Problematiche astrofisica VHE

Problematiche astrofisica VHE

Antonio Stamerra

Università di Siena & INFN Pisa

JC - 10 febbraio 2010

Pisa

Istituto Nazionale di Fisica Nucleare

IACT detector

IACT Imaging Atmospheric Cherenkov Telescope

Atmosphere is opaque to γ- rays

IACT detector IACT detector

= =

Atmosphere + telescope Atmosphere + telescope

Satellite: direct detection of γ- ray

Electromagnetic atmospheric shower

pair-production Bremsstrahlung

R~9/7 X₀~45g/cm²

(in air, 20^oC)

Active mirror control

high reflective diamond milled aluminum mirrors

Light weight Carbon fiber

structure for fast

repositioning

 Stereoscopic mode:

 Improved sensitivity

 Better angular and energy resolution

 New technologies:

 Camera: Photo-detectors with higher QE (HPDs in near future)

 Faster Digitalization: 4 GHz

Florian Goebel Telescopes

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Imaging Air Cherenkov Telescopes

 Direction reconstruction

Shower top

Shower tail

×

γ -ray direction

A telescope placed inside the Cherenkov light A telescope placed inside the Cherenkov light pool can obtain an image of the development pool can obtain an image of the development of the shower above the night sky background of the shower above the night sky background (NSB) fluctuations

(NSB) fluctuations

Distances in camera

= Angular Distances

on sky Shower top

N₁ ,θ C1

Shower tail n₂>n₁ ⇒θ_C2> θ_C1

Background

 Cosmic-ray background

 γ-rays have a definite direction (source position on sky)

 CR are isotropically distributed

ON-OFF selection?

 CR flux overwhelms γ-ray flux…

 Night-Sky background (NSB, LONS)

 Field stars

Gamma/hadron separation

gamma proton

Modelli emissione adronica

Cosmic rays

 “All-particle” spectrum

 Power law spectrum (~E^-

2.7)

 Particles decrease with energy

 Two breaks in the power law

 Knee ~3 PeV (3x10¹⁵ eV)

 Ankle ~1 EeV (10¹⁸ eV)

Underlying physical

Cascade shower Cascade shower

100GeV gamma ray 300GeV Proton

By M. Hayashida

EAS simulation - uncertainties

Reliability of simulation of hadronic interactions (extrapolation of

accelerator data and/or theoretical assumptions) - partially solved by IACTs using real hadrons…

Forward physics unexplored (LHC? E.g. TOTEM) Physical

 Intrinsic shower fluctuations Enviromental

 Weather condition (Calima, high clouds,…)

 Night sky light (Bright stars, Moon, city, …) Instrumental

 Calibration (absolute QE, mirror aging, …)

 Background estimation (inhomogeneity, …)

 Telescopes condition (dead pixels, misspointing, …)

Sensitivity in 50h 5σ & 10 evts

For 5σ: Sensitivity ∝ 1/sqrt(time) For 10 evt: Sensitivity ∝ 1/time

Sensitivity

Depends on the Effective area and CR Background rejection (and background uncertainty)

MAGIC-II

 Overall sensitivity will be Overall sensitivity will be improved by a factor of 2-3 improved by a factor of 2-3

 Energy resolutionEnergy resolution

 ~25% ~25%  15-20% 15-20%

 Angular resolutionAngular resolution

 Substantial improvementSubstantial improvement

Sites of particle acceleration

 Hillas plot

 Compact sites and high B

 Diffuse objects and low B

 The acceleration site

environment plays a key role…

 A deeper (astrophysical)

knowledge of candidate sites is mandatory

Exploring extreme accelerators with gamma-rays

VHEγ-astronomy address diversity of topics related to the nonthermal Universe:

acceleration, propagation and radiation of ultrarelativistic protons/nuclei and electrons

generally under extreme physical conditions in environments characterized with

huge gravitational, magnetic and electric fields, highly excited media, shock waves

and very often associated with relativistic bulk motions linked, in particular, to jets in black holes (AGN, Microquasars, GRBs) and cold ultrarelativistic pulsar

winds

Goal 0: Detection!

Gammas are not for free…

 Signal reconstruction

 Background rejection

 Sensitivity

 Minimum flux detectable

 Shortest time variation

 Observation time

In the following we assume we are lucky and we always get

S s »Rate _g

Rate _B T

Standard candle:

Crab Nebula

Crab broad-band spectrum

UV UV

Optical Optical

Radio Radio

X-Ray X-Ray

MW MW

γγ-ray-ray

VHEVHE

Flux Flux 

sincrotrone

100Mev-10GeV

>100GeV

e^-

γ

e^-

e^- γ

Goals summary

 Spectrum

 #ph in ∆E

 Energy

reconstruction

 E’ energy resolution

 Skymap

 #ph in ∆Ω

 Angular

resolution - PSF

 F.o.V.

 Lightcurve

 #ph in ∆ t

 Time

resolution

 Pulsar ⇒ ms

 AGN ⇒ min.

