UNIT project

4. Developing ways to effectively use small telescopes

4.1 Synchronous observations with distant telescopes 

Ground-based networks of small and medium-sized optical telescopes are an important tool to investigate ultra-rapid variability of stellar brightness, to search for optical afterglow of gamma ray bursts, etc. because observations with a number of remote telescopes operating synchronously give information that cannot be obtained in any other way (Nogami et al. 2000; Zhilyaev et al. 2003). 

Observational sites and instruments of the Synchronous Network of distant Telescopes 

The observations with the Synchronous Network of distant Telescopes (SNT), which involves telescopes in Ukraine, Russia, Bulgaria, and Greece, were started in the late 1990s. The telescopes are equipped with GPS receivers to control local photometer timing systems relative to UTC. The high-speed, multi-site monitoring of variables, as well as digital filtering techniques used for data processing, provided new results: 

Multi-site photometry of a flare on EV Lac on September 12, 2004, 22:53 UT (max), as simultaneously seen by the three instruments: Ukraine (circles), Greece (solid), and Bulgaria (squares) (Zhilyaev et al. 2007) 

(i) high-frequency oscillations in stellar flares were confirmed and (ii) fast color variations of the flare’s radiation were discovered (Zhilyaev et al. 2007). Figure 12 demonstrates a flare on the star EV Lacertae, which was simultaneously observed with the three telescopes on September 12, 2004. Just the coincidence technique allows us to conclude that oscillations in stellar flares are connected with fast magnetoacoustic oscillations in coronal loops. This opens the way to study stellar coronae, i.e. their structure, density, and temperature (coronal seismology). 

 Furthermore, short burst events in some galaxies were revealed. This observational result supports the hypothesis that intermediate-mass black holes exist in the centers of galaxies and dense globular clusters (Zhilyaev et al. 2006). 

Detection of short-lived flare events in centers of the galaxies. Top: The light curves of NGC7331 taken on Sept 19, 2004, 18:27:27.59 UT (start time) synchronously at intervals of 10 ms in the B band using the Terskol 2-m telescope and the Crimean 50-inch telescopes. Both curves are in relative units, the lower one is shifted for convenience. Bottom: The same for the Seyfert galaxy NGC1068 (observations on Sept 22, 2004, 00:30:00.19 UT (start time)). The light curves are taken synchronously at intervals of 10 ms and rebinned to 0.5 s