1. Svom Ground-segment Meeting CNES
2017 / 02 / 02
Fiches produits
ECL VHF
S. Schanne, CEA

2. VHF sequence : recall of principle
Recurrent message
Localization
First alert (>AlertThreshold)
Refined alert
Refined alert (>SlewThreshold) with slew request T0
Tb0
Time window of excess
Time window covered by high priority light curve
High priority light curve
Low priority light curve
Alert descriptor
Alert subimage
Time window covered by low priority light curve
Slew start received

3. Alert_TriggerCriterium
VHF alerts : packet def
APID 16
grouping flag 2
sequence count 14
packet length
Packet time 32
Observation ID
Alert_MsgCount 8
Alert_TimeTbAbs 56
Alert_TimeTb
Alert_SlewRequest
Alert_SkyTheta 24
Alert_SkyPhi
Alert_CatSrcNum
Alert_SkyYpix 8
Alert_SkyZpix
Alert_SkyYfit 16
Alert_SkyZfit
Alert_SkyCnt 32
Alert_SkyCntFit
Alert_SkyVar
Alert_Quality
Alert_TriggerCriterium
Alert_DetCounts 24
Alert_DetBkg
Sat_PositionX
Sat_PositionY
Sat_PositionZ
Sat_AttitudeQ0
Sat_AttitudeQ1
Sat_AttitudeQ2
Sat_AttitudeQ3
Sat_AttQuality
Sat_AttRef

4. TT_ECLAIRs Title: Detection time – ECLAIRs (T0)
Description: The T0 is the time in UTC when Eclairs has produced the first alert of a new alert sequence.
Input: <in blue> Output: <in red>
Method: To produce the T0, use the Packet time of the first VHF packet of a new alert sequence. An alert sequence is identified by the Observation ID in the VHF packet. The first alert of the sequence is identified by the Alert_MsgCount (value 0=first).
Remark1: This it is not the time of the burst, this is the time when the burst has been detected and localized for the first time, after processing time.
Remark2: The T0 is constant for any new burst sequence, since it is the time of the first alert in the sequence.
Kick-off SVOM France – 8/9/ Stéphane Schanne

5. QCL_ECLAIRs Title: Quick confidence level – ECLAIRs
Description: One way to define the quick confidence level of an ECLAIRs burst detection is to use the significance of the detection of the source in the onboard images (SNRi).
Input: <in blue> Output: <in red>
Method: To produce the SNRi, from any Alert packet of a alert sequence, use the Alert_SkyCnt and Alert_SkyVar and compute: SNRi= Alert_SkyCnt /sqrt(Alert_SkyVar)
Remark1: This value evolves during the alert sequence, therefore this has to be recurrently updated. The best confidence on a new alert is contained in the last alert packet of the sequence. This value can also be found in the Alert descriptor packet.
Remark2: The use of the SNRi as definition of the quick confidence level is one method. Other methods have to be studied.
Remark3: From the SNRi can be computed the width of the error box.
Kick-off SVOM France – 8/9/ Stéphane Schanne

6. QPO_ECLAIRs Title: Quick position – ECLAIRs
Description: The quick position of an ECLAIRs burst detection represents the sky position in Ra,Dec coordinates of the alert source.
Input: <in blue> Output: <in red>
Method: To produce the Ra,Dec position of the source, from any alert packet of an alert sequence. Use the Alert_SkyYfit and Alert_SkyZfit (fitted sky position in the ECLAIRs reference frame). Apply to this position the bias corrections in Y and Z (from the ground-based config data-base). Compute SkyTheta and SkyPhi (sky position of the source in the ECLAIRs reference frame: this can be cross-checked with the onboard values Alert_SkyTheta and Alert_SkyPhi, which however do not have the best bias corrections applied and are for corss-check only). Then apply to SkyTheta and SkyPhi the rotation of the ECLAIRs field of view to the global coordinate system (using Sat_Attitude, including Sat_AttRef and Sat_AttQuality infos).
Remark1: This value evolves during the alert sequence, therefore this has to be recurrently updated. The best position of a new alert is contained in the last alert packet of the sequence.
Remark2: It is TBD if the QPO contains only the position or also includes the error box, which can be computed as PSLE = K/SNRi, with SNRi computed from Alert_SkyCnt and Alert_SkyVar: SNRi= Alert_SkyCnt /sqrt(Alert_SkyVar), and K from the config data-base.
Kick-off SVOM France – 8/9/ Stéphane Schanne

7. VHF Light curves : samples
256 samples in 64 Packets (4 samples/Packet)
Low frequency sampling before and lately after Tb0
High frequency sampling shortly before and after Tb0
- 150 s s
Real-time
Tb0
Localization
First alert sent out
real-time
catch-up
Time of first trigger
Downlink T0
Time of first alert
64 Packets for ECL and 64 Packets for GRM
Full VHF bandwidth ~ 1 Packet every 2 s
 to ground : 1 ECL Packet every 4 s + 1 GRM Packet every 4 s.

