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This thesis presents the results of a comprehensive multi-wavelength study of the high mass X-ray binary 2S 0114+650. This enigmatic source has previously been proposed to be the first in a new class of super-slow X-ray pulsars, containing a neutron star revolving once every 2.7 h. The 11.6 d orbital period of this system has been well established in both X-ray and optical wavelengths. During the initial stages of the research presented in this thesis we discovered an additional 30.7 d ???super-orbital??? modulation in the X-ray emission from this source. While similar periodicities seen in other X-ray binaries are commonly attributed to the precession of a warped accretion disc, the observational evidence suggests the absence of such a disc in 2S 0114+650. The purpose of this project is thus to determine the nature of the super-orbital modulation and to better constrain the astrophysical parameters of this system. To investigate the long-term variability we analysed ~8.5 yr of archived data from the Rossi X-ray Timing Explorer space telescope. The problem of the spurious ~24 h periods in this data was solved as a by-product of these studies. Follow-up pointed observations were obtained with this satellite in order to examine the spectral and temporal behaviour over the spin, orbital and super-orbital timescales. Independent confirmation of the super-orbital modulation was performed using ~2 yr of data from the INTEGRAL satellite obtained during a long-term monitoring campaign of the Cassiopeia region. The evolution of the spin, orbital and super-orbital periods over ~10 yr was examined using archived data from the Rossi X-ray Timing Explorer satellite. Radio observations were performed with the Giant Meterwave Radio Telescope to search for any radio emission associated with this source and to determine whether it is variable over the known periodicities. Near infrared observations were performed with the Mt Abu telescope to determine whether a Be star nature can be ruled out for the optical component. Finally, a statistical analysis of the properties of the confirmed super-orbital X-ray binaries was performed in order to search for commonalities between these systems.

The spectroscopic and photometric observations of the optical counterparts to the Be/X-ray binary systems GRO J2058+42 and V0332+53 (BQ Cam), taken with RTT150 (Russian-Turkish 1.5 meter Telescope), are presented in this study. The distance, color and the reddening estimates for both sources, obtained via photometric observations, are consistent with the previous results. The results of our spectroscopic observations performed between May 2006 and June 2008 for optical counterpart to GRO J2058+42 indicate that the double-peaked emission line profile turns into a single-peaked emission after the last outburst of the system. Furthermore, the spectra of the source show clear evidence for the changes in the ratio of the double peaks of H alpha emission line indicative of the precession of the high-density regions confined in the disk. Unlike the spectra of counterpart to GRO J2058+42, the spectra of BQ Cam, taken between September 2006 and December 2007, exhibit single-peaked H alpha and HeI (Lambda 7065 Angstrom) emission lines. In addition, the equivalent width values of H alpha emission lines, shifts from the the laboratory wavelengths for H alpha and HeI emission lines and the variation in optical brightness of BQ Cam show a close correlation.

In this thesis, X-ray spectral and pulse timing analysis of the high mass X-ray binary pulsar 4U 1907+09, based on the observations with Rossi X-ray Timing Explorer (RXTE) and International Gamma-Ray Astrophysics Laboratory (INTEGRAL), are presented. INTEGRAL (October 2005 - November 2007) and RXTE (June 2007 - December 2008) observations confirm that the luminosity of the source is highly variable such that, flaring and dipping activities are observed. The results of time-averaged energy spectra of RXTE and INTEGRAL observations are consistent with the previous studies. Orbital phase resolved spectroscopy with RXTE data, reveals that the Hydrogen column density varies through the orbit reaching to its maximum value just after periastron. This variation approves that the location of the absorbing material is the accretion flow. A slight spectral softening with increasing luminosity is aslo observed. 4U 1907+09 had been steadily spinning down for more than ~15 years with a rate of -3.54x10-14 Hz s-1. RXTE observations of the source in 2001 showed a ~60% decrease in the spin-down rate and INTEGRAL observations in 2003 showed a reversal to spin-up. The timing analysis presented in this thesis reveals a new spin-down episode with a rate of -3.59x10-14 Hz s-1, which is close to the previous steady spin-down rate. This result implies that a recent torque reversal before June 2007 has taken place. The reversal is a rare event for 4U 1907+09 and it indicates the variations in the mass accretion rate and/or geometry. Using RXTE observations, 24 new pulse periods are measured to demonstrate the period evolution. Energy resolved pulse profiles confirm that the profile has a double peak sinusoidal shape at energies below 20 keV, whereas the leading peak significantly loses its intensity above 20 keV. This energy dependence indicates that the physical circumstances of the two polar caps are different.

