Point source analysis: candidate source list, extended

sources and energy

Claudio BogazziAWG Videoconference

13/04/2011

Outline• Candidate source list: review, feedbacks and other

experiments

• Extended sources: how to threat them

• Energy information: update

New candidate source list• The idea is to update the source list including the latest sources

detected by gamma rays experiments.• Old list discussed in ANTARES-PHYS/2009-002 (S. Toscano)• 1st attempt: made by JP and I, presented during last AWG

videoconference. Now wiki page avaialble:

http://antares.in2p3.fr/internal/dokuwiki/doku.php?id=new_candidate_sources_list

• To summarize: 3 cuts 1) Source visible from ANTARES 2) No PWN 3) Angular distance > 3°• Total of 51 (TeV) sources: 20 already in the previous list + 31

new ones

* new* old

What’s new…• Discussion just started.

• Everybody agrees it’s time to update the list.

• Still some points need to be clarify (see next slide).

• Few feedbacks from the e-mail sent to the AWG mailing list (thanks to Teresa, Juande & Mathias for their reply)

• Let’s try to summarize a bit…but do not forget that the candidate search is a “SECONDARY” approach.

• If there is an excess of the events somewhere in the sky we want to see it with the FULL SKY approach.

Crucial points

1 How many sources? Remember the number of sources is important for the trial factor. 50?

2 Do we want to include also GeV sources? If the answer is YES, than we have to decide from which catalogue we should start.

1 Do we want to exclude extended sources? See later about this point…

• After we clarify these 3 points, than we can think which cuts apply.

Example: some numbers• Suppose we want to include GeV sources AND we want to

analyze separately the extended sources.

• Example: 10 GeV sources + 10 extended sources.

• Let’s keep entirely the previous list: 24 TeV sources (7 extended)

• How many sources in total? Example: 50.

• 24 old + 26 new, between these 26 new sources 3 should be extended and 10 should be 10 sources.

Feedbacks• Damien: during last AWG videoconference he suggested to do

NOT limit the list to only TeV sources but to include also some GeV ( in principle ok, but…how many? Where do we look? )

• Damien: do you make a distinction between extended and not-extended sources? Not for the moment.

a) We can remove the extended sources from our list. b) We can include the extended sources but then we need to

modify the likelihood… (see later) c) We can just ignore this distinction…

• For the moment we will run our algorithm on some well known extended sources and see if we can see something…(on the to-do list)

Feedbacks• Mathias: “very important to consider GeV sources in the new

list”.• Most of the quasars detected by FERMI has a large redshift

that does not allow any TeV emission.• Compiling a sample of 50 FERMI-detected radio extragalactic

jets (quasars, BL lacertae and radio galaxies) based on the TANAMI sample which is not yet published (need to keep in contact with the FERMI/LAT collaboration) + a sample of x-ray sources is on the to-do list.

• My opinion: it seems there is too much work that goes well further the purpose of our intentions. Maybe a subsample of this list (only few sources) would be better.

Feedbacks• Teresa: more than 100 sources to really get into trial factor

problems.

• The extra flux required to achieve a stricter p-value is not linear with the number of sources in the list.

• Take care of possible bias when combining samples

• Better to keep the previous list, adding new sources instead of re-make a new list from the beginning.

Other experiments• AMANDA: Final analysis (2009) with 26 sources (no

explanations on the selection)

• ICECUBE: IC22 with 28 sources, IC40 with 39 sources (28 from the Northern Sky + 10 from the Southern Sky + hottest spot from IC22)

• SK: “16 objects identified in various publications as plausible bright sources of astrophysical neutrinos. […] Candidates include magnetars, plerions, SNR and μ-quasars”

Now is the first time they combine detectors IC40+IC59. In this case is important to be careful and try to avoid any possible bias, as samples are not

independent: do not use information from a first analysis to remove any source in the list.

IC40

General opinion• The selection of the candidates list is very subjective. There is

not a single way to do it and it can be extremely different from experiment to experiment.

• We know it’s an important topic but it should be not forgiven that it’s the full sky search our best way to look for an excess of events in the sky (since, by definition, we look at the whole sky)

• It would be great if at the end of this videoconference we all agree at least with the number of sources to include.

The algorithmβ

event

sourceF is the point spread function.B is the background rate.

test statistic

If we want to include an energy estimator:

F F x P ( Ei )

B B x P( Ei )-- atm nu-- E-2 nu

Extended sources

If we want to include the source extension than we have to modify F .

Source “considered” as a 2 D Gaussian of width σs

Convolve the point spread function with the source distribution

x

1-D example

σs

Energy information• Tested the muon energy, smeared with a gaussian (the sigma

of this gaussian should be our uncertainty on the energy estimation)

E-2

Atmospheric nu

As expected, the effect of a sigma = 0.1 is negligible.

Energy information

Discovery potentials for different energy muons smearing

Comparison with the other energy informations

Energy information

Energy distribution:atmospheric cosmic smeared (=0.3) atms.

Discovery potentials

• Tabella con valori per 3 sigma and 5 sigma…

Conclusions• New candidate source list: …

• Extended sources: if we want to make a separate analysis then in principle we know how to do it.

• Energy information: muon energy tested, results look promising.

• Status of the analysis: still some issues to decide (run selection, systematic, choice of the energy estimator) but in general it is going well and we still plan to ask the unblind before summer conferences (-> ICRC) and of course report the full status at the next meeting in Moscow.

BACK UP

Thesis:http://w3.iihe.ac.be/Publications/Thesis/labare.pdf

26 sources in the Analysis using 2000-06

data

IC40 : 39 source selected for a candidate list search

Nhits information on Q

24

β

Basically we multiply both the likelihood for the signal + background case and the likelihood for the background only for the probability to have some hits according with the relative spectrum (E-2 for the signal+bkg lik and atmospheric for the bkg lik)

Note that, for the background-only likelihood we should use the distribution of the number of hits from REAL data.

25

For example, for 100 hits these are the 2 probabilities that we need.