millisecond pulsars and the galactic center excess · 2019. 7. 3. · abdo et al. fermi lat...
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Millisecond Pulsars and the Galactic Center Excess
Peter L. Gonthier
Hope College
Magnetospheres of Neutron Stars and Black HolesA workshop at NASA Goddard Space Flight Center
June 10 - 13, 2019
Peter L. Gonthier (Hope College) MSPs and the Galactic Center Excess June 13, 2019 1 / 28
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Collaborators
Population Synthesis of Millisecond Pulsars fromthe Galactic Disk and Bulge
Gonthier et al. 2018, ApJ, 863, 199
Alice Harding & Elizabeth Ferrara — NASA Goddard Space Flight
Center
Sara Frederick — University of Maryland
Victoria Mohr — Washington and Jefferson College
Yew-Meng Koh — Hope College
Peter L. Gonthier (Hope College) MSPs and the Galactic Center Excess June 13, 2019 2 / 28
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1 Pulsar Zoo
2 Millisecond Pulsars
3 Population Synthesis
4 Globular Clusters
5 Galactic Center Excess
Peter L. Gonthier (Hope College) MSPs and the Galactic Center Excess June 13, 2019 3 / 28
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Pulsar Zoo
Pulsar Zoo with over 2530 subjects
10-2210-2110-2010-1910-1810-1710-1610-1510-1410-1310-1210-1110-1010-9
Perio
d De
rivat
ive
(s/s
)
0.001 0.01 0.1 1 10
Period (s)
Radio Fermi NPs Fermi MSPs X-ray Binary RRAT NR AXPs/SGRs
B=1013B=1015
B=1011
B=109
B=1012
B=108
B=1014
τ = 1010
τ = 108τ = 106
τ = 104
B=1010
ATNF - http://www.atnf.csiro.au/research/pulsar/psrcat Story et al. 2007 & 3FGL - Acero et al. 2015
Peter L. Gonthier (Hope College) MSPs and the Galactic Center Excess June 13, 2019 4 / 28
http://www.atnf.csiro.au/research/pulsar/psrcat
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Millisecond Pulsars
γ-Ray Emission in the Pulsar MagnetosphereHigh-energy emission models
Dyks & Rudak 2003Muslimov & Harding 2004
Cheng et al. 1986Romani & Yadigaroglu 1996
Petri & Kirk 2003Contopoulos et al. 2010Li & Spitkovsky 2010Kalapotharakos et al. 2014
Peter L. Gonthier (Hope College) MSPs and the Galactic Center Excess June 13, 2019 5 / 28
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Millisecond Pulsars
γ-Ray Sky Maps — Magnetic Inclination of 60o
-180 -120 -60 0 60 120 180φ
180
150
120
90
60
30
0
ζ
α = 60°TPC
180120600-60-120φ
α = 60°OG
180120600-60-120φ
α = 60°PSPC
TPC – Two Pole Caustic Model (Slot Gap) — geometric model —narrow emission along the last open field surfaceOG – Outer Gap Model — emission high in the magnetosphere withone pole contributing for a given ζPSPC – Pair Starved Polar Cap Model — emission from the entireopen volume region above the polar cap
Peter L. Gonthier (Hope College) MSPs and the Galactic Center Excess June 13, 2019 6 / 28
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Millisecond Pulsars
High Altitude γ-Ray Emission - Spectral Power of the Vela Pulsar
dNdE — Photon SpectrumdNdE = E
Γe−E/Ec
Γ = −1.51 ± 0.01Ec = 2.89 ± 0.09 GeVSuper-exponential cutoffsdNdE ∝ e
−(E/Ec)b withb = 2 excluded to 16σ
γ-ray emission occurs athigh altitudes near andbeyond the light cylinderin most cases of youngpulsars
10-1 100 101
Energy(GeV)
10-10
10-9
E2dN/dE(ergscm
�
2s�
1)
EGRETFermiExpCutoff
Abdo et al. Fermi LAT Observations of the Vela Pulsar, 2009, The Astrophysical
Journal, Volume 696, Issue 2, pp. 1084-1093
Peter L. Gonthier (Hope College) MSPs and the Galactic Center Excess June 13, 2019 7 / 28
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Millisecond Pulsars
Radiation Models
Radio emission - core and cone beams - Harding et al. 2007 & Story et al. 2007
γ-ray emission - Slot Gap Two Pole Caustic (TPC), Outer Gap (OG),and Pair Starved Polar Cap (PSPC) - Venter et al. 2009; 2012 & Johnson et al. 2014
Phenomenological Luminosities
Lν = fν(6.625× 104
)Pαν−3 Ṗ
βν−20 mJy · kpc
2 ·MHz
Lγ = fγ(4.255× 1047
)Pαγ−3 Ṗ
βγ−20 eV · s
−1
Gonthier et al. 2004; Harding et al. 2007; & Story et al. 2007
Explore six free model parameter space with Markov Chain MonteCarlo (MCMC) techniques.
