VERITAS Observations of Supernova Remnants

1. VERITAS Observations of Supernova Remnants • Reshmi Mukherjee1 for the VERITAS Collaboration • 1Barnard College, Columbia University Chandra SNR Meeting, Boston, Jul 8, 2009

2. Outline • (Quick) introduction to VERITAS • Scientific goals & questions • Observing program • VERITAS -ray results

3. VERITAS at Whipple Observatory Since March 2006 T2 109 m Fall 2006 85 m T3 82 m 35 m T4 T1 April 2007 • Instrument design: • Four 12-m telescopes • 499-pixel cameras (3.5° FoV) • FLWO,Mt. Hopkins, Az (1268 m) • Completed Spring, 2007

4. VERITAS: The Atmospheric Cherenkov Technique g-ray camera ns electronics Cherenkov image Area = 104 – 105 m2 ~60 optical photons/m2/TeV Imaging ACTs use the shape and orientation of the air shower image in the camera plane to distinguish between cosmic & -rays.

5. VERITAS Sensitivity • Sensitive energy range: 100 GeV to > 30 TeV • Spectral reconstruction begins at ~150GeV • Energy resolution: ~15% - 20% • Peak effective area: 100,000 m2 • Angular resolution: 0.1o at 1 TeV, 0.14o at 200 GeV (68% values) • 1% Crab detection (5s) in less than 50 h, 5% crab in ~2.5 h • Observation time per year: 750 h non-moonlight, 100 h moonlight

6. Galactic Science Program • VERITAS Key Science Project • Supernova remnants/PWNe • Non-thermal shells • Shell-molecular cloud interactions • TeVPWNe associated with high E/d2 pulsars Goal of KSP: Constraints on particle acceleration and diffusion. Cosmic ray origin? Measurement of TeV emission from SNRs could resolve the long-standing question of whether these are sites of hadronic cosmic ray acceleration. Is there clear evidence of hadronic emission? Is the TeV IC emission low? Can we demonstrate a robust correlation of TeV emission with target matter? Combining the TeV spectrum with the synchrotron spectra in the radio and X-ray bands can possibly discriminate between IC and pion production/decay models, and provide strong constraints on the acceleration process.

7. VERITAS Observations of SNRs • Supernova remnants are widely considered to be the strongest candidate for the source of cosmic rays below the knee at around 1015 eV. • Several SNRs have been detected at TeV energies. • Here we present results on: • Cas A • IC 443 • W 44 TeVCat:://tevcat.uchicago.edu/

8. Results: Cas A SNR & PWNe KSP: • Young (330 yr), shell-type SNR at a distance of ~3.4 kpc. • Massive star progenitor • 5’ diameter (~TeV ang resolution). • Discovered in TeV by HEGRA (232 hrs, 5 s), confirmed by MAGIC (47 hrs, 5.3 s) • Flux ~ 3.3 % Crab above 1 TeV • Power-law G: 2.3 ± 0.2stat ± 0.2sys • Extensive modeling of cosmic-ray acceleration and g-ray production exists. Stage et al. 2006 credit: NASA/CXC/SAO/ D.Patnaude et al. Deep Chandra image of Cas A (7.3’ by 6.4’)

9. Results: Cas A • VERITAS: • - wobble-mode observations, 0.5º offset, during Oct/Nov 2007 with full 4 Tel. array • Exposure: 22 hr: 8.3 s detection • Flux: ~ 3% Crab • Consistent with a point source. Acciari et al. (2009), in prep.

10. Results: Cas A VERITAS Spectrum G = 2.61 +/- 0.24stat +/- 0.20sys Acciari et al. (2009), in prep. • Well-fit by power law spectrum: dN/dE = N0(E/TeV)-G • Flux (E > 1 TeV): ~ 3.5% Crab (7.76 +/- 1.10stat+/- 1.55sys) X 10-13 cm-2 s-1 • No sign of energy cut-off at high energy

11. MAGIC + Black – optical White – EGRET Color - CO 3-10 keV X-rays Bocchino & Bykov 2001 Results: IC 443 • Shell interacting with molecular cloud -> potential target material • EGRET emission centered on remnant, overlaps cloud • MAGIC emission centered on cloud • PWN at southern edge of shell • Distance ~ 1.5 kpc • Age ~ 30,000 years • Diameter 45’ • Distinct shell in radio, optical Stage et al. 2006 Compelling reasons to search for TeV emission from IC 443: s from cosmic rays, or from the PWN?

