VERITAS Observations of Supernova Remnants Reshmi Mukherjee 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
Outline §(Quick) introduction to VERITAS §Scientific goals & questions § Observing program § VERITAS -ray results
VERITAS at Whipple Observatory T 2 109 m Fall 2006 Since March 2006 85 m T 3 82 m T 4 35 m April 2007 Instrument design: § Four 12 -m telescopes § 499 -pixel cameras (3. 5° Fo. V) § FLWO, Mt. Hopkins, Az (1268 m) § Completed Spring, 2007 T 1
VERITAS: The Atmospheric Cherenkov Technique -ray camera Area = 104 – 105 m 2 ~60 optical photons/m 2/Te. V Cherenkov image ns electronics Imaging ACTs use the shape and orientation of the air shower image in the camera plane to distinguish between cosmic & -rays.
VERITAS Sensitivity § Sensitive energy range: 100 Ge. V to > 30 Te. V § Spectral reconstruction begins at ~150 Ge. V § Energy resolution: ~15% - 20% § Peak effective area: 100, 000 m 2 § Angular resolution: 0. 1 o at 1 Te. V, 0. 14 o at 200 Ge. V (68% values) § 1% Crab detection (5 s) in less than 50 h, 5% crab in ~2. 5 h § Observation time per year: 750 h non-moonlight, 100 h moonlight
Galactic Science Program § VERITAS Key Science Project § Supernova remnants/PWNe § Non-thermal shells § Shell-molecular cloud interactions § Te. V PWNe associated with high E/d 2 pulsars Goal of KSP: Constraints on particle acceleration and diffusion. Cosmic ray origin? Measurement of Te. V 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 Te. V IC emission low? Can we demonstrate a robust correlation of Te. V emission with target matter? Combining the Te. V 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.
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 e. V. § Several SNRs have been detected at Te. V energies. Here we present results on: § Cas A § IC 443 § W 44 Te. VCat: : //tevcat. uchicago. edu/
Results: Cas A SNR & PWNe KSP: Stage et al. 2006 credit: NASA/CXC/SAO/ D. Patnaude et al. § Young (330 yr), shell-type SNR at a distance of ~3. 4 kpc. § Massive star progenitor § 5’ diameter (~Te. V ang resolution). § Discovered in Te. V by HEGRA (232 hrs, 5 s), confirmed by MAGIC (47 hrs, 5. 3 s) § Flux ~ 3. 3 % Crab above 1 Te. V § Power-law G: 2. 3 ± 0. 2 stat ± 0. 2 sys § Extensive modeling of cosmic-ray acceleration and -ray production exists. Deep Chandra image of Cas A (7. 3’ by 6. 4’)
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.
Results: Cas A VERITAS Spectrum G = 2. 61 +/- 0. 24 stat +/- 0. 20 sys Solid: VERITAS Dashed: HEGRA Dotted: MAGIC Acciari et al. (2009), in prep. § Well-fit by power law spectrum: d. N/d. E = N 0(E/Te. V)-G § Flux (E > 1 Te. V): ~ 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
Results: IC 443 MAGIC + Black – optical White – EGRET Color - CO 3 -10 ke. V X-rays Bocchino & Bykov 2001 § Shell interacting with molecular cloud -> potential target material § EGRET emission centered on remnant, overlaps cloud Stage et al. 2006 § MAGIC cloud emission centered on § PWN at southern edge of shell § Distance ~ 1. 5 kpc § Age ~ 30, 000 years § Diameter 45’ § Distinct shell in radio, optical Compelling reasons to search for Te. V emission from IC 443: s from cosmic rays, or from the PWN?
