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Fundamental (astro)physics

with High Energy

Gamma Rays

Alessandro De Angelis

Lisboa, November 2011

• Instruments & methods

• Some physics results – The gamma-cosmic ray connection

– Dark Matter

– propagation (new particles, cosmology)

– Testing fundamental symmetries

Summary of last lecture…

• Understanding phenomena often requires a multiwavelength

approach

• Gamma rays are crucial in this

– HE: 30 MeV – 30 GeV

– VHE: 30 GeV – 30 TeV

– The Universe becomes opaque above

– Energy spectrum: power law with index -2, -3

• Gamma rays point directly to the source

– Great for astrophysics & CR studies

• Technique: satellites (Fermi, AGILE) for HE, Cherenkov

telescopes at ground (HESS, MAGIC, VERITAS) for VHE

– HE: 10x increase of our knowledge of sources in the last 6 years

– VHE: 20x times increase

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2

SELECTED PHYSICS RESULTS

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4

Origin of rays

From non thermal extreme dynamic processes:

E2 d

N/d

E

energy E

e- (TeV) Synchrotron (eV-keV)

(TeV) Inverse Compton (eV)

B

e.m. processes

0decay

-

0

+

(TeV)

p+ (>>TeV)

matter

hadronic cascades

VHE

In the VHE region, dN/dE ~ E- ( : spectral index)

To distinguish between had/leptonic origin study Spectral Energy Distribution (SED): (differential flux) . E2

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Stable sources

(>100 MeV; >100 GeV)

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Variability

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• Supernovae may be source of particles up to >1015 eV

– Nuclei receive energy from the shock wave of the supernova explosion

• The sources for ultrahigh cosmic rays are extragalactic: probably, AGN (and GRB?)

• Galactic (~1000 nG) and extragalactic (~0.1 nG?) fields make it difficult to observe directly the sources of CR

Origin of V(HE) Cosmic Rays

>60 galactic sources detected at VHE

• Inner Galaxy (2004) + extension (2005-2008)

from = -85° (or 275°) to = +60° and |b|<3°

• Survey is complete for fluxes > 0.09 Crab (+ deeper observations)

• Low diffuse flux Individual sources appear clearly

• Most of the revealed sources are mildly extended (D > 3 ' to 4 ')

G.C

.

Sun

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9

RX J1713-3946

RX J0852.0-4622

RCW 86

SN 1006, X-rays,

XMM Newton

SN 1006, VHE -rays

ApJ 661 (2007) 236 A&A 464 (2007)

235

ApJ 692 (2009)

1500

Gamma Rays from Molecular Clouds close to CR sources

•

•

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Connection gamma/CR

• Study of target-accelerator systems: pinpointing sources of

cosmic rays up to the knee

– New “fresh” cosmic rays interacting with matter near the source OR…

• pp -> n 0 -> 2n

Secondary -rays have ~ 1/10 of the energy of the primary p

• For a power-law proton distribution the -ray distribution is

again a power law with the same spectral index

– This property should not be misinterpreted in the sense of a delta-

function approximation: in general the -ray spectrum at energy E does

not trace the proton spectrum at energy Ep/f.

• any feature in the proton spectrum will reappear smoothed in the -ray spectrum (e.g.,

an exponential cutoff in the proton spectrum, exp( Ep/Ecut), is transformed into a sub-

exponential, exp[ (16E /Ecut)1/2]

dN

dE

dNp

dE p

D x =E

E p

IC443 (MAGIC J0616) and CR

index~3.1

MAGIC J0616 Fermi,

Egret

Magic,

Veritas

Evidence for hadronic processes?

Fermi centroid

moves towards Magic for increasing energies

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HESS 2007

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Particle acceleration

in SNR: to which E?

• Two possible processes:

– IC scattering of VHE

electrons on ambient

photons

– Hadronic interactions of

accelerated protons or ions

in the interstellar medium • The -ray energy spectrum of

RX J1713-3946 as measured

by H.E.S.S. suffers at cut-off

above 10 TeV

– But: significant flux >30 TeV

• In the hadronic scenario, this

implies efficient proton

acceleration up to ~2-300

TeV

– (Almost the knee)

Joint HESS-MAGIC-VERITAS campaign on M87

(Science 2009)

VHE

nucleus

Peak flux

knot HST-1

nucleus

X-ray

Radio

HST-1 Core

Knot D Knot A

Colours: 0.2 - 6 keV (Chandra) Contours: 8 GHz radio (VLA)

The M87 radio-galaxy Jet

•

•

•

•

Chandra

jet

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Detection of gamma signals from the starburst galaxies

M82 (Veritas) and NGC253 (H.E.S.S.)