Accepted steps after some burn-in number of steps.
Peter L. Gonthier (Hope College) MSPs and the Galactic Center Excess June 13, 2019 8 / 28
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Population Synthesis
Population Synthesis of MSPs — Comparison Group
To tune radio and γ-ray luminosity model parameters:
Fermi First Point Source Catalog (Abdo et al. 2010) (1FGL)- 11 month viewing - 54 Fermi MSPs detected as point sources
13 radio surveys are included in the simulation - 92 radio MSPs
Target birth rate of 4.5× 10−4 MSPs per century (Story, Gonthier,& Harding 2007, ApJ, 671, 713.) — 4.5 per Myr
After fixing model parameters, we predict Fermi radio-loud andradio-weak MSPs for other viewing periods.
Likelihood of 9 1D histograms of P , Ṗ , DM , S1400, and Fγ
Overview
Peter L. Gonthier (Hope College) MSPs and the Galactic Center Excess June 13, 2019 9 / 28
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Population Synthesis
MCMC Results: the estimated most likely values of thefree model parametersGonthier, P.L., Harding, A.K., Ferrara, E.C., Frederick, S.E., Mohr, V.E., & Koh, Y.M. 2018, ApJ, 863, 199
Free Two Pole Caustic Outer Gap Pair StarvedParameter Slot Gap (TPC) (OG) Polar Cap (PSPC)
Radio Luminosity
fν 3.67± 0.36 4.06± 0.60 4.17± 0.58αν −1.13± 0.09 −1.17± 0.13 −1.19± 0.13βν 0.65± 0.08 0.64± 0.10 0.69± 0.11
γ-ray Luminosity
fγ 0.0122± 0.0012 0.0116± 0.0022 0.0117± 0.0021αγ −2.12± 0.10 −1.93± 0.18 −2.43± 0.17βγ 0.82± 0.05 0.75± 0.13 0.90± 0.12
Peter L. Gonthier (Hope College) MSPs and the Galactic Center Excess June 13, 2019 10 / 28
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Population Synthesis
MC Results - Histograms of Radio Pulsars
!
"#
"!
$#
$!
#
!
%&'()*+,-+./01,+2&34/*4
5 6! 5"6! 5$6! !6!
7,89+2)*1,0+:+94:
+;)$?!!+:+9'IJ:
?!
!
"!
$!
!
%&'()*+,-+./01,+2&34/*4
$$6!$!6!@6!A6!
7,89+KL/*/=
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Population Synthesis
MC Results - Histograms of Fermi Pulsars
!
"#
"!
#
!
$%&'()*+,*-()&
.*/%012)1
345! 3 56 3 57 3 58 3 5 3 5!
9+:;*/().+5! 3"65!
9+:;*/().+
-
Population Synthesis
MC Results - Ṗ − P diagram
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!" '
()*+,-.(/*+,012,0*
!3!! !3! !3 ()*+,-.
!3! !3
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(7-;2)?(@,78912*.
(A1.,-()89:1+:((
(6*+7,()89:1+:
!B4
!B5
!BB
Peter L. Gonthier (Hope College) MSPs and the Galactic Center Excess June 13, 2019 13 / 28
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Population Synthesis
Predicted Fermi -LAT future detections
Catalog Observing Period Detected Simulated — radio-loud & (radio-weak)
TPC OG PSPC
BSL 3 months 12 1 26 (21) 25(32) 26 (7)1FGL 11 months 54 7 52 (46) 50 (66) 53 (16)2FGL 2 years 64 10 78 (71) 75 (101) 80 (26)3FGL 4 years 87 11 111 (104) 105 (145) 114 (40)
5 years 124 (117) 116 (163) 127 (45)10 years 173 (171) 160 (232) 178 (69)
Point Source Catalogs are still incomplete!Catalog Detected Possible Additional MSPs
1FGL 54 102FGL 64 163FGL 87 16
(private communication, Elizabeth C. Ferrara)
Peter L. Gonthier (Hope College) MSPs and the Galactic Center Excess June 13, 2019 14 / 28
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Globular Clusters
47 Tuc seen in γ rays for the first time by Fermi
47 Tuc is a steady γ-raysource - non-variable
There are 23 known radioMSPs in 47 Tuc.
