VERITAS Observations of Supernova Remnants

Reshmi Mukherjee1 for the VERITAS Collaboration1Barnard College, Columbia University

Chandra SNR Meeting, Boston, Jul 8, 2009

Outline

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

85 m

109 m

82 m35 m

T1

Fall 2006

April 2007

T4

T2

T3

SinceMarch2006

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

VERITAS: The Atmospheric Cherenkov Technique

g-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 electronicsArea = 104 – 105 m2

~60 optical photons/m2/TeV

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

Galactic Science Program VERITAS Key Science Project

Supernova remnants/PWNe

Non-thermal shells Shell-molecular cloud interactions TeV PWNe 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.

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 44TeVCat:://tevcat.uchicago.edu/

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 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.

SNR & PWNe KSP:

Deep Chandra image of Cas A (7.3’ by 6.4’)

Stage et al. 2006credit: NASA/CXC/SAO/ D.Patnaude et al.

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.

VERITAS Spectrum G = 2.61 +/- 0.24stat +/- 0.20sys

Acciari et al. (2009), in prep.

Results: Cas A

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

Solid: VERITAS

Dashed: HEGRA

Dotted: MAGIC

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-raysBocchino & Bykov 2001

Black – opticalWhite – 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?

Results: IC 443

Stage et al. 2006

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

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)

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 PictureAcciari et al. ApJL 698 L133 (2009)

Results: IC 443

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

Acciari et al. ApJL 698 L133 (2009)

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.

Observations of Other SNRsFig. from Wolsczcan et al. 1991

Contours: Radio emissionShaded 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.

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 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.

Unidentified Sources: HESS J1857+026 and HESS J1858+020

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 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

Future Directions … Upgrade

New platform for T1Disassembly 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.

Extra Slides

VERITAS Concept

Observations of Other SNRs

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 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.

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)

VERITAS Observations of SNRs

Stage et al. 2006

Cosmic rays accelerated at expanding shock front

electrons and/or nucleisynchrotron radiation observed in radio through X-rays

TeV observations constrain Nature of particlesAcceleration processRole 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+1.1W44

B. Humensky, U. of Chicago31st ICRC, Lodz, Poland Observations 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

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

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.