H.E.S.S. Observations of Galactic Ɣ-ray sources

Transcription

1 H.E.S.S. Observations of Galactic Ɣ-ray sources Searching for the sources of Galactic Cosmic rays APC, 14 Dec 2012 A. Djannati-Ataï APC-CNRS

2 Outline HESS Galactic Plane Survey (GPS) A word on identifi cation issues Few words on Pulsar Wind Nebulae as fi lled bags The evolved PWN HESS J as a prototype Convective vs diffusive regimes Selection of new results on extended sources Hess J Hess J Hess J Summary and outlook

3 HESS Galactic Plane Survey More than 2300 h Covering : l Point-like sensitivity : better than 1.5 % C.U. in l [250, 65 ], b [ 3,+3 ] [320, 50 ] campaigns : more uniform exposure in core region l [282, 60 ] deepening of the exposure in region l [268, 282 ] More than 60 Galactic sources

4 Eger et al. 2011

5 2012

6

7 HESS Galactic Population

8 HESS Galactic Population Identifi cation issues No obvious counterpart in other wave-lengths inherent faint emission at other wave-lengths due to absence of any data Featureless morphology Source confusion : instrument PSF limit, dim sources : lack of statistics Identifi cation classes A) fi rmly established counterpart or clear morphology (e.g. Shell-type) + energy dependent morphology B) identifi ed or plausible counterpart(s) exist-s but further data needed to establish fi rmly the association or the type of emission in a coherent model C) no plausible counterpart known ( dark sources)

9

10 G / HESS J : a huge source... XMM-Newton G : X-ray PWN associated to PSR J A Vela-like pulsar at 4 kpc = erg/s ; P=101ms ; c=21 kyrs; 5' Asymmetric X-ray nebula : extended up to 5' South Assiciation to G diameter of ~ 34 pc: HUGE! HESS J : same asymmetry in -rays, but at much larger scale: ~1 diameter The pulsar is offset by ~14 pc from the -ray nebula c.o.g! 30' HESS

11 Identification : North-South Slices X-rays & TeV XMM-Newton G : X-ray PWN associated to PSR J A Vela-like pulsar at 4 kpc = erg/s ; P=101ms ; c=21 kyrs; Asymmetric X-ray nebula : extended up to 5' South Assiciation to G diameter of ~ 34 pc: 30' HESS J : same asymmetry in -rays, but at much larger scale: ~1 diameter The pulsar is offset by ~14 pc from the -ray nebula c.o.g! de Jager et al. 2006

12 Energy dependent morphology X-ray emitting electrons burn off quickly : synchrotron nebula is made of fresh particles Energy dependent TeV morphology: signature of IC emission of electrons (reverse dependance expected for hadronic emission) TeV emission: entails emission from relic electrons 30' de Jager, Funk et al. 2006

13 Toy time-dependent SED model Explains : TeV Energy dependent morphology TeV fl ux dominance over X-ray fl ux first 2000 yr last 2000 yr

14 Plerions (Pleres Plera or filled bag) [de Jager & Djannati-Ataï 2009] Most fundamental principle for PWNe fl ows : Confi ning pressure post shock pulsar wind slows down from relativistic ( ) to relatively low expansion velocities with V~radial The associated B is determined by : B~B e.g. ~toroidal fi eld [Kennel & Coronti 84] The cross-fi eld mean free path gyroradius It is quite hard for a particle to cross fi eld lines and overtake the convective fl ow through (perpendicular) diffusion fi lled bag PWNe expand convectively until pressure small enough for leakage same holds for ions

15 HESS J : a filled bag [Aliu & de Jager 2006] Advection or Convection time : Given resolved torus : ~15, dist ~4kpc, age~21 kyr if fl ow velocity behaves as ~1/r i.e. approximate size of the VHE nebula = PWN size A model independent constraint on gyroradius : [de Jager 2006] Application to J (R = 30'), 21 kyr : ρ >> cm N L much larger than the gyroradius for 1 TeV emitting electrons : Unlikely that diffusive fl ow dominates advection If some of HESS un-id's are PWNe, diffusion would spread them by a negligible amount relative to convective sizes, e.g. scaling the ~2 Vela-X PWN to 1 kpc would yield = 0.3 / kpc : much too large compared to expected diffusive size diff

