Refined notices (N2)

N2 notices come has as a second set of notices in the alert sequence following the detection of a transient by ECLAIRs. Indeed, following an ECLAIRs trigger that meets validation criteria, the SVOM platform can be automatically repointed in few minutes. This will enable further detections with the smaller field-of-view instruments MXT and VT to better identified and localised the flaring source with its afterglow.

MXT (N2m)

MXT notices are produced as soon as MXT has detect a source at an SNR > 3 sigma level. They are labelled according to the quality factor qf which indicates the accuracy of the localisation:

  • qf = 1: 120 arcsecs < R90 < 300 arcsec

  • qf = 2: 60 arcsecs < R90 < 120 arcsec

  • qf = 3: 30 arcsecs < R90 < 60 arcsec

  • qf = 4: R90 < 30 arcsec

They will be named as follow:

  • mxt-initial_qf# (Packet_Type = 209) for the first detection (# being the value of the quality factor),

  • mxt-update_qf# (Packet_Type = 210) each time the quality factor of the detection increases (for a maximum number of 4 N2m notices).

These notices are meant to be sent quickly, up to few minutes after the first trigger. If no counterpart is found, no N2m notices will be issued. Detailed explanation on the prompt phase of the burst will be gather in the circular. The following table sums up the information they will contain:

VOEvent element

Parameter

Value

Description

<What>
Detection_Info

SNR

float

signal to noise ratio of the detection (saturates at a value=255)

Mean_Flux

float [ergs/cm²/s]

Mean flux of the detected source

Flux_Error

float [ergs/cm²/s]

Mean flux error of the detection

<What>
Target_Info

Within_ECLAIRs_R90

boolean

Whether the detected source is compatible with ECLAIRs localisation

ECLAIRs_Angle

float [arcmin]

Angular distance between MXT and ECLAIRs localisation

<What>
Satellite_Info

Use_VT_Attitude

boolean

Whether the platform is in high stability mode, using the VT instead of the platform star tracker. This leads to an improved localisation estimate.

An example of an N2m can be found here

VT (N2v)

The automatic identification of visual source in the VT field of view is a difficult task, no automatic VT notices are published for now. For the moment the first data taken by VT following a slew of the platform are published in a dedicated VT circular.