Given the misinformation on LIGO’s O3 run exemplified by the lack of multi-messenger events (electromagnetic radiation associated with gravitational wave events),
Christopher Berry from LIGO was kind enough answer a few of my questions to set the record straight.
Christopher Berry was one of the co-authors of the very first gravitational wave discovery paper.
I'm not sure exactly why you decided to start a whole new thread on this topic. One wonders if I dare to cast "doubt" on a few of your assumptions/statements if this thread will become "controversial" and end up where the last one ended up.
Firstly are all SGRBs found assumed to be neutron star mergers or are there alternative mechanisms?
There have been alternative ideas for sGRBs, but at the moment it looks like we can explain them all with neutron star mergers. We'll need to observe a few more to sure that up.
Well, maybe:
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I supposed it depends on whether or not we can determine the origin of the signal. In our previous conversation on this topic you suggested/implied that *any* gamma ray burst, even ones which cannot be isolated to any specific region of the sky should count as confirmation of a GW event. I still don't buy that concept for very obvious reasons. Gamma ray flashes have been shown to originate in electrical discharges processes in our own atmosphere and in flares from the sun as well.
If the gamma ray burst can be directly associated with the very same region of the sky as predicted by Virgo/Ligo, that's a whole different ballgame.
Secondly during the O3 run I have used
this database and found there have only been six definite SGRBs during this period.
I wondered at first why you selected that particular database link rather than the original
GraceDb database where all the events are first recorded, until I noticed that you're evidently leaving out all the events which were later attributed to terrestrial sources, and not counting every event involving a neutron star in the merger process (BHNS events). That's certainly an arbitrary choice.
If we *include all* of the non retracted events which were originally categorized as involving at least one neutron star, the number of failed attempts jumps from 6 to 11 failed attempts at multimessenger astronomy. These include:
s200213t (BNS)
s191213g (BNS)
s181205ah (BHNS)
s190930t (BHNS)
s190923y (BHNS)
s190910h (BNS)
s190910d (BHNS)
s190901ap (BNS)
s190814bv (BHNS)
s190426c (BNS)
s190425z (BNS)
If we add in the events that were originally listed as signals involving neutron stars at greater than say 50 percent likelihood, and then later retracted and attributed to terrestrial noise, we add 8 more attempts:
s2300116a (BHNS)
s191220a (BNS)
s191213ai (BHNS)
s091120aj (BHNS)
s191117j (BHNS)
s190822c (BNS)
s190816i (BHNS)
s1905118b (BNS)
So in terms of how many signals LIGO originally categorized as involving neutron stars, LIGO is actually 0 for 19, or 0 for 11 if we ignore all retracted signals. We have to ask ourselves why we should remove retracted events since apparently terrestrial noise can and does produce signals patterns which are consistent with neutron star mergers, so we cannot rule out terrestrial causes for *any* of these events. About 42 percent of them were already attributed to terrestrial noise/sources and several of them involved multiple detectors. As I surmised in my paper, LIGO still has a serious blip transient problem.
Would the lack of a GW signal with these SGRBs be due to the limited detection range for neutron star mergers?
I haven’t seen any red shift data so I assume even the afterglow event is too faint (and distant) for measuring redshift.
sGRBs typically come from large distances. GW170817/GRB 170817A was luckily close. It's not surprising we can't find gravitational waves from all of them. We do dedicated searches to look for signals corresponding to gravitational waves. I expect those results from O3a will be out in a couple of months. Here are the results from O2 Search for gravitational-wave signals associated with gamma-ray....
Since I've limited my criticisms to 03 events, I won't comment on 02 events. Suffice to say there have been on confirmed multimessenger events associated with 03 published to date by LIGO.
Thirdly there is a lot of nonsense on the Internet that black hole mergers should also be multi-messenger events.
Can you state for the record this is not true or is it possible if there is an accretion disk?
My understanding is that accretion disks around stellar mass black holes are rare anyway.
If there is an accretion disc, it is possible there is an electromagnetic counterpart. For stellar mass binaries (instead of supermassive ones found in the centres of galaxies), that would be quite faint, so it's unlikely we'd observe anything at the distances we typically see binary black hole mergers. Small discs could be quite common, if they formed from material ejected during supernova which didn't quite escape. We don't really know yet though. I think Electromagnetic signals following stellar-mass black hole mergers is the most reasonable paper to look at.
I haven't finished reading the entire paper yet, but interestingly, it states the following:
Here we question the common consensus that the typical stellar–mass binary black hole merger is always dark. We consider a simple possibility for EM signals following binary black hole mergers, with a possible delay of hours. This mechanism requires the BH binary to have a circumbinary disk at the time of merger whose mass need only be a very small fraction of that shed as the system evolved.
It seems to suggest a distance limit of about 500 Mpc for such a detection, but it ends with the following paragraph:
Despite the large uncertainties, we suggest that the potential rewards of a successful detection of the signal discussed here justify the effort of coordinated EM campaigns. It would place unique constraints on the binary evolution before the merger, and thus provide crucial information about the contribution of various progenitor channels. Detection of a radial velocity, as suggested above, would also constrain the recoil predicted by the GW data, and so directly test strong–field predictions of General Relativity.
In other words, they don't rule out the possibility of detecting BBH events in the EM spectrum.
The current record for multi messenger astronomy is in fact 0 from 6 for the O3 run as black hole mergers even with accretion disks are too faint (assuming they do exist) whereas none of the 6 sGRBs (short gamma ray bursts) observed in this period are likely to have been outside the detection range for GWs.
Again however, the paper which Christopher Berry suggested makes no such claims about BBH events being undetectable, and LIGO is actually 0 for 19, or at best case, 0 for 11 in terms of events involving neutron stars. Furthermore, a full 42 percent of events originally attributed to neutron stars were later shown to be nothing more than terrestrial noise, demonstrating conclusively that LIGO still has a serious blip transient problem.
In short, you really didn't demonstrate that anything that I've said in
my previous thread on this topic contains any "misinformation". I stand by my criticisms.
