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> All I can say is that other source clearly describes that the Fermi team announced detection of a gamma ray burst well beforehand, and that the ligo team trea

> All I can say is that other source clearly describes that the Fermi team announced detection of a gamma ray burst well beforehand, and that the ligo team treated the situation as exceptional due to that announcement. I explained this in a reply that I just posted to your other comment. GCN is basically a mailing list where notices are posted in real-time to coordinate the observation of transient phenomena. If you dig into the citations from the paper you quoted, you'll read that the GW data takes on the order of 5 minutes to process before it can register an event, but it was indeed detected in real-time by their algorithms (gstlal). There's nothing in the paper you quoted to support the claim that the LIGO team adjusted their analysis based on Fermi's announcment to GCN. 6 minutes isn't "well beforehand" when the GW data takes 30-60 minutes for human vetting (http://iopscience.iop.org/article/10.1088/0004-637X/748/2/136/meta http://iopscience.iop.org/article/10.1088/0004-637X/748/2/13...). > My understanding is that there is expected to be no accompanying external evidence for waves generated by inspiraling black holes. Multiple signals is the whole point of multi-messenger astronomy. Each detection was independent, but having evidence in GW, GRB, and optical provides multiple lines of evidence, which is a cornerstone of good science.

nonbel 8y ago
How do you interpret this sentence: "Single-detector gravitational-wave triggers had never been disseminated before in low latency. Given the temporal coincidence with the Fermi-GBM GRB, however, a GCN Circular was issued" I interpret it as "Because we read the report from Fermi, we treated this data in an exceptional way". In which case their signal to noise ratio is going to be messed up, for the background estimates to be valid they need to treat everything exactly the same every time. Basically, if they want to do this, Fermi needs to be distributing false positive GRB reports so they can incorporate them into the background. >"Multiple signals is the whole point of multi-messenger astronomy. Each detection was independent, but having evidence in GW, GRB, and optical provides multiple lines of evidence, which is a cornerstone of good science." Ok, but I'm saying it is my understanding that no one expects to detect any supporting evidence in the case of the black holes. Ie, not that it was missed. There is "nothing to see": "These momentous black-hole clashes produced gravitational waves that were audible to LIGO-Virgo but there was nothing to see." https://www.nature.com/collections/gghkrvklfb https://www.nature.com/collections/gghkrvklfb
- raattgift 8y ago
  LIGO is sensitive to binary NS (and NS stellar-BH mergers) too. Binary NS mergers throw off a lot of radiation, even or especially if the result of the merger is a black hole. In the case of GW170817/GRB170817a, the evidence leads to the conclusion that there was one event and that it was almost certainly a binary NS merger. Because gravitational waves' amplitudes fall off linearly with distance rather than quadratically, because gravitational waves are so weakly interacting that they essentially do not scatter and are not absorbed, and because the environments around binary mergers (and between the binaries and us) can strongly absorb or scatter light (incl. radio and gamma), there should be lots of detections which have obscure, dim, or even undetectable optical (also incl. radio and gamma) signals. Distinguishing among the similar inspiral chirps for similar binary masses where the composition of the masses differ is an area of active research. The strong equivalence principle drives the GW similarity, but whereas binary NSes's surfaces can contact, BH surfaces (if they exist) are deep inside their horizons, so (ignoring any matter in the neighbourhood, such as colliding accretion disks) all we get from binary BH mergers is the ringdown as the hair from the lumpy merging horizon falls off leaving a much more symmetrical horizon. A mixed binary can shred the NS, leaving behind a brilliant structure. For binary NS mergers the GW events are brief compared to optical events (and the non-gravtiational radiation can interact with (relatively) nearby gas and dust as light echos and the like, so the results of those emissions can be studied for longer). It is much more likely that a GW detection will spur a search by non-gravitational observatories than the reverse. In any case, everything is carefully timestamped, and the records can be compared well after that, including by people who aren't experimentalists. :D
  - nonbel 8y ago
    > "LIGO is sensitive to binary NS (and NS stellar-BH mergers) too..." Sure, and the extra info is appreciated, but here is what I was responding to: >"Gravitational waves are all candidates until they can be confirmed with external sources." I believe this is false. They expect to detect many gravitational waves that will never be "confirmed with external sources". Namely, those triggered by black holes, and for the reasons you mention.

nonbel 8y ago

How do you interpret this sentence: "Single-detector gravitational-wave triggers had never been disseminated before in low latency. Given the temporal coincidence with the Fermi-GBM GRB, however, a GCN Circular was issued" I interpret it as "Because we read the report from Fermi, we treated this data in an exceptional way". In which case their signal to noise ratio is going to be messed up, for the background estimates to be valid they need to treat everything exactly the same every time. Basically, if they want to do this, Fermi needs to be distributing false positive GRB reports so they can incorporate them into the background. >"Multiple signals is the whole point of multi-messenger astronomy. Each detection was independent, but having evidence in GW, GRB, and optical provides multiple lines of evidence, which is a cornerstone of good science." Ok, but I'm saying it is my understanding that no one expects to detect any supporting evidence in the case of the black holes. Ie, not that it was missed. There is "nothing to see": "These momentous black-hole clashes produced gravitational waves that were audible to LIGO-Virgo but there was nothing to see." https://www.nature.com/collections/gghkrvklfb https://www.nature.com/collections/gghkrvklfb

raattgift 8y ago
LIGO is sensitive to binary NS (and NS stellar-BH mergers) too. Binary NS mergers throw off a lot of radiation, even or especially if the result of the merger is a black hole. In the case of GW170817/GRB170817a, the evidence leads to the conclusion that there was one event and that it was almost certainly a binary NS merger. Because gravitational waves' amplitudes fall off linearly with distance rather than quadratically, because gravitational waves are so weakly interacting that they essentially do not scatter and are not absorbed, and because the environments around binary mergers (and between the binaries and us) can strongly absorb or scatter light (incl. radio and gamma), there should be lots of detections which have obscure, dim, or even undetectable optical (also incl. radio and gamma) signals. Distinguishing among the similar inspiral chirps for similar binary masses where the composition of the masses differ is an area of active research. The strong equivalence principle drives the GW similarity, but whereas binary NSes's surfaces can contact, BH surfaces (if they exist) are deep inside their horizons, so (ignoring any matter in the neighbourhood, such as colliding accretion disks) all we get from binary BH mergers is the ringdown as the hair from the lumpy merging horizon falls off leaving a much more symmetrical horizon. A mixed binary can shred the NS, leaving behind a brilliant structure. For binary NS mergers the GW events are brief compared to optical events (and the non-gravtiational radiation can interact with (relatively) nearby gas and dust as light echos and the like, so the results of those emissions can be studied for longer). It is much more likely that a GW detection will spur a search by non-gravitational observatories than the reverse. In any case, everything is carefully timestamped, and the records can be compared well after that, including by people who aren't experimentalists. :D
- nonbel 8y ago
  > "LIGO is sensitive to binary NS (and NS stellar-BH mergers) too..." Sure, and the extra info is appreciated, but here is what I was responding to: >"Gravitational waves are all candidates until they can be confirmed with external sources." I believe this is false. They expect to detect many gravitational waves that will never be "confirmed with external sources". Namely, those triggered by black holes, and for the reasons you mention.