LIGO, High Gear Science Run Options

[The Messenger]

http://www.spaceref.com/news/viewpr.html?pid=19142

ST. LOUIS, Mo. -- The quest to detect and study gravitational waves with the NSF-funded Laser Interferometer Gravitational-Wave Observatory (LIGO) is now in the fourth month of its first sustained science run since achieving its promised design sensitivity, project personnel announced at the annual meeting of the American Association for the Advancement of Science (AAAS). ...

Now that the LIGO is sensitive enough to detect changes in distance a mere thousandth the diameter of a proton, Marx adds, the science return should be even greater. Recent results from the Swift satellite pinpointing the location of short gamma-ray bursts (GRBs) have also heightened astronomers' interest in the results from LIGO's current observational run.

That level of sensitivity is, in my opinion, the most incredible technical achievement since the VLA.

The very long gamma ray associated with supernova/hypernova 1996aj should also be of great interest.

[antoniseb]

Interesting. Is the GraceDb (https://gracedb.ligo.org/superevents/S190521g/view/) reporting distance in comoving megaparsecs? That seems odd, but would explain why this event was observed at all.
Can you point me to any place where they say or imply that they are reporting in comoving Mpc? Thanks in advance!

[fredk]

Do you mean comoving vs proper distances? It's standard in cosmology to use comoving distances, since it avoids the problem of separations being smaller in the past. For close distances (redshift z << 1) proper distances are well defined and are very close to comoving ones.

[Lucas]

It appears that they are using luminosity distances (see http://www.astro.ucla.edu/~wright/cosmo_02.htm#DL for definition) based on https://lscsoft.docs.ligo.org/ligo.skymap/l...p/bayestar.html (look at min_distance parameter) and https://emfollow.docs.ligo.org/userguide/glossary.html (look at “burst range”). In these units the CMB is at ~15000 Gpc.

[fredk]

Yes, the observed gravitational wave amplitude (and frequency and its rate of change) gives the luminosity distance (once you've got a handle on the polarization), but at this level of accuracy that will agree with any other distance measure. Units, though, are comoving. The CMB is at just under 14 comoving Gpc, not 15 000 - see, eg, sect 3.4 of Planck Inflation. So at very crudely a Gpc, this merger is considerably closer.