4 ms·

The paper describing the event is available to the public at https://dcc.ligo.org/LIGO-P170104/public https://dcc.ligo.org/LIGO-P170104/public The instrument d

by eaq 9y ago

The paper describing the event is available to the public at https://dcc.ligo.org/LIGO-P170104/public https://dcc.ligo.org/LIGO-P170104/public The instrument data of this event is also available to the public at https://losc.ligo.org/events/GW170104/ https://losc.ligo.org/events/GW170104/

nonbel 9y ago
Thanks >"GW170104 was first identified by inspection of low-latency triggers from Livingston data [15–17]. An automated notification was not generated as the Hanford detector’s calibration state was temporarily set incorrectly in the low-latency system. After it was manually determined that the calibration of both detectors was in a nominal state, an alert with an initial source localization [18,19] was distributed to collaborating astronomers [20] for the purpose of searching for a transient counterpart. About 30 groups of observers covered the parts of the sky localization using ground- and space-based instruments, spanning from γ ray to radio frequencies as well as high energy neutrinos [21]." https://dcc.ligo.org/LIGO-P170104/public https://dcc.ligo.org/LIGO-P170104/public Regarding the earlier detection: >"At 11:23:20 UTC, an analyst follow-up determined which auxiliary channels were associated with iDQ’s decision. It became clear that these were un-calibrated versions of h(t) which had not been flagged as “unsafe” and were only added to the set of available low latency channels after the start of ER8. Based on the safety of the channels, the Data Quality Veto label was removed within 2.5 hours and analyses proceeded after re- starting by hand." http://ligo.elte.hu/magazine/LIGO-magazine-issue-8.pdf http://ligo.elte.hu/magazine/LIGO-magazine-issue-8.pdf So both times humans had to take special action for the detection to "count". I really wonder about whether the null model they are using is appropriate/relevant here. Also, the other thing I have been concerned about is the lack of any corroborating evidence that these signals are truly generated by inspiraling black holes(gamma ray bursts, etc). Apparently, in this case the above-mentioned miscalibration has impeded that effort: >"The event candidate was not reported by the low-latency analysis pipelines because re-tuning the calibration of the LIGO Hanford detector is not yet complete after the holiday shutdown. This resulted in a delay of over 4 hours before the candidate could be fully examined. We are confident that this is a highly significant event candidate, but the calibration issue may be affecting the initial sky maps. We will provide an update in approximately 48 hours which may include an improved sky map." https://gcn.gsfc.nasa.gov/other/G268556.gcn3 https://gcn.gsfc.nasa.gov/other/G268556.gcn3 I can't tell from that text file whether they got corroborating evidence or not. IANAP though.
- sleavey 9y ago
  There have been three signals witnessed in about 12 months of observations - of course the models need some tuning to correctly, automatically, trigger alerts. In any case, you are referring to the _online_ triggers which look very quickly at the data and try to guess if an apparent signal is real before informing electromagnetic observatories to follow up. The real analysis is conducted _offline_ in a much slower, careful way with lots of checks and balances on the state of the instruments to rule out artificial signals. That's one of the main reasons why it took 5 months between the first detection and the publication of the paper announcing it. In terms of corroborating evidence, remember that the two independent LIGO detectors - 3000km apart - saw the event within 10ms of each other. That's enough corroborating evidence for a lot of people. The NASA text file you link shows no observed electromagnetic counterpart, but that's expected: unfortunately the best models so far for black hole coalescences predict very little or no electromagnetic emission - so although EM partners were informed, the chances of them seeing anything were slim. Other predicted sources of gravitational waves, like as-yet unseen binary neutron star coalescences, are more likely to emit EM radiation and stand a chance of being witnessed by conventional observatories as "corroboration".
  - nonbel 9y ago
    >"In terms of corroborating evidence, remember that the two independent LIGO detectors - 3000km apart - saw the event within 10ms of each other. That's enough corroborating evidence for a lot of people." I don't see what the first part of the post has to do with the null ("background noise") model being inapplicable to situations where special human intervention comes into play. Do they include any events like that in the background timeseries or not? I am suspecting not (which renders the model false and hence false alarm rates/sigma values meaningless), but do not know for sure. Second, that is just a detection. Corroboration occurs when your model predicts multiple types of observations related to a phenomena (measured by different types of instruments). This weakening of definitions is concerning to me if it has infected physics. I have seen that trick used a lot by "softer" fields such as medicine/psych (eg their definition of a replication is just seeing "an effect" in the same direction).
  - nonbel 9y ago

