Search for Very High Energy Emission from Gamma-Ray
Bursts using Milagro
P. M. Saz Parkinson for the Milagro Collaboration1
Santa Cruz Institute for Particle Physics, University of California, Santa Cruz, CA 95064
Abstract. Gamma-Ray Bursts (GRBs) have been detected at GeV energies by EGRET and models predict emission at > 100
GeV. Milagro is a wide field (2 sr) high duty cycle (> 90%) ground based water Cherenkov detector that records extensive
air showers in the energy range 100 GeV to 100 TeV. We have searched for very high energy emission from a sample of 106
gamma-ray bursts (GRB) detected since the beginning of 2000 by BATSE, BeppoSax, HETE-2, INTEGRAL, Swift or the
IPN. No evidence for emission from any of the bursts has been found and we present upper limits from these bursts.
Keywords: gamma-ray sources; gamma-ray bursts; astronomical observations: gamma-ray
PACS: 98.70.Rz,95.85.Pw
Some of the most important contributions to understanding gamma-ray bursts (GRBs) have come from observations
of afterglows over a wide spectral range [1]. Many GRB models predict very high energy (VHE, > 100 GeV) emission
from GRBs at a level comparable to that at MeV energies (e.g. [2, 3]). EGRET detected several GRBs at energies
above 100 MeV, indicating that the spectrum of GRBs extends at least out to 1 GeV, with no evidence for a spectral
cut-off [4]. A second component was also found in one burst which extended up to at least 200 MeV and had a much
slower temporal decay than the main burst [5]. At very high energies, there has been no conclusive emission detected
for any single GRB, though a search for counterparts to 54 BATSE bursts with Milagrito, a prototype of Milagro,
found evidence for emission from one burst, with an after trials significance slightly greater than 3σ [6]. At these high
energies, gamma rays are attenuated by the redshift-dependent extra-galactic background light (EBL) [7], making the
detection of VHE emission from GRBs very challenging.
A search for an excess of events above those due to the background was carried out for each of the 106 satellite-
detected GRBs in our sample (see Table 1). These represent all the GRBs known to have occurred within the field
of view of Milagro during its first seven years of operations (2000-2006)2. Milagro detected no significant emission
from any of these bursts, and fluence upper limits are given in Table 1.
We acknowledge Scott Delay and Michael Schneider for their dedicated efforts in the construction and maintenance of the Milagro experiment.
This work has been supported by the National Science Foundation (under grants PHY-0245234, -0302000, -0400424, -0504201, -0601080, and
ATM-0002744) the US Department of Energy (Office of High-Energy Physics and Office of Nuclear Physics), Los Alamos National Laboratory,
the University of California, and the Institute of Geophysics and Planetary Physics.
REFERENCES
1. van Paradijs, J., Kouveliotou, C. & Wijers, R. A. M. J. 2000, Annual Review of Astronomy and Astrophysics 38, 379
2. Dermer, C. D., Chiang, J., & Mitman, K. E. 2000, ApJ 537, 785
3. Zhang, B. & Mészáros, P. 2001, ApJ 559, 110
4. Dingus, B. L. 2001, in Aharonian, F. A. and Volk, H. J. (eds), High Energy Gamma Ray Astronomy, AIP Conf. Proc., 558, 383
5. Gonzalez, M. M. et al. 2003, Nature 424, 749
6. Atkins, R. et al. 2000, ApJL 533, L119
7. Primack, J. R. et al. 2005, in Aharonian, F., Volk, H., and Horns, D. (eds) Gamma 2004 Heidelberg, AIP Conf. Proc., 745, 23-33
1 A. Abdo, B. T. Allen, D. Berley, E. Blaufuss, S. Casanova, B. L. Dingus, R. W. Ellsworth, M. M. Gonzalez, J. A. Goodman, E. Hays,
C. M. Hoffman, B. E. Kolterman, C. P. Lansdell, J. T. Linnemann, J. E. McEnery, A. I. Mincer, P. Nemethy, D. Noyes, J. M. Ryan, F. W. Samuelson,
P. M. Saz Parkinson, A. Shoup, G. Sinnis, A. J. Smith, G. W. Sullivan, V. Vasileiou, G. P. Walker, D. A. Williams, X. W. Xu and G. B. Yodh
2 GRB 060218, due to its long duration of more than 2000 s moved out of Milagro’s field of view after the start of the burst. The limit presented
here is for the initial 10 s hard spike reported by the instrument team.
http://arxiv.org/abs/0704.0287v1
TABLE 1. GRBs in the Milagro field of view (2000-2006). Column 1 is the GRB name. A superscript refers to the number
of IPN error regions in the Milagro field of view. A superscript of one implies only one of two error regions fell in the
Milagro field of view, while a two implies that both did, and they are listed one after the other. Column 2 gives the duration
of the burst (in seconds), column 3 the zenith angle (in degrees), column 4 the measured redshift, column 5 the satellite(s)
detecting the GRB, and column 6 gives the Milagro 99% confidence upper limit on the 0.2–20 TeV fluence in erg cm−2.
