TeV γ-ray astronomy and
the project ASTRI*/CTA
Nicola La Palombara (INAF – IASF Milano)
on behalf of the ASTRI Collaboration
XCIX Congresso Nazionale della Società Italiana di Fisica – Trieste – 23-27 September 2013
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The ASTRI Project
The VHE γ–ray sky
> 150 sources
 50 extragalactic
© TeVcat
(May 2012)
N. La Palombara –XCIX Congresso Nazionale della Società Italiana di Fisica –Trieste – 23-27 Settembre 2013
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The ASTRI Project
From the current generation of IACTs…
MAGIC (2 x 17 m)
HESS (4 x 12 m + 1 x 28 m)
CANGAROO (4 x 10 m)
VERITAS (4 x 12 m)
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The ASTRI Project
…to CTA: a worldwide challenge…
N. La Palombara –XCIX Congresso Nazionale della Società Italiana di Fisica –Trieste – 23-27 Settembre 2013
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The ASTRI Project
…for a new observatory for VHE γ–ray astrophysics
CTA goals:
• increase the sensitivity by up to a factor 10 @ 1 TeV
• boost the detection area for transient phenomena and at the highest energies
• increase the angular resolution while maintaining a large field of view
• provide uniform energy coverage from a few tens of GeV to beyond 100 TeV
• enhance the sky-survey capability, monitoring capability and flexibility of operations
thanks to 2-sites (North & South), sub-array and simultaneous multi-mode runs
• operation as an “open” Observatory: peer-reviewed process on submitted proposals
CTA concept (Hofmann & Martinez, 2011, Exp. Astr., 32): array of several tens of
telescopes divided in 3 kinds of configurations, in order to maximize the telescope
performance in 3 different energy ranges.
N. La Palombara –XCIX Congresso Nazionale della Società Italiana di Fisica –Trieste – 23-27 Settembre 2013
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The ASTRI Project
CTA will continue the discovery trend
N. La Palombara –XCIX Congresso Nazionale della Società Italiana di Fisica –Trieste – 23-27 Settembre 2013
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The ASTRI Project
CTA as a priority for the European Union
Construction
cost [M€]
Operations
cost [M€]
Timescale
CTA
150
10
2013
E-ELT
950
30
2018
ELI
400
50
2015
FAIR
1187
120
2016
KM3NeT
200
5
2016
PRINS
1400
300
2009-2015
SKA (GLOBAL)
1500
100-150
2016
SPIRAL2
196
6.6
2014
Project
CTA Project considered as a priority in
roadmaps of:
• ASTRONET (Astrophysics)
• ASPERA (Astroparticles)
• ESFRI (European Strategic Forum
for Research Infrastructures)
N. La Palombara –XCIX Congresso Nazionale della Società Italiana di Fisica –Trieste – 23-27 Settembre 2013
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The ASTRI Project
CTA candidate sites
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The ASTRI Project
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The ASTRI Project
CTA and the ASTRI Program
Few Large Size Telescopes
for the low energy range:
E ≃ 20 GeV – 1 TeV
4 LSTs
~ 1 km2 array of Medium Size
Telescopes for the core energy
range: E ≃ 0.1 – 10 TeV
~ 25 MSTs
Large array of Small Size
Telescopes for the high
energy range: E > 1 TeV
~ 70 SST
Within this framework, ASTRI aims to realize an end-to-end prototype for the SST
N. La Palombara –XCIX Congresso Nazionale della Società Italiana di Fisica –Trieste – 23-27 Settembre 2013
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The ASTRI Project
The ASTRI SST-2M Prototype Program
ASTRI: Astrofisica con Specchi a Tecnologia Replicante Italiana
An Italian “Progetto Bandiera” (Flagship Project)
• funded by the Ministry of Education, University and Research (MIUR)
• led by the Italian National Institute of Astrophysics (INAF)
Aim: development of the “replica” technology for mirrors and new
sensors for VHE astrophysics.
