Francesca Calore Gamma rays from Galactic pulsars: high

Gamma rays from Galactic pulsars: high- and low-

latitude emission

Francesca Calore

NOW 2014 Conca Specchiulla, 8th September 2014

F. Calore, M. Di Mauro & F. Donato, arXiv:1406.2706 F. Calore, I. Cholis & C. Weniger, arXiv:1409.0042

based on:

0 0.05 0.15 0.35 0.74 1.5 3.1 6.2 13 25 50

Fermi all-sky gamma-ray map

Photon energy: 100 MeV - 10 GeV

The Isotropic Gamma-Ray Background (IGRB)

Francesca Calore - University of Amsterdam NOW 20141

M. Razzano presentation about Fermi results !

0 0.05 0.15 0.35 0.74 1.5 3.1 6.2 13 25 50Energy range: 200 MeV - 100 GeV

Resolved Point Sources

Galactic Diffuse Emission

--

- CRs Background & solar photon


Solar photon & CRs background

-

=

-

-

11 months data @ high latitudes

|b| � 10�





0 0.05 0.15 0.35 0.74 1.5 3.1 6.2 13 25 50Energy range: 200 MeV - 100 GeV



--

- CRs Background & solar photon


Abdo et al., PRL’10

/ E�2.41

+ Anisotropy at small scales.

Solar photon & CRs background

-

=

-

-

11 months data @ high latitudes

|b| � 10�





Unresolved Point Sources Diffuse ProcessesBlazars

Most abundant population of LAT detected sources Contribution up to 10 - 20 % !

Non-blazars active galaxies Few resolved members, but large unresolved population. !

!Star-forming galaxies

Outnumber AGN in number density, although 4 detected objects; ca 4 - 20% !!

Galactic Pulsars Second most abundant population, but few % of the diffuse flux.

DM annihilation In the Milky Way and in other galaxies.Uncertainty in the DM distribution. !!UHECRs E.M. cascade from interaction with CMB. Contribution from 1% to 50% . !!Intergalactic shocks Shock waves as electrons accelerators, then IC on CMB; ca. 10% of IGRB. !

Abdo et al., ApJ’10, Ajello et al., ApJ’12, Di Mauro et al, ’13

Inoue, ApJ’11, Di Mauro et al, ApJ’13

I. Tamborra presentation !

Kalashev et al., PRD’09, Berezinsky et al., PLB, ‘10

Keshet et al., ApJ’03, Gabici & Blasi, AP’03

e.g. Fornasa et al., MNRAS’13

The origin of the IGRB








DM annihilation In the Milky Way and in other galaxies.Uncertainty in the DM distribution. !!UHECRs E.M. cascade from interaction with CMB. Contribution from 1% to 50% . !!Intergalactic shocks Shock waves as electrons accelerators, then IC on CMB; ca. 10% of IGRB. !

Abdo et al., ApJ’10, Ajello et al., ApJ’12, Di Mauro et al, ’13



Kalashev et al., PRD’09, Berezinsky et al., PLB, ‘10

Keshet et al., ApJ’03, Gabici & Blasi, AP’03

e.g. Fornasa et al., MNRAS’13



• Pulsars are rapidly spinning neutron stars. !

• Pulsars divided into young Pulsars (P>15 ms) and Millisecond Pulsars (MSPs) . !

• ATNF catalog: about 2000 sources (132 MSPs) !

• Fermi-LAT second Pulsars catalog (2FPC) with 117 sources (40 MSPs and 77 young objects).

10-22

10-21

10-20

10-19

10-18

10-17

10-16

10-15

10-14

10-13

10-12

10-11

10-3 10-2 10-1 100 101

dP/d

t [s/

s]

P [s]

dP/dt vs P for the ATNF catalog Pulsars and MSPs

ATNF MSPsATNF young Pulsars

Fermi-LAT MSPsFermi-LAT Pulsars

P = 0.015 s

Young & Millisecond pulsars

MSPs

Young Pulsars


• Gamma rays from the conversion of rotational kinetic energy.

• The initial rotation period slows down for magnetic-dipole braking.

• The slow down is measured by the period derivative: !!!

• The spin-down luminosity, namely the loss energy rate is: !!

