Galactic GeV
Gamma-ray
Sources Observedby Fermi
Katsuhiro Hayashi(ISAS/JAXA)
On behalf of the Fermi-LAT
Collaboration
Wagner+15

Jan 13, 2016, CTA Conference@Kashiwa, ICRROutline• Status of Fermi-LAT Gamma-ray Analysis•Catalog Sources•Nova/Pulsars•SNR/Diffuse Gamma-rays•GeV excess at the Galactic Center•Summary

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Status of Fermi-LAT Gamma-ray Analysis•Launched in 2008 and steady operation for ~7.5 years•Update the instrumental response function from Pass 7 to Pass 8•Substantial improvementin the capability– Acceptance is ~2 times
larger at very low (<100 MeV) and veryhigh (> 100 GeV)
energies– 40% increase in pointsource sensitivity
http://www.slac.stanford.edu/exp/glast/groups/canda/lat_Performance.htm• Direct impact on the LAT science performance• Pass 8 data publicly available as of June 2015
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The First LAT All-sky Map
E > 100 MeV, Duration: a few days

Katsuhiro Hayashi

4The 3FGL All-sky Map
E > 1 GeV, Duration: 48 months

Katsuhiro Hayashi

5The 2FHL All-sky map
50 GeV < E < 2 TeV, Duration: 80 months
Processed by Pass 8 datasmoothed with a Gaussian kernel minimizing S/N
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Galactic Sources
Ackermann+15
arXiv: 1508.04449•39 Galactic objects, 13 unassociated and 9 Dark Accelerator (|b|<10°)– PWNe/SNRs represent 87% of the Galactic population– Hard spectra: median photon-index ~2•5 new extended sources are found (TS>75)•Count map with E > 50 GeV matches to the H.E.S.S. Galactic plane
surveyKatsuhiro Hayashi

7Gamma-ray Novae/Pulsars

Katsuhiro Hayashi

8Gamma-rays from Nova
• Resulting from thermonuclear explosions on the surface of WD
Fermi-LAT > 100 MeV Detection
Ackermann+14 arXiv: 1408.0735• Compact cataclysmic variable:– Classical novae– WD + Main sequence– Roche lobe overflow• Symbiotic system:– Symbiotic/Recurrent novae– Massive WD + Red Giant– Outburst due to accretion froma red giant wind
– V407 Cyg
Katsuhiro Hayashi

9V339 Delphini
Ahnen+15

August 2013
OpticalIC model>100 GeV (LAT)>300 GeV (MAGIC)

Katsuhiro Hayashi

50 days• IC model of thermal photons from thephotosphere by the electrons accelerated
in the nova shock• Combined the GeV and TeV results limit
the ratio of proton to electron luminosities
to Lp < 0.15 Le
10LAT-discovered Pulsar
Abdo+13 arXiv: 1501.02003• 117 pulsars were identified by 2013 (2nd Pulsar Catalog, Pass 7)– millisecond pulsars(40), young radio-loud(42), young radio-quiet(35)• 160 pulsars are detected by 2014 (Pass 8)– growing fraction of MSP: 18%(2009) —> 43%(2014)
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Pulsar Binary System
PSR J2032+4217 (Lyne+15)
Be star • Gamma-ray and radio-emitting pulsar• Timing models of binary motions fit
the data well —> NS around a Be
star with periastron every 25 years• Expected flaring activity near
periastron in 2018
PSR B1259-63 (Caliandro+15)• In orbit around a Be Star withperiastron every 3.4 years• Flare activity (>50% pulsar’s
rotational energy loss) in both 2010
and 2014, but with somewhat
different characteristics
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VHE Pulsar
Ackermann+15 arXiv: 1305.4385

Ansoldi+15, Saito+15Crab• 12 LAT pulsars were shown to emit pulsations at > 25 GeV– Very high energy gamma-rays (> 100 GeV) from Crab, Vela Pulsars (PWN)– Does not follow a model of PL with exponential cut-off– PL with break around 5 GeV– J0614-3329: candidates of the next very high energy pulsar
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SNR/Diffuse Gamma-rays