Main goal: realization and test, within the framework of the Cherenkov
Telescope Array (CTA), of an end-to-end prototype of the CTA SST
INAF tasks: design and manufacturing of the mirrors and the camera;
development of the software and other related activities; scientific
supervision of the design of the telescope structure; acquisition and analysis
of the prototype data for the technological and scientific verification
N. La Palombara –XCIX Congresso Nazionale della Società Italiana di Fisica –Trieste – 23-27 Settembre 2013
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The ASTRI Project
The ASTRI Collaboration
Principal Investigator: G. Pareschi
Co-PIs:
O. Catalano
S. Vercellone
INAF Institutions
IASF Milano
IASF Bologna
IASF Palermo
OA Brera
OA Padova
OA Torino
OA Bologna
OA Arcetri
OA Roma
OA Capodimonte
OA Catania
INAF HQ Roma
University Partners
University of Padova
University of Perugia
N. La Palombara –XCIX Congresso Nazionale della Società Italiana di Fisica –Trieste – 23-27 Settembre 2013
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The ASTRI Project
The Dual Mirror SST
(SST-2M) Concept
Canestrari
et al. 2013
ASTRI SST-2M concept:
 a large (9.6o) field of view dual-mirror
(Schwarzschild-Couder) telescope
 a light (~ 50 kg) and compact (~ 56 x 56 x 56
cm3) camera based on Hamamatsu Si-PMs, with
a low power consumption
N. La Palombara –XCIX Congresso Nazionale della Società Italiana di Fisica –Trieste – 23-27 Settembre 2013
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The ASTRI Project
The ASTRI SST-2M Optical design
Angular dependence of D80: the amount of
energy contained within 2x2 physical pixels
(6.2 mm logical pixel) is not less than 80 %
along the entire field of view
Schwarzschild-Couder configuration
N. La Palombara –XCIX Congresso Nazionale della Società Italiana di Fisica –Trieste – 23-27 Settembre 2013
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The ASTRI Project
The ASTRI Prototype Mirrors
Main characteristics of the mirrors:
• Primary Mirror diameter: 4.3 m (segmented)
• Secondary Mirror diameter: 1.8 m (monolithic)
• F#: 0.5
• Equivalent focal length: 2150 mm
• Corrected FoV diameter: 9.6o
Primary mirror segment
• off-axis aspherical profile obtained
with
the
glass
Cold-Shaping
technology at INAF – OA Brera
• physical Vapor Deposition of a
multilayer of pure dielectric materials
N. La Palombara –XCIX Congresso Nazionale della Società Italiana di Fisica –Trieste – 23-27 Settembre 2013
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The ASTRI Project
The ASTRI Prototype Mirrors
Primary mirror (M1)
• 18 hexagonal shaped mirrors (11.2 m2)
• 850 mm face-to-face, 1 m diagonal
• 3 types of segments
• 2 actuators + 1 fixed point: tip-tilt
corrections for alignment purposes
Secondary mirror (M2)
• Monolithic
• 3 actuators: tip-tilt and piston for alignment
and focusing purposes
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The ASTRI Project
The ASTRI Prototype Camera
Requirement on the pixel size:
SC optical design

compact (~ 50 cm) camera
(small detection surface)

spatial segmentation of a few square millimeters
(to be compliant with the imaging resolving angular size)
Other requirements:
• photon detection sensitivity in the 300-700 nm range
• fast temporal response
N. La Palombara –XCIX Congresso Nazionale della Società Italiana di Fisica –Trieste – 23-27 Settembre 2013
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The ASTRI Project
The ASTRI Prototype Camera
Main characteristics:
• Detector type: monolithic array of
4 x 4 Si Photomultipliers (SiPM)
provided by Hamamatsu
• Physical pixel: array of 60 x 60
elementary diodes of 50 μm pitch
• Physical Pixel size: 3 x 3 mm2
• Logical Pixel size: 6.2 x 6.2 mm2
[0.17o]
• Plate scale: 37.5 mm/o
• Number of Pixels: 7936
• Number of channels: 1984
(grouping 2 x 2 pixels)
N. La Palombara –XCIX Congresso Nazionale della Società Italiana di Fisica –Trieste – 23-27 Settembre 2013
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The ASTRI Project
The ASTRI Prototype Camera
A modular approach
1 SiPM unit
4x4 physical pixels
2x2 logical pixels
1 Photon Detection
Module (PDM)
4x4 Units
1 Focal Surface Camera
37 PDMs
FoV diameter = 9.6o
N. La Palombara –XCIX Congresso Nazionale della Società Italiana di Fisica –Trieste – 23-27 Settembre 2013
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The ASTRI Project
The ASTRI Prototype Site
"M. G. Fracastoro" Mountain Station at Serra La Nave, on Mt. Etna:
observing site of the INAF Catania Astrophysical Observatory
ASTRI SST-2M Prototype
• Altitude: 1735 m a.s.l.
