Add GECAM alerts

[martinjohndyer]

https://gcn.nasa.gov/missions/gecam https://gcn.gsfc.nasa.gov/gecam.html https://gcn.gsfc.nasa.gov/gecam_events.html

Fairly straightforward to process from the looks of it, just need to filter on SRC_CLASS=GRB since they publish various other alerts as well. Also need to decide on doing both Flight and Ground or just Ground, and what strategy we want to use.

<?xml version='1.0' encoding='UTF-8'?>
<voe:VOEvent xmlns:voe="http://www.ivoa.net/xml/VOEvent/v2.0"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" ivorn="ivo://nasa.gsfc.gcn/GECAM#FLT_Event_2024-01-12T569:03:04.96_000018-768" role="observation" version="2.0" xsi:schemaLocation="http://www.ivoa.net/xml/VOEvent/v2.0  http://www.ivoa.net/xml/VOEvent/VOEvent-v2.0.xsd">
  <Who>
    <AuthorIVORN>ivo://nasa.gsfc.tan/gcn</AuthorIVORN>
    <Author>
      <shortName>GECAM (via VO-GCN/TAN)</shortName>
      <contactName>Yue Huang</contactName>
      <contactEmail>huangyue@ihep.ac.cn</contactEmail>
    </Author>
    <Date>2024-01-12T05:44:54</Date>
    <Description>This VOEvent message was created with GCN/TAN VOE version: 15.08 17jun22</Description>
  </Who>
  <What>
    <Param name="Packet_Type" dataType="int" value="188"/>
    <Param name="Pkt_Ser_Num" dataType="int" value="18"/>
    <Param name="Trigger_Number" dataType="int" value="260" ucd="meta.id"/>
    <Param name="MISSION" dataType="string" value="B">
      <Description>Which Mission.</Description>
    </Param>
    <Param name="EVENT_DATE" dataType="int" value="20321" unit="days" ucd="time">
      <Description>Trucated Julian day.</Description>
    </Param>
    <Param name="EVENT_TIME" datatype="float" value="20485.850" unit="sec" ucd="time">
      <Description>Seconds of the Day UT.</Description>
    </Param>
    <Param name="TRIGGER_SIGNIF" dataType="float" value=" 4.90" unit="sigma">
      <Description>Significance of the trigger.</Description>
    </Param>
    <Param name="TRIGGER_DUR" dataType="float" value="0.200" unit="sec">
      <Description>Duration of the trigger criteria that initiated this event.</Description>
    </Param>
    <Param name="TRIGGER_ERANGE_LoBin" dataType="int" value="1">
      <Description>Energy window in channel bins; Low limit.</Description>
    </Param>
    <Param name="TRIGGER_ERANGE_HiBin" dataType="int" value="2">
      <Description>Energy window in channel bins; High limit.</Description>
    </Param>
    <Param name="TRIGGER_ERANGE_LoEnergy" dataType="int" value="30">
      <Description>Energy window in keV; Low limit.</Description>
    </Param>
    <Param name="TRIGGER_ERANGE_HiEnergy" dataType="int" value="140">
      <Description>Energy window in keV; High limit.</Description>
    </Param>
    <Param name="TRIGGER_DETS" value="0x1030080">
      <Description>Enable/Disable the 25 detectors involved.</Description>
    </Param>
    <Param name="SRC_CLASS" dataType="string" value="GRB">
      <Description>The Event Type is a regular GRB.</Description>
    </Param>
    <Param name="BURST_INTEN" dataType="int" value="1402" unit="[counts/sec]">
      <Description>Intensity of the burst in counts/sec.</Description>
    </Param>
    <Param name="BURST_DUR" dataType="float" value="4.000" unit="[sec]">
      <Description>Duration of the event.</Description>
    </Param>
    <Param name="Phi" dataType="float" value="1.86">
      <Description>YET TO DO.</Description>
    </Param>
    <Param name="Theta" dataType="float" value="90.77">
      <Description>YET TO DO.</Description>
    </Param>
    <Param name="SC_LAT" dataType="float" value="-27.65">
      <Description>Spacecraft location.</Description>
    </Param>
    <Param name="SC_LONG" dataType="float" value="50.31">
      <Description>Spacecraft location.</Description>
    </Param>
  </What>
  <WhereWhen>
    <ObsDataLocation>
      <ObservatoryLocation id="GEOLUN"/>
      <ObservationLocation>
        <AstroCoordSystem id="UTC-FK5-GEO"/>
        <AstroCoords coord_system_id="UTC-FK5-GEO">
          <Time unit="s">
            <TimeInstant>
              <ISOTime>2024-01-12T05:41:25.85</ISOTime>
            </TimeInstant>
          </Time>
          <Position2D unit="deg">
            <Name1>RA</Name1>
            <Name2>Dec</Name2>
            <Value2>
              <C1>290.3500</C1>
              <C2>18.4100</C2>
            </Value2>
            <Error2Radius>3.6099</Error2Radius>
          </Position2D>
        </AstroCoords>
      </ObservationLocation>
    </ObsDataLocation>
    <Description>The RA,Dec coordinates are of the type: source_object.</Description>
  </WhereWhen>
  <How>
    <Description>GECAM FLIGHT</Description>
    <Reference uri="http://gcn.gsfc.nasa.gov/gcn/gecam.html" type="url"/>
  </How>
  <Why importance="1.0">
    <Inference probability="1.0">
      <Concept>process.variation.burst;em</Concept>
    </Inference>
  </Why>
  <Description>
  </Description>
</voe:VOEvent>