Results: IC 443 Acciari et al. Ap. JL 698 L 133 (2009) § Discovered in Te. V 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 J 061705. 3+222127 – Oct / Nov 2007 with 4 telescopes 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) • 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
Results: IC 443 Multiwavelength Picture § Overlap with CO indicating molecular cloud along line of sight § Maser emission suggests SNR shock interacting with cloud § Te. V emission could be – CR-induced pion production in cloud – associated with the pulsar wind nebula to the south Stage et al. 2006 § Ge. V and Te. V emission spatially separated? Acciari et al. Ap. JL 698 L 133 (2009)
Results: IC 443 Acciari et al. Ap. JL 698 L 133 (2009) Stage et al. 2006 § Power-law fit 0. 3 – 2 Te. V: G = 2. 99 ± 0. 38 stat ± 0. 30 sys § Threshold of energy spectrum - 300 Ge. V § The integral flux above 300 Ge. V is (4. 63 ± 0. 90 stat ± 0. 93 sys) X 10− 12 cm− 2 s− 1 (3. 2% Crab), in good agreement with the spectrum reported by MAGIC
Observations of Other SNRs § CTB 109 (G 109. 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 Ge. V) < 2. 5 X 10 -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 J 1503 -582 with an FVW. VERITAS observed for 18. 4 hrs (live time) No emission detected. Flux UL (E> 500 Ge. V) < 0. 26 X 10 -12 cm-2 s-1 (< 1% Crab nebula flux) § W 44: SNR promising source of p 0 induced -rays. 13 hr live time around W 44. No emission detected around SNR. Flux UL (E > 300 Ge. V) < 2% Crab nebula flux.
Observations of Other SNRs Fig. from Wolsczcan et al. 1991 Contours: Radio emission Shaded area: X-rays § W 44 is an SNR with large angular extent. § W 44 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). § 0 FGL J 1855. 9+0126 , marginally coincident with PSR 1853+01, has flux ≃ 2. 5% of Crab in the energy range (1 − 100)Ge. V.
The field of W 44 Unidentified Sources: HESS J 1857+026 and HESS J 1858+020 – 9. 2 hrs livetime on W 44 position. 6. 4 hrs on UIDs – J 1857+026 possibly associated with PWN AX J 185651+0245 powered by newly discovered radio pulsar PSR J 1856+0245 § W 44: UL ~2 % Crab § J 1857+026: 5. 6 s § J 1858+020: not detected Agreement with HESS: § HESSJ 1857+026 is detected in the position reported by HESS. § Morphology of HESS J 1857+026 is well reproduced. Acciari et al. in prep
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 s significance in 22 hrs – Consistent with a point source – Power-law spectrum up to ~5 Te. V; no sign of a cut-off – Well-measured spectrum. Boon to modelers § Other SNRs: Lack of strong (>5% Crab) sources
Future Directions … Upgrade Relocating T 1 will improve the sensitivity of VERITAS by ~15% → equivalent of gaining an annual 300 hr extra in obs. time. Impacts all physics goals. Disassembly of T 1 New platform for T 1
Extra Slides
VERITAS Concept
Observations of Other SNRs
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 –rays, remains one of the most stimulating scientific questions of ground -based –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 p 0 decay produced in inelastic collisions of relativistic protons, the location of the particleacceleration site is less constrained by data in other wavebands.
VERITAS Observations of SNRs Cosmic rays accelerated at expanding shock front electrons and/or nuclei synchrotron radiation observed in radio through X-rays Te. V observations constrain Nature of particles Acceleration process Role of SNRs in production of Galactic cosmic rays Growing class: ~8 known or likely SNR associations Stage et al. 2006 CTB 109 Cas A W 44 IC 443 FVW 190. 2+1. 1
IC 443 • Green – Radio • Red – Optical • Blue – X-rays • Shell interacting with molecular cloud potential target material Stage al. 2006 • et. EGRET emission centered on remnant, overlaps cloud • MAGIC emission centered on cloud • PWN at southern edge of shell 31 st ICRC, Lodz, Poland • Distance ~ 1. 5 kpc • Age ~ 30, 000 years • Diameter 45’ • Distinct shell in radio, optical Compelling reasons to study Te. V emission from IC 443: s from cosmic rays, or from the PWN? Observations of SNRs with VERITAS B. Humensky, U. of Chicago
VERITAS Galactic Science In addition … § Cygnus region sky survey (key science) § Compact sources in the Milky Way § Te. V 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 § Te. V unidentified sources § Fermi unidentified sources & transients J. Paredes
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.
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