12. Results: IC 443 • Discovered in TeV in 2007 • by VERITAS (7.1/6.0 s pre/post-trials in 15.9 hrs) • by MAGIC (5.7 s in 29 hrs) • Wobble-mode observations, 0.5º offset • Observed during two epochs: • Feb / Mar 2007 with 3 telescopes • PWN location, CXOU J061705.3+222127 • Oct / Nov 2007 with 4 telescopes • Center of Feb/Mar hot spot: 06 16.9 +22 33 • Total livetime: 37.1 hrs. • Flux ~3% Crab • 8.2σ peak significance pre-trials Acciari et al. ApJL 698 L133 (2009) Stage et al. 2006 • 2-D Gaussian profile fit: • Centroid: 06 16.9 +22 32.4 ± 0.03º(stat) ± 0.07º(syst) • Extension: σ ~ 0.17º ± 0.02º(stat) ± 0.04º(syst)

13. Results: IC 443 Multiwavelength Picture Acciari et al. ApJL 698 L133 (2009) • Overlap with CO indicating molecular cloud along line of sight • Maser emission suggests SNR shock interacting with cloud • TeV emission could be • CR-induced pion production in cloud • associated with the pulsar wind nebula to the south • GeV and TeV emission spatially separated? Stage et al. 2006

14. Results: IC 443 Acciari et al. ApJL 698 L133 (2009) Stage et al. 2006 • Power-law fit 0.3 – 2 TeV: G = 2.99 ± 0.38stat ± 0.30sys • Threshold of energy spectrum - 300 GeV • The integral flux above 300 GeV is (4.63 ± 0.90stat ± 0.93sys) X10−12 cm−2 s−1 (3.2% Crab), in good agreement with the spectrum reported by MAGIC

15. Observations of Other SNRs • CTB 109 (G109.1-1.0): Shell-type SNR, interacting with a molecular cloud on its eastern rim. Observed briefly for 4.3 hrs (live time). No emission detected. Flux UL (E > 400 GeV) < 2.5X10-12 cm-2 s-1 • FVW 190.2+1.1: Forbidden Velocity Wings may be the vestiges of very old SNRs. FVW 190.2+1.1 shows a clear shell-like morphology in the HI maps. Motivated by the possible association of HESS J1503-582 with an FVW. VERITAS observed for 18.4 hrs (live time) No emission detected. Flux UL (E> 500 GeV) < 0.26X10-12 cm-2 s-1 (< 1% Crab nebula flux) • W 44: SNR promising source of p0 induced g-rays. 13 hr live time around W44. No emission detected around SNR. Flux UL (E > 300 GeV) < 2% Crab nebula flux.

16. Observations of Other SNRs Fig. from Wolsczcan et al. 1991 • W44 is an SNR with large angular extent. • W44 is a bright radio source. • X-ray emission centrally peaked, predominantly thermal X-ray emission • A plerion is visible in radio and X-rays associated with PSR 1853+01 (Harrus 1997). • 0FGL J1855.9+0126 , marginally coincident with PSR 1853+01, has flux ≃ 2.5% of Crab in the energy range (1 − 100)GeV. Contours: Radio emission Shaded area: X-rays

17. The field of W 44 Unidentified Sources: HESS J1857+026 and HESS J1858+020 • 9.2 hrs livetime on W44 position. 6.4 hrs on UIDs • J1857+026 possibly associated with PWN AX J185651+0245 powered by newly discovered radio pulsar PSR J1856+0245 • W44: UL ~2 % Crab • J1857+026: 5.6 s • J1858+020: not detected • Agreement with HESS: • HESSJ1857+026 is detected in the position reported by HESS. • Morphology of HESS J1857+026 is well reproduced. Acciari et al. in prep