Fermi does not seeindividual pulsations fromMSPs - too far - 4 kpc
Using the ephemeridesfrom 21 radio MSPs,Fermi saw no pulsations
γ-ray flux is not due to asingle MSP
Abdo et al. 2009, Science, 325, 845
Peter L. Gonthier (Hope College) MSPs and the Galactic Center Excess June 13, 2019 15 / 28
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Globular Clusters
Fermi Spectrum of 47 Tuc
!"#$ %& '() *+,+'
-./0('&%#
12 3 4 5-67
!"#$ %& '() *+,+'
Peter L. Gonthier (Hope College) MSPs and the Galactic Center Excess June 13, 2019 16 / 28
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Globular Clusters
Expected Number of MSPs from Abdo et al. 2010
The Fermi team assumed that the average spin-down luminosity of aMSP is 〈Ė〉 = (1.8± 0.7)× 1034erg · s−1
With an average γ-ray efficiency of 〈η〉 = 0.08
NMSPs =Lγ
〈Ė〉 〈η〉(Abdo et al. 2010 Eq (1))
Peter L. Gonthier (Hope College) MSPs and the Galactic Center Excess June 13, 2019 17 / 28
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Globular Clusters
Expected Number of MSPs from Abdo et al. 2010
The Fermi team assumed that the average spin-down luminosity of aMSP is 〈Ė〉 = (1.8± 0.7)× 1034erg · s−1
With an average γ-ray efficiency of 〈η〉 = 0.08
NMSPs =Lγ
〈Ė〉 〈η〉(Abdo et al. 2010 Eq (1))
Peter L. Gonthier (Hope College) MSPs and the Galactic Center Excess June 13, 2019 17 / 28
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Globular Clusters
Expected Number of MSPs from Abdo et al. 2010
Name Lγ(1034 erg · s−1
)NMSPs Simulated NMSPs
47 Tucanae 4.8+1.1−1.1 33+15−15 43± 6
Omega Cen 2.8+0.7−0.7 19+9−9 27± 6
M 62 10.9+3.5−2.3 76+38−34 82± 15
NGC 6388 25.8+14.0−10.6 180+120−100 220± 40
Terzan 5 25.7+9.4−8.8 180+100−90 180± 30
NGC 6440 19.0+13.1−5.0 130+100−60 130± 30
M 28 6.2+2.6−1.8 43+24−21 39± 8
NGC 6652 7.8+2.5−2.1 54+27−25 65± 16
Average 0.14+0.04−0.03 per MSP 89+24−19 100± 8
Key Point
expect ∼ 100 MSPs per cluster
Peter L. Gonthier (Hope College) MSPs and the Galactic Center Excess June 13, 2019 18 / 28
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Globular Clusters
Expected Number of MSPs from Abdo et al. 2010
Name Lγ(1034 erg · s−1
)NMSPs Simulated NMSPs
47 Tucanae 4.8+1.1−1.1 33+15−15 43± 6
Omega Cen 2.8+0.7−0.7 19+9−9 27± 6
M 62 10.9+3.5−2.3 76+38−34 82± 15
NGC 6388 25.8+14.0−10.6 180+120−100 220± 40
Terzan 5 25.7+9.4−8.8 180+100−90 180± 30
NGC 6440 19.0+13.1−5.0 130+100−60 130± 30
M 28 6.2+2.6−1.8 43+24−21 39± 8
NGC 6652 7.8+2.5−2.1 54+27−25 65± 16
Average 0.14+0.04−0.03 per MSP 89+24−19 100± 8
Key Point
expect ∼ 100 MSPs per cluster
Peter L. Gonthier (Hope College) MSPs and the Galactic Center Excess June 13, 2019 18 / 28
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Galactic Center Excess
Galactic Center Excess
Ackermann et al. 2017Peter L. Gonthier (Hope College) MSPs and the Galactic Center Excess June 13, 2019 19 / 28
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Galactic Center Excess
Galactic Center Excess - Gordon & Macias 2013
Dark Matter (DM) WIMP with mass MDM (20 – 60 GeV) annihilatevia channels: τ+τ− and b+b− as suggested by this study.
