TABLE OF CONTENTS:
The GCN system has been modified to incorporate the distribution
of temporal and/or spatial coincidences of GRBs/Transients detected by 2 or more space-based instruments.
GCN monitors all of its streams of transient information looking for events (triggers)
that are within 100sec of each other and/or within 10 arcmin of each other (within the last 7-12 days). [was 6 arcmin until 15jul20]
Since January 2009, individual notice types have had a COMMENT-line (in the full email format)
indicating the temporal/spatial coincidence between the current event and
a previous event (of another mission-instrument). But this has only worked for pairs of events, and
only the most recent pair of a multiple at that.
This new COINCIDENCE notice type contains all the missions/instruments contributing
to a given coincidence, and it is available in all the formats GCN produces.
Like all the other sources of GRB information within the GCN system,
users can elect to receive (or not) these COINCIDENCE Notices.
The GCN/COINCIDENCE Notices are archived within the GCN website
in the Table of COINCIDENCE Notices.
The COINCIDENCE notices are issued in real time for every temporal/spatial coincidence detected.
These notices report in real time[*] when two or more detectors in space have detected the same GRB/transient.
A real-time dbase is maintained and checked as each new GRB/Transient event is received by GCN.
The sequence of activities is shown in the figure below (times are suggestive of typical scenarios).
If there is a match between the new event and a notice in the dbase,
then a COINCIDENCE notice is issued giving the temporal and/or spatial match.
The temporal match requirement is |delta_trigger_time| < 100 sec, and
the spatial match is delta_position < 10 arcmin. [was 6 arcmin until 15jul20]
If a 3rd event is received by GCN that matches the first two, then a new COINCIDENCE notice is issued
giving the 3 mission-instruments that have the temporal/spatial match. This continues up to 6 matches
at which point the the first mission-instrument is dropped off the list. (The data packet can only hold
the information for 5 mission-instrument events.)
[*] A couple missions have delivery delays due to telemetry downlinking
restrictions (eg KONUS-Wind), and as such the finding and distribution
of any COINCIDENCE notice involving that mission will be delayed. Of course,
if it was the 3rd mission to join the coincidence, then the original pair
coincidence would have been distributed much earlier very near T_zero.
There is no separate "UPDATE" notice type -- it is its own update notice.
Content and Formats
Samples of the E-mail, Pager, Short-form Pager, and Subject-only
distribution methods of the GCN/COINCIDENCE Notice are included below.
The format is different than the typical GCN notices. Instead of the usual "TOKEN: value" lines
there are 2 to 5 lines containing a TOKEN ("CONTRIB_n:") and 9 values.
The 9 values are:
a '1' or '0' flag each for the Temporal and Spatial coincidences,
a string indicating the mission_instrument that contributed,
the Notice Type (a number from 1-170, for GCN's mostly internal usage),
the Trigger Number identification from that mission_instrument trigger,
the truncated julian day (TJD) and seconds-of-day (SOD) of that trigger, and
the RA,Dec(J2000) of the source position as determined by that mission_instrument
(if the mission_instrument does not have positioning capability, the values are listed as 0.0 0.0).
If more than than 5 contributors are found, then the up to 2 more lines appear,
but because of size limitations those 6th and 7th contributors contain only the first 3 fields.
While limited in its content compared to all the other Notice types within GCN,
it does provide a enough content to point back to the original notices
that contributed to the coincidence.
Then comes the COMMENTS section: (a) couple lines of explaining the format/content, and
a line giving the number of contributors (it can be more than the 7 listed above).
The 160-byte binary socket packet contents and format is described in detail
in the socket packet definition document.
The COINCIDENCE Notice is type=145.
Sites can elect to receive the COINCIDENCE Notice type.
See filtering to see which filter functions are applicable.
This filtering applies to all the existing distribution
methods/media (socket-based, email-based, and voevent-based).
There is no test_notice version of this COINCIDENCE type.
There are several other mission-based test notices within GCN, and
maybe they can fulfill your test notice needs.
There is no retraction form of this COINCIDENCE type.
It is very hard to write code that could detect a false-positive case
for this notice type. Plus given that a coincidence exists,
it is very likley that it is real -- a pure chance coincidence is very unlikely.
Simbad NED Searches
There is no companion SIMBAD_NED notice for this COINCIDENCE type.
Only the small-error_box containing notice types constributing to this coincidence
would be able to contribute to the SIMBAD_NED search, and besides
those same contributing notice types would already have SIMBAD_NED search results notices.