18. Summary • IC 443: Extended and complicated • Extended emission; soft spectrum • Origin: PWN or SNR/MC interaction? • Strong Fermi source: broadband spectral, morphological evolution will be illuminating • Cas A: • Detection with 8.3s significance in 22hrs • Consistent with a point source • Power-law spectrum up to ~5 TeV; no sign of a cut-off • Well-measured spectrum. Boon to modelers • Other SNRs:Lack of strong (>5% Crab) sources

19. Future Directions … Upgrade Relocating T1 will improve the sensitivity of VERITAS by ~15% → equivalent of gaining an annual 300 hr extra in obs. time. Impacts all physics goals. New platform for T1 Disassembly of T1

20. Extra Slides

21. VERITAS Concept

22. Observations of Other SNRs

23. Results: Cas A • The question of whether or not there is a sufficiently high flux of Galactic nuclear CRs resulting in a steady flux of VHE g–rays, remains one of the most stimulating scientific questions of ground-based g –ray astronomy. (Berezhko et al. 2003) • The non-thermal X-ray emission predominantly originates from filaments and knots in the reverse-shock region of Cas A (Helder & Vink 2008). • The presence of a large flux of high-energy electrons in the reverse-shock region, responsible for the non-thermal radio to X-ray emission, will also produce high-energy γ -ray emission through non-thermal bremsstrahlung and IC scattering (Atoyan 2006). • Based on that leptonic emission, Cas A would appear in VERITAS data as a disk or ring-like source with outer radius 2.5′ (Uchiyama & Aharonian 2000). • If, on the other hand, the VHE γ -ray emission from Cas A were dominated by p0 decay produced in inelastic collisions of relativistic protons, the location of the particle-acceleration site is less constrained by data in other wavebands.

24. Cosmic rays accelerated at expanding shock front electrons and/or nuclei synchrotron radiation observed in radio through X-rays TeV observations constrain Nature of particles Acceleration process Role of SNRs in production of Galactic cosmic rays Growing class: ~8 known or likely SNR associations VERITAS Observations of SNRs IC 443 CTB 109 FVW 190.2+1.1 W44 Cas A Stage et al. 2006

25. IC 443 • Green – Radio • Red – Optical • Blue – X-rays • Distance ~ 1.5 kpc • Age ~ 30,000 years • Diameter 45’ • Distinct shell in radio, optical • Shell interacting with molecular cloud potential target material • EGRET emission centered on remnant, overlaps cloud • MAGIC emission centered on cloud • PWNat southern edge of shell Stage et al. 2006 Compelling reasons to study TeV emission from IC 443: s from cosmic rays, or from the PWN? Observations of SNRs with VERITAS

26. VERITAS Galactic Science • In addition … • Cygnus region sky survey (key science) • Compact sources in the Milky Way • TeV observations of X-ray binaries: • Is the compact object BH emitting jet ? • Is it a pulsar with pulsar wind? • Are these systems accreting binaries (microquasars?) Emission mechanisms? • Unidentified Galactic sources • EGRET unidentified sources • TeV unidentified sources • Fermi unidentified sources & transients J. Paredes

27. VERITAS: Astrophysics at the highest energies Supernova remnants, plerions, unidentified sources: - cosmic ray origin? Constraints on particle acceleration and diffusion. Gamma-Ray Bursts. Active galaxies: Relativistic jets. - shock acceleration? - particle type? Fundamental Physics/ Dark Matter Studies (Neutralino Annihilation). Search for Dark matter in Galactic Center. Minihaloes? Diffuse extragalactic background light • VERITAS will explore astrophysical situations in which physics operates under extreme conditions – (e.g. intense gravitational or magnetic fields.) • Study particle acceleration in extreme astrophysical environments (AGN, GRBs). • Use -rays to probe intergalactic space -- Diffuse radiation fields. • Probe novel astrophysical phenomena which could arise as a result of new physics beyond the standard model of particle interactions.