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Gamma-ray Astronomy.

Christian Stegmann EINN, Cyprus November, 2nd 2015

The end of the electromagnetic spectrum

C. Stegmann | Gamma ray astronomy | 2. November 2015 |

Gamma rays – Messengers from the High Energy Universe

> Production § protons: pion-decay: π0 → γγ

§ electrons: Inverse Compton Scattering: e± γ → e± γ

γ-ray band


Why would anybody be interested in research that does not concern cosmology, inflation, dark energy


Why would anybody be interested in research that does not concern cosmology, inflation, dark energy and electromagnetic interaction with nucleons and nuclei?


My answer

> 100 years after discovery of cosmic rays we still don’t fully understand how cosmic accelerators work

> Cosmic accelerators seem extremely efficient § in their energy conversion § in their speed of acceleration

> Cosmic rays probe some of the most extreme environments in the Universe

> Cosmic rays do influence galaxy evolution

> Need to understand cosmic-ray astrophysics before claiming new physics. e.g.

§ electrons/positrons from dark matter

§ effects of quantum gravity


Displaying Cosmic Particle Accelerators

This talk

Radio Optical X-ray Gamma-ray

E2 d

N/d

E


Displaying Cosmic Particle Accelerators

Stellar type

Supernova shell

Pulsars

Pulsar Wind Nebulae

Complex type

Y-ray binaries

Microquasars

ms-PSR

GRBs

Molecular clouds

Collective type

Star forming region

Starburst galaxies

Diffuse Galactic emission Isotropic extragalactic emission

Black-hole type

Galactic centre

AGNs (HBL, FSRQ, …)


Experimental techniques

Satellites (Fermi-LAT)

Air Cherenkov Systems (MAGIC, VERITAS, H.E.S.S.)

Water Cherenkov Systems (HAWC)

MeV GeV TeV PeV

Cherenkov light Particle shower


How to measure gamma-rays from the ground?

Photon



Photon

Camera image

Intensity à Energy

Orientation à Direction

Shape à Primary particle


1989: The first VHE gamma-ray source

Whipple

VLT, optical



Photon

Single telescope event

3 telescope image in common camera plane

Intensity à Energy

Orientation à Direction

Shape à Primary particle


Gamma-ray astronomy – 3rd generation experiments

VERITAS, USA

H.E.S.S., Namibia

MAGIC, La Palma


Number of sources


Data quality


Data quality today

> Morphologies § spacial

§ energy-dependent

> Periodicities/Variability § from ms to years

> Energy-coverage § over several decades

> Source position § on the arc-second level

RX J1713-3946

H.E.S.S.

0.2-0.8 TeV 0.8-2.5 TeV > 2.5 TeV

Vela pulsar

HESS J1825-137

LS 5039

RX J1713-3946

H.E.S.S.

Galactic center

H.E.S.S.

H.E.S.S.


SURVEYS


H.E.S.S. Galactic Plane Scan


H.E.S.S. galactic plane survey

> Source extraction with automatic pipeline

> Likelihood fit of emission by multiple Gaussian components plus diffuse background, Overlapping emission components combined

> 66 VHE sources + 11 complex sources (e.g. shell SNR) excluded from pipeline


The Galactic Plane in Gamma-rays


Identifications

Mostly sources with multiple associations


Current Galactic VHE sources (with distance estimates)

Current Instruments

2% Crab Sensitivity


SUPERNOVA REMNANTS

RX J1713.7-3946


Examples of Supernova Remnants

Gamma rays

X rays

Vela Jr RX J1713.7-3946 SN 1006 RCW 86


RX J1713.7-3946: Details of gamma-ray emission

> High precision morphology

> Comparison of TeV and X-ray morphology


RX J1713.7-3946: Energy Spectrum


Evolution of Supernova Remnants?

( from S. Funk)

No Pevatron yet! Cas A (SN IIb)

RX J1713.7 (SN II/Ib ?)


