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High energy emission from supernova remnants and regions of star formation Diego F. Torres Lawrence Livermore Lab. California,

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Presentation on theme: "High energy emission from supernova remnants and regions of star formation Diego F. Torres Lawrence Livermore Lab. California,"— Presentation transcript:

1 High energy emission from supernova remnants and regions of star formation Diego F. Torres Lawrence Livermore Lab. California, 94550, USA

2 Summary SNRs SNRs  EGRET sources and SNRS  GLAST/MAGIC prospects  SNRs searched at TeV energies with HESS Unidentified gamma-ray sources at TeV Unidentified gamma-ray sources at TeV  Multiwavelength information  Possible ideas for an explanation  Star forming galaxies at TeV  Modeling for Arp 220 with Q-diffuse  : not within this talk. (Torres et al. ApJ Letters 601, 75, 2004)

3 Gamma-rays from Supernova Remants Torres et al. Physics Reports 382, 303, 2003 and references therein + some new results, especially Aharonian et al.’s from HESS

4 Spectrum of cosmic rays The bulk of CRs occurs with energies below the knee and are thought to come from our own galaxy.

5 Accelerated electrons, ok. Accelerated protons? Cassiopeia ACrab Shock front Molecular cloud protons, electrons Synchrotron radiation e p    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 acceleration.

6 Spatially coincident pairs of SNRs and unidentified EGRET sources

7 Identifying the pairs

8 Spatially coincident pairs of SNRs and unidentified EGRET sources Data contained in the3EG

9 Spatially coincident pairs of SNRs and unidentified EGRET sources Variability Variability indices

10 Spatially coincident pairs of SNRs and unidentified EGRET sources Variability Some of the sources are variable. Not related to SNRs

11 3EG J Big variations in the measured flux for adjacent viewing periods. Romero, Torres et al. A&A, 376, 599, 2001 Anchordoqui, Torres, et al. ApJ, 2003  neutrino yield detectable at Earth!

12 High Resolution radio map of the nearby star LS 5039 obtained with VLBA and VLA in phased array mode (similar to a single dish of 115m) at 6 cm. The presence of radio jets is the main evidence supporting its microquasar nature. Contours shown go from 6-50 times mJy per beam, the rms noise. The map is centered at the star position. 1 milliarcsec is equivalent to 3AU (~10 13 cm) for a distance of 3kpc. 3EG J Paredes et al. Science 288, 2340

13 Spatially coincident pairs of SNRs and unidentified EGRET sources Known data for the SNRs From Torres et al. 2003, Physics Reports

14 Most plausible cases appear to present broad correlations Torres et al. 2004, Adv. In Space Physics

15 The GeV future RX J (Pulsar) W66

16 SN1006 – the prototype ? CANGAROO 1997 – the small single telescope observations but H.E.S.S Some recent results from HESS

17 ) The panorama for SNR G (RX J ) 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.

18 1st SNR at TeV energies ! SNR RX J has all the ingredients: extreme X-ray bright, EGRET source nearby, dense molecular cloud region Butt et al Aharonian et al. Nature October 2004 But...

19 evidence for hadronic particle acceleration in SNRs still unclear. -> SNR RX J Enomoto et al (Nature) IC interpretation in conflict with data Butt, Torres et al (Nature), Reimer & Pohl 2002 (A&A)  0 interpretation in conflict with data, too ! Interpretation still in doubt...

20 Partial Summary SNRs are TeV sources! (Even using Whipple criterion – accepting observations by CANGAROO on G ) SNRs are TeV sources! (Even using Whipple criterion – accepting observations by CANGAROO on G ) Thus, evidence suggests that some of them should also be GeV sources, and all theoretical models for GLAST and MAGIC energy ranges await testing. Thus, evidence suggests that some of them should also be GeV sources, and all theoretical models for GLAST and MAGIC energy ranges await testing. Proton acceleration up to TeV energies yet awaits testing. Proton acceleration up to TeV energies yet awaits testing.