Perugia, 22 ottobre 2009 MAPS school a.Stamerra 23

Gamma/Neutrino astronomy

 Fermi acceleration

processes create secondary particles, among them

neutral particles

 γ and ν bring direct information on the acceleration site

But….

 Their emission, and

propagation depends on the environment and source details

 A deep (astrophysical)

knowledge of the source is

Charged particles

Accelerated particles

B pp

HeHe IonsIons

ππ nn µµ

ee

γγ νν

γ-ray production

 Synchrotron radiation

 Bremstrahlung

 Inverse Compton

 Annihiliation

 p/nuclei interaction with ISM (proton induced

ISM

e^-

γ

BB e^-

γ

e^-

e^- γ

γ e⁺ γ

γ e^-

π ⁺ γ

nic sses Leptonic processes

Hadronic or leptonic?

 Emissione γ ray emission from π⁰ decay and

interaction with molecular clouds

 Signature: π⁰ decay spectrum

Hadronic or leptonic?

modelli leptonici modelli leptonici

(IC)(IC) modelli

adronici Yet no “smoking gun” evidence of γ-rays stemmed from

hadronic acceleration and π⁰ decay!

But many hints….

WHAT DO WE LEARN FROM GAMMA RAYS?

WHY IS IT INTERESTING:

II. Large B observed?

TYPICAL THICKNESS OF FILAMENTS: 10^-2 pc The synchrotron limited thickness is:

Dx 4 D E t_syn E »4 pc  B^­3/2_m

EFFICIENT ACCELERATION – LARGE B FIELDS

PROBLEMS: 1. VERY HIGH PHOTON DENSITY FOR ICS

2. LOW B FIELDS (IGNORES X-RAY OBSERVATIONS)

K_ep~0.01 K_ep~0.1

AGN - blazars

 Intense and variable emission up to

~10 TeV

Observed structures:

 accretion disk; obscuring thorus

 Relativistic Jet

 Broad/Narrow line regions (NLR, BLR)

 TeV emitting zone: jet with high relativistic bulk motion

 Particle acceleration at shock

boundaries bundled in a magnetic field (Fermi acceleration processes)

 Gamma-ray emission from

accelerated electrons (synchrotron and inverse-Compton scattering) or hadronic interactions

FR-I, FR-II ^Radio

quasars

BL-Lac

γ-ray emission from AGN: SSC a (minimal)

standard model

 Blazar: collimated emission from jet (relativistic amplification)

 Environment: B, δ, R

 Observed emission (SED) well described by leptonic models, such as SSC and EC.

 Expected X-ray / Tev time correlation

 Synchrotron peak: IR to x-ray

 IC peak: UV to γ-rays

 LBL, IBL, HBL

 Outbursts of e.m. radiation

Synchrotron IC

Emitted power

BB e^-

γ

e^-

e^- γ

γ _min γ_br γ_max γ γ_br γ_maxKN

Relativistic electrons

injection/acceleration/cooling

Blazar Multiwavelength campaigns

Extreme

Extreme (~>1 order of magnitude in flux) and (~>1 order of magnitude in flux) and fast fast (~hours, minutes) (~hours, minutes) vvaarriiaa^bbiililittyy

 Simultaneous Multifreq. Observations covering 15 decades in photon energy:

VHE: H.E.S.S., MAGIC, VERITAS HE: Agile, Fermi

X-ray: Suzaku, Swift, Chandra, Integral Optical: KVA

Radio: Metsahövi, VLBI…

Methods:

 Monitoring (optical, x-ray, radio)

 Intensive planned campaigns

 Target of Opportunity (ToO): react to alerts (internal/external)

Mrk 421 2008 activity

MWL campaigns on Mrk421 in flaring state optical to TeV energies

Simultaneous data

 strong SSC model constraints

 time evolution of the SEDs

New 2009 campaign on Mrk421 and Mrk501

Bonnoli G. et al. (MAGIC Coll.) arXiV:0907.0831 Bonnoli G. et al. (MAGIC Coll.) arXiV:0907.0831 Publication in preparation

Publication in preparation

preliminary

Mrk421 - 2009 campaign

4.5 months

Jan 20th - June 1st

~20 instruments 2-day sampling

Complete coverage 0.1 GeV-10 TeV

preliminary

Fermi

MAGIC Swift/XRT

S5 0716+714

IBL z=0.31(?)

 Bright in optical ⇒ trigger

 MWL campaign (opt-X-γ)

 Clear signal in 2.6 h: 6.9σ

 1st VHE detection

F(>400 GeV) =7.5x10^-12 ph/cm²/s (≈9% Crab)

Significance 6.8 σ

ApJ - accepted arXiv:0907.2386 MAGIC collab. 2008, Atel #1500

SSC model predicts an unplausible IC γ -ray flux

⇒ Spine-layer model Ghisellini et al. 2005, A&A, 432, 401

High redshift Nilsson,A&A 487(2008)L29 reports the detection of the host galaxy:

z=0.31±0.08

S5 0716+714

IBL z=0.31

 Rotation of positional angle of polarization (EVPA) during maximum (60deg/day) Larionov et al.,ATel #1502

 propagation of a polarized knot spiraling down the jet, following helical magnetic field

(e.g. BLLac, Marscher et al., 2008, Nature, 452, 966)

 Similar behavior (degree of polarization) during Fermi campaign on 3C279: polarization degree a good precursor of γ-flares?

