08-09-2010 1Matteo Palermo

“Estimation of the probability of observing a gamma-ray flare based on the analysis of the

Fermi data”

Student: Matteo Palermo

Supervisors: Elisa Bernardini

Jose Luis Bazo Alba

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Cosmic raysCosmic rays

Cosmic Rays: Energetic particles (mainly protons) which energy spectrum extends several orders of magnitude.

• Gamma Rays

• Neutrinos

• Charged particlesUsually are divided in:

Protons, electrons and ionized nuclei. Because of their charge their path is changed by the magnetic field NO info about the direction of the source

They can travel for long distances without any deflection

Direction’s info, but attenuation problems

( 0.5 MeV - 100 TeV)

No charge and interact only via the weak force

Small attenuation and direction’s info

( E > 10 GeV )

Multi-messenger Astronomy: correlation studies between these 3 kinds of particles in CR

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A time dependent OFFLINE analysis using photon and neutrino data enhances the discovery probability by profiting from the photon-neutrino correlation.

PROBLEM: many gamma-ray telescopes have a small field of view, thus they canNOT look at a wide region of sources at the same time (neutrino detectors can look at the entire sky) . Moreover they are NOT taking data CONTINUOUSLY!

for many sources there might be missing photon data, so NO offline analysis

SOLUTION: SOLUTION: ONLINE ANALYSIS!ONLINE ANALYSIS!

Multi-messenger Multi-messenger AstronomyAstronomy

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Once combined observations have been performed

it’s necessary to estimate the overall probability of RANDOM positive detection

this can be done by calculating the following quantity:

m

Nj

jmgam

jgam

Nm

Nm

bkg

coincobs

bkg PPjmj

me

m

N1

)!(!

!

!

Probability of observing at least Nobs alerts above the THR & detecting at least

Ncoinc gamma ray flares

NToO (Neutrino Triggered Target of

Opportunity)

A

L

E

R

T

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The Fermi experiment• it’s not possible to use IACTs (Imaging

Atmospheric Cherenkov Telescopes) data to well estimate Pgam

•Why Fermi? Because Fermi is a satellite telescope which energy range is close to MAGIC’s , has a larger field of view than IACTs and is taking data CONTINOUSLY

• performances:

• energy range 30 MeV – 300 GeV

• angular resolution 0.15, 0.9 and 3.5° @ 10, 1 and 0.1 GeV respectively

• 30 minutes of lifetime for each point in the sky (every 3 hours)

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AnalysisThe basic idea to estimate this

probability:

• Set a threshold in order to define what is a flare and what is not• the estimation of the probability will be roughly

tot

overTHRgam T

TP

THR

3C 273

• Use Fermi data to calculate the Light Curve for a long period (e.g. 2 year)

LC: graph which shows the light intensity over a period of time

selection in energy and direction, bin size = 1 day

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Threshold

• I took the Flux distribution from the Light Curve, which is simply the projection on the flux axis (marginal probability density function for the flux)

1. lognormal fit: the variations in the flux are found to have a lognormal distribution

2. Gaussian fit of the log(flux) distribution: using this fit mode to compare with the previous one since the results should be the same

3. Gaussian fit of the peak of the flux distribution (excluding the tail): this fit should be worse than the other two

iancemeanThr var5

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The cumulative approach

Once we defined the threshold we computed the Pgam by evaluating the cumulative of the flux distribution, actually

In practice we integrated the resulting function from the lognormal fit.

Gauss

Log

norm

al

Gau

ss

log

(flu

x)

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Sources

Criteria used to select these sources:

• they have been classified as variable in the Fermi/LAT bright source catalog

• they should have been observed in TeV scale

• they are monitored by MAGIC

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Energy rangesWe did the same analysis for two different energy ranges, namely:

• from 100 MeV to 300 GeV

• from 1 GeV to 300 GeV in order to answer to the following question:

is the Pgam still the same in the TeV scale (MAGIC range)?

The idea is that if the Pgam does NOT change it is likely that it will NOT change even in the TeV scale

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ResultsSourceSource 100MeV-300 100MeV-300

GeVGeV1GeV-300GeV1GeV-300GeV

3C 2733C 273

M 87M 87

W ComaeW Comae

Mrk 421Mrk 421

3C 66 A/B3C 66 A/B

Mrk 501Mrk 501

1ES1959+6501ES1959+650

NGC 1275NGC 1275

PG 1553+113PG 1553+113

LSI+61 303LSI+61 303

S5 0716 +71S5 0716 +71

002.00015.0005.0

002.00017.0005.0

553 105

0007.00003.00004.0

0008.00006.00020.0

0013.00011.00025.0

00009.000009.000080.0

0015.00010.00022.0

0010.00008.00029.0

0011.00008.00019.0

0009.00007.00020.0

0003.00002.00007.0

0006.00004.00006.0

0004.00003.00009.0

0006.00004.00013.0

00017.000013.000036.0

002.00014.00032.0

0003.000018.000038.0

0010.00007.00018.0

002.00017.00041.0

003.0002.0004.0

003.00017.0004.0

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Improvements

• evaluate the errors for the mean and the variance (thus for the Pgam) for the lognormal and log(flux) fit mode

• re-do the same analysis but with the energy ranges completely separated

• define properly the confidence level for each results

• evaluate the actual spectral index for each source and re-do the analysis (so far to evaluate the exposure we used the same spectral index for all the sources)

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Thanks for the attention

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NToO (Neutrino Triggered Target of

Opportunity)

1. e-mail from the South Pole to Madison (USA), using IRIDIUM SATELLITE (24/7)

2.Chek for the visibility of that source from MAGIC, if so

3.Regular e-mail to MAGIC to the “shifter” in La Palma

4.If possible, focus on it

FUTURE: automatic procedure is under development

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