γ-ray flux from WIMP is factorable into “particle physics” and“astrophysical” factors
Φ (Eγ , b, `) = ΦPP Eγ × J (b, `) (2)
ΦPP (Eγ) =1
2
(〈σv〉
4πM2DM
)∑f
dNfdEγ
Bf (3)
J (b, `) =
∫ ∞0
ρ(r)2 ds (4)
Navarro− Frenk−White ρ(r) = ρs(rrs
)γ [1 +
(rrs
)]3−γ (6)Peter L. Gonthier (Hope College) MSPs and the Galactic Center Excess June 13, 2019 20 / 28
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Galactic Center Excess
Galactic Center Excess - Gordon & Macias 2013 - Fig. 7b
〈σv〉 ∼ 3× 10−26 cm3 · s−1 Thermal annihilation cross section
100 101 102
Eγ [GeV]
10−7
E2dN/dE
[GeV
cm−
2s−
1]
2× 10−8
Inner slope:γ = 1.2
MDM = 23.5 GeV, 55% bb̄, 45% leptons
Peter L. Gonthier (Hope College) MSPs and the Galactic Center Excess June 13, 2019 21 / 28
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Galactic Center Excess
Galactic Center Excess - Gordon & Macias 2013
Peter L. Gonthier (Hope College) MSPs and the Galactic Center Excess June 13, 2019 22 / 28
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Galactic Center Excess
Dark Matter WIMP Constraints
Caputo et al. 2016, Phys. Rev. D 93, 062004.
Is the GCE a result of an unknown DM particle?Or a result of known astrophysical sources, MSPs, which have notbeen observed?
Peter L. Gonthier (Hope College) MSPs and the Galactic Center Excess June 13, 2019 23 / 28
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Galactic Center Excess
The GCE and Point Sources
Two independent studies conclude that point sources are responsiblefor the GCE.
Lee, S. K., Lisanti, M., Safdi, B. R., Slatyer, T. R., & Xue, W., Evidence for
Unresolved γ-Ray Point Sources in the Inner Galaxy, 2016, Phys. Rev. Lett.,
116, 051103. — non-Poissonian template fit. (Princeton, BroadInstitute, and MIT)
Bartels, R., Krishnamurthy, S. & Weniger, C., Strong Support for the
Millisecond Pulsar Origin of the Galactic Center GeV Excess, 2016, Phys.
Rev. Lett., 116, 051102. — wavelet decomposition of the γ-ray sky.(GRAPPA Institute and University of Amsterdam)
How do we understand so many MSPs in the GC?
Peter L. Gonthier (Hope College) MSPs and the Galactic Center Excess June 13, 2019 24 / 28
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Galactic Center Excess
The Source of MSPs in the Galactic Center
The dynamical inspiraling of globular clusters in a dynamical frictionmodel.
Gnedin et al. (2014) estimate that 2 to 6 ×107 M� in globularclusters where dragged into a region of 3 to 5 pc (1.2’ to 2.0’) fromthe GC.
Gnedin & Ostriker (1997) list the masses of 119 globular clustersgiving an average mass of 3.8× 105 M� per cluster.These studies would suggest that 50 to 160 globular clusters mighthave been captured by the GC.
We estimated previously that there are about 100 MSPs per cluster.
100 captured globular clusters could provide 10,000 MSPs needed toaccount for the spectrum of the GCE.
This is in agreement with our prediction.
Peter L. Gonthier (Hope College) MSPs and the Galactic Center Excess June 13, 2019 25 / 28
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Galactic Center Excess
Globular Cluster Streams
GD-1 - Grillmair,C.J. & Diontos, O.2006, ApJ, 643,L17; Webb, J.J. &Bovy, J. 2019,MNRAS, 485, 5929
Acheron, Cocytosand Lethe -Grillmair, C.J. 2009,ApJ, 693, 1118 http://www.spitzer.caltech.edu/images/2136-sig07-
008a-Rings-Around-the-Galaxy
-40
-20
0
20
40
X-Y
-20
0
20
40 X-Z
kpc
-40 -20 0 20 40
-20
0
20
40 Y-Z
kpc
Grillmair, C.J. 2009, ApJ, 693, 1118
Peter L. Gonthier (Hope College) MSPs and the Galactic Center Excess June 13, 2019 26 / 28
h
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Galactic Center Excess
The Future will tell!
10,000 MSPs simulated in the GC
Peter L. Gonthier (Hope College) MSPs and the Galactic Center Excess June 13, 2019 27 / 28
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Galactic Center Excess
Acknowledgments
We also are grateful for the generous support of:
The Michigan Space Grant Consortium
The National Science Foundation under grantNos. REU: PHY/DMR-1004811, and RUI: AST-1009731
The Fermi Guest Investigator Program Cycle 3 under grant No.NNH09ZDA001N-FERMI3
The NASA Astrophysics Theory and Fundamental Physics Programunder the grant No. NNX13AO12G
Peter L. Gonthier (Hope College) MSPs and the Galactic Center Excess June 13, 2019 28 / 28
Pulsar ZooMillisecond PulsarsPopulation Synthesis Globular ClustersGalactic Center Excess
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