THE GALACTIC CENTER


High Precision Measurement of the Galactic Center

> Full dataset: 2004 – 2012 (220 hours)


Cosmic-ray Density Distribution

> Correlation with molecular clouds à pp interaction target mass (M)

> Gamma-ray luminosity (L) in several regions à CR density ~L/M

> CR radial distribution § Homogeneous à impulsive injection

of CRs and diffusive propagation

§ 1/r2 à Wind-driven propagation

§ 1/r à continuous injection and diffusive propagation

> Central accelerator located within 10 pc and injecting CRs continuously for > 1kyrs


Diffuse Emission and Injection Spectra

> Diffuse gamma-ray spectrum § E-2.3 up to 50 TeV w/o cutoff

> Assume central source of protons § Solve transport equation of protons

§ fit to HESS data

> Proton injection spectrum: § E-2.2 power law from GeV to few PeV

§ Cut-off 0.6 PeV at 90% CL 2.9 PeV at 68% CL

> A cosmic PeVatron!


The extra-galactic sky seen with H.E.S.S.


VHE gamma rays from high-redshift AGN

PKS 1441+25 (z=0.939)

MAGIC: ATel 7416 (2015)

VERITAS: ATel 7433 (2015)

S3 218+35 (z=0.944): Gravitationally lensed blazar

MAGIC: ATel 6349 (2014)

B0218+357 (z=0.684) (z=0.944)

1010 yr +10 days

1010 yr

(z=0)



PKS 1441+25 (z=0.939)

MAGIC: ATel 7416 (2015)

VERITAS: ATel 7433 (2015)

S3 218+35 (z=0.944): Gravitationally lensed blazar

MAGIC: ATel 6349 (2014)

MAGIC

Fermi



B0218+357 (z=0.684) (z=0.944)

1010 yr +10 days

1010 yr

(z=0)

De Angelis et al. arXiv:0707.2695,0707.4312

Sanchez-Conde et al., arXiv:0905.3270


Many more science…

> Imaging of cosmic particle acceleration sites > Physics of pulsars and pulsar winds > Binary systems > …

> Properties of AGN > Probing the extragalactic background light > …

> Limits on dark matter and new physics > …

> We just see the tip of the iceberg


How to do better?

> More events § more photons = better spectra, images,

fainter sources

àlarger collection area for gamma-rays

> Better events § more precise measurements of

atmospheric cascades and hence primary gammas

àimproved angular resolution

àimproved background rejection power

àMore telescopes!

Simulation: Superimposed images from 8 cameras


The ideal array W. Hofmann


The affordable compromise W. Hofmann


The affordable compromise

Low energy section Energy threshold of some 10 GeV

Medium energy section mCrab sensitivity in the 100 GeV – 10 TeV domain

High energy section 10 km2 area at multi-TeV energies

W. Hofmann


CTA: A Worldwide Consortium

29 Countries 178 Institutes 1187 Members


Site selection

+30

-30 South: negotiations started with ESO/Chile and Namibia; Conclusion likely not before end of 2015

North: negotiations started with Mexico and Spain Conclusion likely not before end of 2015


Current Galactic VHE sources (with distance estimates)

Current Instruments

mCrab Sensitivity

CTA


CTA – the Cherenkov Telescope Array

> A huge improvement in all aspects of performance § A factor ~10 in sensitivity, much wider energy coverage, much better resolution, field-

of-view, full sky, …

> A user facility / proposal-driven observatory § With two sites with a total of >100 telescopes

> A 29 nation ~€200M investment project § Including everyone from H.E.S.S., MAGIC and VERITAS

The future of ground based gamma-ray astronomy with Air Cherenkov Telescopes


Our local neighbourhood

Christian Stegmann . H.E.S.S. Highlights . IPA 2014 . 18.8.2014


Nearby Sources

ELECTRONS & POSITRONS

Source: AMS

Linear scale!