8. VHF Light curves : samples time

9. VHF Light curve : packet loss
Real-time
Tb0
Proposal : keep consistence on Packet level
 Sample integral of counts since beginning of LC , instead of differential number of counts in time bins  in case of VHF packet loss : no holes, just loss in time-resolution.
 As soon as a new VHF LC packet arrives on ground (~2 s) update the LC received up to now on the screen of the Burst Advocate

10. ECLAIRs VHF Light curve : packet def
APID 16
grouping flag 2
sequence count 14
packet length
Packet time 32
Observation ID
AlertTime_Tb0_Abs 40
LightCurve _PacketNumber 8
Sat_AttitudeLCQ0
Sat_AttitudeLCQ1
Sat_AttitudeLCQ2
Sat_AttitudeLCQ3
Sat_PositionLat
Sat_PositionLon
Sample0_EnergyStrip0_IntCount
Sample0_EnergyStrip1_IntCount
Sample0_EnergyStrip2_IntCount
Sample0_EnergyStrip3_IntCount
Sample0_EnergySat_IntCount
Sample0_Multiple_IntCount
Sample1_EnergyStrip0_DiffCount 16
Sample1_EnergyStrip1_DiffCount
Sample1_EnergyStrip2_DiffCount
Sample1_EnergyStrip3_DiffCount
Sample1_EnergySat_DiffCount
Sample1_Multiple_DiffCount
Sample2_EnergyStrip0_DiffCount
Sample2_EnergyStrip1_DiffCount
Sample2_EnergyStrip2_DiffCount
Sample2_EnergyStrip3_DiffCount
Sample2_EnergySat_DiffCount
Sample2_Multiple_DiffCount
Sample3_EnergyStrip0_DiffCount
Sample3_EnergyStrip1_DiffCount
Sample3_EnergyStrip2_DiffCount
Sample3_EnergyStrip3_DiffCount
Sample3_EnergySat_DiffCount
Sample3_Multiple_DiffCount

11. OBLC_ECLAIRsi Title: On-board count light curve – ECLAIRs (channel i)
Description: The light curve in the energy band i for an ECLAIRs alert sequence represents the detected counts in predefiend time-bins around Tb0 (estimated time of the beginning of the burst at the first alert, at time T0). The channels i are predefined (4 trigger energy strips+1 sat+1 multiple counters).
Input: <in blue> Output: <in red>
Method: Each VHF LC packet contains 4 samples in time for all energy bands (not only channel i). The sample 0 contains integral counters, the samples 1-3 contain differential counters. The light curve for channel i is produced at a given time by taking all LC packets of the current alert and sorting them in time (LightCurve _PacketNumber). From the integral counters of the subsequent packets (Sample0_EnergyStripi_IntCount) it computes the number of counts over the duration of each packet and then derives a finer granularity by using the samples 1-3 (Sample1-3_EnergyStripi_DiffCount). In case of a missing packet, the counts over the duration of each packet can be derived, but not the fine granularity.
Remark1: The LC evolves during the alert sequence, therefore it has to be recurrently updated. The LC is finised when the last packet in the sequence is received (if there is no packet loss, otherwise it has to be updated after each VHF LC repetition. A copy of the complete VHF light curve is in the X-band SciHK).
Remark2: To be useful, such a raw-light curve for a given channel i has to be put into the context using: SatAttitude and SatPosition contained in each LC packet, in order to be able to model the background evolution, including Earth transits, slews and orbital periodicity (e.g. SAA).
Kick-off SVOM France – 8/9/ Stéphane Schanne

12. QLC_ECLAIRsi
Title: Quick light curve in physical units – ECLAIRs (channel i)
Description: The light curve in physical units for the energy band i (for an ECLAIRs alert sequence) is the background corrected light curve of the burst.
Input: <in blue> Output: <in red>
Method: The raw-data LC (OBLC) has to be scientifically analyzed (background fit over the LC, including the context: SatAttitude and SatPosition from which the Earth transits, slews and ortbital events, e.g. SAA, can be modelled). The background model has to be subtracted. The counts have to be converted into physical units, taking into account the position of the source in the FoV and a model of the ECLAIRs response. Error bars have to be added by using the background level.
Remark1: The QLC is probably to be performed manually by the BA, after human inspection of the OBLC and manual adjustment of the fitting methods.
Remark2: The QLC can only be produced for the complete LC (it can be reprocessed once the VHF LC repetition arrives, the final version is built from the copy of the complete VHF light curve is in the X-band SciHK).
Kick-off SVOM France – 8/9/ Stéphane Schanne

13. QT90_ECLAIRs Title: Quick duration – ECLAIRs
Description: The quick duration of the burst is derived from the OBLC (in counts)
Input: <in blue> Output: <in red>
Method: The OBLC for each energy strip (i=0 to 3) have to be computed. The most significant of the 4 has to be identified. This OBLC is fit and background corrected (with +/- numbers). A threshold has to be applied (e.g. 3 sigma to differentiate residual background from source counts). The integral light curve above threshold has to be constructed. The time between 5% and 95% of the maximum is measured: this is the QT90.
Remark1: The QT90 is probably to be performed manually by the BA.
Kick-off SVOM France – 8/9/ Stéphane Schanne

14. QPF_ECLAIRsi Title: Quick peak flux – ECLAIRs (channel i)
Description: Extract from the QLC_ECLAIRsi the time bin with the maximum emission, which is the QPF_ECLAIRsi quick peak flux for channel i.
Input: <in blue> Output: <in red>
Method:
Remark1:
Kick-off SVOM France – 8/9/ Stéphane Schanne

15. QHR Title: Quick hardness ratio
Description: Divide QPF_ECLAIRsi for the lowest and highest channels, giving the Quick hardness ratio QHR. (or is it simply the division of the OBLC_ECLAIRsi between lowest and highest channels?)
Input: <in blue> Output: <in red>
Method:
Remark1:
Kick-off SVOM France – 8/9/ Stéphane Schanne