In this thesis, X-ray observations of four accretion powered pulsars are presented. Using RXTE observations of 4U 1907+09, we found three new pulse periods of the source. We found that the source spun-down almost at a constant rate of $dot nu$ = (-3.54 $pm 0.02) times 10^{-14}$ Hz s$^{-1}$ for more than 15 years. Using RXTE observations, X-ray flux related spectral and timing features in 2S 1417-62 were, in general, interpreted as a sign of a disc accretion with a similar geometry with a varying mass accretion rate, whereas spectral and timing features of the low X-ray flux regions were interpreted as a sign of possible temporary accretion geometry change prior to the next periastron. Using XMM-Newton and RXTE observations of SAX J2103.5+4545, we discovered quasi periodic oscillations around 0.044 Hz (22.7 sec) while the source was spinning-up with a rate of $(7.4pm0.9)times10^{-13}$Hz s$^{-1}$. In the X-ray spectrum, we also found a soft component consistent with a blackbody emission with ${rm{kT}}sim1.9$keV. Using RXTE observations, we also studied spectral evolution of Her X-1

This thesis presents the results of a comprehensive multi-wavelength study of the high mass X-ray binary 2S 0114+650. This enigmatic source has previously been proposed to be the first in a new class of super-slow X-ray pulsars, containing a neutron star revolving once every 2.7 h. The 11.6 d orbital period of this system has been well established in both X-ray and optical wavelengths. During the initial stages of the research presented in this thesis we discovered an additional 30.7 d ???super-orbital??? modulation in the X-ray emission from this source. While similar periodicities seen in other X-ray binaries are commonly attributed to the precession of a warped accretion disc, the observational evidence suggests the absence of such a disc in 2S 0114+650. The purpose of this project is thus to determine the nature of the super-orbital modulation and to better constrain the astrophysical parameters of this system. To investigate the long-term variability we analysed ~8.5 yr of archived data from the Rossi X-ray Timing Explorer space telescope. The problem of the spurious ~24 h periods in this data was solved as a by-product of these studies. Follow-up pointed observations were obtained with this satellite in order to examine the spectral and temporal behaviour over the spin, orbital and super-orbital timescales. Independent confirmation of the super-orbital modulation was performed using ~2 yr of data from the INTEGRAL satellite obtained during a long-term monitoring campaign of the Cassiopeia region. The evolution of the spin, orbital and super-orbital periods over ~10 yr was examined using archived data from the Rossi X-ray Timing Explorer satellite. Radio observations were performed with the Giant Meterwave Radio Telescope to search for any radio emission associated with this source and to determine whether it is variable over the known periodicities. Near infrared observations were performed with the Mt Abu telescope to determine whether a Be star nature can be ruled out for the optical component. Finally, a statistical analysis of the properties of the confirmed super-orbital X-ray binaries was performed in order to search for commonalities between these systems.