A. Kounine, AMS Days, CERN

Secondary positrons Additional

charge-symmetric component

electron plus positron

EXPLANATIONS: DARK MATTER / PULSARS / SNR / PROPAGATION / …

Explaining muon magnetic moment and AMS-02 positron excess in a gauged horizontal symmetric model Wino dark matter in light of the AMS-02 2015 data Revisiting multicomponent dark matter with new AMS-02 data Dark Matter with multi-annihilation channels and AMS-02 positron excess and antiproton Dark matter for excess of AMS-02 positrons and antiprotons Implications for dark matter annihilation from the AMS-02 $bar{p}/p$ ratio AMS-02 Antiprotons from Annihilating or Decaying Dark Matter Explaining AMS-02 positron excess and muon anomalous magnetic moment in dark left-right gauge model Confronting recent AMS-02 positron fraction and Fermi-LAT Extragalactic Gamma-Ray Background measurements with gravitino dark matter Leptophilic Dark Matter and AMS-02 Cosmic-ray Positron Flux Mass of Decaying Wino from AMS-02 2014 AMS-02, Strongly Self-Interacting Dark Matter, and QUD

“AMS” & “Dark Matter” 139 papers “AMS” & “Pulsar” 23 papers “AMS” & “Supernova” 20 papers “AMS” & “Propagation” 38 papers

DARK MATTER ANNIHILATION

Need leptophilic DM Need large boost factors of O(102-103) for annihilation rate Tension with Planck limits (Slatyer, arXiv:1506.03811, 03812)

Cirelli et al. arXiv:0809.2409 (2013 update) also Cholis & Hooper, 1304.1840 and may more

ALTERNATIVE FITS TO POSITRON FRACTION

Pulsars

Secondaries from SNR

Propagation & distribution of sources

§ All describe the data § None needs “new physics” § All use a few free (but

plausible) parameters / assumptions (just like the DM explanation)

Feng & Zhang arXiv:1504.03312

Cowsik et al., arXiv:1305.1242

Mertsch & Sarkar, arXiv:1402.0866,

ANTIPROTON / PROTON RATIO

A. Kounine, AMS Days, CERN

linear scale!

(pre-AMS) Anti- protons

SECONDARY ANTIPROTON PRODUCTION

Kappl et al. arXiv:1506.04145

Updated antiproton production cross sections based on data

log scale!

Similar result: Giesen et al. arXiv:1504.04276

➜ No need to invoke DM contribution



MeV GeV TeV PeV

Fermi-LAT MAGIC

VERITAS

H.E.S.S.

HAWC



MeV GeV TeV PeV

Fermi-LAT MAGIC

VERITAS

H.E.S.S.

HAWC

Fermi LAT IACTs HAWC Effective area 1 m2 105 m2 105 m2

Field of view 20% of the sky 3o – 5o 15% of the sky Energy res. 10% 10% 100% – 20% Angular res. 6o – 0.3o 0.1o 1o – 0.2o

Duty cycle Full year 1400 h/year Full year


Large Size Telescopes LST

> Structure § 23 m diameter (389 m2)

§ 28 m focal length

§ 1.5 m mirror facets

> Camera § 4.5o field of view

§ 0.1o PMT pixels

§ Camera ∅ over 2 m

> Carbon-fiber structure for 20 s positioning

> 4 LSTs on South site

> 4 LSTs on North site

> Prototype = 1st telescope


Medium Size Telescopes MST

> Structure § 12m diameter (100 m2)