• Emission coherent

with what expected

from the SN/massive

star rate

• Supports the CR/

gamma connection

•

•

o

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The gamma/neutrino connection:

“predictions”

• Many model uncertainties present

in the gamma/p relation disappear

when studying gamma/neutrino

(reflects the fact that pions decay

into gamma rays and neutrinos

that carry 1/2 and 1/4 of the

energy of the parent. This assumes that the four leptons in

the charged pion decay equally

share the charged pion’s energy.

An exact expression can be

calculated…)

dN

dE

1

2

dN

dE

Very accurate input for

neutrino detectors

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Dark Matter

• Possible astrophysical signatures

– Gamma line (at suspect clumps), if Majorana

– Gamma continuum (at suspect clumps or diffuse)

• And after 5 years of Fermi, a clear picture of the diffuse gamma

emission will pinpoint possible clumps

– Excess of antimatter

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Self-annihilation of a Majorana WIMP (eg neutralino)

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- other -ray sources in the FoV

=> competing plausible scenarios - halo core radius: extended vs point-like

BUT:

Highest DM density candidate:

Galactic Center?

Close by (7.5 kpc)

Not extended

DM search (Majorana WIMPs)

2 ;1

d2

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Where to look? An obvious place is the GC…

• BH of 3.6 million solar

masses…

• However in a confuse

region

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-ray detection from the Galactic Center

Chandra GC survey NASA/UMass/D.Wang et al.

CANGAROO (80%)

Whipple (95%)

H.E.S.S.

from W.Hofmann, Heidelberg 2004

detection of -rays from GC by Cangaroo,

Whipple, HESS, MAGIC

source < 3’ ( < 7 pc at GC)

hard E-2.21±0.09 spectrum

fit to -annihilation continuum

spectrum leads to: M > 14 TeV

other interpretations possible (probable)

Galactic Center: very crowded sky region, strong

exp. evidence against cuspy profile

Milky Way satellites Sagittarius, Draco, Segue, Willman1, Perseus, …

proximity (< 100 kpc)

low baryonic content, no central BH (which may change the DM cusp)

large M/L ratio

No signal for now…

no real indication of DM…

The spectrum is featurless!!!

…and satellite galaxies

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A lobe-like structure in the Galaxy

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“Conventional” explanations as well:

remnant of an active phase of “our” BH?

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Unpointed e measurements in 2011

• Spectral features in the (e+ + e-) spectrum – possible excess around 600 GeV reported by ATIC

– spectral cutoff measured by H.E.S.S. around 1 TeV

• Pamela reports a unforeseen increase in the positron fraction ~10-100 GeV

• Confirmed by Fermi up to 200 GeV

• More than 400 papers

• Local source of electrons/positrons – astrophysical? Dark Matter?

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Some possible interpretations

• Several papers already published to explain electron spectrum

– Together with other observations (positron fraction, diffuse -ray)

Dark Matter

Strumia+ 2009

But the deviation with respect to the diffuse

emission model can be due to pulsars (D < 1 kpc)

Ackermann+ 2011 arXiv:1109.0521v1

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Adding candidate pulsars within 1kpc works

for Fermi and Pamela too arXiv:0905.0636

Fermi data are nicely reproduced,

assuming for each pulsar a 40% efficiency

in converting spin-down energy into

electrons and positrons

Pulsars are modeled as point-like,

bursting sources, with a power-law

injection spectrum (index=1.7) with

exponential cutoff at 1 TeV

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Conclusions on the (possible) excess of e

• Fermi+ Pamela “excess” can be explained with e.g. – Multifactor standard model (background model with less steep electron

injection spectrum; nearby astrophysical sources like pulsars, reacceleration at old SNRs, localized SNRs, ..)

• Hooper, Blasi, Serpico, JCAP 2009; Fujita & al., PRD 2009; Grasso & al., AP 2009

– Dark matter

• We need more data and understanding to distinguish these scenarios

• Cherenkov telescopes can help – measurements of HE electrons have already been published, and positron measurements using the shadow of the Moon and the planetary field are difficult but not impossible – Upper limits could also be helpful

• Potential of HEA larger than accelerators. However, astrophysical uncertainties are such that, if DM is not found, limits are much less reliable than limits at the accelerators

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Cherenkov telescopes can distinguish positrons

Moon shadow observation mode

developed for the MAGIC telescopes [P. Colin ICRC 2011]

sensitivity (50h): 300-700GeV: ~4.4% Crab

measurement possible in few years

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probe e+/e- ratio at 300-700 GeV

?

