[vsnet-grb-info 22151] LIGO/Virgo S190426c: a possible lensed NS-NS merger

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  24250
SUBJECT: LIGO/Virgo S190426c: a possible lensed NS-NS merger
DATE:    19/04/26 21:27:30 GMT
FROM:    Graham P Smith at U of Birmingham  <gps at star.sr.bham.ac.uk>

G. P. Smith (Birmingham), M. Bianconi (Birmingham), R. Massey (Durham), 
and A. Robertson (Durham) report on behalf of the Gravitationally Lensed 
Gravitational Wave Hunters

The non-zero value of Prob_MassGap identifies S190426c (GCN24237) as a 
possible strongly-lensed NS-NS merger - i.e. its true redshift and 
luminosity distance may be larger, and true mass may be smaller than 
inferred by LIGO/Virgo.  The rate of such detections is predicted to be 
~0.01 per Earth year during O3.

The putative lens could be an individual galaxy, or a group/cluster of 
galaxies.  None of the 130 known strong-lensing clusters in the sample 
discussed by Smith et al. (2018) are located in the updated 90% credible 
sky localization released an hour after detection and stated as the 
currently preferred skymap in GCN24237.

At the estimated luminosity distance to the source (D_L~375Mpc; 
GCN24237) an AT2017gfo-like counterpart would have an apparent B/V-band 
magnitude of AB<~24.5 within ~2 days of the LIGO/Virgo detection.  This 
estimate (albeit redshifted in to the i-band, and time-dilated to ~4 
days post-detection) is also valid if the source is strongly-lensed and 
actually at a redshift of z~1.

We encourage colleagues to observe the sky localization of this source 
down to AB~25, to search for a kilonova-like counterpart, and thus 
explore the possibility that this source is strongly-lensed, for example 
by a massive galaxy or group of galaxies.

Background information on the details of this circular can be found in 
these publications:

Smith, Jauzac, Veitch, et al., 2018, MNRAS, 475, 3823
Smith, Robertson, Bianconi, Jauzac, arXiv:1902.05140
Smith, Bianconi, Jauzac, et al., 2019, MNRAS, 485, 5180