SNR Francesco Longo University and INFN, Trieste, Italy francesco.longo@tsfn.it

1. SNR Francesco Longo University and INFN, Trieste, Italy francesco.longo@ts.infn.it Slides from Diego Torres (Livermore) In collaboration also with M.Ajello (Monaco) and R.Rando (Padova)

2. Raggi Cosmici Galattici e SNR

3. Synchrotron radiation e g p0 p g SNR al GeV • SNR rivelabili tramite IC, Bremsstrahlung e decadimento del π0 • Flusso atteso -> ~ 10-7 ph cm-2 s-1 • Fondo diffuso -> ~ 10-7 ph cm-2 s-1 SNRdifficili da rivelare protons, electrons Shock front Molecular cloud

4. Origine dei CR in astronomia gamma • Trovare traccia d’interazione adronica nello spettro di una sorgente • Nessuna sorgente del III Catalogo EGRET mostra tale caratteristica • Esiste prova della propagazione dei CR-adronici, ma non della loro accelerazione

5. Propagazione dei raggi cosmici Spettro da decadimento del П0 Spettro del piano galattico Spettro da decadimento di 0

6. Possibilità di rivelare SNR al GeV • Canale adronico incrementato ! • FSNR ~ ρISM Fnubi ~ εCR = 1eV/cm3 • Nubi vicino SNR εCR>> 1eV/cm3  canale adronico incrementato • R= CO(J=2->1)/CO(J=1->0) • R~0.7, ma R2.5 per nubi eccitate Nube SNR

7. Sorgente TeV rivelata da CANGAROO Sorgente GeV rivelata da EGRET Nube in interazione col residuo Residuo di supernova rivelato in X da ASCA Osservazione multi-banda • SNR RX J1713.7-3946

8. Synchrotron radiation protons, electrons e g Shock front p0 p g Molecular cloud Where to produce gamma in the galaxy? Nearby molecular clouds can provide targets for ions accelerated at the SNR shock. Gamma-rays are then produced by neutral pion decay pointing out the production of hadronic cosmic rays (e.g. Aharonian et al. 1994: A&A 285, 645).

9. Gamma SNR? CRs below the “knee” are thought to be accelerated at supernova remnats (Syrovatskii 1953). There, charged particles would be accelerated by Fermi mechanism operating at the strong blast wave shock (Bell 1978). Synchrotron emission detected from radio to X-ray energies in SNRs clearly shows the presence of TeV leptons in these sources. Direct emission from locally accelerated hadrons, on the contrary, cannot be observed. Since CRs are deflected by the galactic magnetic field, they do not preserve the information on the location of their source. We must, consequently, look for electromagnetic signatures produced by the protons and ions during their accleration.

10. A case by case analysis • A case by case analysis is needed for each SNR-EGRET source coincident pair. • There should be, nearby, enhancements of molecular material that could act as target for accelerated protons. • This material, then, must be excited by the shock. • Leptonic processes and other candidate sources must be discarded as the origin of the gamma-ray radiation. Torres et al. astro-ph/0209565, Supernova Remnants and gamma-ray sources, Review for the Physics Reports (2002)

11. The most interesting case? [G347.3-0.5] • Positional coincidence of the non-variable EGRET gamma-ray source, 3EG J1714-3857, with a very massive (~3×105 solar masses) and dense (~500 nucleons cm-3) molecular cloud… • This molecular cloud is interacting with the X-ray and TeV gamma-ray emitting SNR G347.3-0.5… • The cloud region is near the shell of the SNR, and shines at GeV, but it is of low radio and X-ray brightness… Initial discussion: Butt, Torres, et al. ApJ Letters, 562, 167 (2001) Recent results: Butt, Torres, et al., Nature 418, 499 (2002)

12. Molecular environment of the SNR G347.3-0.5 Total molecular column density over a wide section of the fourth Galactic quadrant around G347.3-0.5. The lowest contour is well above the instrumental noise (9s) to emphasize the relatively low molecular column density toward the SNR. The clouds that seem to interact with it are pushed away as a cause of the blast wave shock Slane et al. ApJ 525, 357 (1999)

13. More precise indication of interaction with molecular material The distribution of 781 line intensity ratios, R={CO(J=21)/CO(J=10)}, measured every 15′ in the region from l=346.5348.5; b= -0.5+0.5, and averaged over 5km/sec bins of velocity between vlsr= -150 km/sec  +50 km/sec. The mean of the distribution, ~0.72, agrees with the average unexcited value in the Galactic plane. The cloud however, show values 3s above that value. Top 0.5% of all values measured. All other bins with high R are well outside the 3EG field

14. The complete panorama for SNR G347.3-0.5 ROSAT X-ray contours. Emission from the bulk of the SNR rim can be seen with particular enhancements along the west/northwest regions, where bright non-thermal radio emission is also seen. The total radio flux is well below 10 Jy, Slane et al. ApJ 525, 357 (1999) Red depicts the TeV significance contours. The flux was (5.3 ± 0.9 [statistical] ± 1.6 [systematic]) x 10-12 photons cm-2 s-1 (at E>1.8 ± 0.9 TeV). Muraishi et al. AA354, L57 (2000). While electrons give rise to the bulk of the non-thermal radio, X-ray and TeV emission in the NW, the CR protons and ions are exposed at GeV energies via their hadronic interactions in the dense material of cloud A, leading to pion gamma-decay GeV emission in the NE.

