High energy emission from supernova remnants and regions of star formation

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High energy emission from supernova remnants and
regions of star formation

• Diego F. Torres
• dtorres_at_igpp.ucllnl.org

www.angelfire.com/id/dtorres
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Summary

• SNRs
• EGRET sources and SNRS
• GLAST/MAGIC prospects
• SNRs searched at TeV energies with HESS
• 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

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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
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Accelerated electrons, ok. Accelerated protons?
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.
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Spatially coincident pairs of SNRs and
unidentified EGRET sources
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Spatially coincident pairs of SNRs and
unidentified EGRET sources
Identifying the pairs
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Spatially coincident pairs of SNRs and
unidentified EGRET sources
Data contained in the3EG
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Spatially coincident pairs of SNRs and
unidentified EGRET sources
Variability Variability indices
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Spatially coincident pairs of SNRs and
unidentified EGRET sources
Variability
Some of the sources are variable. Not related to
SNRs
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3EG J05352610
Romero, Torres et al. AA, 376, 599,
2001 Anchordoqui, Torres, et al. ApJ, 2003 ?
neutrino yield detectable at Earth!
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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 0.085 mJy per beam, the
rms noise. The map is centered at the star
position. 1 milliarcsec is equivalent to 3AU
(1013 cm) for a distance of 3kpc.
3EG J1824-1514
Paredes et al. Science 288, 2340
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Spatially coincident pairs of SNRs and
unidentified EGRET sources
Known data for the SNRs
From Torres et al. 2003, Physics Reports
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Torres et al. 2004, Adv. In Space Physics
Most plausible cases appear to present broad
correlations
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The GeV future
W66
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Some recent results from HESS
CANGAROO 1997 the small single telescope
observations
SN1006 the prototype ?
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The panorama for SNR G347.3-0.5 (RX J1713.7-3946 )
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 Egt1.8
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.
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1st SNR at TeV energies ! SNR RX J1713.7-3946 has
all the ingredients extreme X-ray bright, EGRET
source nearby, dense molecular cloud region
Butt et al. 2001
But...
Aharonian et al. Nature October 2004
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Interpretation still in doubt...
evidence for hadronic particle acceleration in
SNRs still unclear.
Enomoto et al. 2002 (Nature) IC interpretation
in conflict with data Butt, Torres et al. 2002
(Nature), Reimer Pohl 2002 (AA) p0
interpretation in conflict with data, too !
-gt SNR RX J1713.7-3946
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Partial Summary

• SNRs are TeV sources! (Even using Whipple
  criterion accepting observations by CANGAROO on
  G347.3-0.5)
• 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.

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Gamma-rays from Luminous and Ultra Luminous
Infrared Galaxies
Torres, Reimer, Domingo, Digel ApJ Letters, 607,
99-102 (2004) Torres ? Arp 220 ApJ, 617, 966
(2004) Cillis, Torres Reimer 2005 ApJ in press
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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
  (106 solar)

60 of all EGRET gamma-rays were diffuse
emission from the Milky Way
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Diffuse emission from external galaxies
LMC
EGRET
IRAS
(1.9 0.4) x 10-7 cm-2 s-1
30 Doradus extensive massive SFR and molecular
clouds

• 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 10-8 cm-2 s-1
  (gt100 MeV), well below EGRETs detection limit

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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
(lt10Mpc), Infrared luminosity (gt109 Lsolar) at
latitudes bgt10.
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Barnes and Hernquist 1996 merging of gas-rich
galaxies
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.
Right showing only gas in both galaxies
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Almost all ULIRGs seems to be double or
interacting
Only one within the 100 Mpc sphere Arp 220 And
there are tens of LIRGs (luminosities gt1011
LSUN) detectability depends on the combined
effect of distance and starburst activity.
review on LIRGs and ULIRGs Sanders and Mirabel,
ARAA, 1996
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Detectability of LIRGs

• 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
• 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)
• Several nearby starburst galaxies and a number of
  LIRGs and ULIRGs are plausible candidates for
  detection

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Arp 220

• The best studied and nearest ULIRG (72 Mpc)
• Arp 220s 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.

