TABLE OF CONTENTS:
The GCN system has been modified to incorporate the distribution
of the GECAM Notices (Gravitational Wave High-energy Electromagnetic
Counterpart All-sky Monitor) (GECAM). There are 2 satellites
operating in the X-ray and gamma-ray bands.
OCCURANCE RATE:
The GECAM notices occur about 500 times per year.
LOCATION ERROR:
The location uncertainties are 0-180 deg (radius, stat, 68% containment).
TIME DELAY:
The post-event processing (both pipeline and human involved) lasts less than 60 minutes,
the notice information is sent to GCN for formating, filtering and distribution within 10 sec.
Type / Application: Astronomy, X-Ray / Gamma
Operator: Institute of High Energy Physics (IHEP), Chinese Academy of Sciences (CAS)
Equipment: Dome-shaped array of 25 Gamma-ray detectors (GRD), 8 Charged particle detectors (CPD)
Configuration: Deployable solar array, batteries
GECAM (Gravitational Wave High-energy Electromagnetic Counterpart All-sky Monitor) is a constellation
of two small X-ray and gamma-ray all-sky observatories to search for gamma-ray counterparts to
gravitational wave events.
GECAM fast-tracked selection and development to take advantage of a new scientific opportunity, which
Xiong Shaolin, an astrophysicist at CAS's Institute of High Energy Physics in Beijing, and his colleagues
identified a month after the U.S. Laser Interferometer Gravitational-Wave Observatory announced its
historic detection of gravitational waves in February 2016. They proposed putting two satellites into orbit
on opposite sides of Earth that together could watch the entire sky for gamma rays emanating from the
events that generate gravitational waves. Funding for technical studies arrived a few months later, and the
mission has jumped to the front of the launch queue, with a date of 2020.
Each satellite features a dome-shaped array of 25 Gamma-ray detectors (GRD) and 8 Charged particle
detectors (CPD). Together the satellites will provide a FOV of 100% all-sky. The sensitivity of the detectors
is ~2E-8 erg/cm2/s. They will provide a localization of ~1 degree. The detectors are sensitive in the energy band
from 6 keV to 5 MeV.
Besides detecting the radiation from gravitational wave events, the satellites will also be contributing in
detecting Ultra-long GRBs, X-ray Flashes, X-ray-rich GRBs, Magnetars and Terrestrial Gamma-ray Flashes.
The satellites were launched together on a CZ-11 rocket from China's Xichang space center in December 2020.
See http://www.nssc.cas.cn for more information.
Notice Types, Content, and Purpose
The GECAM has two notice types, GECAM Flight and GECAM Ground.
REAL notices will have Trigger_Number values starting with "1",
TEST notices will have Trigger_Number values starting with 100000000.
The initial design and development is done by CAS's Institute of High Energy Physics.
See http://www.nssc.cas.cn for more information.
The GECAM Flight notices are processed within seconds, GECAM Ground notices take longer to
process.
Samples of the E-mail, Cell/Pager, Short-form Cell/Pager, and Subject-only distribution methods
of the 2 GCN/GECAM Notice types are included below. The format is very similar to the spacecraft-instrument sources
of GRB and Transient locations -- the GCN-standard "TOKEN: value" format.
(Also available in XML format via email and sockets (both binary and xml).)
The socket packet contents and format are similar to the other mission-specific packet types and
are described in detail in the socket packet definition document. This document also has explanations
of the various fields in the packet (their content, values, and implications for use).
(Therefore, it is useful for email-based recipients to read the socket packet definition document
to understand the contents of the email/cell/pager notifications.)
For the 160-byte binary format, if the 2^1 bit in the "trig_id" slot has a value of "1" then it is a "test" event notice, and
and if the 2^1 has a 0 then it is a "real" event notice.
NUM TYPE VOEVENT SOCKET FullFmt_EMAIL PAGER/CELL XML
w/Txt (all 4 variants)
=== ========= ======= ====== ============= ================ ====
188 GECAM_FLT Y P B B B&A
189 GECAM_GND Y P B B B&A
where:
Y = Also available in XML VOEvent format for XML_Sockets and VOEvent server sockets.
P = Packet (the GCN-standard 40 longword socket packet format)
B = Body of email (the GCN-standard "TOKEN: value" format)
A = As an attachment to a full-format email.
--------
See filtering to see the full list of filtering criteria for this Type.
This filtering applies to all the existing distribution methods/media.
The statistical error sizes for 68% containment are provided for each event.
The distance estimation band (with the SN1987A-like flux assumption)
is calculated for 68% containment considering only statistical uncertainty
of both the burst event and the SN1987A events (11 events in SK).
The expected rate of the GECAM events is 500 per year.
Sites are encouraged to acknowledge GECAM in their publications
based on follow-up observations using these GCN/GECAM locations.
The GCN/GECAM Notices are archived within the GCN website
in the Table of GECAM Events.
For further information on this:
see the GECAM website
or please contact Scott Barthelmy (for GCN issues),
Scott Barthelmy (for GCN/TAN issues).
Examples of the 2 Notice types of the various e-mail formats are shown below.
The "/////" divider bars are NOT part of the messages.
Do not take the actual values shown in these examples as real GECAM events.