16 Hess J Discovered through HESS GPS observations [Hess Collaboration, Ahraonian et al. 2008] Bright source at ~10% Crab Rather soft spectrum =2.7± 0.2 Close to the 36 ms PSR J de/dt= erg/s τ = yr c Feature-less morphology Offset wrt PSR ~0.15 Absence of any counterparts in radio to Xrays VHE emission interpreted as wind nebula of PSR J Effi ciency ~0.5% ok Characteristic age : a bit high, making it the oldest PWN GLIMPSE 8 μm

17 Hess J Deeper observations as part of the [ ] HESS GPS ~670 -rays 10.4 A clear shell morphology Discovery paper : only the brightest part [west] of the shell was seen Best fi t r=0.41, (l = 44.47, b=-0.15 ) Preliminary No signifi cant evidence of wind nebula emission Spectrum = 2.7± 0.2 consistent with discovery paper Morphologically similar to the 3 other complete shells : RXJ , RXJ (Vela Jr) HESS J But exhibits the softest spectrum Preliminary

18 X-rays VHE THE BIG FIVE THE BIG SIX?! HESS J th TeV shell-like SNR Vela Jr First SNR of this type discovered in VHE -rays?! RX J RCW 86 SN 1006 HESS J

19 Hess J Hess J Distance, physical size? Line of sight intersects : The inter-arm region Scutum-Sagittarius Inner Sagittarius [4-7] kpc RSNR~ [27-47] pc Association to PSR J ? dpsr~4.5 kpc RSNR ~30 pc Multi-TeV -rays suffi cient shock velocity needed low density ~0.1 cm-3 Age ~7 kpc PSR proj. velocity v~630 km/s IC emission (too low ) If association to PSR and dstance is correct : HESS J would be : the oldest and (one of?) farthest one of the largest and most luminous VHE shell up to now Its soft spectrum old SNR If closer than 4 kpc, size, age and luminosity would be more in line of the others. Name Dist. (Kpc) Diameter (pc) Age (ky) Lγ RXJ HESSJ (1) 6.8 (34) 0.4 (5) 0.26 (6.4) 2.24 RXJ HESSJ RCW 86 HESSJ SN 1006 HESSJ HESSJ HESS J (14) HESSJ ? 60? 7? 9.2? 2.7 (10^33 erg/s)

20

21

22 Population Study [Kargaltsev et al. 2012] 71 X-ray/TeV PWNe + candidates Geminga HESS J ??

23 Hess J HESS GPS + dedicated observations : 82 h SGR : Magnetar with Bsurface ~ G Spin period ~ 7.6 s p-dot ~7.5x10-10 s/s (but varying age ~ kyr d ~ 6 19 kpc x8) spin-down power Lsd ~ few x 1034 erg/s Magnetic dissip. energy ~ erg/s Many short/interm. fl ares erg/s Giant fl are ~1047 erg/s 27 Dec 2004 C : Massive stellar cluster (parent cluster of SGR ?) 4 x WR stars + luminous blue variable LBV combined stellar wind KE > 1038 erg/s Both associated to MC 13A Av ~ 10 ( NH ~ 2x1022 cm-2 ) [Kim&Koo 2002; Corbel etal 2004] Potential site for multi-tev particle acceleration TeV Search for transient & steady TeV emission

24 Hess J HESS GPS + dedicated observations : 82 h ~6 (pre-trial) at radio position (r<0.1 ) >7 (pre-trial) fi tted pos. (r<0.2 ) Extended source : 7.5' x 4' ( PSF) (~38 pc major axis at 8.7 kpc) Similar in scale to radio nebula Energetics TeV (r<0.2 ) : F ~ 1.3x10-12 erg/cm2/s LTeV~ 1.2x1034(d/8.7kpc)2 erg/s dn/de= N E- ph/cm2/s/tev N = 4.2 (± 0.5) x = 2.5(±0.2±0.2) Flux is steady at nightly & 30 min scales G Radio nebula Lradio ~few x1032 erg/s (d=8.7 kpc) Likely powered by LBV rather than SGR [Hurley etal 1999; Gaensler etal 2001; Kaplan etal 2002] Spitzer IR (rb=24/8 m)

