Search for Very High-Energy Gamma-Ray Bursts Research at Baksan Observatory

1. Search for very high energy gamma-ray bursts V.B.Petkov Institute for Nuclear Research of RAS, Baksan Neutrino Observatory

2. The search for high-energy gamma rays from GRB: starting point EGRET (aboard the CGRO) • Positive observations in the GeV range, including the detection of an 18 GeV gamma ray delayed 1.5 hr afterthe onset of the GRB 940217

3. Primary HE γ-rays+ atmosphere → air shower → secondary particles at observation level

4. EAS: extensive air shower

5. Groundbased arrays: energy ranges and methods (1) HE (GeV range): few GeV - hundreds GeV Only few particles at observation level • → Ground-based detectors operating at “single particle” mode (the total count rate of the all array’s detectors is measured) • → Threshold energy mainly depends on altitude (+ detectors type) • → Search for short transient in the total counting rate

6. Groundbased arrays: energy ranges and methods (1) HE (GeV range): few GeV - hundreds GeV • Advantages: • Large effective area: ~ (40 ÷ 5200) m2 • Long data acquisition time • Shortcomings: • Particle energy can not be measured • Particle arrival direction can not be measured → • → Very large background! • → Short bursts are preferable

7. Groundbased arrays: energy ranges and methods (2) VHE (TeV range): hundreds GeV – tens TeV • Ĉerenkov telescopes • EAS arrays at high altitudes with very high density of detectors • Underground (underwater, underice) neutrino telescopes (by the secondary muons). • Advantages: • long data acquisition time • lower cosmic-ray background • Shortcoming: • low efficiency of muon generation by primary gamma rays

8. Groundbased arrays: energy ranges and methods UHE (PeV range): tens TeV – few PeV Conventional EAS arrays • Advantages: • Large effective area: ~ (104 ÷ 105) m2 • long data acquisition time • Primary particle energy can be measured • Primary particle arrival direction can be measured • Shortcoming: • Too high energy of primary gamma rays

9. Flux absorption due to the interaction with the infrared and microwave background HE VHE UHE

10. Groundbased arrays (HE && VHE ranges):only hints at the GRB registration • Milagrito, Eγ ~ 1 ТэВ, GRB970417a: 3σ signal (Morales M., astro-ph/022704, 2002) • Tibet EAS array, Eγ ≥ 8 ТэВ, period 18.06.1990 – 29.09.1992 (live time 598.6 days), 57 BATSE events, cumulative signal ~ 6 σ(Amenomori M. et al, Proc. of 24 ICRC 1995, p. 92.) • GRAND, 10 GeV ≤ Eγ ≤ 1TeV, GRB 971110 ~3σ(Poirier J. et al., astro-ph/0306371, 2003b)

12. Baksan Neutrino Observatory devices: primary gamma-rays detection EAS array “Andyrchy” • Single particle operation mode: Eeff ~ 8 GeV • EAS registration: Eeff ~ 60 ТэВ “Carpet-2” EAS array • Single particle operation mode: • remote stations (RS): Eeff ~ 8 GeV • central part (the Carpet proper): Eeff ~ 200 GeV • EAS registration: • central part: Eeff ~ 10 ТэВ • central part + RS: Eeff ~ 60 ТэВ Baksan Underground Scintillation Telescope (BUST) • Eeff ~ 10 ТэВ

13. “Andyrchy” EAS array “Karpet-2” EAS array BUST Tunnel entrance

14. Eµ ≥ Eth(x) x = x(θ,φ) (Eth)eff = 0.22 TeV

15. Baksan Underground Scintillation Telescope 1977 • Telescope construction completed • Depth: 850hg/cm2 • Size: 17m´17m´11m • Number of tanks: 3185 • Tank size: 70cm´70cm×30cm • Angular resolution: 20 • Time resolution: 5 ns • Trigger: 10Mev in any plane • Rate: 17 Hz • upward/downward: 10-7 17 m 17 m 11 m

16. “Andyrchy” EAS array Stot = 4.4·104 m2 37 plastic scintillation detector (1 m × 1 m × 0.05 m) Shower trigger: ≥ 4 fired detectors Trigger rate: 9 s-1 Single particle operation mode (37 m2) Total count rate: 11390 s-1

17. The “Andyrchy” EAS array

18. “Karpet-2” EAS Array Cherenkov telescope “Karpet”: 400 liquid scintillation detectors (200 m2) 40 m Large Muon Detector: 175 plastic scintillation detectors, 175 m2 E≥ 1 GeV 6 remote stations: 18 liquid scintillation detectors (9 m2) each

19. “Karpet-2” EAS Array Large Muon Detector Cherenkov telescope remote stations

20. Carpet 200 m2, 400 individual detectors

21. Muon Detector 175 m2 (175 individual detectors)

22. Single particle operation mode.Probability to detect a gamma-ray as function of primary energy for θ=0°. 1 – “Carpet” RS, 2 – “Andyrchy” (Eeff ~ 8 GeV)3 – “Carpet” central part (Eeff ~ 200 GeV) 4 – MD (Eeff ~ 2000 GeV)

23. Single particle operation mode.“Andyrchy” S = 37 m2

24. S4 S3 S2 S1 The “Andyrchy” EAS array The count rate of “Andyrchy” array detectors (37 m2) is measured once per second (~11390/sec). A check of stability is provided by means of simultaneous measurements (also once per second) of the counts rates of four parts of the array.

