Adam Hill

R. Dubois (SLAC), R. Corbet (UMBC/NASA, GSFC), G. Dubus (LAOG), T. Tanaka (SLAC), D. Torres (ICREA, Barcelona)on behalf of the Fermi-LAT collaboration

44th Rencontres de Moriond

Fermi was successfully launched June 2008

LAT: 20 MeV – 300 GeV 1’ PSLA for bright sources 2 str FOV In survey mode scans the

whole sky every 3 hours GBM:

8 keV- 30 MeV Views whole unocculted

sky

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A number of X-ray binaries have been detected at > 1 TeV:PSR B1259-63

Radio pulsar in 3.5 yr orbit of Be star HESS detection at periastron

LS 5039 HESS detects 3.9 day orbital period

LS I +61°303 Be HMXB shows periodic radio flares MAGIC & VERITAS see VHE emission

modulated on 26 day orbital period

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3EG J0241+6103 has been associated with LS I +61°303 but position is uncertain.

Hartman et al. (1999)

Evidence of variability found but no periodicity.

Tavani et al. (1998)

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3EG1824-1514 is coincident with LS 5039 but has a 0.5° error box and no indication of variability

Hartman et al. (1999)

SED of LS 5039 including the spectra of EGRET & HESS. The 2 X-ray measurements are from RXTE & XMM.

de Naurois. (2005)

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LS I +61°303 has been fitted to R.A.=40.076, Dec.=61.233 with 95% error radius of 1.8’. This location is consistent with the known position of the optical counterpart.

Flux variability is also clearly evident

PRELIMINARY

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We detect a periodicity in the LS I +61°303 light curve at 26.4±0.5 days

Folded light curve indicates peaks of emission around periastron.

PRELIMINARY PRELIMINARY

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Investigating signs of orbit to orbit variability

As more orbits are observed evidence will become clearer

J.Casares et al (2005) N.B. The light curve is not background subtracted

PRELIMINARY

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Veritas observations in 2006-2007 showed a strongly variable flux at 300 GeV – 5 TeV.

Maximum flux is found during most orbital cycles at apastron.

Acciari et al. (2008)

MAGIC observations in 2005-2006 also showed variable emission (200 GeV – 4 TeV).

See significant flux increase at phase 0.45-0.65

Albert et al. (2006)

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Unbinned likelihood fitting of the Fermi flux to a power law yields

F = A E-γ:

Flux (E>100 MeV) = 0.83 ± 0.04 (stat) ± 0.21 (syst) 10-6 ph/cm2/s

γ = 2.41 ± 0.03 (stat) ± 0.17 (syst)

(Paper in preparation)

(N.B. – The TeV spectral data is not contemporaneous and is not phase averaged)

Points: Fitted energy binsRed: Fermi unbinned power law fitGrey: EGRETBlue: MAGIC (Only phase 0.4-0.7) Veritas data points overlaid(systematic errors not shown)

PRELIMINARY

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MAGIC reported a flare at VHE from Cyg-X1 in 2006.

We are monitoring 68 sources on a daily basis.

Challenging work due to the high contribution of diffuse emission in the galactic plane.

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The LAT has and will discover new unknown sources; some of which could potentially be gamma-ray binaries.

2 bright transients detected in the Galactic Plane (ATels 1771 &1788). 3EG J0903-3531 3EG J0903-3531

Fermi J0910-5041

PRELIMINARY

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First detection in the GeV domain of flux

modulation on the 26.5 day orbital period.

Definitive detection of LS I +61°303 by

Fermi.

LS 5039 to be investigated.

More binaries to look for both persistent and

flaring.

Lots more work to do...

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Pulsar wind model

Massive star

Pulsar wind

Pulsar

e+/e-

Inverse ComptonSynchrotron

Assume orbital modulation of B (expected in pulsar wind model)

Be star

Pulsar wind

Rshock

shockRB /1

High B Low B