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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?