MAGIC

e+/e

++

e-

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Farther out…

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All stable sources associated with Active Galactic Nuclei

(AGN)

• Power comes from

material falling

toward a

supermassive

black hole

• Some of this

energy fuels a jet

of high-energy

particles with large

Lorentz factors

• We observe

primarily blazars,

for which the jet is

pointed toward

Earth.

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Variability: Mkn 421, Mkn501

• Two very well studied sources,

highly variable

– Monitoring from Whipple, Magic…

– TeV-X Correlation • No orphan flares…

– See neutrinos

However, recently Fermi/HESS saw no correlation in PKS 2155

VHE gamma

X

Mkn 421

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Rapid variability

HESS PKS 2155

z = 0.116

July 2006 Peak flux ~15 x Crab

~50 x average

Doubling times 1-3 min

RBH/c ~ 1...2.104 s

H.E.S.S. arXiV:0706.0797

MAGIC, Mkn 501 Doubling time ~ 2 min

astro-ph/0702008 arXiv:0708.2889

GRBs

Another probe

• Interesting for astrophysical reasons,

for propagation physics, for rapid

variability

• Fermi is changing our view, due to its

unprecedented range, self-pointing,

dedicated instrument

• MAGIC is the best IACT, due to its fast

movement & low threshold

But how many can

we expect/year?

0.02 < N < 0.5

De Angelis, Galanti, Roncadelli 2011

with Franceschini EBL modeling

MA

GIC

H.E

.S.S

.

redshift

z

ray energy (TeV)

= 1

> 1

region of opacity

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Fermi GRBs

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• GBM: ~250 GRB/yr

• LAT: ~9 GRB/yr

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Violation of the Lorentz Invariance? Light dispersion expected in some QG models, but interesting “per-se”

0.15-0.25 TeV

0.25-0.6 TeV

0.6-1.2 TeV

1.2-10 TeV 4 min lag

MAGIC Mkn 501, PLB08

Es1 ~ 0.03 MP Es1 > 0.02 MP

HESS PKS 2155, PRL08

Es1 > 0.06 MP

GRB X-ray limits: Es1 > 0.11 MP (Fermi, but…)

anyway in most scenarios

t ~ (E/Es ) , >1 VHE gamma rays are the probe Mrk 501: Es2 > 3.10-9 MP , =2

1st order

V = c [1 +- (E/Es1) – 2 (E/Es2)2 +- …]

> 1 GeV

< 5 MeV

Es1

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LIV in Fermi vs. MAGIC+HESS

• GRB080916C at z~4.2 : 13.2 GeV photon detected by Fermi 16.5 s after GBM trigger. At 1st

order

• The MAGIC result for Mkn501 at z= 0.034 is t = (0.030 +- 0.012) s/GeV; for HESS at z~0.116,

according to Ellis et al., Feb 09, t = (0.030 +- 0.027) s/GeV

• t ~ (0.43 ± 0.19) K(z) s/GeV

Extrapolating, you get from Fermi (26 +- 11) s (J. Ellis et al., Feb 2009)

SURPRISINGLY CONSISTENT:

DIFFERENT ENERGY RANGE

DIFFERENT DISTANCE

Es1

~z

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• z = 1.8 ± 0.4

• one of the brightest GRBs

observed by LAT

• after prompt phase, power-low

emission persists in the LAT data as

late as 1 ks post trigger:

highest E photon so far detected:

33.4 GeV, 82 s after GBM trigger

[expected from Ellis & al. (26 ± 13) s]

• much weaker constraints on LIV Es

(EBL constraints)

Fermi: GRB 090510 GRB 090902

• z = 0.903 ± 0.003

• prompt spectrum detected,

significant deviation from Band

function at high E

• High energy photon detected:

31 GeV at To + 0.83 s

[expected from Ellis & al. (12 ± 5) s]

• tight constraint on Lorentz

Invariance Violation:

– MQG > several MPlanck

[arXiv:0909.247v1]

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Interpretation of the results on rapid

variability • The most likely

interpretation is that the

delay is due to physics at

the source

– By the way, a puzzle for

astrophysicists

• However

– We are sensitive to effects at

the Planck mass scale

– More observations of flares

will clarify the situation

– 2nd order effects?

– Anisotropy?

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Propagation of -rays

x

x x

For rays, relevant background component is optical/infrared (EBL)

different models for EBL: minimum density given by cosmology/star formation

Measurement of spectral features permits to constrain EBL models

VHE bck e+e-

dominant process for absorption:

maximal for:

Heitler 1960

( ) ~

Mean free path

e+

e-

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Selection bias?