 X-ray spectrum shows synchrotron component:

transition between LBL-HBL states?

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BL Lacertae

MAGIC detection in 2005-2006

flare end October 2005 ~MJD 53670

MAGIC Coll., ApJL 666 (2007) L17 MAGIC Coll., ApJL 666 (2007) L17

A. Marscher et al., Nature 452 (2008) 966 A. Marscher et al., Nature 452 (2008) 966

RG z=0.0043, 16.7 Mpc

Radio

VLBA 8 GHz HST-1

knot D knot A

Harris+07

 “misaligned blazar” (15-25^o); 17 Mpc

 HEGRA hint; HESS/VERITAS detection

 Candidate nearby CR site (hadronic emission?)

 Variability?

 Site for TeV emission (core/HST-1)?

M87

 MWL campaign jan-feb 2008

(triggered by MAGIC detection on 1st February flare)

 9.9σ detection; 8.0σ single night 1st-feb

 First spectrum at E>100 GeV

 Marginal hint of spectral hardening

 Clear <~daily variability at E>350GeV

 Chandra observations ⇒ core/HST-1 contribution (core active / HST1 dim)

Science, 325 (2009) 444

Joint paper MAGIC-VERITAS-HESS-VLBI-Chandra MAGIC coll.

ApJL, 685 (2008)

VHE

HST-1 nucleus

X-ray

radio

jet

Nucleus ~100R_s

Nucleus radio brightening

Goal 2: lightcurve

 AGN, µQSO ⇒ days, minutes

 Pulsar ⇒ ms

 #ph / ∆T

 Time resolution

X-ray

TeV

Crab pulsar

26 days

LS I+61 303

0.15-0.25 TeV

0.25-0.6 TeV

0.6-1.2 TeV

1.2-10 TeV 4 min lag

Mrk 501

Crab pulsar

 Cutoff depends on the acceleration and radiation process (outer

gap/polar cap)

 Absorption in magnetosphere

(magnetic/photon pair production)

 Maximum acceleration energy

 First hint at E~>60 GeV

Crab pulsar

 Lower trigger threshold:

new trigger system (sum- trigger)

M. Teshima et al. 2008, Atel #1421 MAGIC coll., Science 322 (2008) 1221

LS I +61 303

o High Mass X-ray Binary (2kpc) o Be star orbiting unknown object

(NS-BH)

o P=26.5d; e=0.72

o X-ray emission at o Φ~0.5

o GeV-emitter (3EG 0241+6103) ⇒ Candidate for TeV emission

Mirabel 2006

Relativistic electrons from accretion powered jet

Relativistic electrons from rotational energy of pulsar

 Relativistic Jet radio structures: µ-QSO

nature? (Massi et al. 2004)

 Cometarylike radio

structure: interaction of

pulsar/jet wind Massi et al 2004

10 mas 100 mas

LS I +61 303

 MAGIC observations 2005-2006 (54 hrs, 6 orbits)

 8.7 sigma; point-like; max at Φ~0.6-0.7

MAGIC Coll. 2006, Science, 312, 1771

F (E > 400 GeV)

LS I +61 303

 2nd campaign - sep-dec 2006;

112 hrs

 Hint of X-ray/TeV emission correlation

 No time correlation with radio

 Highest emission at Φ=0.65

 Periodicity: 26.8±0.2 days

 No significant spectral changes with phase

Swift/XRT

0.3-10 keV

P.Esposito et al 2007

MAGIC

E>400GeV

1^stcampaign

Phase 0.6 - 0.7 Phase 0.5 - 0.6 Phase 0.4 - 0.7 (1st campaign)

MAGIC coll. 2009, ApJ, 693, 303

LS I+61 303

 Simultaneous MWL campaign, single period

 XMM, Swift, MAGIC - sep 2007;

 Clear X-ray/TeV emission correlation

 No radio-TeV(X-ray) correlation

 Highest emission at Φ=0.65

 No significant spectral changes

with phase X-ray

TeV

⇒⇒Interaction with Extragalactic Background Interaction with Extragalactic Background Light (EBL)

Light (EBL)

⇒energy dependent energy dependent γγ -ray absorption -ray absorption

⇒modification of original spectrummodification of original spectrum

Î ¦ _{Î ³}o b s e r v e dE Î ¦ u n a b s o r b e d_{Î ³} E e^{Ï„ EÎ ³ ,z}

ττ (E,z): Optical Depth(E,z): Optical Depth Gamma Ray Horizon (GRH):

Gamma Ray Horizon (GRH):

ττ=1=1

EBL EBL

E_HEε _EBL=3.6(m_ec²)² Emitted

spectrum

observed spect.

High absorpti on

Low Energy

Energy

Energy

λ 1.2 4m mE_g

1T e V1 z²

Cosmic backgrounds

CIB: modelli

Primack (2005)