Jamie Holder
Bartol Research Institute/ University of Delaware

2009 Fermi Symposium

Washington D.C

Overview• Why are they interesting?
• Some history• Observational status• Interpretation• Some questions we can answer soon

The Gamma-ray sky
Fermi-LAT + TeV

Binaries

Cyg X-3
LS I + 61 303

Cyg X-1

LS 5039

Cen X-3
PSR B1259-63

HESS J0632+057

Why are these few so interesting?
• Binaries are the only variable galactic TeV sources• They are natural particle accelerators operating under varying,
but regularly repeating, environmental conditions• Provide a constraining laboratory for models of particle
acceleration, and gamma-ray production, emission and absorption
processes.
• May provide the keys to an understanding of astrophysical jets
• Each system is unique – and the population, as well as the data
quality, is increasing

Brief history of High Energy binary results• Cygnus X-3 caused a lot of
excitement in the 70’s/ early 80’s
• Among 13 gamma-ray sources, COSB detected 2CG 135+01; the error box
contained a periodic radio and X-ray
source (LS I +61° 303).
• Various EGRET sources wereassociated with binaries• 3EG J0241+6103 (LS I +61° 303), Tavaniet al., ApJ 1998
• 3EG J1824-1514 (LS 5039), Paredes et al.,Science, 2000
• 2EG J2033+4112 (Cyg X-3) Mori et al.,ApJ, 1997

• But weak or no variability, noperiodicity, and limited positional
accuracy

3EG J0241+6103, Tavani et al.,1998

• 2004 – 2006: a few TeV sources
strongly detected >100 GeV

LS 5039, HESS

• PSR B1259-63 (HESS)• LS 5039 (HESS)• LS I +61° 303 (MAGIC)• With good positions and clear,orbitally modulated variability, theassociations are definitive.
• Fermi-LAT provides the next leap
• Good sensitivity• Source localization• Near continuous monitoring• Firm ID of LS I +61° 303, LS 5039

• Stop press! AGILE detects transientemission from Cygnus X-3• New LAT results at this conference

LS I +61° 303, Fermi-LAT

PSR B1259-63/
SS2883• 48 ms pulsar orbiting a B2ecompanion with inclined disk
• 3.4 year, high eccentric orbit• ~0.7 A.U separation atperiastron (10 AU at apastron)• Detected by HESS during
2004 periastronLS 5039

to scale• Compact object orbiting an O6.5V
companion (23M)~0.1 AU• 3.9 day, inclined orbit, e=0.35• HESS measure clear periodicity >200GeV• emission peaks at inferior conjuction• spectrum varies~0.2 AUto observer
HESSHESSLS 5039

to scale• Detected by Fermi-LAT (BSL)~0.1 AU• Orbital modulation now measured• See Dubois, this Symposium(and arXiv:0910.5520, ApJL 706, L56)
• Flux variability anti-correlated withHESS• Spectral variability, and ~2 GeV cutoff observed~0.2 AUto observer
Fermi

Fermi

HESS

LS I +61° 303

Superior
conjunction

Apastron
0.7 AU• Compact object orbiting an B0Ve
companion (12.5M).
• 26.5 day, inclined orbit, e=0.54• extended radio structures; microquasar?
• Detected by MAGIC, then VERITAS• Strong emission only detected near
apastron (ϕ=0.5-0.8)

Periastron
0.1 AU
Inferior
conjunction• MAGIC measure periodicity, and X-ray
correlation in 60% of one orbit (arxiv:0910.4381)• X-ray emission is periodic, but shows morethan just orbital variability, and someevidence for bright flares (e.g. Smith et al,2009)

Aragona et al. ApJ 2009

MAGIC

Swift/ XMM

LS I +61° 303

VERITAS• Detected by Fermi-LAT (BSL)• Orbital modulation well measured• See Dubois, this Symposium(and Abdo, ApJ, 2009)• Emission peaks near periastron• ~6 GeV cut-off observed

Fermi

Fermi

MAGIC/VERITAS

What’s going on?
Accretion powered

Wind-driven

Mirabel (Science 309, 714, 2006)

A few things to think about (not exhaustive)…
What is the power source?

Accretion-powered jet

What is the particle
acceleration mechanism?

Jet shocks

Pulsar wind

Magnetic reconnection

Wind shocks

Leptonic

What are the dominant particles?

Hadronic

How are the γ-rays produced?

Pion decay

InverseComptonCurvature
Radiation

Where are the γ-rays produced?

Near the jet

Wind collision
regionPulsar windzone

Circumstellar
environment
What modulates the flux?
Other effects?

Geometry

Wind clumping

Pulsar magnetosphere

Photon fields
Pair cascades

Matter density

B-fields

Unknown geometries

Many of these are not mutually exclusive…

• Difficult, but detailed predictions
can be made, and are beginning to bestrongly tested• (e.g. Sierpowska-Bartosik & Torres, LS 5039)
100 GeV -10 TeV

10-100GeV/1-10GeV

1 GeV -10 GeV

The microquasars• Cygnus X-1 21±8 M compact object, 40±10M O9.7Iab companion.
• 5.6 day circular orbit• Accretion powered• MAGIC observed 40 hours: no emission• See one episode at ~4σ, close to an X-rayflare• Cygnus X-3 10-20 M compact object,
Wolf-Rayet companion.
• 4.8 hour orbit• Accretion powered• AGILE detect 4 episodes of GeV emission
during soft X-ray states• New Fermi-LAT results presented yesterday(Stephane Corbel)• Orbital modulation gives firm identification

AGILE

A mystery…
• HESS J0632+057• Unidentified TeV source in theGalactic plane• A rare unresolved source• VERITAS non-detection implies
gamma-ray variability• X-ray & radio sources coincident witha Be star (MWC148)• Swift measures long term variability
Falcone et al. submitted to ApJ 2009

Swift

Summary• Gamma-ray binaries constitute a small, but uniquely valuable, populationof high energy sources.
• The field is extremely active: some key observational questions which
may be resolved shortly• What is the cause of the Fermi-LAT GeV cutoffs?
• What other binaries does the LAT see?
• What will HESS & Fermi see from PSR B1259-63 in 2010/2011?
• Does Cygnus X-3 produce TeV emission? When?
• What is HESS J0632+057?
• Ongoing multiwavelength campaigns on LS I +61° 303 andHESSJ0632+057. See VERITAS home page and gammamw list fordetails.