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How do you interpret this sentence: "Single-detector gravitational-wave triggers had never been disseminated before in low latency. Given the temporal coincide

by 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.
  - davidcuddeback 8y ago
    I don't think "external sources" necessarily means "multi-messenger." GW detectors are sensitive to local interference, so we have three of them spread across the globe with non-overlapping blind spots. A GW must be detected in at least two of the detectors to be confirmed. I'm not sure if that's what @dogma1138 meant, but I'm pretty sure that's how the past GW detections have been confirmed.
    - nonbel 8y ago
      I agree, thanks.
davidcuddeback 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" If you back up a sentence, it says: > A GCN Notice was issued at 13:08:16 UTC. If you extend your quote a few words: > a GCN Circular was issued at 13:21:42 UTC Note the 13 minute gap between the Notice and the Circular. The Notice was based on LIGO's own detection (which, again, was not rejected as noise by their algorithms as you have claimed). The Circular was issued based on the temporal coincidence with Fermi's detection. The difference between a Notice and a Circular is explained on GCN's website: > The GCN system distributes: > * Locations of GRBs and other Transients (the Notices) detected by spacecraft (most in real-time while the burst is still bursting and others are that delayed due to telemetry down-link delays). > * Reports of follow-up observations (the Circulars) made by ground-based and space-based optical, radio, X-ray, TeV, and other particle observers. https://gcn.gsfc.nasa.gov/ https://gcn.gsfc.nasa.gov/ > In which case their signal to noise ratio is going to be messed up. The LIGO detection was triggered by an algorithm (gstlal) that constantly evaluates the SNR of the data coming off the detector. The Fermi detection had nothing to do with that. You're trying very hard to make a boogieman out of nothing. > 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". This wasn't a black hole merger. It was a neutron star merger, which is expected to produce counterparts.
- nonbel 8y ago
  >"If you back up a sentence..." I'm talking about the sentence where it seems to say they treated the data from a certain time interval exceptionally, ie in a way not addressed by the "background" measurements. This whole post (while containing otherwise interesting/useful info) is about other sentences and totally ignores the one I asked about. >"The LIGO detection was triggered by an algorithm (gstlal) that constantly evaluates the SNR of the data coming off the detector. The Fermi detection had nothing to do with that. You're trying very hard to make a boogieman out of nothing." The sentence I quoted seems to suggest otherwise. I don't know the details of all the ways bias can sneak into the results over there, but I know in general it's not hard, at all. Anyway, its easy to test. Have Fermi, etc send them some fake positive "notices" and see if they detect more gw's than usual during those times. It'd be an even better test if no one at LIGO was in on it at all. Is this something you could agree with in principle? I mean I have no idea what practical difficulties may be involved. > "This wasn't a black hole merger. It was a neutron star merger, which is expected to produce counterparts." Yes, I have no confusion about that. This was a case where we could expect verification. If it were another black hole merger my understanding is we would not expect it possible for other type of measurement to verify it.

by nonbel 8y ago

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.
- davidcuddeback 8y ago
  I don't think "external sources" necessarily means "multi-messenger." GW detectors are sensitive to local interference, so we have three of them spread across the globe with non-overlapping blind spots. A GW must be detected in at least two of the detectors to be confirmed. I'm not sure if that's what @dogma1138 meant, but I'm pretty sure that's how the past GW detections have been confirmed.
  - nonbel 8y ago
    I agree, thanks.

davidcuddeback 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" If you back up a sentence, it says: > A GCN Notice was issued at 13:08:16 UTC. If you extend your quote a few words: > a GCN Circular was issued at 13:21:42 UTC Note the 13 minute gap between the Notice and the Circular. The Notice was based on LIGO's own detection (which, again, was not rejected as noise by their algorithms as you have claimed). The Circular was issued based on the temporal coincidence with Fermi's detection. The difference between a Notice and a Circular is explained on GCN's website: > The GCN system distributes: > * Locations of GRBs and other Transients (the Notices) detected by spacecraft (most in real-time while the burst is still bursting and others are that delayed due to telemetry down-link delays). > * Reports of follow-up observations (the Circulars) made by ground-based and space-based optical, radio, X-ray, TeV, and other particle observers. https://gcn.gsfc.nasa.gov/ https://gcn.gsfc.nasa.gov/ > In which case their signal to noise ratio is going to be messed up. The LIGO detection was triggered by an algorithm (gstlal) that constantly evaluates the SNR of the data coming off the detector. The Fermi detection had nothing to do with that. You're trying very hard to make a boogieman out of nothing. > 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". This wasn't a black hole merger. It was a neutron star merger, which is expected to produce counterparts.

nonbel 8y ago
>"If you back up a sentence..." I'm talking about the sentence where it seems to say they treated the data from a certain time interval exceptionally, ie in a way not addressed by the "background" measurements. This whole post (while containing otherwise interesting/useful info) is about other sentences and totally ignores the one I asked about. >"The LIGO detection was triggered by an algorithm (gstlal) that constantly evaluates the SNR of the data coming off the detector. The Fermi detection had nothing to do with that. You're trying very hard to make a boogieman out of nothing." The sentence I quoted seems to suggest otherwise. I don't know the details of all the ways bias can sneak into the results over there, but I know in general it's not hard, at all. Anyway, its easy to test. Have Fermi, etc send them some fake positive "notices" and see if they detect more gw's than usual during those times. It'd be an even better test if no one at LIGO was in on it at all. Is this something you could agree with in principle? I mean I have no idea what practical difficulties may be involved. > "This wasn't a black hole merger. It was a neutron star merger, which is expected to produce counterparts." Yes, I have no confusion about that. This was a case where we could expect verification. If it were another black hole merger my understanding is we would not expect it possible for other type of measurement to verify it.