Associations of H.E.S.S. VHE -ray sourceswith Pulsar Wind Nebulae

Yves Gallant(LPTA, U. Montpellier II, France)

for the H.E.S.S. Collaboration

“The Multi-Messenger Approach to High Energy Gamma-ray Sources”

Barcelona, July 5, 2006

• “Established” VHE Pulsar Wind Nebula– Crab Nebula, G0.9+0.1, MSH 15-52

– Vela X, Kookaburra (2), HESS J1825-137

• Association criteria, pulsar energetics

• Other possible associations with PWNe

• Summary and prospects

PWN emission mechanisms: the Crab Nebula

• Assume leptonic model: synchrotron and Inverse Compton emission• Relativistic electrons and positrons created and accelerated by the pulsar

H.E.S.S. spectrum

(A&A, submitted):

Spectral curvature,

Consistent with IC

expectations

me c2

me ' c 2

h '

h

Target photons : CMB, interstellar IR, stellar photons, synchrotron (SSC)…

synchrotron

Radio, optical, X-rays

VHE plerion in the composite SNR G0.9+0.1• radio shell and PWN (Helfand & Becker 1984); X-ray non-thermal plerion

(e.g. Porquet, Decourchelle & Warwick 2003 with XMM-Newton)

• H.E.S.S. excess compatible with point source at plerion position

• spectrum compatible with IC and X-ray synchrotron => B = 6G

Radio (90cm), LaRosa et al. (2000) H.E.S.S. excess: A&A 432, L25 (2005)

Pulsar Wind Nebula in MSH 15-52 (a.k.a. G 320.4-1.2)

“Composite” SNR: • radio and X-ray shell

• nonthermal X-ray nebula

• young pulsar B1509-58

H.E.S.S. detection:

A&A 435, L17 (2005)

First angularly resolved

PWN in VHE -rays

Synchrotron emission ne B2 whereas IC emission ne nph , with nph uniform

Spatial distribution of high-energy e, independently of B-field variations

Detection of the Vela X plerionic nebula(A&A 448, L43, 2006)

• In composite Vela SNR (at 290 pc)

• Matches hard X-ray emission seen with ROSAT and ASCA, at position of (larger) radio nebula Vela X

• Nebula “crushed” by asymmetric reverse shock? (Blondin et al. 2001)

• Spectral curvature : F peaks in VHE

• “VHE observations of inverse Compton scattering of the CMBR allow direct inference of the spatial and spectral distribution of non-thermal electrons”

contours : X-rays (ROSAT)

Two new H.E.S.S. sources in the Kookaburra complex(A&A 2006, in press, astro-ph/0606311)

• Target photon densities vary smoothly (except close to stars, e.g. PSR B1259-58) => VHE -ray observations reveal high-energy electron sources in the Galaxy

• H.E.S.S. Galactic plane survey (extended to -60o in longitude in 2005) found new PWN associations

contours : radio (ATCA)

• HESS J1420-609 : associated X-ray (K3) and radio plerion, and energetic PSR J1420-6048

• HESS J1418-607 : associated X-ray and radio plerion (“Rabbit”), candidate pulsar

• Large, offset nebulae in both cases

HESS J1825-137 as the nebula of PSR B1823-13(A&A 2006, submitted)

• Pulsar offset from source, but profile peaks near PSR position

• Much smaller, X-ray nebula trailing in the same direction

• VHE gamma-ray spectral index steepening away from pulsar! (first spectral variations)

• Consistent with energy losses of electrons (also X-ray size)

Association Criteria

• pulsar energy loss rate (”spindown luminosity”) derived from observed timing parameters:

• pulsar distance D derived from radio dispersion measure DM

• as a criterion for pulsar association with TeV source, estimate ratio

/ (4 D)2 vs F0.3-30 TeV

(0.3 - 30 TeV : arbitrary energy range, but representative of H.E.S.S.; actual range depends on zenith angle and high-energy statistics)

• Caveat: assumes short particle lifetime; if delayed energy release (from particles injected earlier in history), apparent efficiency increases

• “Established” association efficiencies range from ~0.01% (Crab, Vela) through ~0.5% (MSH 15-52, Kookaburra) to 2.2% (HESS J1825-137)

Pulsar Energetics

• 7 (+1 : PSR B1259-63) “established” VHE -ray PWN associations

• consistent MWL spectral model (synchrotron + IC), and

• positional and morphological match to lower-energy counterpart, or

• VHE morphological and spectral evidence for association with known pulsar (e.g. HESS J1825-137 with PSR B1823-13), and consistent MWL data

Possible associations of VHE sources with known pulsars

• PSR B1800-21 : D = 3.9 kpc

• Required efficiency : 2.4%

• Other possible counterpart: G8.7-0.1

• PSR J1617-5055 : D = 6.8 kpc

• Required efficiency : 1.3%

HESS J1616-508 HESS J1804-216

Two sources from Galactic plane scan : ApJ 636, 777 (2006)

Deeper X-ray and/or VHE observations needed to confirm associations…

HESS J1303-631 : first H.E.S.S. unidentified sourceA&A 439, 1013 (2005)

No obvious counterpart; most energetic

pulsar in field, PSR J1301-6305, has

• ATNF pulsar catalogue: D = 15.8 kpc

• based on Taylor & Cordes (1993) Galactic ne model

• Latest model (“NE2001”, Cordes & Lazio 2003) yields D = 6.65 kpc!(factor > 5 in D2)

• (now use NE2001 distances throughout, but only such major discrepancy)

• Current implied efficiency in 0.3 - 30 TeV band : ~ 7%

PSR J1301-6305

M. Beilicke / H.E.S.S. Coll.

Other possible assocations with known pulsars

• More data since ApJ (2006) paper:Increased significance of “tail” towards PSR J1702-4128

• D = 4.8 kpc, => required efficiency : ~ 11%(for entire HESS source)

Poster by S. Carrigan, for the H.E.S.S. Collaboration

• Statistical analysis of pulsar catalogue and HESS sources: significant correlation

• New sources possibly associated with energetic pulsars:– HESS J1809-193

– HESS J1718-384

HESS J1702-420

Associations with possible PWNe in composite SNRs

• G0.9+0.1 : no pulsar detected, but consistent MWL plerion in shell

• HESS J1813-178 / SNR G12.82-0.02 could show evidence for a central X-ray plerion in XMM-Newton observations [talk by S. Funk]

• HESS J1634-472 may be associated with SNR G337.2+0.1, revealed by XMM-Newton as a probable Crab-like SNR [poster by J. Combi et al.]

• HESS J1834-087 appears associated with G23.3-0.3 (W41)

• but more centrally concentrated?

• plerionic counterpart in the radio?

Summary and Prospects• 7 (+1) “established” associations of VHE -ray sources with PWNe : most

numerous class of identified Galactic VHE -ray sources

• If Inverse Compton : target photons approximately known and uniform=> direct inference of electron spatial and spectral distribution

• Galactic survey in VHE -rays reveals high-energy electron sources in Galaxy

• Often large offset and physical size : several old PWNe, strongly affected by passage of asymmetric reverse shock?

• 6 additional “possible” associations of H.E.S.S. sources with energetic pulsars, but required efficiency and/or offset often large…

• In 3 additional probable associations with shell SNRs, the VHE -ray emission may be from an embedded plerionic component of the SNR (without a pulsar detection yet, e.g. G0.9+0.1)

• More MWL data on these objects needed to study possible associations

• VHE gamma-ray astronomy provides new, independent observational input into the physics of pulsar wind nebulae

• The fastest-growing class of identified Galactic -ray source?