§ 16 m focal length

§ 1.2 m mirror facets

> Camera § 8o field of view

§ ~2000 x 0.18o PMT pixels

> 25 MSTs on South site

> 15 MSTs on North site

> Prototype operational

MST prototype in Berlin


Medium Size Telescopes (MST) with dual mirror

> Structure § 9.7 m primary

§ 5.4 m secondary

§ 40 m2 eff. coll. area

§ PSF better than 4.5’ across 8o fov

> Camera § 8o field of view

§ 11328 x 0.07o SiPMT pixels

> Extend South array by adding 24 SCTs

➜ increased γ-ray collection area and γ-ray angular resolution


Small Size Telescopes

> 70 SSTs for South site

> Different designs under consideration

> Single mirror design § SST-1M

> Dual mirror design § ASTRI

§ GATE


SST Prototypes

SST-1m

ASTRI

GATE


Sensitivity

LST

MST

SST

background and systematics limited

background limited

rate (=area) limited

nFn (erg/cm2s)


Science drivers for CTA

> Theme 1: Cosmic Particle Acceleration § How and where are particles accelerated?

§ How do they propagate?

§ What is their impact on the environment?

> Theme 2: Probing Extreme Environments § Processes close to neutron stars and black holes?

§ Processes in relativistic jets, winds and explosions?

§ Exploring cosmic voids

> Theme 3: Physics Frontiers – beyond the SM § What is the nature of Dark Matter? How it is distributed?

§ Is the speed of light a constant for high energy particles?

§ Do axion-like particles exist?


Key Science Questions and Key Science Projects


Survey Sensitivity


Angular Resolution


Transients with CTA

Hinton & Funk arXiv:1205.0832


Gamma Ray Bursts (E>30 GeV)

from Gamma-Ray Burst Science in the Era of Cherenkov Telescope Array (Astroparticle Physics special issue article) Susumu Inoue et al., arXiv:1301.3014


Schedule

Pre-Construction Phase

2014-2015

Pre-Production Phase

2016-2017

Production Phase 2018-2020 (?)

7/2016 First telescopes on site (earliest)

Deploy ~10% of tels. Mass deployment

Pre-Construction Phase 2014-2015

7/2014 CTAO GmbH founded

4/2014 Site

narrowing South

8/2015 Site decision South

6/2015 Critical Design Review

Site decision

North

3/2015 Site

narrowing North

Founding Agree- ment


Galactic Plane Surveys


H.E.S.S. Galactic Plane Surveys

> 2673 hours of high-quality data, taken in the years 2004 to 2013. § Longitude l = 250 to 65 degrees, latitude |b| < 3.5 degrees

§ Sensitivity for the detection of point-like sources is at the level of 2% Crab or better

1% Crab

2% Crab


H.E.S.S. Galactic Plane Scan

> 2673 hours of high-quality data, taken in the years 2004 to 2013. § Longitude l = 250 to 65 degrees, latitude |b| < 3.5 degrees

§ Sensitivity for the detection of point-like sources is at the level of 2% Crab or better

1% Crab

2% Crab


Morphology Model

> Source extraction with automatic pipeline

> Likelihood fit of emission by multiple Gaussian components plus diffuse background, Overlapping emission components combined

> HGPS catalog 77 = 64 + 13 complex sources (e.g. shell SNR) excluded from pipeline


Associations

> Systematic association of HGPS sources with nearby PSR, SNR, PWN, GeV sources (3FGL and 1FHL)


Gaussian Band Large-Scale Emission Model


H.E.S.S. Galactic Scan

Blue lines: H.E.S.S. horizons for 1% and 10% Crab Dots: H.E.S.S. Galactic sources

Red: PWNe Yellow: SNRs Black: other sources


Time Variability: IC 310

> The closest blazar (z=0.019) § Previously thought to be a (large viewing angle) radio galaxy, new: VLBI jet

> Extreme variability seen with MAGIC § Despite larger jet viewing angle ~15°

MAGIC

Science 346 (6213)


Historically bright flares of LS I +61 303 in 2014

> VERITAS monitoring of the binary system LS I +61 303

> Peak flux above 25% Crab

> Contemporaneous light curves from Swift-XRT (0.3-10 keV) and Fermi-LAT (0.3-300 GeV) do not show evidence for similarly high emission

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