• A fraction of the spin-down luminosity is converted into gamma rays with a given efficiency:

Pulsar gamma-ray emission


• Gamma rays from the conversion of rotational kinetic energy.

• The initial rotation period slows down for magnetic-dipole braking.

• The slow down is measured by the period derivative: !!!

• The spin-down luminosity, namely the loss energy rate is: !!

• A fraction of the spin-down luminosity is converted into gamma rays with a given efficiency:

Pulsar gamma-ray emission


(1) magnetic field (2)rotation period

(1) luminosity efficiency

0

5

10

15

8 9

N(B

)

Log10(B) [G]

B distribution N(B) of ATNF catalog MSPs

ATNF DistrLog10 Gauss.

0

5

10

15

0.002 0.004 0.006 0.008 0.01

N(P

)

P [s]

P distribution N(P) of ATNF catalog MSPs

ATNF distr.Gauss.

Log10 Gauss.

Parameter distributions (1)


(1)magnetic field (2)rotation period

Radio measurements from ATNF catalog (132 sources)

Novelty!!

hlog10

(B/G)i = 8.27

�log10 B = 0.30

hlog10

(P/s)i = �2.54

�log10 P = 0.19

P [s]N(P

)

N(B

)

log10(B/G)



(3)z distribution (4)r distribution

Radio measurements from ATNF catalog (132 sources)

0

10

20

30

40

3 4 5 6 7 8 9 10 11 12 13

N(r)

r [kpc]

r distribution N(r) of ATNF catalog MSPs

ATNF distr.Gauss.

Exp.

0

5

10

15

20

25

-1.5 -1 -0.5 0 0.5 1 1.5

N(z

)

z [kpc]

z distribution N(z) of ATNF catalog MSPs

ATNF distr.Gauss.

Exp.

distance from the Galactic plane

projected distance from the Galactic center

hri = 7.42 kpc

r0 = 1.03 kpc

hzi = 0kpc

z0 = 0.67 kpc

N(z)

N(r)

r[kpc]z[kpc]



Gamma-ray measurements from Fermi-LAT 2PC (40 sources)

1030

1031

1032

1033

1034

1035

1036

1037

1038

1031 1032 1033 1034 1035 1036 1037

L a [e

rg/s

]

dE/dt [erg/s]

La(dE/dt)

Band¡ = 0.095, _ = 1

Fermi-LAT MSPsFermi-LAT UL

(1) luminosity efficiency

• The scatter of the data points does not allow a statistically robust correlation. • We derive 95% C.L. upper limits on the gamma-ray flux of a sample of 20 sources non-

detected by the Fermi-LAT. • 20 selected sources in the ATNF catalog are the ones (with ) expected to be the

most powerful gamma-ray emitters if standard values of ử = 1 and ỷ =0.1 are assumed.

ỷ is the conversion efficiency.

E[erg/s]

L�[erg/s]

|b| > 10�

↵ = 1 , ⌘ = 0.095Benchmark:

Empirical uncertainty band:⌘ = 0.015, 0.65{ }



(2)spectral index

Gamma-ray measurements from Fermi-LAT 2PC (40 sources)

0

5

10

15

0.5 1 1.5 2

N(K

)

K

K distribution N(K) of MSPs in the 2FPC

Fermi-LATGauss.

0

5

10

3 3.5

N(E

cut)

Log10(Ecut [MeV])

Log10(Ecut) distribution N(Log10(Ecut)) of MSPs in the 2FPC

Fermi-LATGauss.

h�i = 1.29

�� = 0.37hEcuti = 3.38

�Ecut= 0.18

(3)cutoff energy

Spectral energy distribution of observed sources

�

N(�

)

log10(Ecut/MeV)

N(E

cut)

MSP gamma-ray sky


Simulated MSPs distribution

10

For each simulated source we derive: - the position: r, z - the gamma-ray luminosity:

• P, B • a • a • Fermi-LAT source sensitivity

! E

� , Ecut ! F�

⌘ ! L� ! S� ⌘ L�/(4⇡d2)

Fermi-LAT Coll. arXiv:1305.8345

MSP gamma-ray sky



10

For each simulated source we derive: - the position: r, z - the gamma-ray luminosity:

• P, B • a • a • Fermi-LAT source sensitivity

! E

� , Ecut ! F�

⌘ ! L� ! S� ⌘ L�/(4⇡d2)

Fermi-LAT Coll. arXiv:1305.8345

Detected or non-detected source?