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SNRs Observed by Fermi-LAT• SNRs with GeV gamma-rays– 13 identified SNRs: 9 interacting, 4 young SNRs (by 2014)
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Individual Studies of SNR
Cas A

Abdo+10 arXiv: 1001.1419

1GeV

DiVenere et al. 6th Fermi Symposium

1GeV• Young SNRs (DiVenere et al. 6th Fermi Symposium)– Cas A: hadronic model favored thanks to the increased sensitivity– Tycho: no clear evidence that is dominated by hadronic gamma-rays• Middle aged SNRs (Acero et al. 6th Fermi Symposium)– G326.3-18: different spectral signatures b/w SNR and PWN components(Acero+15• TeV SNRs RXJ1713.7-3946, RCW86, SN1006 etc
arXiv: 1506.02307)– Photon index (Γ<1.8) in 0.1 < E < 100 GeV– Bulk emission produced by accelerated electrons (synchrotron, IC)
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SNR Systematic Study• Spatially overlap of sources
detected at GeV energies
with SNRs known fromradio survey

Acero+15 arXiv: 1511.06778
young interacting with MCs• 30 sources and 14 marginal
candidates (with a false
identification < 22%)
• 4 new extended SNR
Candidates• Constrain SNRs’ aggregate, contribution to the study of Galactic CRs– Support changes in spectral slope in TeV range, and a softening andbrightening in GeV range with SNR age– With GeV and MW data, the candidates and upper limits are within
expectations if SNRs provide the majority of Galactic CRs
Katsuhiro Hayashi

17ISM/CRPlanck Collaboration XXVIII

Tibaldo+15(distance from the disk)•CR densities using gamma-rays produced by CR interactions with ISM– High and intermediate-velocity clouds: decease CR density with the altitude– Nearby MCs: do not expect CR gradient in small distance range
Planck Collaboration XXVIII

Katsuhiro Hayashi

gamma-rays

Planck dust

•Correlations with thermal dust
emission in nearby MCs– Study of DNMs, CO-to-H2
conversion factor and dust
properties
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Fermi Bubble• Data analysis : ~50 months, 100 MeV- 500 GeV– Evaluate systematic uncertainty due to the diffuse emission model• Spectrum modeled by log parabola or PL with an exponential cut-off– Exclude a simple PL model
Ackermann+14 arXiv: 1407.7905

Excessemission• Both leptonic and hadronic scenarios describe the spectrum well
– hadronic model including IC emission from secondary leptons• Leptonic model can explain microwave haze for B~8μG
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GeV Excess LineAckermann+13 arXiv: 1305.5597

Ackermann+15 arXiv: 1506.00013• Tentative emission line from the Galactic center was reported at ~133
GeV in the first 3.7 year data (Pass 7)• The excess has further decreased in the 5.8 year data (Pass 8)– The feature is still marginally significant for Earth limb data
– More stacked data and sophisticated background models are needed
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DM Search (dSphs)
Ackermann+14 arXiv: 1310.0828

Wagner+15

DM annihilation
crosse section

thermal reliccrosse section
Katsuhiro Hayashi• Dwarf spheroidal satellite
galaxies (dSphs) are
excellent targets for theindirect detection of darkmatter• New 8 dSphs candidates arefound by DES• No significant gamma-ray• Upper limits on DMannihilation cross section
from a combined analysis• These constraints lie below
the canonical thermal reliccross section for DM ofmass < 100 GeV
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Excess at Galactic Center

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Excess at the Galactic Center• GeV gamma-ray excess at the Galactic Center is claimed in many papers
Goodenough & Hooper+09,
Vital & Morselli 09, Boyarsky+11,
Abazjian & Kaplinghat 12,Abazajian+14, Daylan+14,
Huang+15, Carlson+15, Ajello+15,Zhou+14, Calore+15…

•Extended diffuse emission above– Galactic diffuse emission model– gamma-ray emission at Sgr A*– other 2FGL sources•Radial profile Fγ ∝ r-(2.2-2.6)
Daylan+14• Caveats for using the Galactic diffuse emission model
Model is optimized for reproducing all sky diffuse emission and nottuned for the analysis of specific region like the Galactic center
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Detailed Analysis by LAT Team
(Ajello+15 arXiv: 1511.02938)• Focus on a 15°x15° region around the Galactic Center• 1 — 100 GeV data taken during 62 months• Constructed specialized interstellar emission models (IEMs)– Separation of emission from the inner ~1 kpc about the GC fromthe fore- and background emission
Katsuhiro Hayashi