• Longitude: +14o 58’ 04’’
• Latitude: +37o 41’ 05’’
61cm Dome
Domes
Main entrance
91cm Dome
Guests House, Offices
and Laboratories
N. La Palombara –XCIX Congresso Nazionale della Società Italiana di Fisica –Trieste – 23-27 Settembre 2013
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The ASTRI Project
The ASTRI Prototype Site
"M. G. Fracastoro" Mountain Station at Serra La Nave, on Mt. Etna:
observing site of the INAF Catania Astrophysical Observatory
• Fully operative INAF Observatory
• High-speed internet connection
• Mechanical & Electronics Labs
• Area protected from wind and fallout of volcanic ash
• Medium seismicity risk but no earth faults ⇒ reduced earthquake risk
• Atmosphere transparency and relative humidity: values well inside the
limits required to perform Cherenkov observations
• Fraction of useful nights: > 53 %
• Length of “dark nights”: from ~ 6 h (in July) up to > 11 h (in January)
the ASTRI SST-2M prototype shall start data acquisition within 2014
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The ASTRI Project
The ASTRI Prototype Science
Expected
prototype
sensitivity
Vercellone et al. 2013
Expected differential
rate for the Crab Nebula
Bigongiari et al. 2013
The ASTRI Prototype is mainly a technological demonstrator, but science might be
feasible.
Maximum sensitivity for E > 2 TeV (1 Crab @ 5 s.d. in some hours)
In the range E > 10 TeV : 1 Crab @ 5 s.d. in a few tens of hours
First Crab observations with a Schwarzschild-Couder-SiPM Cherenkov telescope.
Possible sources (from Sicily): Crab, Mkn 421, Mkn 501
Intense flares (~ 5-10 Crab) should allow intra-night variability studies.
N. La Palombara –XCIX Congresso Nazionale della Società Italiana di Fisica –Trieste – 23-27 Settembre 2013
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The ASTRI Project
The Mini-array Concept
The ASTRI Collaboration has proposed also the realization of a miniarray consisting of 5-7 SST-2M telescopes, to be installed at the final
CTA southern site and operated since 2016.
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The ASTRI Project
The Mini-array Goals
The SST-2M mini-array will:
• verify array performance in terms of reliability and cost at the chosen
site
• check the trigger algorithms
• check the wide field-of-view performance, to detect very high energy
showers with the core located at a distance up to 500 m
• check the HW/SW configurations for the array
• check the data-handling chain
• compare the mini-array performance with the MC expectations by
means of deep observations of few selected targets
• validate the performance predictions for the full SST array (need well
chosen target objects and long observations)
• do the first CTA science, with its first solid detections during the first
year of operations
N. La Palombara –XCIX Congresso Nazionale della Società Italiana di Fisica –Trieste – 23-27 Settembre 2013
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The ASTRI Project
The ASTRI Mini-Array
Control SW
Tosti et al. 2013
Both the ASTRI end-to-end prototype
and the mini-array shall be operated
using the Mini-Array Software
System (MASS): set of tools to
perform all the steps of a scientific
observation (proposal preparation,
observation execution, data retrieving,
reduction and analysis)
System based on the ALMA Common
Software (ACS) framework
Compliant with the CTA Data
Management (CTA-DM) and CTA
Data Acquisition and Array Control
(CTA-ACTL)
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The ASTRI Project
The Mini-array Performance
Limiting flux: ~ 10-12 erg/cm2/s @ 10 TeV
Bigongiari et al. 2013
Di Pierro et al. 2013
Angular resolution: ~ a few arcmin
Di Pierro et al. 2013
Energy resolution: ~ 10-15 %
Di Pierro et al. 2013
N. La Palombara –XCIX Congresso Nazionale della Società Italiana di Fisica –Trieste – 23-27 Settembre 2013
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The ASTRI Project
The Mini-array Primary Targets (south)
Galactic sources:
• Pulsar Wind Nebulae: Crab Nebula, Vela X, HESS 1825-137
• SNRs: Vela Junior, RX J1713.7-3946 / HESS J1718, Kepler
• SNRs interacting with MCs: W 28, W 30, W 51C, IC 443
• Microquasars: LS 5039
• The Galactic Centre (central source + diffuse emission)
Extragalactic sources:
• Extreme blazars: PKS 2155-304, 1ES 0229+200
• Nearby and intense BL Lac objects: MKN 421, MKN 501, (M 87)
Electron acceleration+cooling
Relativistic + non-relativistic shocks
Search for CR Pevatrons
CR propagation
FIR EBL
…
PSF and Spectral Calibration
Weak source detection
Point-like and extended objects
N. La Palombara –XCIX Congresso Nazionale della Società Italiana di Fisica –Trieste – 23-27 Settembre 2013
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The ASTRI Project
Summary
We plan to start the activities of the ASTRI SST-2M Prototype at Serra La
Nave at the end of 2014.