21 Gamma-rays from Luminous and Ultra Luminous Infrared Galaxies Torres, Reimer, Domingo, Digel ApJ Letters, 607, (2004) Torres  Arp 220 ApJ, 617, 966 (2004) Cillis, Torres & Reimer 2005 ApJ in press

22 Gamma-ray emission from the interstellar medium   High-energy gamma-rays are produced in cosmic-ray interactions with interstellar gas and photons   Cosmic-ray production is associated with regions of massive star formation (e.g., SNRs, colliding OB stellar winds)   This represents approximately 90% of the high-energy gamma-ray luminosity of the Milky Way (~10 6 solar) ~60% of all EGRET gamma-rays were diffuse emission from the Milky Way

23 Diffuse emission from external galaxies  Only one other external galaxy detected in the light of its diffuse emission – LMC  The problem is distance: Milky Way at 1 Mpc would have a flux of about 2.5 x cm -2 s -1 (>100 MeV), well below EGRET’s detection limit LMC (1.9 ± 0.4) x cm -2 s -1 EGRETIRAS 30 Doradus: extensive massive SFR and molecular clouds

24 Nearby Starbursts: Upper limits with EGRET data [Akyuz et al. 1992, Volk et al. 1996, Paglione et al. 1996, Bloom et al. 1999] 10 starbursts selected by distance (<10Mpc), Infrared luminosity (>10 9 L solar ) at latitudes |b|>10. Bloom et al NGC 253 Average M82 Energy [MeV] Flux [photons cm -2 s -1 MeV -1 ]

25 Left: Time-evolution of a galactic encounter, viewed along the orbital axis. Here dark halo matter is shown in red, bulge stars are yellow, disk stars in blue, and the gas in green. Barnes and Hernquist 1996: merging of gas-rich galaxies Right: showing only gas in both galaxies

26 Almost all ULIRGs seems to be double or interacting [review on LIRGs and ULIRGs: Sanders and Mirabel, ARA&A, 1996] Only one within the 100 Mpc sphere [Arp 220] And there are tens of LIRGs (luminosities >10 11 L SUN ): detectability depends on the combined effect of distance and starburst activity.

27 MW CR Enhancement required for detectability/LAT Detectability of LIRGs Gamma-ray detectability is favored in starburst galaxies (Akyuz, Aharonian, Volk, Fichtel, etc) Gamma-ray detectability is favored in starburst galaxies (Akyuz, Aharonian, Volk, Fichtel, etc) Large M, with high average gas density, and enhanced cosmic ray density Large M, with high average gas density, and enhanced cosmic ray density Recent HCN-line survey of Gao & Solomon (2004) of IR and CO-bright galaxies, and nearby spirals Recent HCN-line survey of Gao & Solomon (2004) of IR and CO-bright galaxies, and nearby spirals Allows estimate of SFR (from HCN luminosity) and minimum required k for detection by LAT and IACTs (from HCN + CO intensities and distance) Allows estimate of SFR (from HCN luminosity) and minimum required k for detection by LAT and IACTs (from HCN + CO intensities and distance) Several nearby starburst galaxies and a number of LIRGs and ULIRGs are plausible candidates for detection Several nearby starburst galaxies and a number of LIRGs and ULIRGs are plausible candidates for detection

28 Arp 220  The best studied and nearest ULIRG (72 Mpc)   Arp 220’s center has two radio-continuum and two IR sources, separated by ~1 arcsec (e.g., Scoville et al. 1997, Downes et al. 1998, Soifer et al. 1999, Wiedner et al. 2002).   The two radio sources are extended and nonthermal (e.g., Sopp & Alexander 1991; Condon et al. 1991; Baan & Haschick 1995), and likely produced by supernovae in the most active starforming regions.   CO line, cm, mm-, and sub-mm continuum (e.g., Downes & Solomon 1998) as well as recent HCN line observations (e.g., Gao & Solomon 2004a,b) are all consistent with these two sources being sites of extreme star formation and having very high molecular densities.  Other less luminous candidates –if closer- can be detected.

29 Downes & Solomon 1998, Gao & Solomon 2004 Arp 220 ~350 pc

30 Arp 220: Geometry

31 Arp 220: Supernova explosion rates 18 cm VLBI (3 x 8 milliarcsec resolution) continuum imaging of Arp 220 has revealed the existence of more than a dozen sources with mJy fluxes (Smith et al. 1998), mostly in the western nucleus. In November 2002, new observations with VLBI revealed 30 supernova remnants candidates, 20 in the western, and 10 in the eastern nucleus. All, the previous result, models of the nuclei using Starburst99 (Shioya et al. 2001); and relationships between the infrared luminosity and the rate of supernova explosions (Van Buren et al. 1994, Manucci et al. 2003) suggest that the rate is ~2 yr ( ! ) This rate is ~300 times larger than the largest of the Local Group Galaxies (M31: ~0.9 SN/century) 7 hours, 17 telescopes. Size of the sources ~0.1 pc No single compact, central core, as in AGNs High brightness argues for non-thermal origin