15. The gamma-ray luminosity The expected g-ray flux at Earth coming from the SNR is (Drury et al. 1994), ESNis the energy of the SN in ergs, q is the fraction of the total energy of the explosion converted into CR energy, and nand d are the number density and distance. In most cases, this flux is far too low to be detected by EGRET, but the existence of massive clouds in the neighborhood can enhance the emission Here M is the mass of the cloud in thousands of solar masses, k is the CR enhancement out of the usual emissivity (~2.2 10-25 s-1 H-atom-1).

16. The gamma-ray luminosity • We have calculated the expected gamma-ray luminosity using the following information: • explosion energy = (1.7-2.2)×1051 ergs • distance to the SNR = 6.3 ± 0.4 kpc • unshocked ambient density, no= 0.01-0.3 cm-3 • The mass of Cloud A, centered at (l,b)=(347.9,-0.25), is ~3×105 Mo and its mean density ~500 nucleons cm-3. • The total gamma-ray luminosity is: • Ftot(E>100MeV) = Fsnr(E>100MeV) + Fcloud A(E>100MeV) • The cosmic ray enhancement factor, ks is computed to be in the range 30-40. • Then, Ftot(E>100MeV) = (4-7) ×10-7 photons cm-2 sec-1 , with the contribution of Cloud A dominating the GeV flux by over 2 orders of magnitude. This predicted flux is fully consistent with the measured value: (4.36 ± 0.65)×10-7 photons cm-2 s-1. (Ellison et al. 1999)

17. Schlickheiser 1982 The gamma-ray spectrum: consistent with hadronic production The spectrum of the EGRET source The single power-law fit (G=-2.3) through all points (solid black line) is not at ease with the enhancement at 50-70 MeV. This feature is consistent with the long-sought SNR neutral pion gamma-decay resonance centered at 67.5 MeV. The red curve is an expected spectrum due to hadronic CR interactions. As Schlickeiser has pointed out, the bremsstrahlung from secondary electrons due to the decay of hadronically produced charged pions, p± ’s, will contribute significantly at energies lower than ~70 MeV. However: deviation from other points is less than 3s. Must yet be Confirmed.

18. One thing is sure: GeV emission is not leptonic The electron flux needed to explain the GeV emission via e- bremsstrahlung in the cloud material should also produce an enhanced synchrotron radio emission. The expected ratio of GeV bremsstrahlung flux to radio synchrotron flux is: Measured from TeV obs.. Measured from CO obs. Observed by EGRET Frequency of observations This is what we want: radio flux prediction if the flux is leptonic Spectral index

19. One thing is sure: GeV emission is not leptonic II The synchrotron radio spectrum which would be expected from Cloud A, under the assumption that the GeV flux were due to electron bremsstrahlung. Since this spectrum violates the observed upper limit (blue) by a factor of 20 at 843 MHz, we rule out a predominantly electronic origin of the GeV luminosity. (An assumed low frequency turnover at ~100 MHz is shown by the red dotted line.) Observed upper limits

20. No other plausible candidate in the 3EG field • There are two recently discovered pulsars within the 95% confidence location contours of 3EG J1714-3857: PSR J1715-3903 and PSR J1713-3844 • Their spin down luminosity is such that they cannot contribute significantly to the observed gamma-ray emission (Torres et al. ApJ Letters, 560, 155, 2001). • Two other SNRs within the EGRET 95% contours: CTB37A&B. They can both be ruled out as strong gamma-ray emitters because of their large distance (11.3 kpc) and the low density medium around them • No WR or Of massive stars in the field, no X-ray binaries or black hole candidates Torres et al. ApJ Letters, 560, 155, 2001

21. Summary • Strong hints that the blast wave shock of SNR G347.3-0.5 is a site of hadronic cosmic ray acceleration • TeV cosmic ray electrons are accelerated in this SNR; • the abutting cloud material is extremely excited; • the cloud region is of low radio and X-ray brightness; • the GeV flux is non-variable and in agreement with that expected from po gamma-decays; • the spectral index is as expected for an hadronic CR source population • there are no other candidate GeV sources within the 95% location contours of 3EGJ1714-3857

22. Resolving the region of gamma-ray emission

23. pulsar Nube molecolare Emissione composita

24. Analisi dei profili Profilo in longitudine Profilo in latitudine

25. Sottrazione Fondo diffuso Conteggi Analisi dei profili (IIb)

26. Conclusions There is a clear hint of an unambiguous connection between unidentified EGRET sources and SNRs. This will lead to the observational definite proof that TeV protons are acelerated in SNR shocks. It is at least plausible that EGRET has detected distant (more than 6 kpc) SNRs. There are 5 coinciding pairs of 3EG sources and SNRs for which the latter apparently lie at such high values of distance and for all these cases, we have uncovered the existence of nearby, large, in some cases giant, molecular clouds that could enhance the GeV signal trough pion decay. AGILE and GLAST, would greatly elucidate the origin for these 3EG sources, since even a factor of 2 improvement in resolution would be enough to favor or reject the SNR connection. Torres et al. astro-ph/0209565, Supernova Remnants and gamma-ray sources, Review for the Physics Reports (2002) Butt, Torres, Romero, Dame, & Combi, Nature 418, 499 (2002)