Future of TeV Astronomy. Roger Blandford KIPAC Stanford

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1 Future of TeV Astronomy Roger Blandford KIPAC Stanford

2 Give a Vision for the Future! As well as building on existing research program,as described by other speakers, there should be fresh discoveries! Will call out three areas where these could come over the next ~5 years Extreme Particle Acceleration (PWN, Blazars ) Diffusive Shock Acceleration (SNR, Clusters) Fast Radio Bursts! Also VHE ν (Halzen) Dark Matter (Buckley) GRB/LIGO (Falcone) 2

3 Major discoveries were unscripted! CMB antenna noise! Quasars (massive BH) radio source identifications! Stellar BHs X-ray source identifications! Massive and mutable ν s checking solar model! Neutron stars lunar X-rays! Pulsars interplanetary scintillation! Gamma ray bursts nuclear weapons monitoring! Dark matter galactic and stellar orbits! Cosmic acceleration supernova explosions! Gravitational lenses quasar follow up! Gravitational radiation pulsar timing! Massive black hole binaries LIGO. 3 Discoveries at interfaces; stovepiping is futile

4 Six Months of Discovery! October April 2015 (APS): Planck results->standard model (wnf nl Ω k m ν ), dusty B-modes 8 habitable?? exoplanets->life in the universe??? 9 new dwarf galaxies -> dark matter limits ~10 10 M sun black hole at z=6->cosmic dawn Gravitational lenses - SN, ALMA-> pre-sn, substructure M82 neutron star with L~100 L edd ->accretion physics PD456 outflows->environmental impact, galaxy formation FRBs 40% circ pol->new transients mHz IceCube neutrinos -> cosmological origin? 4 By contrast we are making science plans for 2030s

5 Heaviside partly anticipated the Cerenkov effect in 1888! 5

6 In QED We Trust! Synchrotron Radiation E γ ~ 160 (E e /1TeV) 2 (B/1T) MeV <100 MeV E γ ~ 20 (E p /1EeV) 2 (B/1T) GeV - t cool ~200(Eγ/1GeV) -1/2 (B/1T) -3/2 s! Compton scattering σ~σ T! γ-γ pair production opacity σ~σ T! γ-p pair, pion production σ~ασ T above threshold p-p pair pion production inefficient 6 Schwinger Limit? B> 4GT

7 In E&M We Trust Unipolar induction by spinning magnetized body V ~ Ω Φ/2π Ε max /Ze I ~ (V / Z 0 )(c/v) Z 0 ~100Ω P ~ V I ~ (V 2 /Z 0 )(c/v) Φ Ω Sun V ~ 100 MV, I~1 GA, P~100PW Crab V~ 30 PV, I~300TA, P~ W AGN V ~ 1 ZV, I ~ 10 EA, P~10 40 W GRB V ~ 0.1 YV, I~1 ZA, P~10 44 W 7

8 Extreme Astrophysics (XAP) e.g.crab Flares ~300MeV flares appear to be synchrotron radiation by ~3PeV electrons in ~mg fields Challenge to particle acceleration Similar problems in TeV sources One photon radiated when turn through angle 90/γ =10,000mas Synchrotron Limit E<B => E γ < α -1 m e ~ 100 MeV 1 lt hr = 3 mas Larmor radius= 60γ 9 B -7-1 mas Without electric field, electrons cool in turning through angle 0.2 How do we accelerate electrons in VERITAS@10 region smaller than Larmor radius? 28 vi

9 Blazar XAP! TeV variation in blazar jets (see Amy F.) PKS min MKN min PKS min! GeV variation in Quasars 3C 279 ~3 min at z~ 0.5! Emission must come from outside gammasphere where opacity to γ-γ pair production is ~1 May originate at much greater radius Hard to reconcile with rapid variation! Compton vs Synchrotron γ-rays Aleksin Uppre hump generally assumed to be However, inner jets are now thought to be (electro) magnetically-dominated Beat Synchrotron Limit by accelerating p to PeV energies 9 and have them cool through photo-pair production, initiating showers mainly cooling by synchrotron emission.

