Probing Particle Acceleration in the Jets ofthe Microquasar SS433 with MeV gamma rays

Takahiro Sudoh (Univ. of Tokyo)
with/ Dmitry Khangulyan, Yoshiyuki InoueJETvz = 0.26c
Ljet ≃ 1039erg/s

JET“Microquasar”
BH + Supergiant

~ 30 pc

5

X-ray knots along the Jets

e3

e2

e1

w1

w2

Safi-Harb & Ogelman (1997)6

X-rayknots
alongtheJets~ 6 pc

e3

e2

e1

w1

w2

Safi-Harb & Ogelman (1997)

7

VHE photons from knots
Abeysekara et al. (2018)
Nature 562, 82-85• Knots in the jets of SS433 are plausible sites of
8 particle acceleration

Interpretations ?

• Abeysekara et al. (2018) :• e1 region
leptonicmodelﬁts•
These are based on verybroadband SED
simple models;
no study addresses moredetailed models yet.

• Xing et al. (2019) :• w1 region• leptonic model does not
explain X-ray/radio data9

Interpretations ?

• Abeysekara et al. (2018) :• e1 region
leptonicmodelﬁts•
These are based on verybroadband SED
simple models;
no study addresses moredetailed models yet.

• Xing et al. (2019) :• w1 region• leptonic model does not
explain X-ray/radio data

10

Our Work• We use a more detailed model of nonthermal
emission from microquasar jet, with aim of :• see whether leptonic model works• quantify acceleration eﬃciency• make predictions for future observations
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Our Work• We use a more detailed model of nonthermal
emission from microquasar jet, with aim of :• see whether leptonic model works→ It works• quantify acceleration eﬃciency→ Very high (nearly Bohm limit)• make predictions for future observations→ Hard X-ray / MeV gamma-ray is the key
12ModelParticle Production• Energetics : Total jet power is distributed for proton,relativistic electron (Le), and magnetic ﬁeld (LB).
rL• Acceleration : parametrized as tacc = ηacc c• Maximum energy : deﬁned by cooling or conﬁnement- cooling limit tcool > tacc
- conﬁnement limit R >6DtacccrL• Diﬀusion : scaled to the Bohm limit D = ηgDBohm = ηg 3
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Particle Cooling• Cooling due to adiabatic and radiative (synchrotronand inverse Compton) losses.
v
γdlnρ
2∂Rz·
• We include adiabatic loss : γad = 3 dt = − 3 ΓR(z) ∂z γ

• To evaluate adiabatic loss rate, we parametrize thejet radius as R(z) = zαj (i.e., conical jets).

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Particle Evolution and Emission• Transport Eq. describes evolution of spatial-energy
density :∂n(γ, z, t)∂n(γ, z, t)∂ ··+ vz
+ [γn(γ, z, t)] = q(γ)δ(z − z0)∂tdz∂γ−pinj·• Steady injection above energy of 1 GeV : q(γ) ∝ γ• Integrate to obtain electron spectrum in the knots:
z1dN=ndz∫zdγ0• Emission from electrons : Synchrotron + Inverse-Compton
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Comment on GeV observations• Various analysis on Fermi data
• Emission region is uncertain• We treat all GeV data as upper
limits on knot emission
Bordas+15

Xing+19

Rasul+19

Sun+1917

Results

Overall SED• Overall SED explainedwith leptonic models forboth regions• Assuming that maximum
particle energy is limited
by synchrotron loss.

• Derived magnetic ﬁelds
are 16 μG and 9 μG fore1 and w119

Overall SED• Overall SED explainedwith leptonic models forboth regions• Assuming that maximum
particle energy is limited
by synchrotron loss.

• Derived magnetic ﬁelds
are 16 μG and 9 μG fore1 and w1

20

GeV data• GeV data remain
unexplained within theknot model• Mostly from otherregions? Hadronicemission?

21

Comparison with other work (e1)• Very diﬀerent spectral
shape at hard X-ray.

• Adiabatic loss is signiﬁcant
below ~ 100 TeV.

Abeysekara et al.,e1 region

22

Comparison with other work (w1)

• Radio/X-ray data areexplained with ourleptonic models• Electrons are injectedwith a soft spectral index
pinj = 2.55 in our case.

23Xing et al.,w1 region

Need for High Acceleration Efficiency• A high eﬃciency ofηacc ≲ 102 is needed toexplain the X-ray data:
−1/2
−1/2
η
B
acc
synEe,max = 1.5 PeV( 102 )
( 16 μG )• This suggests thepresence of PeV protons:
conEp,max= 6 PeV

24( 102 )
ηaccηg−1/2

Need for High Acceleration Efficiency
2Ourmodelrequire
to explain the X-ray dataη
≲10acc•• In the framework of the diﬀusive shock acceleration, thishints at the Bohm limit: ηg ∼ 1•βsh200DSAηacc =ηg ( 0.26 )−2• Such a fast acceleration is also observed in somesupernova remnants: ηg ∼ 1 (e.g., Uchiyama et al. 2007)• However, jets from BL Lacs appear to have much lower
eﬃciency of particle acceleration: ηg ∼ 104 (e.g., Inoue&Tanaka 2016)25

Future Prospects• Hard X-ray and MeV
gamma-ray observations
will detect spectral
turnover and cutoﬀ• Critical test of our models
and constraints on ηacc• CTA and LHAASO may
also detect VHE emission.

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Summary

Nonthermal Particles SS433 Jets

• Spectral energy distribution from knots can be explainedwith leptonic models.

• GeV data remain unexplained: from other regions and/or
hadronic component?
2Needavery
higheﬃciency
of… hint at diﬀusive
η≲
10acc
•

shock acceleration near the Bohm limit?

• Future hard X-ray and MeV gamma-ray observations will
critically test our models.
→ Critical probe of particle acceleration in astrophysical jets
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