Numbers in bold (also labelled with a #) take into account absorption by the EBL (using the Primack 05 model) for a redshift
given in column 4. Those with three dots imply the redshifts are so high that all the emission is expected to be absorbed.
GRB Dur. θ z Inst. 99% UL
000113 370 21 ... BATSE 5.5e-6
0001311 12 41 ... IPN 6.5e-7
000205 23 25 ... BSAX 6.9e-7
000206 10 39 ... BSAX 9.3e-7
000212 8 2.2 ... BATSE 1.1e-6
000220 2.4 49 ... BATSE 1.1e-5
000226 10 32 ... BATSE 3.4e-6
000226b1 94.5 32 ... IPN 7.8e-7
000301C 14 38 2.03 BATSE ...
000302 120 32 ... BATSE 6.8e-6
000314 12.8 45 ... BSAX 3.6e-5
000317 550 6.4 ... BATSE 7.9e-6
000330 0.2∗ 30 ... BATSE 1.0e-6
000331 55 38 ... BATSE 1.2e-5
000402 120 48 ... BSAX 4.5e-5
000408 2.5 31 ... BATSE 1.0e-6
000424 5 36 ... BATSE 7.6e-7
000508 30 34 ... BATSE 3.7e-6
0006071 0.12 42 ... IPN 4.6e-7
000615 10 39 ... BSAX 1.6e-6
000630 20 32 ... IPN 2.2e-6
0007072 18 43 ... IPN 1.9e-6
0007072 18 41 ... IPN 1.0e-6
000727 10 41 ... IPN 2.6e-6
000730 7 19 ... IPN 4.2e-7
0008211 8 27 ... IPN 6.9e-7
0008301 8 35 ... IPN 9.1e-7
000926 25 16 2.04 IPN ...
001017 10 42 ... IPN 2.2e-6
001018 31 32 ... IPN 2.1e-6
001019 10 20 ... IPN 1.1e-6
001105 30 8.5 ... IPN 1.4e-6
001204 0.44 48 ... BSAX 1.2e-5
010104 2 20 ... IPN 4.0e-7
010220 150 27 ... BSAX 2.1e-6
010613 152 25 ... IPN 2.9e-6
010706 48 37 ... IPN 2.6e-6
010903 41 49 ... IPN 2.9e-5
010921 24.6 10 0.45 HETE 2.9e-5#
011130 83.2 34 ... HETE 3.4e-6
011212 84.4 33 ... HETE 6.7e-6
020311 11.5 27 ... IPN 1.7e-7
0204292 16 39 ... IPN 4.6e-7
0204292 16 30 ... IPN 3.0e-7
020625b 125 38 ... HETE 5.7e-6
020702 26 34 ... IPN 1.4e-6
0209081 17 19 ... IPN 7.3e-7
020914 9 5.7 ... IPN 4.2e-7
021104 19.7 13 ... HETE 7.5e-7
021112 7.1 34 ... HETE 9.4e-7
021113 20 18 ... HETE 6.4e-7
021211 6 35 1.01 HETE ...
030413 15 27 ... IPN 1.0e-6
030823 56 33 ... HETE 2.8e-6
GRB Dur. θ z Inst. 99% UL
031026 0.24 45 ... IPN 1.1e-6
031220 23.7 43 ... HETE 4.0e-6
040506 175 49 ... IPN 6.0e-6
040924 0.6 43 0.859 HETE 1.4e-3#
041211 30.2 43 ... HETE 4.8e-6
041219a 520 27 ... INTGR. 5.8e-6
050124 4 23 ... Swift 3.0e-7
050213 17 23 ... IPN 1.3e-6
050319 15 45 3.24 Swift ...
050402 8 40 ... Swift 2.1e-6
050412 26 37 ... Swift 1.7e-6
050502 20 43 3.793 INTGR. ...
050504 80 28 ... INTGR. 1.3e-6
050505 60 29 4.3 Swift ...
