TITLE: GCN CIRCULAR NUMBER: 9316 SUBJECT: ICSP VLF observation of GRB090424 from four receivers DATE: 09/05/01 13:25:00 GMT FROM: Sandip K. Chakrabarti at S.N. Bose Nat. Centre for Basic Sci. ICSP VLF observation of GRB090424 from four receivers Sandip K. Chakrabarti (S. N. Bose Centre and ICSP), Sushanta K. Mondal (ICSP), Asit Choudhury (ICSP, Malda branch), Achintya Chatterjee (ICSP, Malda Branch), Narendra N. Patra (Univ. Pune) and D. Bhowmick (ICSP) Three ICSP VLF receivers clearly observed the effects of GRB090424 (GCN#s 9223, 9230) on the ionosphere simultaneously. The subflare point (16.8d N , 123.76d E) being closer to eastern India the signal was prominent. Two receivers were kept at Kolkata (22.5N, 88.5d E) at sixteen kilometers (~ 10 miles) apart, while a third receiver was kept at Malda (25d N, 88d E) which is about 200 miles away. All the three receivers detected the GRB right after triggering and the correlation of the signals were found excellent for about ~100 seconds. Before the triggering, the correlation was poor. The signal from a fourth ICSP receiver at Pune (~1000 miles from Kolkata) in western India (18.5d N, 74d N) was very poor. A comparison of the smoothed signals can be found in allthree.jpg in http://www.bose.res.in/~chakraba/grb090424-1.html. This message may be cited.