IA U Colloquium. 164: Radio Emission from Galactic and Extragalactic Compact Sources ASP Conference Series, Vol. 144, 1998 J. A. Zensus, G. B. Taylor, & J. M. Wrobel (eds.) Two-Frequency VLA Monitoring of LSI+61°303 during a Full Radio Period J. M. Paredes, M. Peracaula, & M. Ribo Departament d'Astronomia i Meteorologia, Universitat de Barcelona, Barcelona, Spain J. Marti CEA / DSM / DAPNIA / Service d'Astrophysique, Centre d'Etudes de Saclay, F-91191 Gif-Sur-Yvette, France M. Tavani Columbia Astrophysics Laboratory, Columbia University, New York, NY, U.S.A. D. A. Kniffen Department of Physics and Astronomy, Hampden-Sydney College, VA, U.S.A. J. R. Mattox Astronomy Department, Boston University, Boston, MA, U.S.A. Abstract. We report observations of the radio periodic Be X-ray binary LSI+61°303, ob- tained with the VLA at 3.6 and 2.0 cm during a full 26.5 d cycle. These observations were car- ried out in coordination with CGRO monitoring of its possible 7-ray counterpart 2CG 135+1. 1. Introduction The massive X-ray binary LSI+61°303 is well known for its periodic radio out- bursts every orbital period of 26.5 d (Taylor & Gregory 1984), reaching centi- metric peak flux densities of typically ~ 100 mJy. Recently, evidence of X-ray periodicity in LSI+61°303 with the same 26.5 d radio period has also been dis- covered (Paredes et al. 1997). This system lies well within the ~ 10' error box of 2CG 135+1 as determined by EGRET (von Montigny et al. 1993, Kniffen et al. 1996). In the present paper, we report the results of our recent radio moni- toring of LSI+61°303 during the latest CGRO observations of 2CG 135+1. The main goal of our coordinated radio and 7-ray campaign was aimed to provide more insight into the suspected identity of LSI+61°303 and 2CG 135+1. The high energy data will be presented elsewhere, while the present work is mainly devoted to look into some interesting aspects of the radio results. 2. Observations and Results Radio monitoring of LSI+61°303 was carried out using the VLA interferometer of NRAO. The radio observations covered more than one orbital period of the system, from 1996 September 6 to 1996 October 3. We observed at the wave- lengths of 3.6 and 2.0 cm. In Figure 1 we present the observed light curves at the two wavelengths, as well as the corresponding spectral index (5„ oc u a ) for each session. The horizontal axis is labeled in terms of radio phase (top) and date of the year (bottom). The origin of radio phase is set at JD 2443366.775 and a period value of 24.496 d has been used (Taylor & Gregory 1984). 347 of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0252921100045863 Downloaded from https://www.cambridge.org/core. IP address: 207.90.35.13, on 12 Jun 2019 at 11:16:14, subject to the Cambridge Core terms