Gamma rays from Galactic pulsars: high- and lowlatitude

Transcription

1 Francesca Calore Gamma rays from Galactic pulsars: high- and lowlatitude emission Conca Specchiulla, 8th September 2014 based on: F. Calore, M. Di Mauro & F. Donato, arxiv: F. Calore, I. Cholis & C. Weniger, arxiv:

2 The Isotropic Gamma-Ray Background (IGRB) Fermi all-sky gamma-ray map M. Razzano presentation about Fermi results Photon energy: 100 MeV - 10 GeV Francesca Calore - University of Amsterdam 1

3 The Isotropic Gamma-Ray Background (IGRB) Fermi all-sky gamma-ray map - 11 months high latitudes b 10 Resolved - Point Sources Galactic Diffuse Emission - Resolved Point Sources Galactic Diffuse Emission Solar photon & CRs background CRs Background & solar = photon Energy range: 200 MeV GeV Francesca Calore - University of Amsterdam

4 The Isotropic Gamma-Ray Background (IGRB) Fermi all-sky gamma-ray map - 11 months high latitudes b 10 Resolved - Point Sources Galactic Diffuse Emission /E Resolved Point Sources Galactic Diffuse Emission Solar photon & Abdo et al., PRL 10 CRs background CRs Background & solar = photon + Anisotropy at small scales. Energy range: 200 MeV GeV Francesca Calore - University of Amsterdam

5 The origin of the IGRB Unresolved Point Sources Blazars Most abundant population of LAT detected sources Contribution up to % Non-blazars active galaxies Few resolved members, but large unresolved population. Abdo et al., ApJ 10, Ajello et al., ApJ 12, Di Mauro et al, 13 Inoue, ApJ 11, Di Mauro et al, ApJ 13 Star-forming galaxies Outnumber AGN in number density, although 4 detected objects; ca 4-20% Galactic Pulsars Second most abundant I. Tamborra presentation population, but few % of the diffuse flux. Diffuse Processes DM annihilation In the Milky Way and in other galaxies.uncertainty in the DM distribution. e.g. Fornasa et al., MNRAS 13 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. Kalashev et al., PRD 09, Berezinsky et al., PLB, 10 Keshet et al., ApJ 03, Gabici & Blasi, AP 03 Francesca Calore - University of Amsterdam 3

6 The origin of the IGRB Unresolved Point Sources Blazars Most abundant population of LAT detected sources Contribution up to % Non-blazars active galaxies Few resolved members, but large unresolved population. Abdo et al., ApJ 10, Ajello et al., ApJ 12, Di Mauro et al, 13 Inoue, ApJ 11, Di Mauro et al, ApJ 13 Star-forming galaxies Outnumber AGN in number density, although 4 detected objects; ca 4-20% Galactic Pulsars Second most abundant I. Tamborra presentation population, but few % of the diffuse flux. Diffuse Processes DM annihilation In the Milky Way and in other galaxies.uncertainty in the DM distribution. e.g. Fornasa et al., MNRAS 13 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. Kalashev et al., PRD 09, Berezinsky et al., PLB, 10 Keshet et al., ApJ 03, Gabici & Blasi, AP 03 Francesca Calore - University of Amsterdam 3

7 Young & Millisecond pulsars dp/dt [s/s] ATNF MSPs ATNF young Pulsars Fermi-LAT MSPs Fermi-LAT Pulsars P = s MSPs Young Pulsars P [s] 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). Francesca Calore - University of Amsterdam 4

8 Pulsar gamma-ray emission Gamma rays from the conversion of rotational kinetic energy. The initial rotation period slows down for magneticdipole 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: Francesca Calore - University of Amsterdam 5

9 Pulsar gamma-ray emission Gamma rays from the conversion of rotational kinetic energy. The initial rotation period slows down for magneticdipole braking. The slow down is measured by the period derivative: (1) magnetic field (2)rotation period 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: (1) luminosity efficiency Francesca Calore - University of Amsterdam 5