by eaq 9y ago

nonbel 9y ago

Thanks >"GW170104 was first identified by inspection of low-latency triggers from Livingston data [15–17]. An automated notification was not generated as the Hanford detector’s calibration state was temporarily set incorrectly in the low-latency system. After it was manually determined that the calibration of both detectors was in a nominal state, an alert with an initial source localization [18,19] was distributed to collaborating astronomers [20] for the purpose of searching for a transient counterpart. About 30 groups of observers covered the parts of the sky localization using ground- and space-based instruments, spanning from γ ray to radio frequencies as well as high energy neutrinos [21]." https://dcc.ligo.org/LIGO-P170104/public https://dcc.ligo.org/LIGO-P170104/public Regarding the earlier detection: >"At 11:23:20 UTC, an analyst follow-up determined which auxiliary channels were associated with iDQ’s decision. It became clear that these were un-calibrated versions of h(t) which had not been flagged as “unsafe” and were only added to the set of available low latency channels after the start of ER8. Based on the safety of the channels, the Data Quality Veto label was removed within 2.5 hours and analyses proceeded after re- starting by hand." http://ligo.elte.hu/magazine/LIGO-magazine-issue-8.pdf http://ligo.elte.hu/magazine/LIGO-magazine-issue-8.pdf So both times humans had to take special action for the detection to "count". I really wonder about whether the null model they are using is appropriate/relevant here. Also, the other thing I have been concerned about is the lack of any corroborating evidence that these signals are truly generated by inspiraling black holes(gamma ray bursts, etc). Apparently, in this case the above-mentioned miscalibration has impeded that effort: >"The event candidate was not reported by the low-latency analysis pipelines because re-tuning the calibration of the LIGO Hanford detector is not yet complete after the holiday shutdown. This resulted in a delay of over 4 hours before the candidate could be fully examined. We are confident that this is a highly significant event candidate, but the calibration issue may be affecting the initial sky maps. We will provide an update in approximately 48 hours which may include an improved sky map." https://gcn.gsfc.nasa.gov/other/G268556.gcn3 https://gcn.gsfc.nasa.gov/other/G268556.gcn3 I can't tell from that text file whether they got corroborating evidence or not. IANAP though.

sleavey 9y ago
There have been three signals witnessed in about 12 months of observations - of course the models need some tuning to correctly, automatically, trigger alerts. In any case, you are referring to the _online_ triggers which look very quickly at the data and try to guess if an apparent signal is real before informing electromagnetic observatories to follow up. The real analysis is conducted _offline_ in a much slower, careful way with lots of checks and balances on the state of the instruments to rule out artificial signals. That's one of the main reasons why it took 5 months between the first detection and the publication of the paper announcing it. In terms of corroborating evidence, remember that the two independent LIGO detectors - 3000km apart - saw the event within 10ms of each other. That's enough corroborating evidence for a lot of people. The NASA text file you link shows no observed electromagnetic counterpart, but that's expected: unfortunately the best models so far for black hole coalescences predict very little or no electromagnetic emission - so although EM partners were informed, the chances of them seeing anything were slim. Other predicted sources of gravitational waves, like as-yet unseen binary neutron star coalescences, are more likely to emit EM radiation and stand a chance of being witnessed by conventional observatories as "corroboration".
- nonbel 9y ago
  >"In terms of corroborating evidence, remember that the two independent LIGO detectors - 3000km apart - saw the event within 10ms of each other. That's enough corroborating evidence for a lot of people." I don't see what the first part of the post has to do with the null ("background noise") model being inapplicable to situations where special human intervention comes into play. Do they include any events like that in the background timeseries or not? I am suspecting not (which renders the model false and hence false alarm rates/sigma values meaningless), but do not know for sure. Second, that is just a detection. Corroboration occurs when your model predicts multiple types of observations related to a phenomena (measured by different types of instruments). This weakening of definitions is concerning to me if it has infected physics. I have seen that trick used a lot by "softer" fields such as medicine/psych (eg their definition of a replication is just seeing "an effect" in the same direction).
- nonbel 9y ago