Neutrino pair annihilation above
neutron star merger remnants
Hannah Yasin, Albino Perego and Almudena Arcones
A. Perego,
H. Yasin,
A. Arcones
Submitted toJ. Phys. G.
arXiv:1701.02017
GRB 050709(Credit: NASA/University of
Copenhagen)16.01.2017 | Hirschegg 2017 | Hannah Yasin |1

Outline• Gamma ray bursts (GRB)• Neutron star (NS) merger• Neutrinos• Results• Comparison to observations

16.01.2017 | Hirschegg 2017 | Hannah Yasin |2

Gamma ray bursts (GRB)• Intense flashes of electromagnetic radiation
Review: e.g. Berger 2014

• Two classes: short (t < 2s) and long GRB (t ~ 30s)
θ• Nonthermal spectrum, observed energies: Eiso 1051 erg• Collimated Outflows: source emitting into two cones✓
◆2
⌦
Eiso
✓
Etrue = Eiso ·⇡
·4⇡
65
10
• Etrue 1048 - 1049 erg

16.01.2017 | Hirschegg 2017 | Hannah Yasin |Rosswog,Brüggen 2007

Lee & Ramirez-Ruiz 20073

Gamma ray bursts (GRB)• GRB are distributed isotropically → extragalactical• Possible progenitor candidate: NS merger• Fireball modele. g. Paczynski 1986,Eichler et al. 1989

e. g. Piran 1999, Nakar 2007

➜ Central engine needs to provide a large enough energy reservoir andaccount for relativistic acceleration• Other mechanisms (e.g. magnetic fields) also possible
e.g Metzger 2008

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NS merger simulation

Perego et al. 2014

• 3D, Newtonian, based on SPH
merger simulation Price & Rosswog 2006
• MNS ~ 2.6 M⨀, Mdisk ~ 0.18 M⨀
ν̅• TM1 EOSν• Neutrino treatment: Energy
dependent, spectral leakage scheme• Three neutrino species: νe, ν̅e, νxSnapshot at t ≈ 40 ms➜ Neutrinos from the NS and disk can deposit energy and momentum via
pair annihilation Eichler et al. 1989
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Neutrino-antineutrino annihilation• Possibility for energy deposition: ν + ν̅ → e+ + e1q⌫,¯⌫ =62
20 (cA + cV )c (me c2 )2

Zd⌦⌫

Zd⌦⌫¯

Zd✏⌫

Zd✏⌫¯ (✏⌫ + ✏⌫¯ ) I⌫ I⌫¯ (1cos )2Dessart et al. 2009

• σ0 ≃ 1.71  10-44 cm2• Energy deposition rate q depends on: Neutrino intensities (luminosities)
 Angle between the neutrinos Φ Neutrino energies

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Neutrino luminosities and energies⌫-¯⌫ annihilation above merger remnants: implications of a long-lived MNS

6Figure 3. Evolution of the neutrino total luminosities (left) and root mean squared

absorption
processes outside last scattering surfaces included• Cooling: Noenergies(RMS, right). Blue lines (triangles) refer to ⌫ , red lines (stars) to ⌫¯ , blackeelines (circles) to ⌫x . All quantities are measured at infinity. Solid and dashed lines
refer to net and cooling luminosities (or RMS energies), respectively. In the former
from cooling/diffusion, disk luminosity from accretion• NS luminosity
case neutrino absorption processes outside the last scattering surfaces are included; inthe latter, not.
16.01.2017 | Hirschegg 2017 | Hannah Yasin |7Results⌫-¯⌫ annihilation above merger remnants: implications of a long-lived MNS
140ms

30.0

40ms

29.5
29.050z [km]10028.5
28.0νeν̅e

0

27.5
27.0
26.5

50

26.0

240ms

100
100

340ms
500x [km]

50

100

25.5
25.0

Log10 ( q⌫x,¯⌫x [erg s 1 cm 3 ] )
140ms

30.0

40ms

29.5
29.0

50

z [km]

100

Log10 ( q⌫e ,¯⌫e [erg s 1 cm 3 ] )

11

28.5
28.0

νxν̅x

0

27.5
27.0
26.5

50

26.0

240ms

100
100

340ms
500x [km]

50

100

25.5
25.0

νeν̅ise thelarger
to νxrateν̅x: q⌫,¯⌫ , as a function of the• Energy deposition
Figure 4. rate
Color forcoded
localcompared
energy deposition
cylindrical coordinates, in the= 11⇡/45 plane and in the intervals [0, 100] km ⇥2)
2+ c 2)( cA2 + c[0,cAthe≈plot
4.6the rate for ⌫e , ⌫¯Le ,νeinLthe( LνxoneLν̅xfor) ≈⌫x12ν̅e /right
V 100]
νeν̅km.
νxν̅xwee / (InleftVpanel, ⌫¯x . The

four quadrants refer to di↵erent times, as indicated by the labels. If ⇢ > 1011 g cm 3
we set the rates to the minimum (blue area).

