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

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

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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

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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

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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

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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.

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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/

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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.

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Results: Cas A VERITAS: - wobble-mode observations, 0.5 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.

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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

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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?

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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, 0.5 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 8.2 peak significance pre-trials 2-D Gaussian profile fit: Centroid: 06 16.9 +22 32.4 0.03(stat) 0.07(syst) Extension: ~ 0.17 0.02(stat) 0.04(syst) Acciari et al. ApJL 698 L133 (2009)

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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)

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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 ux 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)

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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.

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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 ux 2.5% of Crab in the energy range (1 100)GeV.

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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

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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

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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.

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Extra Slides

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VERITAS Concept VERITAS Concept

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Observations of Other SNRs

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Results: Cas A The non-thermal X-ray emission predominantly originates from laments and knots in the reverse-shock region of Cas A (Helder & Vink 2008). The presence of a large ux 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 -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)

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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

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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

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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

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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.