32 High energy emission computed from first principles   Q-DIFFUSE set implements   Spectral computation of secondary and tertiary particles and their emissions at different frequencies (pions, muons, electrons, positrons, neutrinos)   Solution of the diffusion-loss equation => steady population of particles   Radio emission through synchrotron and free emission of primary and secondary electrons   Free-free absorption processes   IR and FIR spectra through the dust emissivity   Gamma-emission through Brem, IC, of the primary and secondary populations and pion decay (emission of the steady distributions)   Minimize the set of assumptions, relate them to observations Q-DIFFUSSE

33 SN rate, mass, density, & IR luminosity Injection proton and electron spectrum, diffusion/escape timescales diffusion-losses: steady spectrum of protons & electrons Secondary production: knock-on process, neutral and charged pion decay Synchrotron, IC, Bremsstrahlung, Pion Decay. Absorption of gamma-rays, opacities, eq. of radiation transport. Model predictions from radio to IR with emission of secondaries, FIR with emission of dust. Parameter fixing: B-field. Model Predictions at high energy: gamma-rays, cosmic- ray & neutrino fluences. Comparison with corresponding sensitivities of RXTE, INTEGRAL, GLAST, ICECUBE, MAGIC, HESS at each energy band. 2 nd and 3 rd generation of particles is computed with the steady spectrum of protons. Electron and positron sources taken into account to define the steady steady electron distribution Q-DIFFUSSE Observational measurements The slope for the injection spectrum for protons and electrons is assumed. The normalization is defined by the SNR rate. Computed without further assumptions The model reproduces the FIR emission with dust emissivity, and uses it + the CMB for computing losses. The magnetic field is defined by requiring that the synchrotron- free free emission of the steady population of electrons matches observations.

34 IR-FIR luminosity of Arp 220 Blackbody optical contribution Non-thermal radio contribution the FIR emission is modelled by dust, having an emissivity law proportional to Radiation is coming from each of the components of Arp 220, assuming that it is radiated with a single temperature and emissivity law. The model (sum of the three contributions) derived to fit the data (  = 1.5, T = 42.2 K) simple & conservative model avoids model degeneracies by increasing the number of free parameters

35 Steady distribution of protons in each of the components of Arp 220. Example for a steady distribution of electrons and positrons in a western-like starburst (with B = 10 mG). The contribution to the total steady distribution of the primary and secondary electrons and positrons is separately shown. The horizontal rectangle shows the region of electron kinetic energies where the steady distribution of secondary electrons is larger than that of the primary electrons. It is in this region of energies where most of the synchrotron radio emission is generated.

36 Radio emission of the steady population of electrons EAST WEST DISK Infrared With the magnetic field strength given in the Table and the relativistic steady state populations of previous Figures, only the molecular disk is in magnetic energy equipartition. Lines are not fits to the data but predictions of the model for a particular choice of parameters.

37 Now we have the steady population of electrons and positrons and the IR dust emission that is in agreement with all observations & with that population we compute the gamma-ray flux EGRET upper limits The emissivity of high energy photons is the largest in the western extreme starburst, the most active region of star formation. The differential flux, shown in the right panel without considering absorption effects, shows the influence of volume. The disk flux is the largest, and the nuclei are now subdominant. Nevertheless, only the western starburst provides more than one fourth of the total flux

38 Opacities to gamma-ray escape in the different components of Arp 220 as a function of energy. At the highest energy, the opacity is dominated by  processes, whereas  Z dominates the opacity at low energies. Significant opacities are only encountered above 1 TeV. The inset shows the total, and the contributions to the total opacity, in the case of the western nucleus of Arp 220 for this range of energy. The equation of radiation transport is solved to compute the predicted fluxes taking into account all absorption processes.

39 Results for integrated gamma-ray fluxes are: This would make Arp 220 observable for GLAST and VERITAS/HESS/MAGIC telescopes. The latter would need < 100 hours to detect it. Be aware of cross sections for pion decays above 1 TeV. Proof of concept beyond ARP 220 detectability itself: LIRGs well within the 100 Mpc sphere should be TeV sources!

40 Summary  LIRGs and ULIRGs, following simple population analysis, are to be detected as gamma-ray sources  Starburst activity – cosmic ray populations – difussion  Detailed analysis for ULIRG Arp 220 confirms this. Many other LIRGs (several tens) may appear in the forthcoming catalogs  first multiwavelength analysis of Arp 220 (the strongest site of star formation known, the nearest ULIRG)  first estimation of the magnetic field – compatible with Zeeman splitting measurements in Galactic active star forming sites  observations with GLAST & Cherenkov telescopes are possible  IC hard X-ray emission in the model were also computed and found in agreement with OSSE and RXTE upper limits  EBL do not affect photon propagation once gamma-rays leave the galaxy (very low redshift)

41 Thank you.

42 Scoville et al. 1997: Arcsec imaging of CO emission Integrated intensity map for the brightest CO (2-1) components peaks at the positions of the near-infrared nuclei, indicated by the + symbols.

