Very High-Energy Gamma- Ray Astrophysics

Transcription

1 Very High-Energy Gamma- Ray Astrophysics David A. Williams Santa Cruz Institute for Particle Physics UC Santa Cruz Quarknet July 12, 2013

2 Detecting High Energy Gamma Rays High Sensitivity HESS, MAGIC, CANGAROO, VERITAS, CTA Low Energy Threshold Fermi Large Aperture/High Duty Cycle Milagro, Tibet, ARGO, HAWC Large Effective Area Excellent Background Rejection (>99%) Low Duty Cycle/Small Aperture >50 GeV (5 x ev) Space-based (small area) Background Free Large Duty Cycle/Large Aperture 100 MeV 300 GeV Large Effective Area Good Background Rejection Large Duty Cycle/Large Aperture > 1 TeV (10 12 ev) 2

3 2000 Aurore Simonnet Detecting >100 GeV -Rays Detect shower in the atmosphere What reaches the ground? Some particles Cherenkov light 3

4 Simulation of Shower in Milagro 4

5 Simulation of Shower in Milagro 5

6 Cherenkov Radiation cos c v x v v/c = Figure from Emma Ona Wilhelmi 6

7 Milagro: Water Cherenkov Detector e m 7

8 Simulation of Shower in Milagro 8

9 Simulation of Shower in Milagro 9

10 Shower Direction & Core Position Real air shower event Simulated gamma-ray shower 10

11 Simulation of Shower in Milagro 11

12 Milagro s Successor: HAWC High Altitude Water Cherenkov Detector 12

13 VERITAS: Imaging Atmospheric Cherenkov Telescope Very Energetic Radiation Imaging Telescope Array System Whipple Observatory Basecamp (el m) at foot of Mt. Hopkins 13

14 Atmospheric Imaging Technique -ray 499-PMT camera 12 m Mirror Area = m 2 ~60 optical photons/m 2 /TeV -rays above ~100 GeV Cherenkov image 500-MHz FADC electronics 14

15 Shower Direction & Core Position 15

16 SC γ-ray Shower Energy: 1 TeV Impact Distance: 100m Proton Shower Energy: 3.16 TeV Impact Distance: 0m DC 16

17 Image of a Supernova Remnant RX J RX J First image of a -ray source HESS result Contours are ASCA 1 3 kev Color is VHE -rays Acceleration of particles (e ±? p?) to >100 TeV 17

18 Discovery of VHE Crab Pulsar E. Aliu et al. 2011, Science 334, Work led by, A. Nepomuk Otte UCSC postdoc, now asst. prof. at Georgia Tech 18

19 TeV activity coincides with near-apastron passage

20 Microquasar or binary pulsar? From Mirabel 2006, Science 312, p

21 Radio Galaxy: M 87 1 period = 1 month = 1 dark run Giant radio galaxy (class of AGN) Distance ~16 Mpc, redshift Central black hole ~6 x 10 9 M sun Jet angle Knots resolved in the jet Jet is Every variable dark in run all in good agreement! wavebands 21

22 M 87 Radio and TeV flares 1 period = 1 month = 1 dark run Rapid TeV flares coincident with the core brightening TeV particles accelerated within ~100 R s of BH Best determination so far of location of particle acceleration Every dark run in good agreement! V. Acciari et al. 2009, Science 325,

23 Markarian 501 July 9, period = 1 month = 1 dark run Rapid flare MAGIC telescope (Albert et al., submitted to Astrophys. J.) Flux doubling times ~2 minutes Indication of a 4±1 minute lag between lowest and highest E events TeV TeV TeV Constrains details of emission Every dark run in good agreement! 23

24 Size of Emission Region d 2 1 T 2 T 1 3 T 3 Instantaneous flash emits photons from 1, 2, and 3 at the same time Observer sees them arrive at different times: T 2 T 1 ~ d/c T 3 T 1 ~ d/2c Duration of flash seen by observer is at least of order d/2c long for opaque emission region; d/c for transparent one Short bursts must come from small regions 24

25 Emission Region in Motion t v t 1 2 T 2 T 1 t lab = t 2 t 1 = v/c = 1/(1-2 ) 1/2 T obs = T 2 T 1 If emission region is moving towards observer, apparent time between events is reduced Limiting case: v = c & = 0 T obs = 0 Apparent motion can be superluminal 25

26 Emission Region in Motion v t 1 t 2 T 2 T 1 T 2 T 1 T obs = (t 2 t 1 ) (v (t 2 t 1 ) cos )/c = t lab (1 cos ) t lab (1 ) (for cos ~ 1) t lab (1 )(1 + )/2 (for ~ 1) t lab (1 2 )/2 t lab /(2 2 ) Time intervals seen by observer are ~2 2 times shorter than intervals at source Lorentz factors of 10 to 50 not uncommon Emission region not ~2 light minutes across, but still small 26

27 The CTA Concept light pool radius R m typical telescope spacing Arrays in northern and southern hemispheres for full sky coverage 4 large (~23 m) telescopes in the center (LSTs) Threshold of ~30 GeV 25 medium (9 12 m) telescopes (MSTs) covering ~1 km 2 Order of magnitude improvement in 100 GeV 10 TeV range Small (~4 m) telescopes (SSTs) covering >3 km 2 in south >10 TeV observations of Galactic sources Construction begins in ~2015

28 From current arrays to CTA Light pool radius R m typical telescope spacing Sweet spot for best triggering and reconstruction: Most showers miss it! Large detection area More images per shower Lower trigger threshold

29 A Novel Telescope for CTA Schwarzschild-Couder optics Camera using multianode photomultiplier tubes or Geiger-APDs with integrated electronics 29

30 Simulated Galactic Plane surveys H.E.S.S. CTA, for same exposure Expect ~1000 detected sources over the whole sky

31 3 < an v>[ cm s Dwarf spheroidal galaxies (dsph) show astrophysical factors in & CTA the range of GeV 2 cm -5 and an expected low g ray background. Considering 100 h observations on Segue-1 Fermi dwarf dsph, annihilation spheroidal cross and sections CTA down Galactic to 10 Center -24~ cm 3 s -1 could searches be excluded are (see Fig. complementary 5). Assuming the same observation time and a canonical annihilation cross section of 3x10 26 cm 3 s 1, we find that the minimum astrophysical factor that would provide a detection by CTA would be Dark matter searches with Fermi Assuming b b-bar decay channel LAT 2-year result from Ackermann et al. 2011, Phys. Rev. Lett. 107, of the EGB accounts for more than 20% o total flux. -1 ] Fermi combined DSG analysis (10 DSGs), 2 years Fermi combined DSG analysis, 10 years Galactic Halo, 100 h, CTA array B (Ring Method) Fornax Cluster, 100 h, CTA array B ( max = 1.0 ) Segue 1 DSG, 100 h, CTA array B WIMPparameter space 2 10 mdm [GeV] Fig. 5: Comparison of exclusion curves of Fermi-LAT in 24 months and expected for 10 years. The exclusion curves for the various targets studied in this contribution are also reported for the