Associations of H.E.S.S. VHE  -ray sources with 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, G , MSH –Vela X, Kookaburra (  2), HESS J 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 Target photons : CMB, interstellar IR, stellar photons, synchrotron (SSC)… synchrotron Radio, optical, X-rays

VHE plerion in the composite SNR G 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 = 6  G Radio (90cm), LaRosa et al. (2000) H.E.S.S. excess: A&A 432, L25 (2005)

Pulsar Wind Nebula in MSH (a.k.a. G ) “Composite” SNR: radio and X-ray shell nonthermal X-ray nebula young pulsar B H.E.S.S. detection: A&A 435, L17 (2005) First angularly resolved PWN in VHE  -rays Synchrotron emission  n e B 2 whereas IC emission  n e n ph, with n ph  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/ ) Target photon densities vary smoothly (except close to stars, e.g. PSR B ) => VHE  -ray observations reveal high-energy electron sources in the Galaxy H.E.S.S. Galactic plane survey (extended to -60 o in longitude in 2005) found new PWN associations contours : radio (ATCA) HESS J : associated X-ray (K3) and radio plerion, and energetic PSR J HESS J : associated X-ray and radio plerion (“Rabbit”), candidate pulsar Large, offset nebulae in both cases

HESS J as the nebula of PSR B (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 F TeV ( 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 J ) Pulsar Energetics 7 (+1 : PSR B ) “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 J with PSR B ), and consistent MWL data

Possible associations of VHE sources with known pulsars PSR B : D = 3.9 kpc Required efficiency : 2.4% Other possible counterpart: G PSR J : D = 6.8 kpc Required efficiency : 1.3% HESS J HESS J Two sources from Galactic plane scan : ApJ 636, 777 (2006) Deeper X-ray and/or VHE observations needed to confirm associations…

HESS J : first H.E.S.S. unidentified source A&A 439, 1013 (2005) No obvious counterpart; most energetic pulsar in field, PSR J , has ATNF pulsar catalogue: D = 15.8 kpc based on Taylor & Cordes (1993) Galactic n e model Latest model (“NE2001”, Cordes & Lazio 2003) yields D = 6.65 kpc! (factor > 5 in D 2 ) (now use NE2001 distances throughout, but only such major discrepancy) Current implied efficiency in TeV band : ~ 7% PSR J 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 J 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 J –HESS J HESS J

Associations with possible PWNe in composite SNRs G : no pulsar detected, but consistent MWL plerion in shell HESS J / SNR G could show evidence for a central X-ray plerion in XMM-Newton observations [talk by S. Funk] HESS J may be associated with SNR G , revealed by XMM-Newton as a probable Crab-like SNR [poster by J. Combi et al.] HESS J appears associated with G (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. G ) 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?