A. Resolved MSPs (max 39) B. Unresolved MSPs

Total of about 1000 - 1500 simulated sources for 1000 MC simulations.

MSP gamma-ray sky



11

Resolved MSPs counterpart

MSP gamma-ray sky



11

Unresolved MSPs counterpart

1000 MC realisations of MSPs population. Uncertainty band due to parameter distributions errors and LAT sensitivity.

10-8

10-7

10-6

10-5

10-4

10-3

10-1 100 101 102 103

E2 dN

/dE

[GeV

/cm

2 /s/s

r]

E [GeV]

Unresolved MSPs flux in the high-latitude region

1m BandAverage

Ackermann 2012

High-latitude emission


|b| > 10�

Calore, Di Mauro, Donato (2014)

10-8

10-7

10-6

10-5

10-4

10-3

10-1 100 101 102 103

E2 dN

/dE

[GeV

/cm

2 /s/s

r]

E [GeV]

Unresolved MSPs flux in the high-latitude region

1m BandAverage

Ackermann 2012


High-latitude emission


|b| > 10�MSPs contribution to the IGRB is about 0.1% - 0.9% at the peak (2 GeV) and

about 0.02% - 0.13% of the integrated IGRB intensity. Uncertainty band of O(10) at all energies.

Low-latitude emission: the Fermi-LAT GeV excess


0 0.05 0.15 0.35 0.74 1.5 3.1 6.2 13 25 50

Claim of a gamma-ray excess emission over standard astrophysical background in the inner region of the Galaxy:



0 0.05 0.15 0.35 0.74 1.5 3.1 6.2 13 25 50


Macias & Gordon (2013)


• Galactic Center region: |b| 3.5� & |l| 3.5�

Abazajian et al. (2014), Macias & Gordon (2013), etc.


• Galactic Center region:

• Inner Galaxy: inner tens of degrees about the GC, Daylan et al. (2014), Huang et al. (2013), Hooper & Slatyer (2013), etc.

|b| > 1�

|b| 3.5� & |l| 3.5�

Abazajian et al. (2014), Macias & Gordon (2013), etc.



0 0.05 0.15 0.35 0.74 1.5 3.1 6.2 13 25 50

Calore, Cholis, Weniger (2014)

100 101 102

E [GeV]

10−8

10−7

10−6

10−5

E2dN/d

E[G

eVcm

−2s−

1sr

−1]

broken PL

PL with exp. cutoff

DM bb

DM τ+τ−

GC excess spectrum withstat. and corr. syst. errors



Parametric fits to the spectrum of the GCE emission.


100 101 102

E [GeV]

10−8

10−7

10−6

10−5

E2dN/d

E[G

eVcm

−2s−

1sr

−1]

broken PL

PL with exp. cutoff

DM bb

DM τ+τ−






100 101 102

E [GeV]

10−8

10−7

10−6

10−5

E2dN/d

E[G

eVcm

−2s−

1sr

−1]

broken PL

PL with exp. cutoff

DM bb

DM τ+τ−






100 101 102

E [GeV]

10−8

10−7

10−6

10−5

E2dN/d

E[G

eVcm

−2s−

1sr

−1]

broken PL

PL with exp. cutoff

DM bb

DM τ+τ−




Can young pulsars and MSPs explain the GC excess emission?


Pulsars low-latitude emission


Galactic Center

Inner Galaxy

|b| 3.5� & |l| 3.5�

10� |b| 20�



Galactic Center

Inner Galaxy

|b| 3.5� & |l| 3.5�

10� |b| 20�


Pulsars and MSPs might explain up to 5% of the GeV excess in the Inner Galaxy and

8% in the Galactic Center region.

Pulsars low-latitude emission

1. Spectral argument

Power-law with exponential cutoff is consistent with observed pulsar gamma ray properties.

2. Luminosity (flux) argument

The emission from unresolved pulsars can account for at most 10% of the excess emission in both the Galactic Center and Inner Galaxy regions.

