One of the primary goals for ANTARES is the identification of neutrino sources, whose signature would appear in ANTARES data (in form of neutrino arrival directions) as clusters of events at given sky coordinates.
The significance of a neutrino excess from a given sky position must be assessed over the expected background fluctuations using, for instance the Feldman-Cousins statistics.
This ANTARES use case allows to inspect a sample of neutrino arrival directions in equatorial coordinates (RA, dec), evaluate from it the expected background rate for a user-selected sky position, and finally assess the significance of a cluster defined as 'all arrival directions that fall inside a given radius, selected by the user and indicated here 'region of interest' (RoI).
Here follow the step-by-step description of the code provided at https://git.km3net.de/srgozzini/workflow_ps/-/blob/master/PS.ipynb
- The function *bkg_evaluation(decl, roi)* permits to evaluate the expected background for a give sky declination and a given region of interest ('half width' of the declination band around the source declination). The right ascension is not used here, as the background distribution depends only on the visibility of the given sky position from the location of ANTARES, and therefore on the declination only.
This function uses a polynomial interpolation to smoothen the background distibution otherwise obtained from the data. This function returns the number of expected background events that in the following will be indicated as nbkg.
- the functions *UL(nbkg, nobs)* and *LL(nbkg, nobs)* compute the upper and lower limits in presence of nbkg backgroud events, if the measurements is nobs observed events inside the region of interest.
- the function *Sens(nbkg)* is used to calculate the sensitivity, defined as average upper limit, that is reached in presence of nbkg events in the declination band of the source.
- the two functions *make_vector(Decl, RA)* and *calc_angle(v1, v2)* are auxilary functions used later. *make_vector* fills a 3-dimensional vector using the sky coordinates of an event (Decl, RA), and assigning length 1. *calc_angle* computes the angular distance (in units degrees) between two points in the sky defined as the angle between their corresponding vectors v1 and v2.
- The function *compute_limits(ra_source, dec_source, gamma, RoI)* is the main function of this script and computes the flux upper limits for a given direction in the sky defined from the coordinates ra_source and dec_source, and for the two additional source parameters gamma (spectral index) and RoI (region of interest, representing the source extension).
## Using ANTARES data
ANTARES data has already been published to the VO for two data sets by using the services of the German Astrophysical Virtual Observatory (GAVO) which run the DaCHS software. The most recent public data sample is available through the ANTARES website, however, it is thus not findable through VO and does not match the FAIR criteria. Including ANTARES data in the development of future VO data types allowes to increase the chance for a long-term availability of high-quality ANTARES data. On the other hand, the KM3NeT VO server could be registered to the VO and protocols be tested using the ANTARES 2007-2017 sample.
