#obv the reason i'm able to scoop major news sources on this is bc this is fairly dull and dry

[wumblr]

GRAVITATIONAL WAVE EVENT S190408AN

Summary: Yesterday, LIGO detected what is likely a binary black hole merger. Anybody who has access to a telescope immediately spun to look at it, and most of them are reporting null results for electromagnetic and/or gamma ray burst counterparts to the event, with upper limits for these (i.e. if a GRB did occur but was too weak to trigger detection). Analysis ongoing. Details scarce. 

April 8 2019, 6:08-6:26pm UTC(?): LIGO reports detection of a gravitational wave event, the first event detected during Observing Run 3, which began days ago. (Note: It seems I did not receive the original alert -- only responses to it. Not sure why. Possibly because I admitted I'm an amateur with no institutional affiliation -- I assume there's a "priority" email list I am not on.)

8:42pm: AGILE MCAL reports "no event candidates within a time interval covering -15/+8 sec" from LIGO's reported event. Additional analysis in progress.

8:58pm: J-GEM reports on "optical and near-infrared imaging observations of 7 nearby galaxies within the probability skymap." Data reduction in progress.

9:00pm: The Fermi telescope reports that it was "passing through the South Atlantic Anomaly 14mins prior to 15mins after the trigger time, therefore detectors were disabled." The SAA is an area where the van allen belt comes closer to the surface of the earth, which poses dangers for orbiting satellites.

9:04pm: INTEGRAL reports "a search for a prompt gamma-ray counterpart." I'm having a hard time reading this one, but I think they report a null result, with maximal upper values for "small" gamma-ray bursts they could have missed: "We do not detect any significant counterparts and estimate a 3-sigma upper limit on the 75-2000 keV fluence of 2.5e-07 erg/cm^2 for a burst lasting less than 1 s with a characteristic short GRB spectrum (an exponentially cut off power law with alpha=-0.5 and Ep=600 keV) occurring at any time in the interval within 300 s around T0."

9:08pm: HAWC reports that "80% of the GW candidate sky location probability fell within our observable field" -- due to pure chance a telescope in Puebla, Mexico was pointed in basically the right direction. They also report null results for a gamma ray burst: "No significant gamma-ray detection above the steady-state cosmic-ray background was observed."

9:14pm: IceCube reports on their search for associated "track-like muon neutrinos events consistent with sky localization of GW candidate in a time range of 1000 seconds centered on the alert event time during which IceCube was collecting good quality data. No track-like events are found ..."

9:36pm: LIGO reports that they have identified it as "a compact binary merger candidate." They report 99% likelihood it is a binary black hole merger. "There is strong evidence against the lighter compact object having a mess less than 3 solar masses ... There is evidence against matter outside the final compact object" (meaning, neutron stars usually exhibit powerful and easily visible ejecta, so this supports the black hole hypothesis, although they report higher uncertainty for remnant matter.) Message includes link to skymap, etc: https://gracedb.ligo.org/superevents/S190408an/

10:44pm: MASTER Global Robotic Net reports optical observations. "Reduction and observation will be continued."

April 9, 12:04am: AGILE reports technical details on their null result, and includes refined estimates of upper limits for gamma ray bursts associated with the event. (I'm going to venture a guess that this team, and likely many of the others, pulled an all nighter to make these analyses and send these circulars.)

2:56am: KMTNet reports a search "for the electromagnetic counterpart" (i.e. visible spectrum, I think). They give a list of coordinates.

4:16am: Swift/BAT reports search results +/-100 seconds of the event. "No significant detections" and further upper limits.

7:58am: MASTER Global Robotic Net reports a discovery. "Found optical transient (no known sources in VIZIER database inside 5")"

http://master.sai.msu.ru/static/OT/140518.22-395309.9.png

8:57am: Insight-HXMT reports "taking data normally around trigger time. At T0, localization region was fully covered without occultation by the earth." Null results for counterpart gamma ray burst, more upper limits.

9:08am: ATLAS reports that MASTER GRN discovery above is a month-old foreground supernova candidate with "no obvious catalogued host galaxy," which honestly only raises more questions, but they're comparatively dull questions. ("How common is an isolated supernova?" Etc.)

1:32pm: MAXI/GSC reports that this event was also responsible for an alert trigger at their site. ("A bright uncatalogued x-ray transient source.")

1:40pm: SAGUARO reports observations and analysis ongoing.

1:56pm: AGILE reports further analysis.

4:22pm: Fermi-LAT reports on what they observed after the satellite left the South Atlantic Anomaly. (Null results, upper limits, analysis ongoing.) 

5:17pm: MASTER GRN clarifies that their discovery was not intended to be associated with this GW event (although it was found during that search), and reports two additional discoveries.