10 Parameter distributions (1) Radio measurements from ATNF catalog (132 sources) B distribution N(B) of ATNF catalog MSPs 15 hlog 10 (B/G)i =8.27 log 10 B =0.30 ATNF Distr Log 10 Gauss. 15 ATNF distr. Gauss. Log 10 Gauss. hlog 10 (P/s)i = 2.54 N(B) 10 N(P ) 10 log 10 P = Log (B) [G] log 10 (B/G) P [s] (1)magnetic field (2)rotation period Novelty Francesca Calore - University of Amsterdam 6

11 Parameter distributions (1) Radio measurements from ATNF catalog (132 sources) hzi =0kpc z 0 =0.67 kpc ATNF distr. Gauss. Exp. 30 hri =7.42 kpc r 0 =1.03 kpc ATNF distr. Gauss. Exp. N(z) N(r) z[kpc] (3)z distribution distance from the Galactic plane r[kpc] (4)r distribution projected distance from the Galactic center Francesca Calore - University of Amsterdam 7

12 L [erg/s] Parameter distributions (2) Gamma-ray measurements from Fermi-LAT 2PC (40 sources) Band = 0.095, = 1 Fermi-LAT MSPs Fermi-LAT UL Ė[erg/s] (1) luminosity efficiency ỷ is the conversion efficiency. Benchmark: =1, =0.095 Empirical uncertainty band: =0.015, 0.65 { } 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 nondetected by the Fermi-LAT. 20 selected sources in the ATNF catalog are the ones (with b > 10 ) expected to be the most powerful gamma-ray emitters if standard values of ử = 1 and ỷ =0.1 are assumed. Francesca Calore - University of Amsterdam 8

13 Parameter distributions (2) Gamma-ray measurements from Fermi-LAT 2PC (40 sources) Spectral energy distribution of observed sources N( ) h i =1.29 =0.37 Fermi-LAT Gauss. N(Ecut) 10 5 hẽcuti =3.38 Ẽ cut =0.18 Fermi-LAT Gauss (2)spectral index log 10 (E cut /MeV) (3)cutoff energy Francesca Calore - University of Amsterdam 9

14 MSP gamma-ray sky Simulated MSPs distribution For each simulated source we derive: - the position: r, z - the gamma-ray luminosity: P, B Ė L S L /(4 d 2 ) a a,e cut F Fermi-LAT source sensitivity Fermi-LAT Coll. arxiv: Francesca Calore - University of Amsterdam 10

15 MSP gamma-ray sky Simulated MSPs distribution For each simulated source we derive: - the position: r, z - the gamma-ray luminosity: P, B Ė L S L /(4 d 2 ) a a,e cut F Fermi-LAT source sensitivity Detected or non-detected source? A. Resolved MSPs (max 39) B. Unresolved MSPs Fermi-LAT Coll. arxiv: Total of about simulated sources for 1000 MC simulations. Francesca Calore - University of Amsterdam 10

16 MSP gamma-ray sky Simulated MSPs distribution Resolved MSPs counterpart Francesca Calore - University of Amsterdam 11

17 MSP gamma-ray sky Simulated MSPs distribution Unresolved MSPs counterpart Francesca Calore - University of Amsterdam 11

18 High-latitude emission Calore, Di Mauro, Donato (2014) Band Average Ackermann 2012 E 2 dn/de [GeV/cm 2 /s/sr] b > E [GeV] 1000 MC realisations of MSPs population. Uncertainty band due to parameter distributions errors and LAT sensitivity. Francesca Calore - University of Amsterdam 12

19 High-latitude emission Calore, Di Mauro, Donato (2014) Band Average Ackermann 2012 E 2 dn/de [GeV/cm 2 /s/sr] MSPs contribution to the IGRB b > is 10 about 0.1% - 0.9% at the peak (2 GeV) and about 0.02% % of the E [GeV] integrated IGRB intensity. Uncertainty band of O(10) at all energies. Francesca Calore - University of Amsterdam 12