25. Andyrchy HE Sky survey: 1996 – 2006. 2290.1 days of live time, ω = 11390 s-1 Δt = 1 s for Fi=6 && Δt = 1 s fluence W = 5.6∙10-3 erg/cm2 Fi=7.9 Year 2002 day 107 Run 82

26. a – “Carpet” Remote Stations, S=54 m2 max excess = 3.2 σ b – “Andyrchy” Eeff ~ 8 GeV Power line disturbance ?

27. Andyrchy HE Sky survey: 1996 – 2006. The limit on frequency of gamma-ray bursts with durations Δt = (1 ÷ 50) s and corresponding fluencies W(Δt) ≥ 5.6∙10-3·√Δt ergs/cm2 in declination band (10° ≤δ≤ 70°) is 2.3·10-8 s-1at 99% c.l. Search in correlation with satellites events 1996 – 2004. 147 BATSE events (1996-2000) + 30 events (2000 -2004) The range of upper limits on energy fluencies for (3σ excess): Wmax = 6.5·10-4 – 0.15 ergs/cm2 The large dispersion of Wmax is due to different zenith angles and time durations T90 of the bursts.

28. Andyrchy EAS arrayProbability to detect EAS as function of primary gamma-ray energy for different θ.θ=0° → Eeff ~ 60 ТэВ

29. The search for high energy gamma ray bursts on ashower array reduces to the search of space and timecorrelations (clusters) of registered EAS. • For each shower i having registration time ti and arrival angles (θ,φ)i the cluster of events i, i + 1, i + 2, …, i + n - 1 is sought for, using a condition that arrival directions should differ less than αr from the weighted mean direction. Thus, each cluster is characterized by multiplicity n, duration Δt, absolute time T, and arrival direction (θ,φ)i . • During such a search, experimentally obtained dependencies (e.g., cluster registration frequencies for each n) are compared to the ones expected from the background of accidental coincidences. If measured frequencies of cluster registration can be explained with distributions expected for accidental coincidences, one can obtain the constraints on a gamma ray burst frequency producing clusters with a given multiplicity (and thus having particular energy flux). • Andyrchy data: • 1996–2001 (live time ∼1100 days) • the total number of events is∼ 6.22×108

30. Integral duration distributions for clusters withmultiplicity n = 2, 3, 4, 5, detected by the array for thewhole region of zenith angles. Points represent the experimentalresults; lines show the calculated distributionsexpected from the cosmic ray background.

31. “Andyrchy” EAS sky survey:1996–2001 (live time ∼1100 days), ~ 6.22×108 events upper limits on clusters rate as fluence function

32. “Andyrchy” EASSearch in correlation with satellites events. 127 BATSE events (1996-2000) The range of upper limits on energy fluencies for (3σ excess): Wmax = 2.5·10-6 – 5.0·10-5 ergs/cm2 The large dispersion of Wmax is due to different zenith angles and time durations T90 of the bursts.

33. Primordial Black Holes Three theoretical model of the evaporation process was used for the analysis. • a non-chromospheric model: evaporated particles do not interact with each other; MW90 (J. H. MacGibbon and B. R. Webber, Phys. Rev. D 41, 3052, 1990.) • 2 chromospheric models: evaporated particles interact with each other and forms anearly thermal chromosphere; H97(A. F. Heckler, Phys.Rev. Lett. 78, 3430, 1997) and DK02(R. G. Daghigh and J. I. Kapusta, Phys.Rev. D 65, 064028, 2002).

34. Time duration of gamma burst vs. gamma-rays threshold energy1 - MW90, 2 - DK02, 3 - H97

35. Model MW90 Burst time vs. zenith angle for the Andyrchy EAS array

36. “Andyrchy” EAS sky survey, model MW90:1996–2001 (live time ∼1100 days),

37. Upper limits on the number density of evaporating PBHs vs. effective gamma-rays energy(at the 99% confidence level)1 - “Andyrchy“: (5.4×108 pc-3 yr-1); 2- Tibet; 3 - Whipple

38. Time duration of gamma burst vs. gamma-rays threshold energyFor chromospheric models (2 - DK02, 3 - H97) → single particle operation mode only

39. Upper limits on the number density of evaporating PBHsAndyrchy (6.27 yr) + Carpet-2 RS (2.34 yr) • DK02: 109 pc-3 yr-1 • H97: 5×109 pc-3 yr-1 MW90 • Single particle mode: 6.8×109 pc-3 yr-1 • EAS mode: 5.4×108 pc-3 yr-1

40. Probability to detect muon as function of primary gamma-ray energy for different muon threshold energy.Eeff ~ 10 ТэВ

41. BUST sky survey: 2001 – 2004 (live time ∼1240 days)~7.8×108events upper limits on clusters rate as fluence function

42. BUSTSearch in correlation with satellites events. 39 satellites events (2001-2004 ) The range of upper limits on energy fluencies for (3σ excess): Wmax = 4.0·10-3 – 3.7·10-2 ergs/cm2

43. Future plans Run-time search for optical counterparts of the high energy events, registered by the Baksan Neutrino Observatory installations.For this goal optical telescopes of the Peak Terskol observatory will be used.Robotic telescopes: Celestron NextStar GPS 11'' and Meade LX200 GPS 14''

45. Experimental search for evaporating primordial black holes Method: synchronous registration for gamma-ray and optical bursts from evaporating PBH. Events signatureis different for usual 3+1 dimensional space-time and space-time with extra dimensions.

46. Optical follow-up of high-energy neutrinos detected by IceCube • At the moment IceCube alerts get forwarded tothe Robotic Optical Transient Search Experiment(ROTSE).