The ASTRI Prototype will allow us:
• to test the main innovative components with respect to the current
IACTs: the optical dual-mirror design, the SiPM-based focal plane, the
Front-End electronics and the software/data-handling architecture
• to obtain a direct measurement of prominent gamma-ray sources, such
as the Crab nebula, MRK 421 and MRK 501
The planned ASTRI mini-array, operated starting from 2016, will
constitute the first seed of the future CTA Project, and will be open to the
CTA Consortium for both technological and scientific exploitation.
N. La Palombara –XCIX Congresso Nazionale della Società Italiana di Fisica –Trieste – 23-27 Settembre 2013
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The ASTRI Project
THANKS!
http://www.brera.inaf.it/astri/
N. La Palombara –XCIX Congresso Nazionale della Società Italiana di Fisica –Trieste – 23-27 Settembre 2013
The ASTRI Project
Extra-galactic mini-array science: AGN
Two possibilities to describe the
spectrum of 1ES 0229+200:
• γ–ray-induced cascade
• proton-induced cascade
Uncertainty in EBL model

difficult distinction at 0.1-1 TeV
E > 1 TeV:
• UHECR-induced cascade
emission harder than γ–rayinduced cascade
• emission spectrum due to
injection of VHE/UHE photons
strongly suppressed at E > 10
TeV

detection at E > 25 TeV implies
hadronic origin of γ–rays
N. La Palombara –XCIX Congresso Nazionale della Società Italiana di Fisica –Trieste – 23-27 Settembre 2013
The ASTRI Project
Contributions to the Mini Array
• ASTRI consortium
• University of the Witwatersrand, Johannesburg, South Africa
• Brasil
• CHEC (Cherenkov High Energy Camera) – UK consortium
 in kind contribution on cameras
• GATE SST group - Observatoire de Paris
 in kind contribution on structures
• University of Amsterdam  pending proposal for in-kind
contribution
• CNEA, Argentina  in-kind contribution
• DESY (MST)  MOU under finalization
N. La Palombara –XCIX Congresso Nazionale della Società Italiana di Fisica –Trieste – 23-27 Settembre 2013
The ASTRI Project
CTA sensitivity in units of Crab flux
Population studies,
extended sources,
variability, precision
TeV astronomy
High-z AGN,
GRBs, PSRs, DM
Cut-off regime of
CR accelerators
N. La Palombara –XCIX Congresso Nazionale della Società Italiana di Fisica –Trieste – 23-27 Settembre 2013
The ASTRI Project
CTA angular and spectral resolution
N. La Palombara –XCIX Congresso Nazionale della Società Italiana di Fisica –Trieste – 23-27 Settembre 2013
The ASTRI Project
Key science questions for CTA
• Where and how are the bulk of CR particles accelerated in the Galaxy
and beyond?
• How do cosmic rays propagate, interact, and heat the environment?
Which are the consequences from Galactic to cosmological scenarios?
• What makes black holes of all sizes such efficient particle accelerators?
• What do high-energy gamma-rays tell us about the star formation history
of the Universe, the structure of space-time, or the fundamental laws of
physics?
• What is the nature of the dark matter? Can it be discovered via indirect
searches? Can we map dark-matter halos?
• Are there short-timescale phenomena at very high energies? Are GRBs
gamma-ray emitters? Is there a new Galactic phenomenology to uncover?
