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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
08-09-2010 Matteo Palermo 2
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
08-09-2010 Matteo Palermo 3
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
08-09-2010 4Matteo Palermo
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
08-09-2010 5Matteo Palermo
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)
08-09-2010 Matteo Palermo 6
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
08-09-2010 7Matteo Palermo
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
08-09-2010 8Matteo Palermo
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)
08-09-2010 9Matteo Palermo
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
08-09-2010 10Matteo Palermo
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
08-09-2010 11Matteo Palermo
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
08-09-2010 12Matteo Palermo
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)
08-09-2010 15Matteo Palermo
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