Olaf Reimer Innsbruck University & KIPAC Stanford

Variable Galactic Gamma-Ray Sources, Barcelona April 18, 2013 • Montmerle & Cesarsky 1979: Link between “SNOBs” and gamma-ray sources “New evidence at X-ray and COS-B gamma-ray frequencies for non-thermal phenomena in Wolf-Rayet ” (Pollock 1987)

“Possible identification of unidentified EGRET sources with Wolf-Rayet stars” (Kaul & Mitra 1997)

“We propose, on the basis of positional correlation, the possible association of 8 EGRET unidentified galactic plane sources with Wolf-Rayet stars having strong stellar winds.” → hypothesis for few unidentified low-latitude UNIDs Unidentified 3EG gamma-ray sources at low galactic latitudes (Romero Benaglia Torres 1999)

A variability analysis of low-latitude unidentified gamma-ray sources (Torres , Romero + 2001) e.g. Eichler & Usov 1993

• Radio synchrotron radiation from collision region „proof“ for: existence of relativistic e- existence of magnetic field

⇒ inverse Compton (IC) scattering in photospheric radiation field & relativistic e--bremsstrahlung are garantueed HE processes

• ~100+ EGRET unidentified γ-ray sources: - population studies imply spatial correlation of some Unids with massive populations (OB-associations, WR-, Of-stars, SNRs) [Montmerle 1979, Yadigaroglu & Romani 1996, Romero et al. 1999, …]

⇒ role of colliding winds from massive stars as γ-ray emitter ? [e.g. White 1985, Chen & White 1991, White & Chen 1992, ...: NT processes in single massive stars Usov 1992, Stevens et al. 1992, ...: thermal X-ray production in massive binaries Eichler & Usov 1993, Benaglia & Romero 2003, Pittard et al. 2005, ....: NT processes in m. binaries] expected mean γ-ray (>100 MeV) ~1032-35 erg/s based on Thomson-limit appr. for IC emission process, NT bremsstrahlung, π0-decay γs,...

still to investigate: - Klein-Nishina (KN) & anisotropy effects in IC scattering process,

- propagation effects (tconv ~ trad !) & adiabatic losses (tad ~ trad !) , - secondary particle production from hadronic interactions, - time-dependent calculations • uniform wind • neglect interaction of stellar radiat. field on wind structure ⇒ consider only wide binaries • cylinder-like emission region (x >> r, emission from large r negligible) • radiation field from WR-star negligible (D >> x)

• photon field of OB-comp. monochromatic: n(ε) ~ δ(ε−εT) , εT ≈ 10 eV electron distribution isotropically • convection velocity V = const. • magnetic field B = const. throughout emission region Phase=0.2 Phase=0.67

Phase=0.95 Phase=0.8 Phase=0 Phase=0.25

0.75

B0.5V 0.5 0 WN8 l.o.s.

Phase=0.75 0.25 Phase=0.5 • Klein-Nishina effects may influence spectral shape & cutoff energy of IC-photon spectrum • propagation effects may lead to a deficit of high-energy photons in the convection region (spectral softening) • variability of γ-ray emission expected due to - modulation of (target) radiation field density in eccentric - changes in wind outflow - modulations of emitting region (size, geometry) - orbital variation of observed IC scattering angle (time scale of !) ⇒ massive binary systems are predicted to show orbital variability at γ-rays ⇒ WR 140 & WR 147 detectable with GLAST-LAT at all phases if electrons reach sufficient high energies • 227 WR-stars detected in the Milky Way [van der Hucht 2001: 7th catalog of gal. WR-stars] • WR-binary frequency (incl. probable binaries) ~ 39 % (indications: photometric periodicity, absorption lines/dilution of emission lines, dust formation, X-ray excess, radio imaging,...) • 7 out of 9 non-thermal (radio !) WR-sources are binaries [Dougherty & Williams 2000]

• WR 20a – (at that time) the most massive in our (two stars of

~80 Msolar in a 3.8 day ) s t n v e e 150point source s x c e e

# 100 for H.E.S.S. observed source extension 50 σ = 0.18° ± 0.02° WR20a WR20b 0

-50 0 0.05 0.1 0.15 0.2 0.25 θ2 (deg 2) VHE γ-ray image

• origin of energetic γ-rays unlikely the WR stars itself  HESS J1023-575 is an extended and non-variable source

• revisitied in the light of more data and addition MWL information (Abramowski+ HESS 2010)

• MAGIC observations towards WR147 (Aliu+ MAGIC 2008)  orbital parameter constraints (Reimer & Reimer 2009) No coincidences in 1FGL, none in 2FGL → dedicated population study Study based on sample selection as of Reimer & Reimer 2007 WR140 WR147

 Fermi-LAT data gives most sensitive upper limits on CWBs to date

 WR 140 and WR 147: data is sufficiently sensitive to test emission models and/or constrain orbital parameters

 theoretical models need to be revised (e.g, acceleration efficiency, ease for producing exactly matching predictions)

 Comparison with WR 140 hints at comparably more efficient gamma-ray emission processes in η Car system ∅ COS-B

∅ EGRET

! AGILE !

!! FERMI-LAT !!

DETECTION OF GAMMA-RAY EMISSION FROM THE ETA-CARINAE REGION (Tavani + AGILE 2009) DETECTION OF GAMMA-RAY EMISSION FROM THE ETA-CARINAE REGION (Tavani + AGILE 2009) Fermi Large Area Telescope Observation of a Gamma-ray Source at the Position of (Abdo+ FERMI-LAT 2010) location spectrum

non-confirmation of AGILE flare PARTICLE ACCELERATION IN THE EXPANDING BLAST WAVE OF η ’S GREAT ERUPTION OF 1843 (Ohm+ 2010)

High-energy radiation from the massive binary system Eta Carinae (Bednarek & Pabich 2011) η Carinae: a very large hadron collider (Farnier+ 2011) Gamma-ray follow-up studies on η Car (Reitberger + FERMI-LAT 2012)

Spatial analysis 0.2-10 GeV 10-300 GeV Gamma-ray follow-up studies on η Car (Reitberger + FERMI-LAT 2012)

Spectral analysis Gamma-ray follow-up studies on η Car (Reitberger + FERMI-LAT 2012) Lightcurve & variability analysis

0.2-10 GeV

10-300 GeV Gamma-ray follow-up studies on η Car (Reitberger + FERMI-LAT 2012)

Spectro-variability

first 10 months latter 25 months Gamma-ray follow-up studies on η Car (Reitberger + FERMI-LAT 2012)

external black-body absorber internal absorber (hot shocked gas (hot gas surrounding the binary system?) in the wind collision region) Spectro-variability unabsorbed spectrum

γγ attenuated spectrum interpretation in a Colliding Wind Binary model (e.g. Bednarek and Pabich 2011, Reimer et al. 2006)

● two spectral components can be accounted for by a) two underlying particle populations (as in Farnier et al. 2011) → would imply same amplitude of variability in both spectral components → problematic, does not correspond to observations

b) one underlying particle population + γγ absorption → reproduces observational features reasonably. → prefered interpretation

● scenario of Ohm et al. 2010 (no modulation expected) can be excluded

● prediction for variability towards periastron! (confirmation of ID, model)

● still non-detection with HESS (Abramowski+ HESS 2012)  HESS 2 commissioning target