20 Low-latitude emission: the Fermi-LAT GeV excess Claim of a gamma-ray excess emission over standard astrophysical background in the inner region of the Galaxy: Francesca Calore - University of Amsterdam 13

21 Low-latitude emission: the Fermi-LAT GeV excess Claim of a gamma-ray excess emission over standard astrophysical background in the inner region of the Galaxy: Galactic Center region: b apple 3.5 & l apple 3.5 Abazajian et al. (2014), Macias & Gordon (2013), etc. Macias & Gordon (2013) Francesca Calore - University of Amsterdam 13

22 Low-latitude emission: the Fermi-LAT GeV excess Claim of a gamma-ray excess emission over standard astrophysical background in the inner region of the Galaxy: Galactic Center region: b 3.5 & l 3.5 Abazajian et al. (2014), Macias & Gordon (2013), etc. Inner Galaxy: inner tens of degrees about the GC, b > 1 Daylan et al. (2014), Huang et al. (2013), Hooper & Slatyer (2013), etc. Calore, Cholis, Weniger (2014) Francesca Calore - University of Amsterdam 50 13

23 Low-latitude emission: the Fermi-LAT GeV excess E 2 dn/de [GeV cm 2 s 1 sr 1 ] broken PL PL with exp. cutoff DM bb DM τ + τ GC excess spectrum with stat. and corr. syst. errors E [GeV] Parametric fits to the spectrum of the GCE emission. Calore, Cholis, Weniger (2014) Francesca Calore - University of Amsterdam 14

24 Low-latitude emission: the Fermi-LAT GeV excess E 2 dn/de [GeV cm 2 s 1 sr 1 ] broken PL PL with exp. cutoff DM bb DM τ + τ GC excess spectrum with stat. and corr. syst. errors E [GeV] Parametric fits to the spectrum of the GCE emission. Calore, Cholis, Weniger (2014) Francesca Calore - University of Amsterdam 14

25 Low-latitude emission: the Fermi-LAT GeV excess E 2 dn/de [GeV cm 2 s 1 sr 1 ] broken PL PL with exp. cutoff DM bb DM τ + τ GC excess spectrum with stat. and corr. syst. errors E [GeV] Parametric fits to the spectrum of the GCE emission. Calore, Cholis, Weniger (2014) Francesca Calore - University of Amsterdam 14

26 Low-latitude emission: the Fermi-LAT GeV excess E 2 dn/de [GeV cm 2 s 1 sr 1 ] broken PL PL with exp. cutoff DM bb DM τ + τ GC excess spectrum with stat. and corr. syst. errors E [GeV] Can young pulsars and MSPs explain the GC excess emission? Calore, Cholis, Weniger (2014) Francesca Calore - University of Amsterdam 14

27 Pulsars low-latitude emission Inner Galaxy 10 apple b apple 20 Galactic Center b apple 3.5 & l apple 3.5 Calore, Di Mauro, Donato (2014) Francesca Calore - University of Amsterdam 15

28 Pulsars low-latitude emission Inner Galaxy 10 apple b apple 20 Galactic Center b apple 3.5 & l apple 3.5 Pulsars and MSPs might explain up to 5% of the GeV excess in the Inner Galaxy and 8% in the Galactic Center region. Calore, Di Mauro, Donato (2014) Francesca Calore - University of Amsterdam 15

29 Pulsars interpretation of the GeV excess 1. Spectral argument Power-law with exponential cutoff is consistent with observed pulsar gamma ray properties. 2. Luminosity (flux) argument t t 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 disklike population. Nevertheless, it is possible to have a bulge component. It is anyhow unlikely that it extends up to 10 degrees in latitude.? e.g Cholis, Hooper, Linden [arxiv: ] Francesca Calore - University of Amsterdam 16

