1. VERITAS Observations of Supernova Remnants Reshmi Mukherjee 1 for the VERITAS Collaboration 1 Barnard 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. 85 m 109 m 82 m 35 m T1 Fall 2006 April 2007 T4 T2 T3 Since March 2006 Instrument design:  Four 12-m telescopes  499-pixel cameras (3.5° FoV)  FLWO,Mt. Hopkins, Az (1268 m)  Completed Spring, 2007 VERITAS at Whipple Observatory

4. VERITAS: The Atmospheric Cherenkov Technique   ray camera Cherenkov image Imaging ACTs use the shape and orientation of the air shower image in the camera plane to distinguish between cosmic &  -rays. ns electronics Area = 10 4 – 10 5 m 2 ~60 optical photons/m 2 /TeV

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 m 2  Angular resolution: 0.1 o at 1 TeV, 0.14 o at 200 GeV (68% values)  1% Crab detection (5  ) 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  TeV PWNe associated with high E/d 2 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 10 15 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  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  ), confirmed by MAGIC (47 hrs, 5.3   Flux ~ 3.3 % Crab above 1 TeV  Power-law  2.3 ± 0.2 stat ± 0.2 sys  Extensive modeling of cosmic-ray acceleration and  ray production exists. SNR & PWNe KSP: Deep Chandra image of Cas A (7.3’ by 6.4’) Stage et al. 2006 credit: NASA/CXC/SAO/ D.Patnaude et al.

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  detection  Flux: ~ 3% Crab  Consistent with a point source. Acciari et al. (2009), in prep.

10. VERITAS Spectrum  = 2.61 +/- 0.24 stat +/- 0.20 sys Acciari et al. (2009), in prep. Results: Cas A  Well-fit by power law spectrum: dN/dE = N 0 (E/TeV) -   Flux (E > 1 TeV): ~ 3.5% Crab (7.76 +/- 1.10 stat +/- 1.55 sys ) X 10 -13 cm -2 s -1  No sign of energy cut-off at high energy Solid: VERITAS Dashed: HEGRA Dotted: MAGIC

11. Results: IC 443 Stage et al. 2006  Distance ~ 1.5 kpc  Age ~ 30,000 years  Diameter 45’  Distinct shell in radio, optical 3-10 keV X-rays Bocchino & Bykov 2001 Black – optical White – EGRET Color - CO + MAGIC  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 Compelling reasons to search for TeV emission from IC 443:  s from cosmic rays, or from the PWN?

12. Results: IC 443 Stage et al. 2006  Discovered in TeV in 2007 –by VERITAS (7.1/6.0  pre/post-trials in 15.9 hrs) –by MAGIC (5.7  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 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) Acciari et al. ApJL 698 L133 (2009)

13. Results: IC 443 Stage et al. 2006  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? Multiwavelength Picture Acciari et al. ApJL 698 L133 (2009)

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

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  0 induced  -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 Contours: Radio emission Shaded area: X-rays  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.

17. The field of W 44 –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   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. Unidentified Sources: HESS J1857+026 and HESS J1858+020 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 8.3  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 New platform for T1 Disassembly of T1 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.

20. Extra Slides

21. VERITAS Concept VERITAS Concept

22. Observations of Other SNRs

23. Results: Cas A  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  -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  0 decay produced in inelastic collisions of relativistic protons, the location of the particle- acceleration site is less constrained by data in other wavebands.  The question of whether or not there is a sufficiently high flux of Galactic nuclear CRs resulting in a steady flux of VHE  –rays, remains one of the most stimulating scientific questions of ground-based  –ray astronomy. (Berezhko et al. 2003)

24. VERITAS Observations of SNRs Stage et al. 2006 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 IC 443 Cas A CTB 109 FVW 190.2+1.1 W44

25. B. Humensky, U. of Chicago31 st ICRC, Lodz, PolandObservations of SNRs with VERITAS IC 443 Stage et al. 2006 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 PWN at southern edge of shell Compelling reasons to study TeV emission from IC 443:  s from cosmic rays, or from the PWN? Green – Radio Red – Optical Blue – X-rays

26. VERITAS Galactic Science  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? J. Paredes  Unidentified Galactic sources  EGRET unidentified sources  TeV unidentified sources  Fermi unidentified sources & transients In addition …  Cygnus region sky survey (key science)  Compact sources in the Milky Way

27. VERITAS: Astrophysics at the highest energies 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? Supernova remnants, plerions, unidentified sources: - cosmic ray origin? Constraints on particle acceleration and diffusion. 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.