24Modeling the Interstellar Emission• Construct IEM with a combinationof templates from model GALPROP(Ackermann+12 arXiv: 1202.4039)– Two models of CR source
distribution• Determine intensity for π0 and IC
contributions in galactocentric rings
Pulsars (Yosifov & Kucuk 04)
OB stars (Bronfman 00)– intensity scaled Pulsars/OBstars– intensity & index scaled modelPulsars/OBstars 4 IEMs

Katsuhiro Hayashi

25Modeling the 15°x15° ROI• Model the emission from 15°x15°
ROI• Point source model in ROI is selfconsistently constructed– Identify point source
candidates by“PGWave” (Damiani +97)
– Find and characterize the point
sources near the GC for eachIEM• Source-seeds and IEMs are combined in a maximum Likelihood fit– Intensities for HI/H2 (π0) and IC are determined by fitting data
concurrently with point source candidates• Bremsstrahlung and HII (π0) emissions are fixed to GALPROP prediction
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Fitting Results (Pulsars index-scaled)

Residual Map(1.6–10 GeV)• Residuals map in which interstellar emission and point-source
contributions are subtracted– Some general peaks are seen around the Galactic center• IC contribution is dominant– strongly enhanced compared to previous studies
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Fitting with Additional Component

Residual Map(1.6–10 GeV)

•Test the possibility of additional components in the Galactic center– Centrally peaked template model (2D gaussian, NFW, unresolved sources)•Overall improvement for all the spectral models up to ~30 GeV– IC is ~2-3x smaller, HI ring is ~2-5x larger•Still has extended positive residuals on the Galactic plane
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Spectrum Additional Component (NFW)• Differential fluxes in the ROI of the additional component (NFW model)– Spectra are modeled with an exponential cut-off power-law with fit
uncertainties for the normalization and spectral-index• Different spectral shapes depending on the IEMs– Interpretation for residuals is difficult
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Possible Interpretations• DM annihilation (Hooper & Goodenough 09; Vitail & Moselli 09)– Typical DM annihilation spectra, cross-section• Star formation in central molecular zone (Carlson +15)
– IC emission from electrons accelerated by star formation• Leptonic outburst from the SMBH (Petrovich +13)
– Multiple bursts with varying injection indices could do the trick• Millisecond gamma-ray pulsar (O’Leary +15; Bartels+15)– MSP in globular clusters, spilled out into the bulge by tidal disruption• Unresolved point sources (Lee+15)– By using Wavelet analysis, 5-10% of the flux can be accounted for by
a population of unresolved point sources, which can absorb theexcess
Katsuhiro Hayashi

30Future Prospectivity• More stacked data can reduce systematic uncertainties in the diffuse
emission model, and define better source populations.
→ Resolve the interpretation of the inner Galaxy GeV excess• Thermal relic cross section for WIMP masses in 200—400 GeV byobservations of dSphs → hint of DM origin from the Galactic Center• CTA necessary to probe WIMP models ~1 TeV
DM annihilation crosse section

Katsuhiro Hayashi

Ackermann+15 arXiv: 1503.02641
expected sensitivities of LAT and CTA are overlaid31

Summary• Fermi-LAT yields significant progress on the study of Galactic GeV
gamma-ray sources (substantial improvement of the response function)– Update of catalog sources (3FGL, 2FHL, pulsar, SNR)
– Gamma-rays from binary systems (nova, pulsar)– SNR study (individual and systematic studies)– Diffuse gamma-rays (ISM/CR, Fermi Bubble)– Dark Matter search (GeV line, dSphs)– Excess at the Galactic Center– Detailed analysis subtracting fore/backgrounds emissions– Residuals are robust but the cause is still unclear• More stacked Fermi-LAT data and CTA results are expected to beadvanced for further study of Galactic GeV gamma-ray sources
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