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It was actually detected by two gravitational wave facilities (Hanford and Livingston) before the GRB was detected by Fermi. What you're referring to is that th

It was actually detected by two gravitational wave facilities (Hanford and Livingston) before the GRB was detected by Fermi. What you're referring to is that the gravitational wave was in a third facility's blind spot (Virgo). So yes, they had to dig it out of Virgo's data to triangulate the location of the signal so that they could confirm the event in optical wavelengths (which they did). No, that doesn't affect my opinion, because your characterization is inaccurate. It was in fact detected independently as a GW and a GWB.

nonbel 8y ago
>"On 2017 August 17 12:41:06 UTC the Fermi Gamma-ray Burst Monitor (GBM; Meegan et al. 2009) onboard flight software triggered on, classified, and localized a GRB. A Gamma-ray Coordinates Network (GCN) Notice (Fermi-GBM 2017) was issued at 12:41:20 UTC announcing the detection of the GRB, which was later designated GRB 170817A (von Kienlin et al. 2017). Approximately 6 minutes later, a gravitational-wave candidate (later designated GW170817) was registered in low latency (Cannon et al. 2012; Messick et al. 2017) based on a single-detector analysis of the Laser Interferometer Gravitational-wave Observatory (LIGO) Hanford data. The signal was consistent with a BNS coalescence with merger time, tc, 12:41:04 UTC, less than 2 s before GRB 170817A. A GCN Notice was issued at 13:08:16 UTC. 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 at 13:21:42 UTC (LIGO Scientific Collaboration & Virgo Collaboration et al. 2017a) reporting that a highly significant candidate event consistent with a BNS coalescence was associated with the time of the GRB959 ." http://iopscience.iop.org/article/10.3847/2041-8213/aa91c9 http://iopscience.iop.org/article/10.3847/2041-8213/aa91c9
- dogma1138 8y ago
  Both LIGO detectors detected and classified it as GW event at the same time as the GRB classification then it was confirmed through VIRGO data and localized. https://www.ligo.caltech.edu/page/press-release-gw170817 https://www.ligo.caltech.edu/page/press-release-gw170817 Gravitational waves are all candidates until they can be confirmed with external sources.
  - nonbel 8y ago
    >"Both LIGO detectors detected and classified it as GW event at the same time as the GRB classification then it was confirmed through VIRGO data and localized." 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. >"Gravitational waves are all candidates until they can be confirmed with external sources." My understanding is that there is expected to be no accompanying external evidence for waves generated by inspiraling black holes.
    - davidcuddeback 8y ago
      > 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
- davidcuddeback 8y ago
  I'm not sure how you arrived at your conclusion from reading that. I can only guess that you're reading something into this sentence: > Approximately 6 minutes later, a gravitational-wave candidate (later designated GW170817) was registered in low latency (Cannon et al. 2012; Messick et al. 2017). "Registered in low latency" means that it was detected by their data analysis algorithms, which directly contradicts your conclusion that "they found data their algorithms had previously rejected as noise." If you doubt me, you can follow the citations from that paper. Cannon et al. 2012 resolves to 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..., which discusses the data processing and latencies involved (~5 minutes to trigger a detection and ~30 minutes for human vetting), which is consistent with the timeline you quoted. They even published the source code: > We have implemented a prototype of the low-latency filtering stage using an open-source signal processing environment called GStreamer. ... We have extended the GStreamer framework by developing a library called gstlal that provides elements for GW data analysis. gstlal's home page is https://wiki.ligo.org/DASWG/GstLAL https://wiki.ligo.org/DASWG/GstLAL The part you quoted mentions a few notices that were circulated through GCN. That's basically a mailing list to coordinate observation of transient phenomena. It's home page is https://gcn.gsfc.nasa.gov/ https://gcn.gsfc.nasa.gov/. The circulars discussing the GW are here: https://gcn.gsfc.nasa.gov/other/G298048.gcn3 https://gcn.gsfc.nasa.gov/other/G298048.gcn3. From the first post in the circulars: > The online CBC pipeline (gstlal) has made a preliminary identification of a GW candidate associated with the time of Fermi GBM trigger. gstlal is the library we met earlier in Canon et al. 2012. "Online" means it was processing the data in real-time. Your claim that the data was rejected by their algorithms as noise isn't supported by the paper you're quoting or the original sources.