N. La Palombara –XCIX Congresso Nazionale della Società Italiana di Fisica –Trieste – 23-27 Settembre 2013
The ASTRI Project
Science potential for CTA
N. La Palombara –XCIX Congresso Nazionale della Società Italiana di Fisica –Trieste – 23-27 Settembre 2013
The ASTRI Project
CTA performance goals
Improvement of angular resolution by a
factor ~ 5 (from 0.1° to 0.02°)

substructure of SNR shock fronts can
then be resolved
Better understanding of the energy
dependent morphology of Pulsar Wind
Nebulae.
HESS J1825-137: PWN size decreases
with energy:
> 2.5 TeV
1 – 2.5 TeV
< 1 TeV
N. La Palombara –XCIX Congresso Nazionale della Società Italiana di Fisica –Trieste – 23-27 Settembre 2013
The ASTRI Project
Resolving complex
sources
CTA performance
goals
SN 1006 — a
detected VHE
gamma-ray source
CTA
(Credit:X-ray: NASA/CXC/Rutgers/
G.Cassam-Chenai, J.Hughes et al.;
Radio: NRAO/AUI/NSF/GBT/VLA/
Dyer, Maddalena & Cornwell;
Optical: Middlebury College/
SN 1006
SN 1006
F.Winkler, NOAO/AURA/NSF/CTIO
resolution
H.E.S.S. resolution
Schmidt & DSS)
N. La Palombara –XCIX Congresso Nazionale della Società Italiana di Fisica –Trieste – 23-27 Settembre 2013
The ASTRI Project
CTA performance goals
Aim: factor of 10 improvement in sensitivity.
Comparison of ~ 500 hour simulated HESS image of galactic plane...
...with simulation for the same exposure with higher CTA sensitivity:
Expectation to observe ~ 1000 sources (galactic and extra-galactic)
N. La Palombara –XCIX Congresso Nazionale della Società Italiana di Fisica –Trieste – 23-27 Settembre 2013
The ASTRI Project
CTA science: expected contribution
E (eV) 1010
1011
1012
1013
1014
LST
MST
SST
CR origin & prop.
PWN
PSR physics
microQSOs
AGN physics
GRB physics
Galaxy clusters
Dark matter
Cosmology &
fundamental physics
N. La Palombara –XCIX Congresso Nazionale della Società Italiana di Fisica –Trieste – 23-27 Settembre 2013
1015
The ASTRI Project
The ASTRI Mirrors: panel manufacturing
Main steps of the panels manufacturing. From top-left, clockwise: mold
realization; front glass is made to adhere by vacuum suction to the mold;
the epoxy resin structural adhesive is spread on the glass; the Aluminum
honeycomb is positioned and the back glass foil is added on the top. The
resin is made polymerize with the proper curing cycle and sandwich is
finally released and coated.
N. La Palombara –XCIX Congresso Nazionale della Società Italiana di Fisica –Trieste – 23-27 Settembre 2013
The ASTRI Project
The Prototype Primary Mirror (M1)
Primary mirror segment
 off-axis aspherical profile obtained with the glass ColdShaping technology at INAF – OA Brera
 Physical Vapor Deposition of a multilayer of pure
dielectric materials
3D CAD model of the supporting and alignment structure of
the primary mirror segments. The triangular frame hosts two
motorized axial actuators for tip/tilt corrections and one
fixed point.
N. La Palombara –XCIX Congresso Nazionale della Società Italiana di Fisica –Trieste – 23-27 Settembre 2013
The ASTRI Project
The Prototype Secondary
Mirror (M2)
Scaled-down prototype of the
curved honeycomb core structure
of the monolithic secondary mirror
3D CAD view of the support and
alignment system of M2
N. La Palombara –XCIX Congresso Nazionale della Società Italiana di Fisica –Trieste – 23-27 Settembre 2013
The ASTRI Project
The ASTRI Prototype Camera
1 SiPM Unit
1 PDM Unit
(4x4 SiPMs)
Matrix of 4x4 PDMs
N. La Palombara –XCIX Congresso Nazionale della Società Italiana di Fisica –Trieste – 23-27 Settembre 2013
The ASTRI Project
The ASTRI Prototype Camera
Drawing (left) and mock-up (right) of the
mechanical housing
Sketch of the ASTRI Camera with
the Camera-Telescope I/F.
37 PDMs mounted on the mechanical housing
N. La Palombara –XCIX Congresso Nazionale della Società Italiana di Fisica –Trieste – 23-27 Settembre 2013