050509b 0.128 10 0.226? Swift 1.1e-6#
050522 15 23 ... INTGR. 5.1e-7
050607 26.5 29 ... Swift 8.9e-7
050703 26 26 ... IPN 1.2e-6
050712 35 39 ... Swift 2.5e-6
050713b 30 44 ... Swift 4.0e-6
050715 52 37 ... Swift 1.7e-6
050716 69 30 ... Swift 1.6e-6
050820 20 22 2.612 Swift ...
051103 0.17 50 0.001? IPN 4.2e-6#
051109 36 9.7 2.346 Swift ...
051111 20 44 1.55 Swift ...
051211b 80 33 ... INTGR. 2.6e-6
051221 1.4 42 0.55 Swift 9.8e-4#
051221b 61 26 ... Swift 1.8e-6
060102 20 40 ... Swift 2.0e-6
060109 10 22 ... Swift 4.1e-7
060110 15 43 ... Swift 3.0e-6
060111b 59 37 ... Swift 2.3e-6
060114 100 41 ... INTGR. 5.1e-6
060204b 134 31 ... Swift 2.7e-6
060210 5 43 3.91 Swift ...
060218 10 44.6 0.03 Swift 3.8e-5#
060306 30 46 ... Swift 7.2e-6
060312 30 44 ... Swift 3.3e-6
060313 0.7 47 ... Swift 2.7e-6
060403 25 28 ... Swift 1.0e-6
060427b 0.22 16 ... IPN 2.1e-7
060428b 58 27 ... Swift 1.1e-6
060507 185 47 ... Swift 1.8e-5
060510b 330 43 4.9 Swift ...
060515 52 42 ... Swift 9.6e-6
060712 26 35 ... Swift 3.8e-6
060814 146 23 ... Swift 2.5e-6
060904A 80 14 ... Swift 2.4e-6
060906 43.6 29 3.685 Swift ...
061002 20 45 ... Swift 4.0e-6
061126 191 28 ... Swift 4.3e-6
061210 0.8 23 0.41? Swift 6.1e-6#
061222a 115 30 ... Swift 5.6e-6

  Gamma-Ray Bursts (GRBs) have been detected at GeV energies by EGRET and
models predict emission at > 100 GeV. Milagro is a wide field (2 sr) high duty
cycle (> 90 %) ground based water Cherenkov detector that records extensive air
showers in the energy range 100 GeV to 100 TeV. We have searched for very high
energy emission from a sample of 106 gamma-ray bursts (GRB) detected since the
beginning of 2000 by BATSE, BeppoSax, HETE-2, INTEGRAL, Swift or the IPN. No
evidence for emission from any of the bursts has been found and we present
upper limits from these bursts.

Search for Very High Energy Emission from Gamma-Ray
Bursts using Milagro
P. M. Saz Parkinson for the Milagro Collaboration1
Santa Cruz Institute for Particle Physics, University of California, Santa Cruz, CA 95064
Abstract. Gamma-Ray Bursts (GRBs) have been detected at GeV energies by EGRET and models predict emission at > 100
GeV. Milagro is a wide field (2 sr) high duty cycle (> 90%) ground based water Cherenkov detector that records extensive
air showers in the energy range 100 GeV to 100 TeV. We have searched for very high energy emission from a sample of 106
gamma-ray bursts (GRB) detected since the beginning of 2000 by BATSE, BeppoSax, HETE-2, INTEGRAL, Swift or the
IPN. No evidence for emission from any of the bursts has been found and we present upper limits from these bursts.
Keywords: gamma-ray sources; gamma-ray bursts; astronomical observations: gamma-ray
PACS: 98.70.Rz,95.85.Pw
Some of the most important contributions to understanding gamma-ray bursts (GRBs) have come from observations
of afterglows over a wide spectral range [1]. Many GRB models predict very high energy (VHE, > 100 GeV) emission
from GRBs at a level comparable to that at MeV energies (e.g. [2, 3]). EGRET detected several GRBs at energies
above 100 MeV, indicating that the spectrum of GRBs extends at least out to 1 GeV, with no evidence for a spectral
cut-off [4]. A second component was also found in one burst which extended up to at least 200 MeV and had a much
slower temporal decay than the main burst [5]. At very high energies, there has been no conclusive emission detected
for any single GRB, though a search for counterparts to 54 BATSE bursts with Milagrito, a prototype of Milagro,
found evidence for emission from one burst, with an after trials significance slightly greater than 3σ [6]. At these high
energies, gamma rays are attenuated by the redshift-dependent extra-galactic background light (EBL) [7], making the
detection of VHE emission from GRBs very challenging.
