Long-term OVRO monitoring of LS I +61°303: confirmation of the two close periodicities
Abstract
Context. The gamma-ray binary LS I +61°303 shows multiple periodicities. The timing analysis of 6.7 yr of GBI radio data and of 6 yr of Fermi-LAT GeV gamma-ray data both have found two close periodicities P1,GBI = 26.49 ± 0.07 d, P2,GBI = 26.92 ± 0.07 d and P1,γ = 26.48 ± 0.08 d, P2,γ = 26.99 ± 0.08 d.
Aims: The system LS I +61°303 is the object of several continuous monitoring programs at low and high energies. The frequency difference between ν1 and ν2 of only 0.0006 d-1 requires long-term monitoring because the frequency resolution in timing analysis is related to the inverse of the overall time interval. The Owens Valley Radio Observatory (OVRO) 40 m telescope has been monitoring the source at 15 GHz for five years and overlaps with Fermi-LAT monitoring. The aim of this work is to establish whether the two frequencies are also resolved in the OVRO monitoring.
Methods: We analysed OVRO data with the Lomb-Scargle method. We also updated the timing analysis of Fermi-LAT observations.
Results: The periodograms of OVRO data confirm the two periodicities and .
Conclusions: The three independent measurements of P1 and P2 with GBI, OVRO, and Fermi-LAT observations confirm that the periodicities are permanent features of the system LS I +61°303. The similar behaviours of the emission at high (GeV) and low (radio) energy when the compact object in LS I +61°303 is toward apastron suggest that the emission is caused by the same periodically (P1) ejected population of electrons in a precessing (P2) jet.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- March 2015
- DOI:
- 10.1051/0004-6361/201525643
- arXiv:
- arXiv:1502.00934
- Bibcode:
- 2015A&A...575L...9M
- Keywords:
-
- radio continuum: stars;
- X-rays: binaries;
- X-rays: individuals: LSI +61°303;
- gamma rays: stars;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 4 pages, 7 figures, A&