TITLE: GCN CIRCULAR NUMBER: 11914 SUBJECT: GRB 110407A:VLF observations on 20.27kHz DATE: 11/04/09 16:17:17 GMT FROM: Matus Kocka at AI AS CR, Ondrejov Matus Kocka (AI AS CR), Rudolf Slosiar (Rudy BASE Observatory Bojnice), Vladimir Karlovsky (Observatory Hlohovec), Richard Marko (AI AS CR), Jan Karlovsky (Observatory Hlohovec), Rene Hudec (AI AS CR) We observed the ionospheric perturbation on Apr. 7th which started at 14:06:21 UT from 3 different VLF receivers, so called SID monitors (Sudden Ionospheric Disturbance) on ICV channel 20.27kHz. This event is with a high probability GRB 110407A (Wolf et al., GCN 11895). The detectors are located in Bojnice (Slovakia), Hlohovec (Slovakia) and Brno (Czech Republic). Those places are so far apart that we can rule out a possibility of a local disturbance. The plot from all three SID-monitors is here: http://zeus.asu.cas.cz/~koci/grb110407a/GRB110407A_vlf.png Further analysis is ongoing.