A search for an excess of events above those due to the background was carried out for each of the 106 satellite-
detected GRBs in our sample (see Table 1). These represent all the GRBs known to have occurred within the field
of view of Milagro during its first seven years of operations (2000-2006)2. Milagro detected no significant emission
from any of these bursts, and fluence upper limits are given in Table 1.
We acknowledge Scott Delay and Michael Schneider for their dedicated efforts in the construction and maintenance of the Milagro experiment.
This work has been supported by the National Science Foundation (under grants PHY-0245234, -0302000, -0400424, -0504201, -0601080, and
ATM-0002744) the US Department of Energy (Office of High-Energy Physics and Office of Nuclear Physics), Los Alamos National Laboratory,
the University of California, and the Institute of Geophysics and Planetary Physics.
REFERENCES
1. van Paradijs, J., Kouveliotou, C. & Wijers, R. A. M. J. 2000, Annual Review of Astronomy and Astrophysics 38, 379
2. Dermer, C. D., Chiang, J., & Mitman, K. E. 2000, ApJ 537, 785
3. Zhang, B. & Mészáros, P. 2001, ApJ 559, 110
4. Dingus, B. L. 2001, in Aharonian, F. A. and Volk, H. J. (eds), High Energy Gamma Ray Astronomy, AIP Conf. Proc., 558, 383
5. Gonzalez, M. M. et al. 2003, Nature 424, 749
6. Atkins, R. et al. 2000, ApJL 533, L119
7. Primack, J. R. et al. 2005, in Aharonian, F., Volk, H., and Horns, D. (eds) Gamma 2004 Heidelberg, AIP Conf. Proc., 745, 23-33
1 A. Abdo, B. T. Allen, D. Berley, E. Blaufuss, S. Casanova, B. L. Dingus, R. W. Ellsworth, M. M. Gonzalez, J. A. Goodman, E. Hays,
C. M. Hoffman, B. E. Kolterman, C. P. Lansdell, J. T. Linnemann, J. E. McEnery, A. I. Mincer, P. Nemethy, D. Noyes, J. M. Ryan, F. W. Samuelson,
P. M. Saz Parkinson, A. Shoup, G. Sinnis, A. J. Smith, G. W. Sullivan, V. Vasileiou, G. P. Walker, D. A. Williams, X. W. Xu and G. B. Yodh
2 GRB 060218, due to its long duration of more than 2000 s moved out of Milagro’s field of view after the start of the burst. The limit presented
here is for the initial 10 s hard spike reported by the instrument team.
http://arxiv.org/abs/0704.0287v1
TABLE 1. GRBs in the Milagro field of view (2000-2006). Column 1 is the GRB name. A superscript refers to the number
of IPN error regions in the Milagro field of view. A superscript of one implies only one of two error regions fell in the
Milagro field of view, while a two implies that both did, and they are listed one after the other. Column 2 gives the duration
of the burst (in seconds), column 3 the zenith angle (in degrees), column 4 the measured redshift, column 5 the satellite(s)
detecting the GRB, and column 6 gives the Milagro 99% confidence upper limit on the 0.2–20 TeV fluence in erg cm−2.
Numbers in bold (also labelled with a #) take into account absorption by the EBL (using the Primack 05 model) for a redshift
given in column 4. Those with three dots imply the redshifts are so high that all the emission is expected to be absorbed.
GRB Dur. θ z Inst. 99% UL
000113 370 21 ... BATSE 5.5e-6
0001311 12 41 ... IPN 6.5e-7
000205 23 25 ... BSAX 6.9e-7
000206 10 39 ... BSAX 9.3e-7
000212 8 2.2 ... BATSE 1.1e-6
000220 2.4 49 ... BATSE 1.1e-5
000226 10 32 ... BATSE 3.4e-6
000226b1 94.5 32 ... IPN 7.8e-7
000301C 14 38 2.03 BATSE ...
000302 120 32 ... BATSE 6.8e-6
000314 12.8 45 ... BSAX 3.6e-5
000317 550 6.4 ... BATSE 7.9e-6
000330 0.2∗ 30 ... BATSE 1.0e-6
000331 55 38 ... BATSE 1.2e-5
000402 120 48 ... BSAX 4.5e-5
000408 2.5 31 ... BATSE 1.0e-6
000424 5 36 ... BATSE 7.6e-7
000508 30 34 ... BATSE 3.7e-6
0006071 0.12 42 ... IPN 4.6e-7
000615 10 39 ... BSAX 1.6e-6
000630 20 32 ... IPN 2.2e-6
0007072 18 43 ... IPN 1.9e-6
0007072 18 41 ... IPN 1.0e-6
000727 10 41 ... IPN 2.6e-6
000730 7 19 ... IPN 4.2e-7
0008211 8 27 ... IPN 6.9e-7
0008301 8 35 ... IPN 9.1e-7
000926 25 16 2.04 IPN ...
