababa University, 2017-11-03) Gidey, Tesfay; Reshid, Remudin (PhD)In this thesis, magnetic _eld decay due to gravitational radiation in neutron star (NS) is theoretically studied. By considering the inuence of the \dynamo mechanism"on the generation of a strong magnetic _eld in NS. A NS formed as a large star die in a type II supernova, and their magnetic _elds during formation is 1012 Gauss and 1015 Gauss for both magnetars and pulars, respectively. But their magnetic _eld is decreased. Thus, this study focuses on by how much does the magnetic _eld decay using the mathematical calculation of decay law equation. Based on our _ndings, we have two results. The _rst result shows that, the magnetic _eld of a rotating NS depends only on the decaying time since the moment of inertia is constant. The second result also shows, the magnetic _eld of a rotating NS depends on the decaying time and rotational frequency since moment of inertia varies as a function of rotational frequency. The variation in moment of inertia causes to the variation in braking index as a function of rotational frequency. Thus, the quadrapole magnetic _eld is decaying for positive _ and increased for negative _ , respectively.Item Non-Thermal Radio Emission From Dark Matter Annihilation Processes in Simulated Coma Like Galaxy Clusters(Addis Ababa University, 2018-07-04) W/Gerima, Fitsum; Reshid, Remudin (PhD)Taking secondary particles produced from dark matter annihilation process to the origin of the extended diffuse radio emissions observed in galaxy clusters, we studied both their morphology and radio spectral profile using simulated Coma like galaxy clusters. We have considered a neutralino annihilation channel dominated by bb species with a branching ratio of 1 and neutralino mass of 35 GeV with annihilation cross-section times velocity value of 1_10��26 cm3 s��1. The radio emission maps produced for the two simulated galaxy clusters which are based on the MUsic SImulation of galaxy Clusters (MUSIC)-dataset reveal the observed radio halo morphology showing radio emissions both from the central regions of the cluster and substructures lying off-center. The flux density curve is in a good agreement for _ _ 2 GHz with the obsevational values of (Thierbach et al., 2003) for the Coma cluster of galaxies showing a small deviation at higher frequencies. The small spectral index fluctuations observed in the wide cluster regions corresponds to the DM substructures scattered with in the clusters. The spectral index values _ (-0.8, -1.0) and _ (-1.6, -2.2) obtained in the very center and dark matter substructure (cluster periphery) are in a good agreement with the work of (Giovannini et al., 1993). The central spectral flattening and the peripheral steepening explain the dense central and underdense peripheral DM regions, respectively.Item Pulsar's Magnetic Field Decay Due to Photon Emissions(Addis Ababa University, 2017-12-05) Tuge, Iyasu; Reshid, Remudin (PhD)Now a days there is no clear understanding of how pulsar's magnetic _eld decays. This is the motivation behind the development of this particular model for pulsar _eld dissipation. The work will be based on previous work in which it was shown that spinning polarization charges are the most likely sources of Neutron Star (NS) magnetic _eld. These _elds were indicated to be internal temperature dependent. Therefore, they are expected to decay as a result of cooling the NS interior. The present model for _eld decay is strongly linked to the long term (1-10 billion) yrs cooling of the NS core due to neutrino and photon emissions. Magnetic decay laws are formulated corresponding to each of the neutrino and photon branches of a standard NS cooling curve. So that this thesis work intends to show the decay of pulsar magnetic _eld due to photon emission. There after, magnetic _eld decays as a result of photon emission will be prominent for about 10 billion yrs. We will derive the magnetic _eld decay law and investigate how this law could be consistant with observations.Item Statistical Studies of Dm Dominated Subhalos(Addis Ababa University, 2018-10-05) Mehari, Kifelom; Reshid, Remudin (PhD)The content of the universe is highly dominated by dark matter (DM). We can identify it using gravitational lensing and it may be detected using direct method, after scattered with the nuclie of germanium which is held underground and indirect method, after annihilation into electron or positron, which shows a scientilation effect. The viable candidates of DMs are weakly interacting particles (WIMPS), Axions, MACHOS, Sterile Neutrinos, superWIMPS and gravitinos. All these candidates are