30 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% % 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. Francesca Calore - University of Amsterdam 17

31 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% % 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 :) Francesca Calore - University of Amsterdam 17

32 Backup slides Francesca Calore - University of Amsterdam 18

33 The origin of the IGRB Unresolved Point Sources Blazars Most abundant population of LAT detected sources Contribution up to % Non-blazars active galaxies Few resolved members, but large unresolved population. Abdo et al., ApJ 10, Ajello et al., ApJ 12, Di Mauro et al, 13 Inoue, ApJ 11, Di Mauro et al, ApJ 13 Star-forming galaxies Outnumber AGN in number density, although 4 detected objects; ca 4-20% Galactic Pulsars Second most abundant I. Tamborra presentation population, but few % of the diffuse flux. Diffuse Processes DM annihilation In the Milky Way and in other galaxies.uncertainty in the DM distribution. Potential to be one of the most efficient future means of probing thermally produced DM. Bringmann, Calore, Di Mauro, Donato, PRD 13 Francesca Calore - University of Amsterdam 3

34 Gamma-ray anistropy Anisotropy of the IGRB recently measured by the Fermi-LAT Collab. in the multipole range : 22 month of data Energy range: Region: 1 50 GeV b > 30 ` = (high latitudes) Ackermann et al.,prd 12 ` 155 apple 2 Anisotropy detected at small scales, ( ) Consistent with Poisson-like anisotropy from an unresolved population of point-like sources. No-energy dependence C p hii 2 =9.05 ± sr s =2.40 ± 0.07 Francesca Calore - University of Amsterdam 18

35 Gamma-ray anistropy from MSPs Calore, Di Mauro, Donato (2014) The 1σ upper limit angular power from the unresolved MSPs together with Fermi-LAT data. Francesca Calore - University of Amsterdam 18

36 Low-latitude emission: the Fermi-LAT GeV excess 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); Francesca Calore - University of Amsterdam 13

37 Low-latitude emission: the Fermi-LAT GeV excess 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. Francesca Calore - University of Amsterdam 13

38 Low-latitude emission: the Fermi-LAT GeV excess 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. Francesca Calore - University of Amsterdam 13

39 Low-latitude emission: the Fermi-LAT GeV excess 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 Francesca Calore - University of Amsterdam 13

40 Low-latitude emission: the Fermi-LAT GeV excess 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 A. CRs (p) vs ISM: emission. 0 Francesca Calore - University of Amsterdam 13

41 Low-latitude emission: the Fermi-LAT GeV excess 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 A. CRs (p) vs ISM: 0 emission. B. CRs (e) vs ISM: Bremsstrahlung. Francesca Calore - University of Amsterdam 13

42 Low-latitude emission: the Fermi-LAT GeV excess 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 A. CRs (p) vs ISM: 0 emission. B. CRs (e) vs ISM: Bremsstrahlung. C. CRs (e) vs ISRF: ICS emission. Francesca Calore - University of Amsterdam 13

43 Low-latitude emission: the Fermi-LAT GeV excess 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 A. CRs (p) vs ISM: 0 emission. B. CRs (e) vs ISM: Bremsstrahlung. C. CRs (e) vs ISRF: ICS emission. Francesca Calore - University of Amsterdam 13

44 Low-latitude emission: the Fermi-LAT GeV excess 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 A. CRs (p) vs ISM: 0 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. Francesca Calore - University of Amsterdam 13

45 Low-latitude emission: the Fermi-LAT GeV excess 2 apple b apple 20 & l apple 20 Energy spectra of different components from the template fit to the data. Longitude dependence of the different components in a latitude strip. Calore, Cholis, Weniger (2014) Francesca Calore - University of Amsterdam 14

46 Low-latitude emission: the Fermi-LAT GeV excess Spectrum of the GCE emission with statistical and background model systematics. Calore, Cholis, Weniger (2014) Francesca Calore - University of Amsterdam 15