10 Event Horizon Telescope! Data already taken with EHT should image the M87 jet within ~10m and test RMHD models We expect spine-sheath polarization and a lateral shift Ω Η! If the jet and torus are simple as conjectured we should be able to learn about particle acceleration of which we are quite ignorant.! Circular polarimetry is also prescriptive 28 vi 2017! Many more jets can be VERITAS@10 10 observed on larger scales

11 Magnetoluminescence The efficient conversion of electromagnetic energy into γ-rays as observed in PWN, blazars, GRB - Gevatrons to Zevatrons Shocks too slow and not strong when EM dominant - New mechanisms needed Relativistic reconnection has been much studied using PIC codes and shows great promise However 28 vi 2017 it may be too slow VERITAS@10 for the fastest flares 11 Belaborodov

12 Untangling Flux Tubes! Magnetic field often evolves to a lower energy state with similar magnetic helicity (topology of current-carrying flux tubes).! Slower, relativistic reconnection may be responsible for most of the particle acceleration.! This can create magnetic slip knots which can release energy volumetrically on a light crossing time, as observed. 28 vi 2017 X VERITAS@10 12

13 Unstable EM Configurations B E/B 13 Yuan,Nalewajko, Zrake, East, RB

14 Diffusive Shock Acceleration and Galactic Cosmic Rays! Simple mechanism produces inferred source in amplitude and slope (see Martin Pohl)! Old problems Can t reach PeV energy/diffusion coefficient Spectrum is transmitted and decompressed Injection of elements and electrons Composite shocks and time-dependence! New problems SNR observations, especially TeV Detailed CR elemental spectra More detailed models needed 14

15 Magnetic Bootstrap B must grow by ~ 100 in shock Several instabilities invoked Weibel only when B small Bell - λ < rl Higher energies and improved angular resolution of CTA should help a lot Resonant - λ ~ rl Firehose - λ> rl P(E) / 0.1 P(E) / ρu2 ρu2 GeV TeV E PeV PeV TeV X GeV Shock Propose that highest energy CR streaming furthest ahead of spherical shock are unstable and grow field Details TBD! 28 vi 2017 VERITAS@10 15 Explain origin of UHECR at cluster accretion shocks?

16 Fast Radio Bursts! New population(s) of apparently high redshift radio transients! Dispersion => cosmological origin! One repeater in z=.2 dwarf galaxy! ~ erg ~ GHz emission in < ms K!! ~ one every few minutes! Only observed in radio! Sources: Compact binary mergers,pulsars, AGN jets, magnetar explosions! Rapid response observational program 16 Like pulsars, FRBs may be powerful γ-ray sources!

17 Magnetar Model! ~100 GT rotating neutron stars! Magnetar birthrate > ~10-4 yr -1 Galaxy -1! Repeat activity! Magnetic, elastic energy ~ J! Magnetars glitch, wander, flare, repeat! Pulsars produce coherent radio waves! Conservative explanation involves superconducting, superfluid, rotating nuclear matter endowed with ~100GT magnetic field! 17

18 Relativistic Current Fronts! Magnetic flare or starquake may launch a relativistic, Alfvenic disturbance into the magnetosphere.! May steepen to form double current layer at r ~ 100 R NS! Produces radio pulses either directly if Γ>>1 or indirectly if current filaments! Current carried by pairs which may radiate incoherently at γ-ray energies Other explanations of radio emission are 18 candidate γ-ray sources for nearby FRBs

19 Summary! Still much discovery space in the TeV! Still well worth the DM quest! New transients VHE ν, LIGO, FRB! Intrinsically multi-messenger! EHT will be very instructive! Non-negotiable physics constrains models and possibilities! We have much to learn about particle acceleration 28 vi 2017 Happy Birthday 19 VERITAS