HIGH ENERGY ASTROPHYSICS ray emission from galactic radioactivity

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HIGH ENERGY ASTROPHYSICS ?-ray emission from
galactic radioactivity

• Relevant radioactive nuclei for galactic ?-ray
  line emission
• how and where they are synthesized
• nucleosynthesis (hydrostatic and explosive), in
  stars
• interaction with cosmic rays, in the
  interstellar medium
• Electron-positron annihilation emission (line
  and continuum)
• e from ?- unstable nuclei
• BUT other sources of e (? radioactivity) exist
• Type of emission point-source or diffuse

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Radioactive decay and ?-ray line emission

• Energy levels of atomic nuclei are spaced
  typically by 1MeV
• nuclear transitions involve absorption or
  emission of ?s
• with E1MeV
• ?-ray line emission (with E 1MeV) is expected
  from
• nuclear deexcitation

• Nuclear excitation occurs
• radioactive decay, either ? (p n) or ?- (n
  p), and electron capture produce nuclei in
  excited states
• collisions with energetic cosmic rays

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Radioactive decay and ?-ray line emission
Q
? decay e emission
X
Y
electron capture no e emission
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Sites of explosive nucleosynthesis relevant for
?-ray line astronomy

• SUPERNOVAE
• Thermonuclear supernovae (SN Ia) exploding
  white dwarfs in binary systems (no remnant)
• Core collapse supernovae (SN II, SN Ib/c)
  exploding massive stars (M ? 10 M?) (neutron star
  or black hole remnant)
• v ? 104 km/s, E ? 1051 erg, Mej ? M?
• CLASSICAL NOVAE
• Explosion of the external H-rich accreted shells
  of a white dwarf in a binary system
• v ? 102 - 103 km/s, E ? 1045 erg, Mej ? 10-4 -
  10-5 M?

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Radioactive isotopes relevant for ?-ray line
astronomy
Supernovae mainly
Novae mainly
e- capture ? ?-
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Example 56Ni

• 8.8 111.3 days detectable in
  individual sources very early after its
  synthesis supernovae

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Radioactive isotopes relevant for ?-ray line
astronomy
Supernovae mainly
Novae mainly
e- capture ? ?-
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Example 57Ni

• 52h 390 days detectable in individual
  sources very early after its synthesis
  supernovae

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Radioactive isotopes relevant for ?-ray line
astronomy
Supernovae mainly
Novae mainly
e- capture ? ?-
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Example 44Ti
Diehl Timmes, 1998
? 89 yrs detectable in individual
sources years after its synthesis supernova
remnants
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44Ti halflive
Weighted mean t1/260?1 yrs (Motizuki et al.
2004)
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56,57Ni and 44Ti production sites
Explosive burning in massive stars (core collapse
supernovae 56,57Ni and 44Ti are produced in the
same internal zones details in SNe course
Diehl Timmes, 1998
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Radioactive isotopes relevant for ?-ray line
astronomy
Supernovae mainly
Novae mainly
e- capture ? ?-
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Example 26Al

• 106 yrs very difficult to detect in
  individual sources cumulative effect
• it samples ongoing
  nucleosynthesis in the Galaxy

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Example 26Al nucleosynthesis path in novae
José, Coc Hernanz, 1999
details in Novae and Supernovae courses
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Radioactive isotopes relevant for ?-ray line
astronomy
Supernovae mainly
Novae mainly
e- capture ? ?-
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Example 60Fe
Diehl Timmes, 1998

• 2x106 yrs very difficult to detect in
  individual sources cumulative effect
• it samples ongoing
  nucleosynthesis in the Galaxy

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26Al and 60Fe production sites
Massive stars hydrostatic and explosive burning
(H and O-Ne burning shells) 26Al and 60Fe are
produced in similar regions and in comparable
amounts details in SNe course
Diehl Timmes1998
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26Al and 60Fe production sites
Diehl Timmes, 1998
Stars with Mgt25 M? produce more 26Al than 60Fe
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Radioactive isotopes relevant for ?-ray line
astronomy
Supernovae mainly
Novae mainly
e- capture ? ?-
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Example 7Be
Diehl Timmes, 1998

• 77 days detectable in individual
  sources, novae, shortly after the explosion the
  cumulative effect of many novae may also be
  detectable, since ? gt ?t (between two succesive
  galactic novae)
• details in Novae course
• 7Li can also be a non nucleosynthetic product,
  but the result of energetic particle collisions
  (spallation reactions) ? ?

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Example 22Na
Diehl Timmes, 1998

• 3.8 yrs detectable in individual
  sources, novae, shortly after the explosion the
  cumulative effect of many novae may also be
  detectable, since ? gt ?t (between two succesive
  galactic novae)

details in Novae course
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Observations of radioactivities
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Observations of radioactivities
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Observations of radioactivities
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Observations of radioactivities Comptel
instrument
The Imaging Compton Telescope (COMPTEL) utilizes
the Compton Effect and two layers of gamma-ray
detectors to reconstruct an image of a gamma-ray
source in the energy range 1 to 30 million
electron volts (MeV). COMPTEL's upper layer of
detectors are filled with a liquid scintillator
which scatters an incoming gamma-ray photon
according to the Compton Effect. This photon is
then absorbed by NaI crystals in the lower
detectors. The instrument records the time,
location, and energy of the events in each layer
of detectors which makes it possible to determine
the direction and energy of the original
gamma-ray photon and reconstruct an image and
energy spectrum of the source.
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Observations of radioactivities Comptel
instrument
The operating principle of COMPTEL. An incoming
photon enters from above and Compton scatters in
the first detection layer (blue), then is
(partially) absorbed in the second layer (green).
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COMPTEL map of the 1.8 MeV line of 26Al
Carina
Vela
Inner Galaxy
Cygnus
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But 26Al was discovered in 1984, well before
CGROs launch
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Observations of 26Al
Reported 1.809 MeV fluxes for the inner Galaxy
(Diehl Timmes 1998)
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Diehl Timmes 1998
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HEAO 3 line profile of the 1.8 MeV emission from
26Al(Mahoney et al 1984)FWHMlt3keV
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GRIS (Ge detector on a balloon flight) line
profile of the 1.8 MeV emission from 26Al(Naya
et al 1996)
FWHM5.4?1.4keV vgt500km/s Tgt5x108K
during 106 yrs!
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RHESSI (Ge detector) line profile of the 1.8
MeV emission from 26Al(Smith et al 2003) FWHM2
?1keV
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Observations of 26Al comparison of line widths
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INTEGRAL/SPI observation of the 1.8 MeV line of
26Al
Diehl et al. 2003 FWHM 2.1-3.1keV uncertainty
0.7 keV