Long-lived GWs from GRBs and NS-NS merger remnants

The detection of gravitational waves (GWs) from the binary neutron star (NS) merger GW170817, associated with the off-axis short gamma-ray burst (GRB) 170817, has marked the start of multi-messenger Gravitational Wave Astronomy. In addition to proving that GRBs are sources of GWs and electromagnetic radiation, the discovery of GW170817 alone has impacted a very diverse set of fields including nuclear physics, cosmology, gravitational physics, and relativistic astrophysics. Among the key questions left open by GW170817 is the one regarding the nature of the merger remnant. Knowing whether a NS or a black hole (BH) was ultimately formed in the merger is key to understanding the merger dynamics, to constraining the Equation of State (EoS) of nuclear matter, and to clarifying the mechanisms that power GRBs.

 

 

 

 

 

 

 

 

 

 

 

With new discoveries of GWs from GRBs being likely in the forthcoming years, I am carrying out a study aimed at searching for GW signatures of long-lived NSs formed in GRBs and NS-NS mergers using LIGO data. Inspired by my 2009 work on the GW signatures of magnetized NSs (magnetars; see Figure above and  Corsi & Meszaros 2009), with my group at TTU I have developed a new LIGO data analysis technique dubbed the "Cross-Correlation Algorithm" (CoCoA) which can be used to discover GWs from the long-lived remnants of GRBs and binary mergers. This technique is expected to improve substantially on the previously published results for long-lived GWs from the remnant of GW170817, and potentially yield detections or significantly constraining upper-limits once Advanced LIGO reaches its nominal sensitivity (see bottom-left Figure).

CoCoA searches are computational expensive, and currently take advantage of the TTU High Performance Computing Cluster (HPCC).

Top Figure: GW signal frequency (left) and amplitude (right) as a function of time for the waveforms expected from secularly unstable magnetars as described in Corsi & Meszaros 2009. The thick black portions of the CM09short/long waveforms represent the 256/1024 s-long segments where the sliding average of the signal strain is maximized. See also Sowell, Corsi, Coyne 2019 and Coyne, Corsi, Owen 2016.

Left Figure: Horizon distances for the STAMP algorithm as in Abbott et al. 2017, compared to the ones of a CoCoA stochastic search. CoCoA (dark and light blue), even with the less sensitive stochastic limit, is more sensitive than STAMP (red and green). The gained sensitivity comes at the expenses of computational cost. A CoCoA search for long-duration GWs within a time window of 8.5 d since GW170817 (light blue), in computationally unrealistic. A CoCoA search withing a 2 s time window around GW170817 (dark blue) produces a number of trials about a factor of two smaller than a STAMP search with a much longer timing uncertainty of 8.5 d. See Sowell, Corsi, Coyne 2019 for more details.

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