25 Hess J / SGR Steady/Extended X-ray Emission Radius < few arcsec (unpulsed ~90-95%) PL index : -2, kt~10 kev 2-10 kev , kt~0.8 kev -1.7 [B-SAX Mereghetti etal 2000] 2-10 kev [XMM Mereghetti etal 2007] kev 2006/2007 [INTEG. Esposito etal 2007] Lx (2-10 kev) ~few x 1035 erg/s > ~ Lspin down No evidence for X-ray PWN; Radius < ~0.2 pc Extreme B-fi eld PWN short-lived (few yrs) and small. Other magnetar PWN: 1E ? [Yes - Vink etal 2009, No - Olausen etal 2011] Pulsar-powered? Magnetically-powered? Spin-down power : Lsd ~ 3 to 6 x1034 erg/s LTeV/Lsd ~ 0.2 to 0.3 Magnetic dissipation (reconnection) power (e.g. Zhang 2009) : LB ~ 1035 to 36 erg/s LTeV/LB ~ 0.01 TeV luminosity from spin-down possible but magnetic dissipation power clearly available

26 Hess J Massive Star Cluster C [Figer etal 2005] 4 x WR stars; 4 x O stars Lum. Blue Variable (LBV) : LBV (similar to Pistol star, h-car) Cluster wind KE LKE > 1038 erg/s LTeV/LKE < 10-4 Stellar cluster origin possible through windwind/ism interactions dominated by LBV and/or WRs? Other possibilites : candidate counterparts for TeV sources : WR/O/B clusters : Cyg-OB2, Wd1,Wd2(partially) Molecular cloud MC13A : If hadronic processes at play : need CR enhacement factor ~ 590 for 8.7 kpc.

27 HESS J Published fi rst in 2005 as part of 2004 HESS GPS Total observations : ~45 hr live-time Complex fi eld with 2 PWNe seen in X-rays PSR J : Discovered in 2008 [Gotthelf et al] A 23 kyr young pulsar Spin period ~ 70.5 ms Edot ~5.5x1036 erg/s Enough to power the whole TeV source 0.08 offset V ~350 (d/6.5 kpc) km/s psr

28 HESS J Published fi rst in 2005 as part of 2004 HESS GPS Total observations : ~45 hr live-time Complex fi eld with 2 PWNe seen in X-rays PSR J : Discovered in 2008 [Gotthelf et al] A 23 kyr young pulsar Spin period ~ 70.5 ms Edot ~5.5x1036 erg/s Enough to power the whole TeV source 0.08 offset V ~350 (d/6.5 kpc) km/s psr Source is copmposite : A second point-like source to the South Remains Un-Id

29 Hess-II First light 26 July 2012 Reflector : 32.6 m by 24.3 m : equivalent to 28 m Focal length : 36 m 875 hexagonal facets of 90 cm Camera : 3.2 f.o.v /4 photo multipliers; /pixel weight : 2.8 tons Total weight : 580 tons Operation modes : Mono : < 50 GeV < Stereo Commissioning phase ongoing Stay tuned on : Pulsars PSR B , Vela Psr,... AGNs...

30

31 Summary Recent exciting identifi cations & discoveries through deeper HESS GPS : HESS J better morphology : It is a shell! Distance? [4-7] kpc DSNR~ [27-47] pc If associated to PSR J : 4.5 kpc But revise Pulsar age Age? Multi-TeV -rays age < ~ 104 yr No counterparts known at other wavelengths : The fi rst TeV discovered SNR shell?! HESS J : LTeV ~ 1034 (d/8.7kpc)2 erg/s towards SGR / C First clear sign of multi-tev particle acceleration towards these objects : Electrons and/or cosmic-rays? not clear Source of energy? magnetar/pulsar spindown? B-fi eld dissipation-powered? Stellar cluster winds (LBV, WRs..)? SNR? Possibly new type of multi-tev particle accelerator knowing that there are other AXPs/SGRs towards TeV sources: e.g. Westerlund 1; CTB37B [Halpern etal 2010] Better view of HESS J : two sources Discussion on diffusion vs convection : Unlikely that diffusive lf ow dominates advection If some of HESS un-id's are PWNe, diffusion would spread them by a negligible amount relative to convective sizes

32 Outlook +30 dark/uid sources still are to be identifi ed : For PWNe VHE detections imply particle dominated nebula ( _tot <<1) Synchrotron losses are low expect bright IC nebulae + under luminous X-ray PWN effect might be amplifi ed if rapid expansion of PWN (high Edot) + OB excavated environment Other Shell-type SNRs expected to pop-up Some of Large Un-Id VHE sources are expected to be resolved with more data/next generation of telescopes