Les binaires X, composées d'un objet compact (naine blanche, étoile à neutrons ou trou noir stellaire) et d'une étoile donneuse, sont des objets fascinants qui ont permis faire des découvertes majeures dans le domaine de l'astrophysique des hautes énergies. Toutefois, l'environnement immédiat de ces dernières, à l'échelle de $\sim$ 100--10,000 unités astronomiques, n'est pour sa part que très peu compris et exploré. Dans ce mémoire, on s'intéresse à la présence de compagnons, autant de masse planétaire que stellaire, dans lesdits environnements des binaires X. Pour ce faire, on a fait appel à des techniques observationnelles qui sont normalement utilisées pour la recherche d'exoplanètes jeunes, chaudes et en orbite autour d'étoiles situées à quelques parsecs de la Terre : il s'agit de l'imagerie directe ou plus précisément de l'imagerie à haut contraste. Ainsi, pour la toute première fois, on a appliqué ces méthodes sur un échantillon de binaires X avec l'instrument proche infrarouge NIRC2 de l'Observatoire W. M. Keck, avec l'aide d'un système d'optique adaptative et d'un coronographe. Ici, on a présenté les premières images à haut contraste de 14 binaires X. Le but était de détecter des sources lumineuses dans les images et de calculer leur flux et leur position avec des méthodes d'optimisation. Ensuite, il s'agissait de définir via diverses analyses si celles-ci sont cohérentes avec des compagnons liés par la gravité à la binaire X, ou plutôt avec des étoiles de fond. Ces travaux se veulent donc une introduction à un nouveau sous-domaine de l'astrophysique qui tente de relier l'exoplanétologie et l'astrophysique des hautes énergies. / X-ray binaries, consisting of a compact object (white dwarf, neutron star or stellar-mass black hole) and a donor star, are fascinating objects that have allowed major breakthroughs in the field of high-energy astrophysics. However, their immediate environments, on the scale of $\sim$ 100--10,000 astronomical units, are still poorly understood. In this Master's thesis, we investigated the presence of companions, ranging from planetary to stellar masses, in the environments of X-ray binaries. In order to do so, we used observational techniques that are normally used for the search of young, hot and distant exoplanets orbiting stars located at a few parsecs from the Earth: direct imaging or more precisely high-contrast imaging. Thus, for the very first time, we applied these techniques on a sample of X-ray binaries with the near-infrared instrument NIRC2 of the W. M. Keck Observatory, with the help of an adaptive optics system and a coronagraph. Here, we present the first high-contrast images for 14 X-ray binaries. The goal was to detect point sources in the images and to calculate their flux and position with optimization methods. Afterward, we determined via a variety of analyses if these were consistent with companions gravitationally bounded to the X-ray binary, or rather with background stars. This work acts as an introduction, albeit exploratory, to a new subfield of astrophysics that attempts to link exoplanetology and high-energy astrophysics.

Gamma-ray binaries are systems that comprise a young, massive star and a compact object that can be either a young pulsar or a black hole. They emit radiation from radio up to tens of TeV and show flux variability along the whole electromagnetic spectrum. For three of the four detected gamma-ray binaries, the nature of the compact object is unknown. In this thesis we present a study of gamma-ray binaries through three approaches that involve the simultaneous study of these sources in X-rays and very high energy (VHE) gamma-rays. We present the discovery of correlated X-ray and VHE gamma-ray emission from LS I +61 303. The correlations indicates that the emission from these two bands could be originated in the same parent particle population, and we explore this idea through the calculation of a radiative model. This model allows us to significantly constrain the physical properties of the non-thermal emitter in LS I +61 303. For those systems where the compact object is a young pulsar, the interaction between the stellar and pulsar winds will give rise to strong shocks. The shocked pulsar wind is the candidate location for non-thermal emission from these systems. The shocked stellar wind should give rise to a thermal X-ray spectrum, but no such features have been detected in the X-ray spectrum of gamma-ray binaries. We present a model of the thermal emission of the shocked stellar wind and use it to constrain the pulsar properties. We have applied this method to two X-ray observations of LS 5039 and have successfully constrained the pulsar spin-down luminosity. Finally, we present a search for VHE emission from Scorpius X-1 through a simultaneous X-ray and VHE gamma-ray campaign. The X-ray observations allowed us to select black-hole states where non-thermal X-ray emission has been detected. We did not find significant VHE emission in any of the black hole states, but the upper limits derived will prove useful in future modelling of the non-thermal emitter in the source. / Les binàries de raigs gamma són sistemes binaries formats per una estrella jove i massiva i un objecte compacte, que pot ser un púlsar jove o un forat negre, que emeten radiació fins a desenes de TeV i mostren variabilitat orbital en totes les bandes d'emissió, des de radio fins a raigs gamma. En el cas de tres de les quatre binàries de raigs gamma detectades avui dia, se'n desconeix la natura de l'objecte compacte. En aquesta tesi presentem un estudi de les binàries de raigs gamma mitjançant tres treballs complementaris que involucren l'estudi simultani d'aquestes fonts en raigs X i raigs gamma de molt alta energia. En primer lloc presentem el descobriment d'emissió en raigs X i raigs gamma de molt alta energia correlades en el temps al sistema LS I +61 303. Aquesta correlació ens indica que l'emissió en les dues bandes pot provenir d'una única població d'electrons, i ho confirmem mitjançant la realització d'un model teòric de radiació que ens permet restringir significativament les propietats físiques de l'emissor no tèrmic de la font. En cas que la font energètica dels sistemes sigui un púlsar, la interacció entre els vents de l'estrella i el púlsar dona lloc a una regió d'interacció on el vent xocat del púlsar accelera partícules i emet des de radio fins a raigs gamma. A l'espectre de raigs X, però, no es detecta l'emissió tèrmica del vent xocat de l'estrella, que s'escalfa fins a desenes de milers de graus. Això ens ha permès estudiar la forma de la regió d'interacció, determinada principalment per la potència del púlsar, i fer un càlcul teòric de l'emissió en raigs X tèrmics. Hem aplicat aquest model al sistema LS 5039 i hem pogut determinar la potència del púlsar, fet important per a la modelització de l'emissió no tèrmica de la font. Finalment, presentem la cerca d'emissió de raigs gamma provinent de sistemes binaris fins ara no detectats. Una campanya simultània en raigs X i raigs gamma ens va permetre seleccionar les dades de molt alta energia del microquàsar Sco X-1 en funció de l'estat d'acreció sobre l'objecte compacte. Tot i no detectar la font en raigs gamma, els límits superiors obtinguts permeten restringir les propietats físiques de Sco X-1 rellevants per a l'emissió en molt alta energia.