001017 10 42 ... IPN 2.2e-6
001018 31 32 ... IPN 2.1e-6
001019 10 20 ... IPN 1.1e-6
001105 30 8.5 ... IPN 1.4e-6
001204 0.44 48 ... BSAX 1.2e-5
010104 2 20 ... IPN 4.0e-7
010220 150 27 ... BSAX 2.1e-6
010613 152 25 ... IPN 2.9e-6
010706 48 37 ... IPN 2.6e-6
010903 41 49 ... IPN 2.9e-5
010921 24.6 10 0.45 HETE 2.9e-5#
011130 83.2 34 ... HETE 3.4e-6
011212 84.4 33 ... HETE 6.7e-6
020311 11.5 27 ... IPN 1.7e-7
0204292 16 39 ... IPN 4.6e-7
0204292 16 30 ... IPN 3.0e-7
020625b 125 38 ... HETE 5.7e-6
020702 26 34 ... IPN 1.4e-6
0209081 17 19 ... IPN 7.3e-7
020914 9 5.7 ... IPN 4.2e-7
021104 19.7 13 ... HETE 7.5e-7
021112 7.1 34 ... HETE 9.4e-7
021113 20 18 ... HETE 6.4e-7
021211 6 35 1.01 HETE ...
030413 15 27 ... IPN 1.0e-6
030823 56 33 ... HETE 2.8e-6
GRB Dur. θ z Inst. 99% UL
031026 0.24 45 ... IPN 1.1e-6
031220 23.7 43 ... HETE 4.0e-6
040506 175 49 ... IPN 6.0e-6
040924 0.6 43 0.859 HETE 1.4e-3#
041211 30.2 43 ... HETE 4.8e-6
041219a 520 27 ... INTGR. 5.8e-6
050124 4 23 ... Swift 3.0e-7
050213 17 23 ... IPN 1.3e-6
050319 15 45 3.24 Swift ...
050402 8 40 ... Swift 2.1e-6
050412 26 37 ... Swift 1.7e-6
050502 20 43 3.793 INTGR. ...
050504 80 28 ... INTGR. 1.3e-6
050505 60 29 4.3 Swift ...
050509b 0.128 10 0.226? Swift 1.1e-6#
050522 15 23 ... INTGR. 5.1e-7
050607 26.5 29 ... Swift 8.9e-7
050703 26 26 ... IPN 1.2e-6
050712 35 39 ... Swift 2.5e-6
050713b 30 44 ... Swift 4.0e-6
050715 52 37 ... Swift 1.7e-6
050716 69 30 ... Swift 1.6e-6
050820 20 22 2.612 Swift ...
051103 0.17 50 0.001? IPN 4.2e-6#
051109 36 9.7 2.346 Swift ...
051111 20 44 1.55 Swift ...
051211b 80 33 ... INTGR. 2.6e-6
051221 1.4 42 0.55 Swift 9.8e-4#
051221b 61 26 ... Swift 1.8e-6
060102 20 40 ... Swift 2.0e-6
060109 10 22 ... Swift 4.1e-7
060110 15 43 ... Swift 3.0e-6
060111b 59 37 ... Swift 2.3e-6
060114 100 41 ... INTGR. 5.1e-6
060204b 134 31 ... Swift 2.7e-6
060210 5 43 3.91 Swift ...
060218 10 44.6 0.03 Swift 3.8e-5#
060306 30 46 ... Swift 7.2e-6
060312 30 44 ... Swift 3.3e-6
060313 0.7 47 ... Swift 2.7e-6
060403 25 28 ... Swift 1.0e-6
060427b 0.22 16 ... IPN 2.1e-7
060428b 58 27 ... Swift 1.1e-6
060507 185 47 ... Swift 1.8e-5
060510b 330 43 4.9 Swift ...
060515 52 42 ... Swift 9.6e-6
060712 26 35 ... Swift 3.8e-6
060814 146 23 ... Swift 2.5e-6
060904A 80 14 ... Swift 2.4e-6
060906 43.6 29 3.685 Swift ...
061002 20 45 ... Swift 4.0e-6
061126 191 28 ... Swift 4.3e-6
061210 0.8 23 0.41? Swift 6.1e-6#
061222a 115 30 ... Swift 5.6e-6
