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Jamie HolderVERITAS Collaboration
Bartol Research Institute/ University of Delaware
LS I +61LS I +61°° 303: The High Energy View 303: The High Energy View
"Getting Involved with GLAST" Workshop, Harvard, June 2007
LS I +61° 303
• HMXB composed of a Be star with circumstellar disk and a compact object (neutron star or BH)
• highly eccentric ( e=0.72±0.15)
• distance 2 kpc
• orbital period 26.4960 days (strong periodic radio outbursts)
• Detected by COS-B; confirmed by EGRET
• MAGIC detected variable TeV emission
J.Casares et al (MNRAS 360, 1105 (2005))
LS I +61LS I +61°° 303: High energy emission. 303: High energy emission.
LS I +61° 303: supporting evidence
• Radio observations show rotating tail
• X-ray observations show no spectral features (no jet break, accretion disk bump)
• Supports pulsar wind model
Dhawan et al.Proceedings of the VI Microquasar Workshop
Romero et al. astro-ph/0706.1320
• Relative wind strengths are such that you cannot produce simple elongated shape seen in VLBI images.
• Gamma-ray lightcurve is more easily explained by variable accretion
• Prefer microquasar model
pulsar wind
Be star wind
• Within both of these scenarios, the details can still vary widely: e.g. leptonic or hadronic particle acceleration? Importance of Be star wind clumping? Is the gamma-ray lightcurve dominated by photon-photon absorption? etc etc.
LS I +61° 303 - data
Chernyakova et al. MNRAS, 372, 1585, 2006
• Also 50ks exposure with Chandra at phase 0.0
• but, in general, we don't have a very detailed picture of the emission from LS I +61° 303
LS I +61LS I +61°° 303: VERITAS-II Results 303: VERITAS-II Results• 44 hours of data from September 2007 - February 2008
• Majority of observations with only two telescopes
• Four Telescopes now operating - sensitivity for future observations will be much better.
Source Strength(% Crab Flux)
Time for a 5σ detection
100% 1.45 mins
20% 20 mins
10% 67 mins
5% 4 hours
3% 10 hours
2% 23 hours
1% 89 hours
measured 3 Telescope sensitivity
Maier et al, Merida ICRC , 2007
LS I +61LS I +61°° 303: Swift Results 303: Swift Results
• Swift XRT observations from September to December 2007
• Preliminary analysis shows strong variability
• Orbital structure of lightcurve is not terribly clear
• Contemporaneous UVOT data also available
Holder, Falcone & Morris, Merida ICRC , 2007
LS I +61LS I +61°° 303: Summary and Straw Proposal 303: Summary and Straw Proposal
• In order to constrain the models and understand the nature of LS I +61 303 and the origin of the high energy emission we need better data
• This must be contemporaneous, broad-band, well sampled, and with time resolved spectra.
• It should cover multiple orbital cycles
• GLAST will provide excellent coverage over its energy range
• These observations should be supported at other wavelengths by e.g.:
• TeV: VERITAS-IV / MAGIC (II?)
• Optical: Swift / VERITAS Multiwavelength Associates
• X-ray: Swift / RXTE
• Radio: NRAO?
• A possible scenario, at least for VERITAS-IV, would be to make limited observations in the 2007 - 2008 observing season, then sample every few days from September 2008 - February 2009, as well as taking a deep exposure over one orbital cycle.
• Other ideas/ suggestions welcome!