43 Losses for protons and electrons: example D. F. Torres 2004

44

45

46 Arp 220: Geometry 1.6 GHz OH emission. The grayscale is continuum and the boxes are line observations done with MERLIN (Rovilos et al. 2003)

47

48 , COS-B, orbit resulted in a large and variable background of charged particles, ~200,000 γ-rays. Context: The evolution of the gamma-ray sky , EGRET, large effective area, good PSF, long mission life, excellent background rejection, and >1.4 × 10 6 γ-rays Unidentified sources: 120 at high latitudes, 80 at low (|b|<10) latitudes. 66 Possible gamma- ray active galactic nuclei pulsars. D. F. Torres 2004

49 Simulated LAT maps (>100 MeV, >1 GeV, 1 yr). More than point sources. Simulations by Seth Digel Future surveys (with GLAST) D. F. Torres 2004

50 The multi-messenger context & the evolution of the sensitivity From S. Ritz From Torres & Anchordoqui 2004 Complementary Capabilities D. F. Torres 2004

51 Perhaps the main discovery in the EGRET era… Diversity of high-energy gamma-ray sources Variability: the more direct way to acknowledge the existence of several different gamma-ray sources *Clearly defined variable and non-variable sources *No correlation with sky position Possible Galactic Sources: -Pulsars, Plerions and SNRs (NV) -Isolated Black holes, X-ray binaries, microquasars (V) -Stars (?) Possible Extragalactic Sources: -AGNs (V), Radiogalaxies (?) -Clusters of galaxies (NV) -Regions of star formation, starbursts and ULIGS (NV) D. F. Torres 2004

52 Gamma-ray emission from the interstellar medium   High-energy gamma-rays are produced in cosmic-ray interactions with interstellar gas and photons   Cosmic-ray production is associated with regions of massive star formation (e.g., SNRs, colliding OB stellar winds)   This represents approximately 90% of the high-energy gamma-ray luminosity of the Milky Way (~10 6 solar) ~60% of all EGRET gamma-rays were diffuse emission from the Milky Way

53 Diffuse emission from external galaxies  Only one other external galaxy detected in the light of its diffuse emission – LMC  The problem is distance: Milky Way at 1 Mpc would have a flux of about 2.5 x cm -2 s -1 (>100 MeV), well below EGRET’s detection limit LMC (1.9 ± 0.4) x cm -2 s -1 EGRETIRAS 30 Doradus: extensive massive SFR and molecular clouds

54 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… Butt et al. ApJ Letters, 562, 167 Butt et al., Nature 418, 499 Enomoto et al., Nature 416, 823 Reimer & Pohl, A&A 390, L43 Torres et al. Phys. Rept. 2003

55 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 Slane et al. ApJ, 1999

56 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 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. 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

57 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.

58 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

59 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 However: deviation from other points is less than 3  ust yet be Confirmed.

60 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 GeV emission is not leptonic Violates the observed upper limit by a factor of 20 at 843 MHz.

61 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. Two other SNRs within the EGRET 95% contours: CTB37A&B. They can both be ruled out as strong gamma-ray emitters because of both: 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, Butt, Camilo, ApJ Letters, 560, 155

62 In summary: 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 (but the desired confidence level not yet reached) there are no other candidate GeV sources within the 95% location contours of 3EGJ This is probably the best existing evidence for a connection between EGRET unidentified sources and supernova remnants. There are other very similar cases though: W66, W28, etc.

63 Recent claims: TeV detection of RXJ by CANGAROO II: Enomoto et al. 2002, Nature 416, 823 Source location: NW rim of the SNR (basically the same position found by Muraishi et al. 2000, coincident with X- ray maximum). Against their own previous claims: CANGAROO favor a hadronic origin for the measured TeV emission. Can the TeV emission be hadronic as well? Power law with steep index -2.8.

64 Problems with Enomoto’s fit Problems with Enomoto’s fit Reimer & Pohl, astro-ph/ ; Butt, Torres, et al., Nature 418, 499 (2002) The source is not sub-GeV! Furthermore: Matter density in the NW rim: less than 0.1 cm -3, not 100 cm -3, as CANGAROO assumed to plot their curve. Finally, EGRET and TeV source are not even spatially coincident !

65 But, there is still the possibility for a hadronic origin if the TeV photons detected are actually coming from Cloud B!

66 EGRET stacking searches Cillis, Torres, Reimer Submitted to ApJ D. F. Torres 2004


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