3. Morphology argument

The source distribution is well compatible with a disk-like population. Nevertheless, it is possible to have a “bulge” component. It is anyhow unlikely that it extends up to 10 degrees in latitude.

Pulsars interpretation of the GeV excess


✓t

✓t

?

e.g Cholis, Hooper, Linden [arXiv:1407.5625]


Conclusions✓ Up-to-date and systematic analysis of MSPs population

properties from radio (ATNF catalog) to gamma rays (Fermi-LAT).

✓ MSPs are a marginal component of the IGRB: 0.02% - 0.13% within an uncertainty of O(10).

✓ MSPs are also a negligible contributor to the gamma-ray anisotropy signal measured by the Fermi-LAT, thus indicating that this should be dominated by other sources.

✓ At low latitudes, the contribution from both young pulsars and MSPs can explain up to about 10% of the excess emission measured in the inner part of the Galaxy.

✓ The MSPs interpretation of the Fermi-LAT GeV excess is nowadays in tension with spectral and morphological properties of the MSPs population as we model it from radio and gamma-ray observations.


Conclusions✓ Up-to-date and systematic analysis of MSPs population

properties from radio (ATNF catalog) to gamma rays (Fermi-LAT).

✓ MSPs are a marginal component of the IGRB: 0.02% - 0.13% within an uncertainty of O(10).

✓ MSPs are also a negligible contributor to the gamma-ray anisotropy signal measured by the Fermi-LAT, thus indicating that this should be dominated by other sources.

✓ At low latitudes, the contribution from both young pulsars and MSPs can explain up to about 10% of the excess emission measured in the inner part of the Galaxy.

✓ The MSPs interpretation of the Fermi-LAT GeV excess is nowadays in tension with spectral and morphological properties of the MSPs population as we model it from radio and gamma-ray observations.

Thanks for your attention!! :)


Backup slides







DM annihilation In the Milky Way and in other galaxies.Uncertainty in the DM distribution. !Abdo et al., ApJ’10, Ajello et al., ApJ’12, Di Mauro et al, ’13





!Potential to be one

of the most efficient future means of probing thermally

produced DM. Bringmann, Calore, Di Mauro, Donato, PRD’13


Gamma-ray anistropyAnisotropy of the IGRB recently measured by the Fermi-LAT Collab. in the multipole range :

• 22 month of data • Energy range: • Region: (high latitudes) !➡ Anisotropy detected at small scales, ( ) ➡ Consistent with Poisson-like anisotropy from an

unresolved population of point-like sources. ➡ No-energy dependence

1� 50GeV|b| > 30�

` � 155 ✓ 2�

Ackermann et al.,PRD’12

` = 155� 504

Cp

hIi2 = 9.05± 0.84⇥ 10�6sr �s = 2.40± 0.07


Gamma-ray anistropy from MSPs

The 1σ upper limit angular power from the unresolved MSPs together with Fermi-LAT data.




Possible strategy applied to single out the excess: 1. to generate counts map of Fermi-LAT data for the region of interest

and subtract/mask point sources (PSC Fermi catalogs);

Possible strategy applied to single out the excess: 2. to perform a pixel based maximum likelihood analysis on the

counts map, by fitting the data (bin-by-bin) with a sum of spatial templates.











1. Galactic diffuse emission





1. Galactic diffuse emissionA. CRs (p) vs ISM: emission.⇡0





1. Galactic diffuse emissionA. CRs (p) vs ISM: emission. B. CRs (e) vs ISM: Bremsstrahlung.A. CRs (p) vs ISM: emission.⇡0





A. CRs (p) vs ISM: emission. B. CRs (e) vs ISM: Bremsstrahlung. C. CRs (e) vs ISRF: ICS emission.














2. Isotropic diffuse emission; 3. Fermi Bubbles brightness-uniform

emission; 4. Spherically symmetric template

for the GC emission.



Energy spectra of different components from the template

fit to the data.

2� |b| 20� & |l| 20�

Longitude dependence of the different components in a

latitude strip.




Spectrum of the GCE emission with statistical and background model systematics.


Documents

Francesca Calore Gamma rays from Galactic pulsars: high