Compact Objects & Transients

Keywords: Black Holes, Neutron Stars, Pulsars, X-ray binaries, Fast Radio Bursts (FRBs), Gamma Ray Bursts (GRBs)

• Black Holes

Black holes are the end-state of stellar evolution that offers an unparalleled laboratory for testing theories of gravity under the strong field regime. Multi-wavelength observational studies ranging from the radio to X-ray band offer a unique opportunity to probe the emission mechanism and variability around the black holes. Magnetohydrodynamic simulations of the jets and accretion dynamics around black holes pave the way for understanding the relativistic astrophysics around these enigmatic objects.

• Neutron Star 

Neutron stars are extremely dense compact objects whose core reaches supranuclear densities, thereby offering ideal laboratories to probe strong gravity and the properties of supranuclear matter. Several observational features, like thermonuclear bursts, burst oscillations, jets, and Quasi-periodic oscillations, are studied to probe the exotic neutron star conditions. Multi-wavelength observations spanning radio to X-ray wavebands are carried out to pursue the above science goals. 

• Pulsars

Pulsars are cosmic lighthouses that exhibit highly periodic, coherent emission and offer a glimpse into the physics under ultrastrong magnetic fields. The emission mechanism of pulsars - accretion powered, rotation powered, and magnetically powered - is investigated to shed light on the underlying physics, the beam geometry , and the evolution of pulsars across different subclasses. The timing study of pulsars, as undertaken by the pulsar timing arrays (PTAs), provides a unique tool for using them as clocks - especially for the purpose of detecting nanoHertz Gravitational Waves.   

• Fast Radio Bursts (FRBs)

Fast Radio ursts are extremely enigmatic events exhibiting an intense burst of radio emission in a very short span of time (fraction of seconds). Their origin still remains a mystery, even though recent observations argue for a magnetar origin scenario. The characteristic, radiative behaviour, and comparison with pulsar-like emission pose numerous compelling scientific questions. The extragalactic origin of the FRBs also presents an excellent way of utilizing them as cosmological probes.  

• Gamma Ray Bursts (GRBs)

Gamma-Ray Bursts are one of the most luminous astronomical phenomena originating from either the collapse of very massive stars or the merger of two neutron stars. Investigation of GRBs can offer clues on their emission mechanism and provide an essential tool for investigating the electromagnetic counterpart of gravitational waves generated during the binary neutron star mergers.

• Gravitational Waves, Kilonovae, and Binary Neutron Star (BNS) Mergers
  Exploring compact object mergers through gravitational-wave detections and their electromagnetic counterparts, with a focus on high-energy emission from kilonovae and r-process nucleosynthesis.  Employing pulsar timing arrays to search for low-frequency gravitational waves or Nano-Hertz Gravitational Waves (nHz GWs) arising from supermassive black hole binaries and galaxy evolution.

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