1 Detections of SID Due to Gamma Ray Bursts and Soft Gamma ray Repeater S. K. Chakrabarti, S. K. Mondal, S. Sasmal, D. Bhowmick Indian Centre for Space Physics, Kolkata, India The Sharjah-Stanford AWESOME VLF Workshop Feb 22-24, 2010, Sharjah, UAE

Plan of my talk Gamma Ray Bursts Previous VLF detections of GRBs VLF detections of GRBs and SGR VTX and our receiving stations Terminator and the sub-flare point of the SGR Burst Signatures of the SGR on VLF data GOES data on the event days Detection of GRB from three receivers BAT light curve for GRB VLF signature of GRB from two different places

3 Gamma Ray Bursts ➢ Gamma Ray Bursts (GRBs) are very powerful incidents, which release unbelievable amount of energy ( ergs) in a very short time (~sec) mostly in the form of Gamma rays. ➢ GRBs are result of highly energetic explosion Supernova explosion Collapsing star ➢ A small fraction of the short gamma ray comes from the Soft Gamma ray Repeater (SGR)

4 Previous VLF detections of GRBs 1. First observation of ionospheric disturbance caused by a gamma ray burst (GRB830801). G. J. Fishman & U. S. Inan, Ionospheric Disturbances caused by SGR in Tanaka et al. 3. XRF : Sudden Ionospheric Disturbance (SID) in Fishman et al. 4. GRB observed as a Sudden Ionospheric Disturbance in Schnoor et al. 5. SGR : Detection of a Sudden Ionospheric disturbance in Campbell et al. 6. Massive disturbance of the daytime lower ionosphere by the magnetar SGR in Inan et al.

5 Three Recent VLF Detections of GRB with ICSP Receiver SGR J1550 –5418 bursted many times on January 22, 2009 as observed by the space based satellites (GCN-8833,8838). We find the signature of SID due to many of these bursts in our VLF data while receiving VTX (18.2 KHz) signal using gyrator-II type receiver (GCN-8881, 9315). GRB has been detected from three VLF receivers (GCN-9223, 9230, 9317) Two receivers detected the signature of the burst from GRB (GCN-9277, 9296, 9317)

6 VTX and Our Receiving Stations During the Bursts

7 VLF detection of SGR J ● B ursts from this source were last seen in early Oct., ● The multi-burst from the SGR during 22 nd Jan, 09 period highly disturb the ionosphere (GCN-8881, 9315). ● The burst started at 00:53:52 UT (3232 sec) with count rate count/sec and remained active till 10:49:56 UT on that day. ● We found that 73 of our detections in VTX signal coincided with the satellite observations within the time period the source was over our sky. ● Receiver position was at Kolkata (22.5 N, 88.4 E) ● The sub-burst point for the source was ( S, E) and the altitude during the burst as seen from receiver was S.

8 Terminator during the SGR burst and the sub-burst point

9 Signatures of the SGR

10 GOES data on 22 nd January 2009

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13 GRB detection from three receivers ● GRB has been detected in VLF from three places (GCN-9316). ● Receivers were at ICSP (22.5N,88.4E) Saltlake (22.5N,88.4E) Malda (25 N, 88 E) ● The signal from a fourth receiver at Pune (~1000 miles from Kolkata) in western India (18.5d N, 74d N) was very poor. ● The event occurred at 14:12:09 UT (51129 sec) or 19:42:09 IST with peak count rate ~50000 count/s and the event fluence was (5.2 +/- 0.1)E-05 erg/cm 2. ● At Saltlake sample rate was 4/sec and 2/sec in the others. ● Sub-flare point for the source was ( N, E).

14 GRB detection from ICSP (Garia) and Saltlake station

15 Terminator during the burst of GRB and the sub-flare point

16 GOES data on April 24 th

17 GRB as received from three receiver

18 Detection of GRB from two receivers ● GRB has been detected from two of our receiving stations (GCN9317). ● The event occurred at 23:26:27 UT (84387 sec), as observed by Konus-Wind the burst had a fluence of (1.03 +/- 0.05)x10 -4 erg/cm2 ● VLF Receivers were at Kolkata (22.5N, 88.4E) VTX (8.43N, E) Pune (18.5N, 74 E) ● Sample rate at Kolkata was 4/sec and 2/sec at Pune. ● Sub-flare point for the source was ( S, E), which is nearer to Pune.

19 VTX and Our Receiving Stations During the Bursts

20 GRB as Received in Pune & Kolkata

21 GOES data on April 27 th

22 Terminator during the burst of GRB and the sub-flare point

23 Discussion ● The highly tangential source illumination of the ionosphere as seen from Kolkata was probably advantageous for the detection of the SGR. ● 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. ● During the burst VTX-Pune baseline was in the night side of the terminator. Therefore, signal was prominent from our Pune receiver (18.5 N, 74 E) while it was weaker at our Kolkata (22.5N, 88.5 E) receiver.

25 THANK YOU

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30 BAT light curve GCN Report Jun-09 (Cannizzo K., et al.)

31 References ➢ Observation of an ionospheric disturbance caused by a gamma-ray burst, Fishman G. J. & Inan U. S., Nature VOL.331, Feb,1988 ➢ Massive disturbance of the daytime lower ionosphere by the giant gamma ray flare from magnetar SGR , Inan U.S., Lehitinen G., et al., GRL, VOL.34, L08103, ➢ Ionospheric Disturbances caused by SGR giant gamma ray flare in 1998: Constraints on the energy spectrum of the flare, Tanaka Y.T., Terasawa T., et al., GR, VOL.113, A07307, ➢ XRF : Sudden Ionospheric Disturbance (SID) Fishman et al., GCN 1394, ➢ GRB observed as a Sudden Ionospheric Disturbance Schnoor et al., GCN 2176, ➢ SGR : Detection of a Sudden Ionospheric Disturbance. Campbell et al., GCN 2932, ➢ GCN-8881, GCN-9315, GCN-9316, GCN-9317, Chakrabarti S. K., Mondal S. K., Sasmal S., Bhowmick D., et al., 2009 ➢ Swift observation of GRB , Cannizzo, et al., GCN Report Jun09

32 Whole day data of the event day & before and after the event day Time in seconds after 00:00:00 IST (ISThr=UThr+5.5hr)

33 Blackbody and power law component are shown seperately with dashed curve (Kaneko Y., et al.)