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Radio Variability of Sagittarius A* - A 106 Day Cycle | | Jun-Hui Zhao
; G. C. Bower
; W. M. Goss
; | | Date: |
8 Nov 2000 | | Subject: | astro-ph | | Affiliation: | CfA), G. C. Bower (NRAO/UC-Berkeley), W. M. Goss (NRAO | | Abstract: | We report the presence of a 106-day cycle in the radio variability of Sgr A* based on an analysis of data observed with the Very Large Array (VLA) over the past 20 years. The pulsed signal is most clearly seen at 1.3 cm with a ratio of cycle frequency to frequency width f/Delta_f= 2.2+/-0.3. The periodic signal is also clearly observed at 2 cm. At 3.6 cm the detection of a periodic signal is marginal. No significant periodicity is detected at both 6 and 20 cm. Since the sampling function is irregular we performed a number of tests to insure that the observed periodicity is not the result of noise. Similar results were found for a maximum entropy method and periodogram with CLEAN method. The probability of false detection for several different noise distributions is less than 5% based on Monte Carlo tests. The radio properties of the pulsed component at 1.3 cm are spectral index alpha ~ 1.0+/- 0.1 (for S nu^alpha), amplitude Delta S=0.42 +/- 0.04 Jy and characteristic time scale Delta t_FWHM ~ 25 +/- 5 days. The lack of VLBI detection of a secondary component suggests that the variability occurs within Sgr A* on a scale of ~5 AU, suggesting an instability of the accretion disk. | | Source: | arXiv, astro-ph/0011169 | | Services: | Forum | Review | PDF | Favorites | |
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