16.01.2017 | Hirschegg 2017 | Hannah Yasin |8Results• Volume integrated energy deposition rates: Qν(t) = ∫V qν(t,x) dV• Time integrated energy deposition rates: Eν(t) = ∫t Qν(t’) dt’• At t = 380 ms: Etot = 1.95  1049 erg
16.01.2017 | Hirschegg 2017 | Hannah Yasin |9Role of the hypermassive NS• Split neutrinos into two groups: NS and disk (DS)• Intensity calculated via:Iν = Iν, NS + Iν, DS• Deposition rate:qν = qν, NS-NS +qν, NS-DS +qν, DS-NS +qν, DS-DS}

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Role of the hypermassive NS⌫-¯⌫ annihilation above merger remnants: implications of a long-lived MNS
Log10 ( q⌫e,¯⌫e [ erg s 1 cm 3 ] ), at 40 ms
NS-NSTOTAL

30.0
29.5
29.0

50z [km]1828.5

νeν̅e

28.0

νeν̅e

0

27.5
27.0
26.5

50

26.0

DS-DS

NS & DS50

0x [km]

50

25.5
25.0

• Contribution
from12.
NS Left:
not negligible
FigureEnergy deposition rate by electron neutrino pair annihilation
at 40 ms inside our simulation. In the four quadrants, we plot the three di↵erent
contributions
obtainedandby tagging
thecomparable
emitted neutrinos based on their production sitefrom NS-DSDS-DS• Contributions(neutron star (NS), or disk (DS)) together with their sum. Right: Contributions tothe |volume-integrated
energy rate (Q⌫,¯⌫ , solid lines) and cumulative deposited energy
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Hannah Yasin |11

Relativistic effects• Include relativistic effects in theν propagation:⌫-¯⌫ annihilation above merger remnants: implq⌫rele,¯⌫e /q⌫e ,¯⌫e , at 40 ms
NS-NSDoppler effect ↑✤ Beaming effects ↓✤ Redshift ↓, blueshift ↑✤Light bending ↑• Local changes up50%

1.50
1.35501.20z [km]✤TOTAL

1.05

νeν̅e

00.90
0.75

500.60• Effects do not change behavior
qualitatively

16.01.2017 | Hirschegg 2017 | Hannah Yasin |DS-DS

NS & DS50

0x [km]0.45

50

Figure 14. Left: Plot of the ratio
annihilation of ⌫e , ⌫¯e pairs, with 12and w

Comparison, NS collapse• Differentiate energy deposition in the local
frames Qrel and measured by an infinitely
distant observer Qrel, ∞• Impact of a possible NS collapse (at tBH) andblack hole (BH) formation (only DS-DScontribution) can be investigatedEν, nrelEν, relEν, rel∞[1049 erg]

[1049 erg]

[1049 erg]

380 ms

1.95

1.88

1.64

1000 ms

2.24

2.15

1.89

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Geometrical factor• Investigation of a possible parametrization for the deposition rates Qν

(Q⌫,¯⌫ )i,j ⇡ const. · L⌫,i L⌫¯,j (G⌫,¯⌫ )i,jνeν̅e"h✏2⌫,i ih✏⌫,i i+h✏2⌫¯,j ih✏⌫¯,j i#i, j ={NS; DS}e.g. Goodman 87, Janka 91• Provide global information
about Qν based on neutrino
emission (Lν) and on geometryof the system (Gν)• Cooling luminosities more const.
• Similar for νx

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Comparison with observations• Comparison of extrapolated Eνν̅ with energetics of observed short GRBs
• Rescale: Lν → αν Lν• αν = αν̅ = 1 corresponds to oursimulation• Solid lines: values for opening
angle available• Dashed lines: only lowerestimates• NS ↔ DS also possible
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Conclusions

arXiv:1701.02017• Energy deposition at 380 ms of Etot = 1.95  1049 erg• The hypermassive NS adds important contribution (factor of 2),
relativistic effects affect E by at most 20%• Possible parametrization introduced• Comparison to observations require higher luminosities (GR simulations?)• BH formation + energy extraction from accreting BH also possible(baryonic pollution problem) e.g Just et al. 2016
• Other mechanisms (e.g. magnetic fields) are also likely to contribute

e.g Metzger 2008

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