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The search for VHE emission from satellite-triggered GRBs with Milagro

Pablo Saz Parkinson University of California, Santa Cruz LANL Collaboration Meeting, 2 June 2005. The search for VHE emission from satellite-triggered GRBs with Milagro. What we would like in a GRB:. Low z (< 0.5) [1]

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The search for VHE emission from satellite-triggered GRBs with Milagro

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  1. Pablo Saz Parkinson University of California, Santa Cruz LANL Collaboration Meeting, 2 June 2005 The search for VHE emission from satellite-triggered GRBswith Milagro

  2. What we would like in a GRB: • Low z (< 0.5) [1] • Good zenith angle (< 45 degrees) [2] • Bright (Fluence > 1 x 10-4 erg cm-2) [3]

  3. What we get: • 25 in 2000-2001 (10 from BATSE alone) • 17 of these well localised • 3 with redshifts (2.03, 2.04, 0.45) • 1 GRB (010921) at good zenith angle (~ 10 degrees), • relatively low z (0.45), but relatively faint • (10-6 erg cm-2 between 8-85 keV) • Milagro upper limits 2.9 (5.8) x 10-5 erg cm-2 • Paper submitted to ApJ

  4. GRBs in Milagro FOV since 2002 5 (19) in 2002 4 (6) in 2003 3 (8) in 2004 8 (21) so far (5/31) in 2005 • GRBs since 2002: • New trigger • Outriggers

  5. The Swift Era: 2005 (up to 5/31) • In 5 months we have a sample of 21 GRBs (~ 50 GRBs/year), compared to 33 GRBs for the previous 3 years (~ 11 GRBs/year) • Only 5 with redshift: 3.24, 3.793, 4.3 at < 45 deg, 1.29, 2.9 at > 45 deg • From 2002-2004 we have 6 or 7 more with redshift: 1.01 and 0.859 at < 45 deg, 3.198, 0.2 (?), 1.25, 0.25 at > 45 deg.

  6. A few interesting candidates • GRB 041219a -> Brightest • Very long and bright (10-4 erg cm-2 15-200 keV) • Good zenith angle (26.9 degrees) • No redshift • 520 s 816 events (766 Bckgd) -> 1.7 sigma • GRB 040924 -> Closest z=0.859 • -> -0.25 sigma

  7. GRB 050509b (GCN Circular 3411) • Very good zenith angle (10 degrees) but very faint (2.3x10-8 erg cm-2 15-350 keV), • redshift ~ 0.2 (some controversy) • E2dN/dE @ 2.5 TeV < 5.4 x 10-8 erg cm-2 (No EBL absorption assumed) • E2dN/dE @ 150 GeV < 5.5 x 10-7 erg cm-2 (Stecker et al. EBL model) • E2dN/dE @ 300 GeV < 2.0 x 10-7 erg cm-2 (Primack et al. EBL model)

  8. A different kind of burst: 27 Dec 2004 SGR 1806-20 Giant flare • Very close (z=0) and Very bright(0.3-0.8 erg cm-2), but very bad zenith angle (68 degrees) • Brightest transient event ever recorded • Effective area of Milagro is ~ 0.5 m2 • Our upper limit is ~ 6 x 10-4 erg cm-2 • Preparing draft of paper

  9. The 27 Dec 2004 SGR 1806-20 Flare

  10. Conclusions • No VHE emission detected from GRBs • Need to run for 2 more years to get another ~ 100 GRBs in our FOV, more than doubling our current sample. • Hopefully in that time we’ll get a bright, nearby GRB at a good zenith angle.

  11. To do: • Finish computing effective area at angles greater than 45 degrees. • Search for emission for GRBs at high zenith angles. • Write ICRC paper by June 30 including preliminary analysis of all GRBs through June 2005. • Submit SGR 1806-20 draft.

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