//////////////////////////////////////////////////////////////////////
TITLE: GCN/GECAM_FLT NOTICE
NOTICE_DATE: Thu 22 Sep 22 06:13:39 UT
NOTICE_TYPE: GECAM_FLT
MISSION: B
TRIGGER_NUMBER: 117526367
SRC_RA: 33.8500d {+02h 15m 24s} (J2000),
34.0924d {+02h 16m 22s} (current),
33.3179d {+02h 13m 16s} (1950)
SRC_DEC: -35.0399d {-35d 02' 23"} (J2000),
-34.9347d {-34d 56' 04"} (current),
-35.2718d {-35d 16' 18"} (1950)
SRC_ERROR68: 9.18 [deg radius, stat-only, 68% containment]
EVENT_DATE: 19844 TJD; 265 DOY; 22/09/22 (yy/mm/dd)
EVENT_TIME: 22367.650 SOD {06:12:47.65} UT
TRIGGER_SIGNIF: 4.2 [sigma] (Signif of the Trigger)
TRIGGER_DUR: 2.000 [sec] (Duration of Trigger)
TRIGGER_ERANGE: 2 - 4 [Chan] 65 - 491 [keV]
TRIGGER_DETS: 0x1008040 (Enable/Disable the 25 detectors involved)
SRC_CLASS: GRB
BURST_INTEN: 180 [counts/sec]
BURST_DUR: 2.000 [sec]
PHI: 38.38 [deg]
THETA: 40.79 [deg]
SC_LAT: -5.13 [deg]
SC_LON: -90.40 [deg]
COMMENTS: GECAM In-flight report.
//////////////////////////////////////////////////////////////////////
TITLE: GCN/GECAM_GND NOTICE
NOTICE_DATE: Wed 21 Sep 22 11:21:24 UT
NOTICE_TYPE: GECAM_GND
MISSION: B
TRIGGER_NUMBER: 117457560
SRC_RA: 66.1300d {+04h 24m 31s} (J2000),
66.3180d {+04h 25m 16s} (current),
65.7190d {+04h 22m 53s} (1950)
SRC_DEC: -42.0199d {-42d 01' 11"} (J2000),
-41.9686d {-41d 58' 06"} (current),
-42.1335d {-42d 08' 00"} (1950)
SRC_ERROR68: 1.46 [deg radius, stat-only, 68% containment]
EVENT_DATE: 19843 TJD; 264 DOY; 22/09/21 (yy/mm/dd)
EVENT_TIME: 39960.650 SOD {11:06:00.65} UT
SRC_CLASS: GRB
BURST_INTEN: 1308 [counts/sec]
BURST_DUR: 17.000 [sec]
PHI: 326.81 [deg]
THETA: 29.57 [deg]
SC_LAT: -20.50 [deg]
SC_LON: -124.69 [deg]
COMMENTS: GECAM Ground-processed report.
//////////////////////////////////////////////////////////////////////////////
Cell/Pager Examples:
Examples of the (regular) cell/pager formats are shown below. There are no "Subject" lines for these e-mails sent to the cell/pager companies because the Subject line would use up valuable character counts from the maximum displayable for the body of the message. The RA,Dec is Current epoch.
/////////////////////////REAL Cell/Pager format//////////////////////////////// GCN/GECAM_FLT RA=318.520d DEC=+31.457d Err=0.6 (68%) T=08:30:01.22 UT /////////////////////////TEST Cell/Pager format//////////////////////////////// GCN/GECAM_FLT RA=318.520d DEC=+31.457d Err=0.6 (68%) TrigNum=100000001 T=08:30:01.22 UT ///////////////////////////////////////////////////////////////////////////////Short-form Cell/Pager Examples:
Examples of the short-form cell/pager format are shown below. There are no "Subject" lines for these e-mails sent to the cell/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 cell/pager method in the first place. The RA,Dec is 1950 epoch.
/////////////////////////REAL Short-Cell/Pager format////////////////////////// GECAM_FLT RA=317.773 DEC=+31.163d DATE: 20/11/13 T=08:30:01.22 TRIG_NUM=1 /////////////////////////TEST Short-Cell/Pager format////////////////////////// GECAM_FLT RA=317.773 DEC=+31.163d DATE: 20/11/13 T=08:30:01.22 TRIG_NUM=100000001 ///////////////////////////////////////////////////////////////////////////////Subject-only Examples
There are two variations of the Subject-only format: decimal degrees (Current epoch) and RA=hh:mm:ss Dec=DDdMMmSSs format (J2000 epoch). The two variations are shown below:
/////////////////////////REAL Subject-only format (Current epoch)////////////// GECAM_FLT RA=318.5203 DEC=+31.4569d T=08:30:01.22 UT TrigNum=1 /////////////////////////////////////////////////////////////////////////////// /////////////////////////TEST Subject-only format (Current epoch)////////////// GECAM_FLT RA=318.5203 DEC=+31.4569d T=08:30:01.22 UT TrigNum=100000001 /////////////////////////////////////////////////////////////////////////////// ///////////////REAL Subject-only format HH:MM:SS format (J2000 epoch)////////// GECAM_FLT RA=+21:13:12 DEC=+31:22:12 Num_events=54029 /////////////////////////////////////////////////////////////////////////////// ///////////////TEST Subject-only format HH:MM:SS format (J2000 epoch)////////// GECAM_FLT RA=+21:13:12 DEC=+31:22:12 Num_events=54029 ///////////////////////////////////////////////////////////////////////////////VOEvent by Email or Socket Examples
/////////////////////////REAL VOEvent format///////////////////////////////////
///////////////////////////////////////////////////////////////////////////////