Current Research

We are focusing on studying multiwavelength and multimessanger aspect of various high-energy phenomena occurring in the Universe. By definition these phenomena must be associated with extreme energy-density environments and huge energy release which occur in the supernova explosions and inside and around compact objects (neutron stars, pulsars, black holes, white dwarfs). The manifestations of these phenomena typically occur over a broad range of electromagnetic frequencies and require both spectral and temporal analysis to understand their nature. Furthermore, some of these extreme high-energy events are expected to produce gravitational wave and neutrino signals. As a result members of our group are actively involved in working with the data from the word's best observatories which include both space missions (Hubble Space Telescope, Chandra , XMM-Newton , and Suzaku X-ray Observatories, Fermi gamma-ray observatory, Swift multi-wavelength observatory) and top ground based facilities ( Laser Interferometer Gravitational Wave Observatory (LIGO) , Jansky Very Large Array , Atacama Large Millimeter Array (ALMA) , VERITAS Cherenkov imaging array). Our faculty and postdocs design and carry out observational projects using most of the above observatories.

Active Projects include:

• Gamma-ray burst (GRB) studies: GRBs are now known to be extragalactic in origin with an enormous energy release (10⁵⁰-10⁵⁴ ergs). Historically, most GRBs have been detected as brief (from a few milliseconds to ~1000 seconds) and very intense flares (10^-4-10^-7 erg/s at the Earth) seen in gamma-rays and hard X-rays. This corresponds to the frequency range where most of the burst energy is emitted, although we now understand that the GRBs are intrinsically multi-wavelength phenomena. The first major effort in studying GRBs is associated with the BATSE mission which detected during its lifetime about 2,700 GRBs in 20-600 keV band. However, due to the lack of multi-wavelength capabilities and poor angular resolution, it was challenging to determine distances to GRBs solely with BATSE data. The slow but steady improvement in ground-based follow-up has finally established an association between GRBs and remote galaxies. Yet the exact physical nature of the GRB phenomenon still remains elusive. With the launch of modern space telescopes designed to detect GRBs (such as the Swift and Fermi observatories) the amount of information available about individual GRBs virtually exploded. The number of detected GRBs has also grown to ~4,000. Although most GRBs can be related to the massive object collapse or binary merger, there are ongoing debates about the type of object undergoing collapse/merger (progenitor) and the mechanism responsible for converting pre-existing gravitational energy to radiation (accretion, shocks, reconnection). The total GRB rate is also unknown because it is surmised that much of the high-energy radiation we receive comes from collimated outflows (jets) which happen to point at us, but the properties of these jets are still poorly understood. GRBs are expected to produce strong gravitational wave and neutrino signals. GRB studies have far reaching implications for cosmological studies and gravitational wave detection. We are investigating the still mysterious GRB phenomena using data Fermi, Swift, VLA, LIGO and other observatories. Our group developed a number of novel techniques for temporal and spectral GRB analysis. We also collaborate with the members of the high-energy astrophysics group at the Naval Research Laboratory (Charles Dermer, Soebur Razzaque). The GRB group is led by Prof. Kalvir Dhuga and includes Profs. Leonard Maximon, Bill Parke, Bethany Cobb Kung, Alessandra Corsi, and Oleg Kargaltsev.

  
  

• Supernova and GRB connection: Since the discovery of an association between long-duration GRBs and core-collapse supernovae (SNe), it has become evident that long GRBs are related to a rare sub-class of SNe, which develop highly energetic and collimated relativistic outflows, likely powered by a central engine (an accreting black hole or neutron star). However, it is still a mystery what makes some core-collapse SNe explode producing an associated relativistic ejecta (long GRB). The mystery of the GRB-SN connection is tightly linked to a question of broad interest in the field of astrophysics, namely, how do massive stars end their lives. Massive stars, as primary sources of radiative ionization, heating, and nucleosynthesis products, play a crucial role in the evolution of galaxies and the whole Universe. The mystery of their connection to the most relativistic explosions of stellar origin (GRBs) is puzzling astronomers all over the world. Motivated by the key fact that relativistic ejecta in SN explosions can be probed using radio observations, the astro group at GWU, in an effort led by Prof. Corsi, is working to unravel the missing link between GRBs and SNe using the K. Jansky Very Large Array , in direct collaboration with the Palomar Transient Factory team and with Dr. D. A. Frail at the National Radio Astronomy Observatory .