Percentabge Participations and Participation Rate
Percentage participation and rates statistics:
As of 23 Sep 2020, there was a total of 762 events with coincidences of instruments (17 Mar 2017 to 23 Sep 2020, ie 3.52 yrs)
The table below shows the percentage participation of each mission-instrument in the total of 762 events.
By far, FERMI_GBM has the highest partcipation (725 events & 95.1% participation percentage), with SWIFT_BAT at half that rate.
Mission_Instrument Percent Participation Annual rate of Participation FERMI_GBM 725/762 = 95.1% 725/3.52yr = 206/yr SWIFT_BAT 360/762 = 47.2% 360/3.52yr = 102/yr INTEGRAL_SPIACS 230/762 = 30.2% 230/3.52yr = 65/yr CALET_GBM 174/762 = 22.8% 174/3.52yr = 49/yr INTEGRAL 77/762 = 10.1% 77/3.52yr = 29/yr KONUS 55/762 = 7.2% 55/3.52yr = 16/yr AGILE 18/762 = 2.4% 18/3.52yr = 5/yr MAXI 15/762 = 2.0% 15/3.52yr = 4/yr Out of the 762 coincidences, there are 22 events that had a 5-way coincidence; 22 that had 4-way, and 107 3-way; the remaining 631 were 2-way coincidence events. The criteria for satisfying "coincidence" are within 100sec of each other and/or within 10 arcmin of each other (with the reporting within the last 7-12 days). [was 6 arcmin until 15jul20]
For further information on this, please contact
Scott Barthelmy (for GCN issues),
GCN main web page, and
GCN/COINCIDENCE notices archive.
Examples of the COINCIDENCE Notice type of the e-mail formats are shown below.
The "/////" divider bars are NOT part of the messages.
For those sites/people that use demons and/or incoming e-mail filters,
the "Subject" lines for the notice type:
////////////////////////// COINCIDENCE e-mail format ///////////////////////////////// TITLE: GCN/COINCIDENCE NOTICE NOTICE_DATE: Wed 24 May 17 14:52:14 UT NOTICE_TYPE: Coincidence LABELS: T P Mission_Inst NoticeType TrigNum TJD TrigSOD RA Dec CONTRIB_1: 1 0 KONUS 59 1789738438 17897 38438.000 0.000 0.000 CONTRIB_2: 1 0 INTEGRAL_SPIACS 52 7858 17897 38439.000 0.000 0.000 CONTRIB_3: 1 0 CALET_GBM 160 1179657247 17897 38493.000 0.000 0.000 COMMENTS: Coincidence between 2 or more events within the GCN streams. COMMENTS: There were 3 mission/instruments that contributed to this COINCIDENCE notice. COMMENTS: A '1' in the 'T' and 'P' columns indicates that the event participated in the Temporal and/or Positional coincidence. COMMENTS: Mission_Instruments that do not produce locations have their RA,Dec values listed as 0. //////////////////////////////////////////////////////////////////////////////////////
Examples of the (regular) pager formats are shown below.
There are no "Subject" lines for these e-mails sent to the pager companies
because the Subject line would use up valuable character counts
from the maximum displayable for the body of the message.
//////////////////// COINCIDENCE Pager format ///////////////////////////// GCN/Coincidence Notice CONTRIB: 1 0 KONUS 59 1789738438 17897 38438.000 0.000 0.000 CONTRIB: 1 0 INTEGRAL_SPIACS 52 7858 17897 38439.000 0.000 0.000 CONTRIB: 1 0 CALET_GBM 160 1179657247 17897 38493.000 0.000 0.000 ///////////////////////////////////////////////////////////////////////////
Examples of the short-form pager format are shown below.
There are no "Subject" lines for these e-mails sent to the pager companies,
because the Subject-line would use up valuable character counts
from the maximum displayable for the body of the message. And it was
the very limited display character count of some companies that motivated
the short-form pager method in the first place. The location(s) are in B1950 epoch.
//////////////////// COINCIDENCE Short-Pager format //////////////////////// [fill this in] ////////////////////////////////////////////////////////////////////////////
Normally for GCN Notice Subject-only formats, there are two variations shown
for the Subject-only format: decimal degrees (Current epoch) and
RA=hh:mm:ss Dec=DDdMMmSSs format (J2000 epoch).
But since there is seldom no RA,Dec information for a COINCIDENCE notice (only the time,
and it is the TrigTime for CONTRIB_1),
so both variations are identical:
//////////////////// COINCIDENCE Subject-only format //////////////////////// COINCIDENCE T=10:40:38 UT ///////////////////////////////////////////////////////////////////////////// COINCIDENCE T=10:40:38 UT /////////////////////////////////////////////////////////////////////////////