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!