WSU Relativity Group

Shaon Ghosh


I worked as a LIGO Scientific Collaboration (LSC) member in the WSURG from August 2007 to July 2013. Currently I am a Postdoctoral researcher at the Department of Astrophysics in Radboud University, Nijmegen, Netherlands (Link).

Research interests as a member of WSURG

At Washington State University I worked on detection of gravitational waves from progenitors of short duration gamma ray bursts (GRB) using LIGO gravitational wave data and electromagnetic triggers from gamma ray satellites like Fermi, IPN, Swift, etc. Short gamma ray bursts are intense flashes of gamma rays reaching to us from distant corners of the universe. These flashes typically lasts for less than 2 seconds. They are distinct from the long duration counterparts which are believed to have supernovae as their progenitors. We now have strong evidences that suggests that these short bursts do not originate from supernovae.

  • No short GRB has been discovered till date with an associated supernova.

  • Large fraction of short GRBs are found in elliptical galaxies, which are old and tend to have many “dead stars”. This is in contrast with the long duration GRBs that are found in both elliptical and spiral galaxies

  • Some short GRB locations are offset from host galaxies by hundreds of kilo parsecs (supernova kick), thus the typical sources are not giant stars but compact neutron stars.

  • Even for the short GRBs that were found inside a host galaxy, they exhibit very weak spatial correlation with star formation or stellar mass.

  • Time scales of core collapse supernovae do not match well with the short GRB time scales.

  • For detailed discussions of the progenitor models and observations of short GRBs please refer to the References.

    One of the most popular progenitor model of short GRBs that one can find in the literature is that of the coalescing compact binaries with at least one neutron star (CBCNS). The physics of this phenomenon is explained by the 'Fireball' mechanism. What is interesting from gravitational wave perspective is that these sources are also strong emitters of gravitational wave and LIGO is specifically sensitive at the frequencies at which these coalescences occur. Using the electromagnetic alerts from the aforementioned gamma ray satellites as a cue, one can search for gravitational waves in the archived LIGO data. A coincident detection of gravitationa wave with a GRB will be the strongest evidence for the compact binary coalescence model of the GRB progenitor.
    I have worked with Sukanta Bose in developing tools that coherently search for gravitational waves from electromagnetically triggered systems in a hierarchical fashion. This is called the hierarchical coherent external trigger search pipeline.
    I am also working on developing signal based vetoing techniques that are powerful enough to distinguish between real signals and glitches even when there are systematic errors present in the templates used to search, notably the absence of spin in the templates while natural systems are spinning. Astrophysical sources are likely to be spinning. However due to computational constraints, current search algorithms in LIGO uses non-spinning template banks. This not only jeopardizes parameter estimation of the source, but reduces detection efficiency also. One of the prime ways in which the detection efficiency is hampered is through reduced performance of signal discrimination tests in presence of this systematic error.

    Multiple detector analysis

    Cumulative fraction of detectable sources increases with increasing number of detectors
  • H1 = LIGO Hanford

  • L1 = LIGO Livingston

  • V1 = Virgo Italy

  • I1 = LIGO India

  • K1 = KAGRA Japan

  • Horizon distance is the farthest distance that can be observed by a detector or a network of detectors. Tyically this corresponds to the farthest observable distance of a source located overhead.

    Links to talks and posters presented

    1. Poster : The BlackGEM array, a dedicated gravitational waves trigger followup facility, APLI, Pune, India, December 2013, Link

    2. Poster : Gravitational wave astronomy using compact binary systems and their Electromagnetic counterparts, GWPAW 201, Pune, India, December 2013, Link

    3. Poster : Coherent multi-detector searches for gravitational waves from short duration gamma-ray bursts. 7th International Conference on Gravitation and Cosmology, Goa, India, December 2011. Link

    4. Talk : Targeting gravitational wave signals from short duration gamma ray bursts with large sky position errors. American Physical Society meeting, Anaheim, CA April 2011. Link

    5. Poster : Coherent compact binary coalescence searches for external triggers with large sky-position errors, GWPAW, Milwaukee, WI, 26 Jan 2011

    6. Talk : Robust multi-detector statistics for coherently searching for signals from coalescing compact binaries. GAWDAW 14, Rome, Italy 2010. Link