nonbel 8y ago

>"On 2017 August 17 12:41:06 UTC the Fermi Gamma-ray Burst Monitor (GBM; Meegan et al. 2009) onboard flight software triggered on, classified, and localized a GRB. A Gamma-ray Coordinates Network (GCN) Notice (Fermi-GBM 2017) was issued at 12:41:20 UTC announcing the detection of the GRB, which was later designated GRB 170817A (von Kienlin et al. 2017). Approximately 6 minutes later, a gravitational-wave candidate (later designated GW170817) was registered in low latency (Cannon et al. 2012; Messick et al. 2017) based on a single-detector analysis of the Laser Interferometer Gravitational-wave Observatory (LIGO) Hanford data. The signal was consistent with a BNS coalescence with merger time, tc, 12:41:04 UTC, less than 2 s before GRB 170817A. A GCN Notice was issued at 13:08:16 UTC. 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 at 13:21:42 UTC (LIGO Scientific Collaboration & Virgo Collaboration et al. 2017a) reporting that a highly significant candidate event consistent with a BNS coalescence was associated with the time of the GRB959 ." http://iopscience.iop.org/article/10.3847/2041-8213/aa91c9 http://iopscience.iop.org/article/10.3847/2041-8213/aa91c9

dogma1138 8y ago
Both LIGO detectors detected and classified it as GW event at the same time as the GRB classification then it was confirmed through VIRGO data and localized. https://www.ligo.caltech.edu/page/press-release-gw170817 https://www.ligo.caltech.edu/page/press-release-gw170817 Gravitational waves are all candidates until they can be confirmed with external sources.
- nonbel 8y ago
  >"Both LIGO detectors detected and classified it as GW event at the same time as the GRB classification then it was confirmed through VIRGO data and localized." 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. >"Gravitational waves are all candidates until they can be confirmed with external sources." My understanding is that there is expected to be no accompanying external evidence for waves generated by inspiraling black holes.
  - davidcuddeback 8y ago
    > 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
davidcuddeback 8y ago
I'm not sure how you arrived at your conclusion from reading that. I can only guess that you're reading something into this sentence: > Approximately 6 minutes later, a gravitational-wave candidate (later designated GW170817) was registered in low latency (Cannon et al. 2012; Messick et al. 2017). "Registered in low latency" means that it was detected by their data analysis algorithms, which directly contradicts your conclusion that "they found data their algorithms had previously rejected as noise." If you doubt me, you can follow the citations from that paper. Cannon et al. 2012 resolves to 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..., which discusses the data processing and latencies involved (~5 minutes to trigger a detection and ~30 minutes for human vetting), which is consistent with the timeline you quoted. They even published the source code: > We have implemented a prototype of the low-latency filtering stage using an open-source signal processing environment called GStreamer. ... We have extended the GStreamer framework by developing a library called gstlal that provides elements for GW data analysis. gstlal's home page is https://wiki.ligo.org/DASWG/GstLAL https://wiki.ligo.org/DASWG/GstLAL The part you quoted mentions a few notices that were circulated through GCN. That's basically a mailing list to coordinate observation of transient phenomena. It's home page is https://gcn.gsfc.nasa.gov/ https://gcn.gsfc.nasa.gov/. The circulars discussing the GW are here: https://gcn.gsfc.nasa.gov/other/G298048.gcn3 https://gcn.gsfc.nasa.gov/other/G298048.gcn3. From the first post in the circulars: > The online CBC pipeline (gstlal) has made a preliminary identification of a GW candidate associated with the time of Fermi GBM trigger. gstlal is the library we met earlier in Canon et al. 2012. "Online" means it was processing the data in real-time. Your claim that the data was rejected by their algorithms as noise isn't supported by the paper you're quoting or the original sources.