Jamie Holder VERITAS Collaboration Bartol Research Institute/ University of Delaware LS I +61° 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 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 +61° 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/ 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° 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 +61° 303: VERITAS-II Results 44 hours of data from September 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 +61° 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 +61° 303: Summary and Straw Proposal In order to constrain the models and understand the nature of LS I 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 observing season, then sample every few days from September February 2009, as well as taking a deep exposure over one orbital cycle. Other ideas/ suggestions welcome!