<?xml version='1.0' encoding='UTF-8'?>
<voe:VOEvent xmlns:voe="http://www.ivoa.net/xml/VOEvent/v2.0"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" ivorn="ivo://nasa.gsfc.gcn/GECAM#GND_Event_2024-01-12T569:03:04.96_000020-810" role="observation" version="2.0" xsi:schemaLocation="http://www.ivoa.net/xml/VOEvent/v2.0  http://www.ivoa.net/xml/VOEvent/VOEvent-v2.0.xsd">
  <Who>
    <AuthorIVORN>ivo://nasa.gsfc.tan/gcn</AuthorIVORN>
    <Author>
      <shortName>GECAM (via VO-GCN/TAN)</shortName>
      <contactName>Yue Huang</contactName>
      <contactEmail>huangyue@ihep.ac.cn</contactEmail>
    </Author>
    <Date>2024-01-12T05:57:06</Date>
    <Description>This VOEvent message was created with GCN/TAN VOE version: 15.08 17jun22</Description>
  </Who>
  <What>
    <Param name="Packet_Type" dataType="int" value="189"/>
    <Param name="Pkt_Ser_Num" dataType="int" value="20"/>
    <Param name="Trigger_Number" dataType="int" value="260" ucd="meta.id"/>
    <Param name="MISSION" dataType="string" value="B">
      <Description>Which Mission.</Description>
    </Param>
    <Param name="EVENT_DATE" dataType="int" value="20321" unit="days" ucd="time">
      <Description>Trucated Julian day.</Description>
    </Param>
    <Param name="EVENT_TIME" datatype="float" value="20485.850" unit="sec" ucd="time">
      <Description>Seconds of the Day UT.</Description>
    </Param>
    <Param name="SRC_CLASS" dataType="string" value="GRB">
      <Description>The Event Type is a regular GRB.</Description>
    </Param>
    <Param name="BURST_INTEN" dataType="int" value="3655" unit="[counts/sec]">
      <Description>Intensity of the burst in counts/sec.</Description>
    </Param>
    <Param name="BURST_DUR" dataType="float" value="3.000" unit="[sec]">
      <Description>Duration of the event.</Description>
    </Param>
    <Param name="Phi" dataType="float" value="8.09">
      <Description>YET TO DO.</Description>
    </Param>
    <Param name="Theta" dataType="float" value="91.19">
      <Description>YET TO DO.</Description>
    </Param>
    <Param name="SC_LAT" dataType="float" value="-27.65">
      <Description>Spacecraft location.</Description>
    </Param>
    <Param name="SC_LONG" dataType="float" value="50.31">
      <Description>Spacecraft location.</Description>
    </Param>
  </What>
  <WhereWhen>
    <ObsDataLocation>
      <ObservatoryLocation id="GEOLUN"/>
      <ObservationLocation>
        <AstroCoordSystem id="UTC-FK5-GEO"/>
        <AstroCoords coord_system_id="UTC-FK5-GEO">
          <Time unit="s">
            <TimeInstant>
              <ISOTime>2024-01-12T05:41:25.85</ISOTime>
            </TimeInstant>
          </Time>
          <Position2D unit="deg">
            <Name1>RA</Name1>
            <Name2>Dec</Name2>
            <Value2>
              <C1>351.9100</C1>
              <C2>1.1900</C2>
            </Value2>
            <Error2Radius>1.9299</Error2Radius>
          </Position2D>
        </AstroCoords>
      </ObservationLocation>
    </ObsDataLocation>
    <Description>The RA,Dec coordinates are of the type: source_object.</Description>
  </WhereWhen>
  <How>
    <Description>GECAM GROUND</Description>
    <Reference uri="http://gcn.gsfc.nasa.gov/gcn/gecam.html" type="url"/>
  </How>
  <Why importance="1.0">
    <Inference probability="1.0">
      <Concept>process.variation.burst;em</Concept>
    </Inference>
  </Why>
  <Description></Description>
</voe:VOEvent>

[martinjohndyer]

There's a paper here on the localisation: The localization method of GECAM and simulation analysis. I can't read most of it but Figure 4 implies it should have a similar localisation to Fermi GBM. With Fermi we take into account a 5.6deg systematic error (https://github.com/GOTO-OBS/gtecs-alert/commit/85d5b5059eb7fd096a8cbd9ce9dda3abc58807ce, #57) - I don't know if we need that here.