  
  

• Galactic compact object studies: Galactic copmact objects include neutron stars, black holes, and white dwarfs. Physical processes on these objects result in many facinating physical phenomena such as accretion, relativistic magnetized outflows, shock waves, particle acceleration, reconnection, various high-energy radiation processes, etc. We are studying all of these phenomena as well as the population of Galactic compact objects using multiwavelength observations. Our current research efforts focus on neutron stars, pulsars and their nebulae, microquasars and interacting binaries, galactic TeV sources and strong gravity enviroment in the black hole vicinity. Neutron stars are collapsed stars whose surfaces can be hot enough to emit radiation in ultraviolet and X-rays. In addition many neutron stars manifest themselves as pulsars - objects that emit short intense bursts of radio waves, x-rays, or visible electromagnetic radiation at regular intervals. Due to the extreme conditions in the neutron star interiors, these objects can be used as natural laboratories for studying the poorly understood properties of the superdense, strongly magnetized, superconducting matter. Such conditions can never be reproduced in Earth laboratories and therefore studying neutron stars provides the only way to learn about the nuclear reactions and interactions of the elementary particles under these extreme conditions. This information is of fundamental importance for particle and quantum field physics. Studying pulsar winds allows one to understand the complicated PWN morphologies, elucidate the dynamics of relativistic magnetized outflows and their interaction with the ambient medium (e.g., host Supernova Remnants ), and learn about particle acceleration in magnetized relativistic plasma. X-ray, gamma-ray, and optical observations of neutron stars provide valuable diagnostics of all these processes. Microquasars are the most extreme manifestations of stellar black holes . In these system (which are in many respects analogues to their supermassive counterparts in active galactic nuclei) matter pulled from a massive companion star falls into a black hole or onto a neutron star. In this proccess the matter heats up to very high temperatures and emits intense X-ray radiation. Due to the rapid rotation of the compact object s fraction of infalling matter is being ejected from the system along the compact object spin axis leading to formation of jets whose nonthermal emission can be seen througout a wide range of frequencies. Some microquasars are also emit very high energy (VHE) radiation in GeV and TeV bands. The exact mechanism responsible for the VHE radiation is has not yet been established with several possibilitites being currently explored. You can learn more about the compact object studies at GWU here . The compact object studies are led by Prof. Kargaltsev with participation of other faculty postdocs and students. We also collaborate closely with the Neutron Star group at the Astronomy and Astrophysics Department at Penn State University.

  
  

• Using automated algorithms for astrophysical object classification: We are applying intellegent machine-learning classification algorithms to determine the nature of thousands of X-ray sources and GRBs. This effort is led by Prof. Kargaltsev with participation of several other faculty and students.

  
  

• Gravitational wave search and detection: Gravitational waves (GWs) offer a remarkable opportunity to open a totally new view of the Universe, providing the chance to solve mysterious questions on some of the most fascinating astrophysical sources.  Gravitational waves, for example, could probe \textit{for the first time directly}, the nature of GRB progenitors. Indeed, being related to catastrophic events involving stellar-mass objects, gamma-ray bursts are good candidates for the detection of gravitational waves. Ground-based gravitational wave detectors like the Laser Interferometer Gravitational-Wave Observatory ( LIGO and Virgo ), have been carrying out GRB-triggered searches for gravitational waves during the last decade. Starting from 2016, with the advent of the advanced LIGO , a totally new view of these sources is likely to be opened. Motivated by these exciting prospects, our GW group (led by Dr. Corsi at GWU) is working on the study of GRBs as gravitational wave sources, and more generally on joint electromagnetic and gravitational wave studies of transient astrophysical sources. This effort is led by Prof. Corsi, and sees the participation of several GWU students. Data analysis investigations are developed within the LIGO Scientific Collaboration . Source modeling and related phenomenological studies include collaborations with Prof. P. Meszaros and Prof. B. J. Owen at Penn State University.

  
  

• Cataclysmic Variable studies: Cataclysmic variables (CVs) are close-binary star systems which undergo systematic brightenings ('novae'). Evidence indicates that CVs are undergoing mass transfer from a 'doner star' to a white dwarf due to gravitational tidal forces from the white dwarf acting on the doner star (such as a nearby red giant). The material from the doner star forms an accretion disk, made largely of hydrogen, around the white dwarf. As this hot material in the accretion disk radiates and falls onto the surface the white dwarf, it accumulates until it reaches a sufficient temperature and density to undergo a thermonuclear reaction, producing a novae. This process can repeat many times, although residual accumulated helium may bring the white dwarf to critical mass. Because of the quasi-stochastic nature of the light from CV outbursts, CVs can be a test bed for the study of such light from explosive events, such as GRBs. Data from the Kepler mission, with fine time resolution, is now available.