New physics? adapted from De Angelis, Mansutti,

Persic, Roncadelli MNRAS 2009

Are our AGN observations

consistent with theory?

Selection bias? New physics ?

obse

rved s

pect

ral in

dex

redshift

The most distant:

MAGIC 3C 279

(z=0.54)

~ E-2

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• Explanations go from the standard

ones

– very hard emission mechanisms with

intrinsic slope < 1.5 (Stecker 2008)

– Very low EBL, plus observational bias

• to almost standard

– gamma-ray fluxes enhanced by

relatively nearby production by

interactions of primary cosmic rays or emitted from the same source

• to possible evidence for new physics

– Oscillation to a light “axion”? (DA,

Roncadelli & MAnsutti [DARMA],

PLB2008, PRD2008)

» Axion emission (Hooper et al.,

PRD2008)

Could it be seen?

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• Needs magnetic field

– In the intergalactic space (De Angelis, Roncadelli, Mansutti)

– At the emitter and in the Milky Way (Hooper, Serpico, Simet)

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Recent confirmation

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We are (maybe) making

two extraordinary claims

• A possible relation between arrival time and energy

• Signal from sources far away hardly compatible with EBL

– But warning: not incompatible!

• We should keep in mind that

– Extraordinary claims require extraordinary evidence

• New Scientist, SciAm blog/news, …, and then?

– Claims must be followed up

• If we see this in such sources, what else do we expect?

• Fundamental implications of unexpected findings?

• Are we seeing a part of the same big picture?

– Warning: this is a very connected world… If you touch

dispersion relations, the Universe might become transparent

To photons beyond the GZK (Galaverni & Sigl 2008)

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A no-loss situation: if propagation is

standard, cosmology with AGN

GRH depends on the –ray path and there the Hubble constant and the

cosmological densities enter => if EBL density is known, the GRH might be used as a distance estimator

GRH behaves differently than other observables already used for cosmology

measurements. Blanch & Martinez 2004

Simulated measurements

Mkn 421 Mkn 501

1ES1959+650 Mkn 180

1ES 2344+514

PKS2005-489

1ES1218+304

1ES1101-232

H2356-309 PKS 2155-304 H1426+428

EBL constraint is paving the

way for the use of AGNs to

fit M and …

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Determination of H0, M and

Using the foreseen precision on the GRH measurements of 20 extrapolated AGNs at

z>0.2, the COSMOLOGICAL PARAMETERS can be fitted.

=> The 2=2.3 2-parameter contour

improves by more than a factor 2 the 2004’ Supernovae combined result !

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Fermi catalog and the

VHE instruments

• The Fermi catalog includes all sources at 1%

Crab at 1 GeV

• Data on energies up to 30 GeV

– Hardness

Perfect trigger for IACT

Close to map of the Universe at ~1% Crab

between 1 GeV and 10 TeV

AND THEN?

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Still looking for

• Sample of sources not suffering selection bias

• …

• Proof that SNR quantitatively account for galactic CRs

• …

• Deep understanding of particle (& matter) acceleration in AGN

• …

• VHE gamma rays from GRB

• …

• Real cosmology with gamma rays

• Signs of Dark Matter

• Violation of Lorentz invariance

And even more

exotic physics • Cherenkov telescopes

have the largest optical

surfaces in the world

• If ET would use optical

(laser) communication,

they might send their

signal to IACT (Howard 2004)

– With current Terrestrial

laser technologies, 3 ns

optical pulses could be

broadcasted that would be

detectable at a distance of

300 pc, outshining starlight

from the host system

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A summary (oversimplified…) Crab

10% Crab

1% Crab

Glast

Magic2

Se

nsitiv

ity [

TeV

/cm

2s ]

Agile

C T A

Argo

Hawc

Hess/Veritas

Far universe

Cutoff of pulsars Fundamental physics

Cosmic rays At the knee

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(V)HE astronomy/astrophysics:

Summary / future

• Cosmic Rays:

– SNR as galactic sources established

• Astronomy with charged CR is difficult

• Astronomy with neutrinos will be difficult

– Results comsistent with AGN as extragalactic sources above the knee

• Still no detection of DM

– Interesting results (but…)

• The information from no detection is not as good as for accelerators

• A few things still not fully explained

– Photon propagation

• Safe fundamental science (and astronomy/astrophysics) from gamma rays – unique sensitivity, and room for improvement

– HEA can explore regions beyond the reach of accelerators