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F.Longo SNR 1 GLAST LAT GLAST Italian SW meeting 11 march 2004 SNR Francesco Longo University and INFN, Trieste, Italy Slides.

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Presentation on theme: "F.Longo SNR 1 GLAST LAT GLAST Italian SW meeting 11 march 2004 SNR Francesco Longo University and INFN, Trieste, Italy Slides."— Presentation transcript:

1 F.Longo SNR 1 GLAST LAT GLAST Italian SW meeting 11 march 2004 SNR Francesco Longo University and INFN, Trieste, Italy Slides from Diego Torres (Livermore) In collaboration also with M.Ajello (Monaco) and R.Rando (Padova)

2 F.Longo SNR 2 GLAST LAT GLAST Italian SW meeting 11 march 2004 Raggi Cosmici Galattici e SNR

3 F.Longo SNR 3 GLAST LAT GLAST Italian SW meeting 11 march 2004 SNR al GeV SNR rivelabili tramite IC, Bremsstrahlung e decadimento del π 0 Flusso atteso -> ~ ph cm -2 s -1 Fondo diffuso -> ~ ph cm -2 s -1 SNR difficili da rivelare Shock front Molecular cloud protons, electrons Synchrotron radiation e p

4 F.Longo SNR 4 GLAST LAT GLAST Italian SW meeting 11 march 2004 Origine dei CR in astronomia gamma Trovare traccia dinterazione 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 F.Longo SNR 5 GLAST LAT GLAST Italian SW meeting 11 march 2004 Spettro da decadimento del П 0 Propagazione dei raggi cosmici Spettro da decadimento di 0 Spettro del piano galattico

6 F.Longo SNR 6 GLAST LAT GLAST Italian SW meeting 11 march 2004 Possibilità di rivelare SNR al GeV Canale adronico incrementato ! F SNR ~ ρ ISM F nubi ~ ε CR = 1eV/cm 3 Nubi vicino SNR ε CR >> 1eV/cm 3 canale adronico incrementato R= CO(J=2->1)/CO(J=1->0) R~0.7, ma R 2.5 per nubi eccitate SNR Nube

7 F.Longo SNR 7 GLAST LAT GLAST Italian SW meeting 11 march 2004 Osservazione multi-banda SNR RX J Sorgente GeV rivelata da EGRET Nube in interazione col residuo Sorgente TeV rivelata da CANGAROO Residuo di supernova rivelato in X da ASCA

8 F.Longo SNR 8 GLAST LAT GLAST Italian SW meeting 11 march 2004 Where to produce gamma in the galaxy? Shock front Molecular cloud protons, electrons Synchrotron radiation e p 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 F.Longo SNR 9 GLAST LAT GLAST Italian SW meeting 11 march 2004 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. Gamma SNR?

10 F.Longo SNR 10 GLAST LAT GLAST Italian SW meeting 11 march 2004 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/ , Supernova Remnants and gamma-ray sources, Review for the Physics Reports (2002)

11 F.Longo SNR 11 GLAST LAT GLAST Italian SW meeting 11 march 2004 The most interesting case? [G ] Positional coincidence of the non-variable EGRET gamma-ray source, 3EG J , with a very massive (~3×10 5 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 G … 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 Slane et al. ApJ 525, 357 (1999) The clouds that seem to interact with it are pushed away as a cause of the blast wave shock Total molecular column density over a wide section of the fourth Galactic quadrant around G The lowest contour is well above the instrumental noise (9 ) to emphasize the relatively low molecular column density toward the SNR. Molecular environment of the SNR G

13 F.Longo SNR 13 GLAST LAT GLAST Italian SW meeting 11 march 2004 The distribution of 781 line intensity ratios, R={CO(J=2 1)/CO(J=1 0)}, measured every 15 in the region from l= ; b= , and averaged over 5km/sec bins of velocity between v lsr = -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 3 above that value. More precise indication of interaction with molecular material Top 0.5% of all values measured. All other bins with high R are well outside the 3EG field

14 F.Longo SNR 14 GLAST LAT GLAST Italian SW meeting 11 march 2004 The complete panorama for SNR G 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 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 F.Longo SNR 15 GLAST LAT GLAST Italian SW meeting 11 march 2004 The expected -ray flux at Earth coming from the SNR is (Drury et al. 1994), E SN is the energy of the SN in ergs, is the fraction of the total energy of the explosion converted into CR energy, and n and 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 (~ s -1 H-atom -1 ). The gamma-ray luminosity

16 We have calculated the expected gamma-ray luminosity using the following information: explosion energy = ( )×10 51 ergs distance to the SNR = 6.3 ± 0.4 kpc unshocked ambient density, n o = cm -3 The mass of Cloud A, centered at (l,b)=(347.9,-0.25), is ~3×10 5 M o and its mean density ~500 nucleons cm -3. The total gamma-ray luminosity is: F tot (E>100MeV) = F snr (E>100MeV) + F cloud A (E>100MeV) The cosmic ray enhancement factor, k s is computed to be in the range Then, F tot (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) The gamma-ray luminosity

17 The single power-law fit ( =-2.3) through all points (solid black line) is not at ease with the enhancement at 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, ± s, will contribute significantly at energies lower than ~70 MeV. Schlickheiser 1982 The spectrum of the EGRET source The gamma-ray spectrum: consistent with hadronic production However: deviation from other points is less than 3 ust yet be Confirmed.

18 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 CO obs. Measured from TeV obs.. Frequency of observations Spectral index Observed by EGRET This is what we want: radio flux prediction if the flux is leptonic One thing is sure: GeV emission is not leptonic

19 F.Longo SNR 19 GLAST LAT GLAST Italian SW meeting 11 march 2004 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 One thing is sure: GeV emission is not leptonic II

20 F.Longo SNR 20 GLAST LAT GLAST Italian SW meeting 11 march 2004 No other plausible candidate in the 3EG field There are two recently discovered pulsars within the 95% confidence location contours of 3EG J : PSR J and PSR J 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 F.Longo SNR 21 GLAST LAT GLAST Italian SW meeting 11 march 2004 Strong hints that the blast wave shock of SNR G 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 o 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 3EGJ Summary

22 Resolving the region of gamma-ray emission

23 F.Longo SNR 23 GLAST LAT GLAST Italian SW meeting 11 march 2004 Emissione composita pulsar Nube molecolare

24 F.Longo SNR 24 GLAST LAT GLAST Italian SW meeting 11 march 2004 Analisi dei profili Profilo in longitudine Profilo in latitudine

25 F.Longo SNR 25 GLAST LAT GLAST Italian SW meeting 11 march 2004 Analisi dei profili (IIb) Conteggi Fondo diffusoSottrazione

26 F.Longo SNR 26 GLAST LAT GLAST Italian SW meeting 11 march 2004 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/ , Supernova Remnants and gamma-ray sources, Review for the Physics Reports (2002) Butt, Torres, Romero, Dame, & Combi, Nature 418, 499 (2002)


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