Abstract

1. The -ray Binaries LS 5039 and LS I +61 303 in the Fermi Era M. Virginia McSwain (Lehigh Univ.), Christina Aragona (Lehigh Univ.), Paul S. Ray (NRL), Jacob M. Hartman (NRC Research Fellow, NRL), Mallory S. E. Roberts (Eureka Scientific), Scott M. Ransom (NRAO), Sean Dougherty (NRC Herzberg), Vivek Dhawan (NRAO), Guy Pooley (Cambridge, MRAO) KPNO Coudé Feed telescope The observing run starts Oct. 16! M. V. McSwain et al. will monitor the Be disk in LS I +61 303 over a full 28-day orbital period for simultaneous observations with the RXTE program. VLA, VLBA S. Dougherty is leading an ongoing radio flux monitoring program of LS I +61 303 in conjunction with the continuous RXTE program. See Figs. 7-8 for results. Australia Telescope Compact Array M. Roberts is leading the radio flux monitoring of LS 5039, which began Oct. 1. Ryle Telescope G. Pooley is performing occasional radio flux measurements of LS I +61 303 as that telescope is being refurbished to join the Arcminute MicroKelvin Imager (AMI) array. Green Bank Telescope S. Ransom is leading radio pulsar searches in LS I +61 303 and LS 5039. He is currently processing the results from LS I +61 303 and one observation of LS 5039, but no strong candidate pulses have been found yet. Additional observations of LS 5039 are scheduled for late October. Abstract LS 5039 and LS I +61 303 are exceptionally rare examples of HMXBs with MeV-TeV emission, making them two of only four known "-ray binaries". Both have long been modeled as microquasars with stellar winds accreting onto a compact object, producing high energy emission and relativistic jets. However, their emission properties might be better explained by a relativistic pulsar wind colliding with the stellar wind. To resolve the controversy, we are exploiting a unique opportunity to combine Fermi monitoring with a coordinated multiwavelength campaign to identify the nature of the two sources and understand the high energy emission mechanisms. We present preliminary results from our ongoing RXTE, optical, and radio flux monitoring as well as pulsar searches with the Green Bank Telescope. An Observers Dream! (Or Worst Nightmare?) Our team has a number of ongoing and upcoming observing programs across the electromagnetic spectrum in order to comprehend the stellar/compact companion interactions in both of these -ray binaries. Due to differences in their declinations, a number of different facilities are participating. Fermi Gamma-ray Space Telescope Fermi is currently surveying the -ray sky with the Large Area Telescope. Light curves for LS I +61 303 are currently public, but LS 5039 data are proprietary and will not be released until Phase 2. RXTE P. Ray is leading an ongoing semi-weekly X-ray flux monitoring program of LS I +61 303 and LS 5039 with RXTE. Starting in late October, a second RXTE program will observe LS I +61 303 closely over one 28-day orbital period. See Figs. 1-5 for results. CTIO 1.5m telescope M. V. McSwain and C. Aragona have obtained new radial velocity measurements of LS 5039 to update the orbital ephemeris. They are also performing an ongoing monitoring campaign of LS 5039 to correlate the stellar mass loss rate with the X-ray and radio fluxes. See Figs. 5-6 for results. Figure 1: We discovered a brief X-ray burst from LS I +61 303 on Aug. 21 (Ray et al. 2008, ATEL 1730). RXTE fluxes from LS I +61 303 are plotted as a function of date (top) and radio phase (bottom). Figure 2: PCA lightcurve from the 2008 August 21 outburst of LS I +61 303 with 1 second resolution. Note the very strong variability. Figure 3: PCA power spectrum from the 2008 August 21 observation of LS I +61 303. The observations was binned at 0.01 seconds and power spectra of length 1024 bins were averaged. The power spectrum is in units of RMS2/Hz, and the expected Poisson level has been subtracted. Figure 4: Comparison of the 2008 August 21 power spectrum of LS I +61 303 with the average power spectrum from 56 other monitoring observations. The QPO at 0.2 Hz and a possible 10-second pulsed emission are not visible during our other observations. Figure 7: VLA radio flux observations of LS I +61 303 taken at 8.4 GHz. These data were taken in the days following the 2008 September 10 outburst that was detected by the Swift BAT (GCN Circ. 8209, 8211, 8215) that occurred at phase 0.38. These data are compared to archival GBI data of the source. Figure 5: RXTE flux measurements (green) and the stellar mass loss rate from H equivalent width measurements (red) of LS 5039. Figure 6: New radial velocity variations of LS 5039 from the CTIO 1.5m telescope. We confirm the 3.9 day orbital period found by Casares et al. (2005). Figure 8: The VLBA X-band image of LS I +61 303 obtained four days after the 2008 September 10 outburst.The image is consistent with previous observations of LS I +61 303 at this phase.