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Arp 220
Downes Solomon 1998, Gao Solomon 2004
350 pc
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Arp 220 Geometry
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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
0.2-1.2 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
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High energy emission computed from first
principles
Q-DIFFUSSE

• 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 gt 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

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Q-DIFFUSSE
Observational measurements
The slope for the injection spectrum for protons
and electrons is assumed. The normalization is
defined by the SNR rate.
SN rate, mass, density, IR luminosity
Injection proton and electron spectrum,
diffusion/escape timescales
Secondary production knock-on process, neutral
and charged pion decay
2nd and 3rd 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
diffusion-losses steady spectrum of protons
electrons
Synchrotron, IC, Bremsstrahlung, Pion Decay.
Absorption of gamma-rays, opacities, eq. of
radiation transport.
Computed without further assumptions
Model predictions from radio to IR with emission
of secondaries, FIR with emission of dust.
Parameter fixing B-field.
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.
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.
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IR-FIR luminosity of Arp 220

• 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 (s 1.5,
  T 42.2 K)
• simple conservative model
• avoids model degeneracies by increasing the
  number of free parameters

Blackbody optical contribution
Non-thermal radio contribution
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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.
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Radio emission of the steady population of
electrons
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.
Infrared
DISK
Lines are not fits to the data but predictions of
the model for a particular choice of parameters.
WEST
EAST
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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
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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 gg processes, whereas gZ 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.
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Results for integrated gamma-ray fluxes are
This would make Arp 220 observable for GLAST and
VERITAS/HESS/MAGIC telescopes. The latter would
need lt 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!
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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)

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Thank you.
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Scoville et al. 1997 Arcsec imaging of CO
emission
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D. F. Torres 2004
Losses for protons and electrons example
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D. F. Torres 2004
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)
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D. F. Torres 2004
Context The evolution of the gamma-ray sky
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D. F. Torres 2004
Future surveys (with GLAST)
Simulated LAT maps (gt100 MeV, gt1 GeV, 1 yr).
More than 10000 point sources. Simulations by
Seth Digel
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D. F. Torres 2004
The multi-messenger context the evolution of
the sensitivity
From Torres Anchordoqui 2004
Complementary Capabilities
From S. Ritz
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D. F. Torres 2004
Perhaps the main discovery in the EGRET
eraDiversity 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)
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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
  (106 solar)

60 of all EGRET gamma-rays were diffuse
emission from the Milky Way
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Diffuse emission from external galaxies
LMC
EGRET
IRAS
(1.9 0.4) x 10-7 cm-2 s-1
30 Doradus extensive massive SFR and molecular
clouds

• 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 10-8 cm-2 s-1
  (gt100 MeV), well below EGRETs detection limit

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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 (3105 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

Butt et al. ApJ Letters, 562, 167 Butt et al.,
Nature 418, 499 Enomoto et al., Nature 416, 823
Reimer Pohl, AA 390, L43 Torres et al. Phys.
Rept. 2003
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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, 1999
Slane et al. ApJ 525, 357 (1999)
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More precise indication of interaction with
molecular material
The distribution of 781 line intensity ratios,
RCO(J2?1)/CO(J1?0), measured every 15' in
the region from l346.5?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.
Top 0.5 of all values measured. All other bins
with high R are well outside the 3EG field
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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 Egt1.8
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.
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The gamma-ray luminosity
The expected g-ray flux at Earth coming from the
SNR is (Drury et al. 1994), ESN is the energy
of the SN in ergs, q 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 (2.2
10-25 s-1 H-atom-1).
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The gamma-ray spectrum
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.
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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
Violates the observed upper limit by a factor of
20 at 843 MHz.
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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.
• Two other SNRs within the EGRET 95 contours
  CTB37AB. 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
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• In 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 (but the desired confidence
  level not yet reached)
• there are no other candidate GeV sources within
  the 95 location contours of 3EGJ1714-3857
• 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.

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Recent claims TeV detection of RXJ 1713.7-3946
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.
Power law with steep index -2.8.
Can the TeV emission be hadronic as well?
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Problems with
Enomotos fit
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 !

• The source is not sub-GeV!

Reimer Pohl, astro-ph/0205256 Butt, Torres,
et al., Nature 418, 499 (2002)
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But, there is still the possibility for a
hadronic origin if the TeV photons detected are
actually coming from Cloud B!
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D. F. Torres 2004
EGRET stacking searches
Cillis, Torres, Reimer 2004. Submitted to ApJ