This thesis concerns with the study of X-ray binaries which are gravitationally bound systems consisting of a compact object (either a neutron star or a black hole) and usually a non degenerate companion star, both rotating around the common centre of mass. The compact star shines brightly in the X-ray regime. Emission from these systems are powered by accretion which is the most radioactively efficient mechanism known in the universe by the release of gravitational potential energy when matter from the companion star falls on the compact object. Accretion onto high magnetic field neutron stars are special as the magnetic field plays a crucial role in governing the dynamics of gas flow and the flow of the matter close to the compact object. The radiation emitted from these systems are anisotropic and for a distant observer, the intensity is modulated at the spin period of the neutron star, hence these objects are called accretion powered pulsars. The angular pattern of the emitted radiation is also highly anisotropic and depends on the mass accreted and hence the luminosity. The beaming pattern commonly known as the pulse profiles exhibit a wide variety in the pulse shape and pulse fraction and vary with energy as well as intensity. They also exhibit cyclotron absorption features in their energy spectrum which are a direct probe to the magnetic field geometry of these systems. This thesis is dedicated to the study of the magnetic field and emission geometry of accretion powered pulsars through the pulse phase resolved studies of the cyclotron absorption features which are a direct probe of the magnetized plasma. In order to study these features in detail broadband continuum modeling of the energy spectrum is done, taking care of all other factors which may smear the pulse phase dependence. Another prerequisite for detailed continuum modeling is accounting for the low absorption dips in the pulse profiles of many these sources. The dips are presumably formed by phase locked accretion stream causing partial covering absorption when the stream is along our line of sight towards the emission region. Studying the pulse phase dependence of this partial covering absorber also provides us with important clues on the local environment of the neutron star and the structure of the accretion stream. All of these studies are performed with data from the broadband and most sensitive instruments onboard the Japanese satellite Suzuki. Lastly we provide estimates of the polarization expected to be detected from these sources by a Thomson scattering polarimeter being developed to observe the polarization of X-rays in the energy range of 5--30 keV. Along with the X-ray pulsars, we also make an estimate of the likelihood of detection of X-ray polarization from black hole X-ray binaries in different spectral states. This is a particularly interesting topic as it will play a crucial role in providing additional handles on the magnetic field geometry in accretion powered pulsars as well as constrain the fundamental parameters of a black hole like its spin.