This document summarizes a study analyzing spatially coincident high-energy neutrino events detected by the IceCube Neutrino Observatory and gamma-ray sources observed by the Fermi Gamma-ray Space Telescope. The study found that three out of fifteen high-energy neutrino events detected by IceCube were spatially coincident with gamma-ray sources in the Fermi 3FGL catalog, including one Fermi blazar and two BL Lac objects. To interpret these results, the study calculated the probability of such spatial coincidences occurring by chance based on the positions of known gamma-ray sources and found it to be low. This suggests astrophysical neutrino sources may be identified through multi-messenger observations with IceCube and Fermi.

1. A S T U D Y O F S P A T I A L L Y - C O I N C I D E N T
I C E C U B E N E U T R I N O S A N D F E R M I G A M M A -
R A Y S O U R C E S
H A N N A H S E Y M O U R - B A R N A R D C O L L E G E
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2. • Multi-messenger Astronomy Search for Cosmic-Ray
Sources
• IceCube Neutrino Observatory and Fermi Gamma-Ray
Observatory
• Neutrino Events and Fermi Blazars
• Implications of Data
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3. N E U T R I N O / M U L T I -
M E S S E N G E R
A S T R O N O M Y
• Neutrinos mostly interact via weak force
• Cross-section is very low
• Cosmic rays-mainly charged particles
and nuclei
• Can be scattered by B-fields
• Don’t “point back” to source
• Cosmic rays thought to be produced by
astrophysical nuclear processes
• Charged pion decay
• Same processes produce neutrinos
and gamma rays
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4. N E U T R I N O
A S T R O N O M Y -
P O T E N T I A L
S O U R C E S
• TeV-PeV neutrinos most likely produced in
extreme astrophysical environments
• Proton interaction with gas
• Starburst Galaxies
• Blazars and other AGN
• FSRQs more likely to be neutrino-bright
• Optically thick accretion disk/strong
external radiation field
• Expect ~1e-6 neutrinos detected by IceCube
for Mrk 501 flare*
• ~30% probability of detecting neutrinos from
flare, few per year*
• Could detect a few neutrinos from flares
(i.e., 3C 279)*
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*A. M. Atoyan and C. D. Dermer. Neutral Beams from Blazar Jets. , 586:79–96, March 2003.

5. I C E C U B E
N E U T R I N O
O B S E R V A T O R Y
• >2km of ice near South Pole
• 86 strings of 60 PMTs and electronics
• Charged-current interaction
• Cherenkov Radiation
• Detects muon events as tracks, other
events as showers (in case of charged-
current interaction)
• Much better angular resolution for muons
• Compare ~1º to ~20º
• Select for events going through Earth
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6. E A R L I E S T
L I G H T
L A T E S T
L I G H T
B I G B I R D * *
2 P E V
7 1 T E V
6
**(Icecube.wisc.edu, 2016)

7. I C E C U B E S K Y M A P
7
W H E R E
A R E T H E
P O I N T
S O U R C E
S ?
***Phys. Rev. Lett. 115, 081102 (2015)

8. F E R M I S P A C E
T E L E S C O P E
• Sensitive to energies up to 1
TeV
• LAT sees 20% of sky
• Covers entire sky in 3hrs
• Gamma ray -> e-e+ pair
• Si measures path to
determine direction
• Calorimeter measures
energy
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9. S K Y , M O D E L , R E S I D U A L S M A P S F O R
E A C H N E U T R I N O E V E N T
• Fermi analysis of a 7ºx7º region around 15 IceCube track events
• 1-300 GeV
• Search for Fermi sources with ~1º radius of neutrino
• 2 events with one source, 1 event with two
• 1 FSRQ and 3 BL LAC
• Analysis using Fermi Science Tools, P7REP_SOURCE_V16
• Light Curves
• 14 one-day bins (one week before neutrino event, one week after)
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10. Neutrino Event 11
Count Model Residual
1 0
7 º X 7 º
P H / S / C M
^2
P H O T O N
+ / -
W E E K

11. Neutrino Event 12
Count Model Residual
1

12. Neutrino Event 17
Count Model Residual
1

13. I N T E R P R E T A T I O N
• Probability of spatial
coincidence
• Constant declination,
random right ascension
• IceCube positions
dependent on declination
• Compare to FSRQ, BL LAC
Positions for 3FGL
• Repeat 10000x
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14. F U T U R E
D I R E C T I O N S
• VERITAS analysis of point
sources
• Higher energy gamma
rays
• Better understanding of
AGN and cosmic rays?
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15. M A R C O S S A N T A N D E R
J O H N P A R S O N S
M I K E S H A E V I T Z
R E S H M I M U K H E R J E E
T H E N A T I O N A L S C I E N C E F O U N D A T I O N
T H E N E V I S L A B O R A T O R I E S R E U
Acknowledgements
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