studied under super symmetric model, which is the extension of standard model. In these thesis we are focusing on statistical studies of DM dominated subhalos. We will describe the statistical distribution of DM using ROCKSTAR halo finders. Using marenostrum-multidark simulation of galaxy Clusters, we analyse mass to light ratio of the clusters in r r200 . So the mass to light ratio is high at _ r200. These show that the concentration of DM halos is high at radius of r200. From the statistical studies of all the subhalos we have found that the radial distribution of the mass to light DM subhalos is more strongly peaked at r200. These may suggest that the search for content of DM from subhalos in clusters is most promising at r200. We also determine the DM fraction for five different clusters with in 30 kpc and the minimum number of particle is 100. We also compare its value with in 15 kpc and the minimum number of particle is 50. We found that the statistical distribution of sub halo is high in 15 kpc than in 30 kpc. But in both cases the concetration of DM is high with in a mass of 1 10 _ 1010M0. In our simulation we are focusing on ROCKSTAR halo finder, but still there are different types of halo finders such as Amiga halo finder, body density maximum algorithm, surv finder, SUBFIND algorithm and FOF based algorithm. In all condition the density distribution of DM is gaussian distribution. We also analyse the existence of DM by using generalized viral theorm in f(R) gravity. It helps to show that the mass of DM is dominant in the cluster. Non interacting mathematical model of DMItem The Structure and Evolution of Intermediate-Mass Stars(Addis Ababa University, 2021-01-02) Gezie, Dessalegn; Reshid, Remudin (PhD)We explore the structure and evolution of intermediate-mass stars. Under this, we focus on the mass-luminosity relation of the single main sequence interme diate-mass stars. We derivate the stellar structure equations and put the fundamental stellar quantities in terms of mass. After this, we derivate the lifetime of intermediate-mass stars in three nuclear burning phases and relate the stellar quantities with their lifetime. Thus we predict the relation MLR, MRR, and MTR in hydrogen core burning, hydrogen shell burning, and helium core burning. The mass-luminosity relation is in good agreement for O.Yu. Malkove observational work of the absolute MLR relation.In the effects of temperature gravity and nuclear reaction, the star’s structure was varied. To determine the final differential results of star’s structure equations, we must used the derivative of interior stars structure equations with central radius r. This allows us to compute the M, T, P, L, and R relations. Those are quantities derived from the stellar structure equations. From those equations, we have obtained the mass-luminosity relation equation and using nuclear reactions we studied the star’s mass and age relation using the simplified form of the equations. We showed the graphical relationship of Mass to Luminosity, Mass to Temperature, and Mass to Radius of stars in terms of a parameter of a nuclear burning lifetime. The lifetime equation of the star in hydrogen core burning and the mass-luminosity equation are good ways to measure the mass-luminosity relation of B-type stars.Item Verification of Einstein General theory of Relativity with Gravitational Waves(Addis Ababa University, 2021-07-11) Habtie, Abel; Reshid, Remudin (PhD)Gravitational wave science is one of direct observation of the waves predicted by Einstein’s general theory of relativity and opening the exciting new field of gravitational wave astronomy. In this thesis work we study gravitational waves and we also present some of the general relativity test of gravitational wave such as linear approximation of Einstein field equation which is Einstein equation for a weak gravitational field simply _h__ = 0, thus, the metric perturbations satisfy the flat space wave equation and the solutions can therefore be interpreted as gravitational waves polarization(plus and cross polarization). In this thesisWe also found that gravitational wave emites when BBHs are spiraling with each other. We suggested that high amplitude of gravitational waves are formed around merger of BBHs, the amplitude of GWs large for high masses and also the amplitude fails when the waves moves away from the source like standard siren’s of h / 1 r . We also checked that SEOBNR and IMRPhenom models are matched with pridiction of GR simulated by NR and the waveform observed from LIGO. These waveform comparison tells us Einstein general theory of relativity passes the test of GW.