1. Recent results from the Milagro TeV gamma-ray observatory
Pablo Saz Parkinson
Santa Cruz Institute for Particle Physics
University of California, Santa Cruz
La Thuile, 18 March 2005

2. Pablo Saz Parkinson, Recontres de Moriond
Outline
Introduction: The Milagro Gamma-ray Observatory (astro-ph/ )
Recent Results
VHE emission from the Galactic Plane (astro-ph/ )
Other extended Sources (astro-ph/ )
Gamma Ray Bursts (astro-ph/ )
Future (astro-ph/ )
Pablo Saz Parkinson, Recontres de Moriond
12 January 2019

3. Current Milagro Collaboration List
A. Abdo7, B. Allen1, D. Berley2, E. Blaufuss2, S. Cassanova4, D.G. Coyne3,
T. DeYoung2, B.L. Dingus4, D.E. Dorfan3, R.W. Ellsworth5, M.M. Gonzalez6,
J.A. Goodman2, E. Hays2, C.P. Lansdell2, J.T. Linnemann7, J.E. McEnery8,
A.I. Mincer9, P. Nemethy9, D. Noyes2, J.M. Ryan10, P. Saz Parkinson3,
A. Shoup1, G. Sinnis4, A.J. Smith2, G.W. Sullivan2, V. Vasileiou2, G. Walker4, D.A. Williams3, G.B. Yodh1
Department of Physics and Astronomy, University of California, Irvine.
Department of Physics, University of Maryland.
Santa Cruz Institute for Particle Physics, University of California, Santa Cruz.
Group P-23, Los Alamos National Laboratory.
Department of Physics and Astronomy, George Mason University.
Department of Physics, University of Wisconsin.
Department of Physics and Astronomy, Michigan State University.
NASA Goddard Space Flight Center.
Department of Physics, New York University.
Department of Physics, University of New Hampshire.
Pablo Saz Parkinson, Recontres de Moriond
12 January 2019

4. The Milagro TeV observatory
2630 m above sea level in the Jemez Mountains, Los Alamos, New Mexico
Operational since 2000 (with outriggers since 2003)
Duty cycle greater than 90%
~ 2sr field of view
Angular resolution of 0.75 degrees (0.45 with outriggers)
Energy: ~ 100 GeV – 100 TeV
(median ~ 2.5 TeV)
8” PMTs with “baffles”
2.8 x 2.8 m spacing
Top Layer: 450 PMTs, 1.5 m deep
Bottom Layer: 273 PMTs, 6.5 m deep
Outriggers: 175 black plastic tanks each with a PMT, spread over 40,000 m2
Pablo Saz Parkinson, Recontres de Moriond
12 January 2019

5. Pablo Saz Parkinson, Recontres de Moriond
Galactic Plane
EGRET All-sky survey above MeV
EGRET diffuse GeV flux (in black)
Milagro exposure (in red)
Pablo Saz Parkinson, Recontres de Moriond
12 January 2019

6. g-rays from Galactic Plane
significance (s)
4.5 s excess for the “Milagro inner galaxy” ~ 4.7 x 10-5 of CR flux
First detection of the Galactic plane at TeV energies.
Pablo Saz Parkinson, Recontres de Moriond
12 January 2019

7. Profile and Energy Spectrum
Consistent with extrapolation from EGRET
Any rapidly rising component to explain >1 GeV excess cannot continue to 1 TeV
Previous upper limits in this energy range well above extrapolation
Submitted to PRL
astro-ph/
Pablo Saz Parkinson, Recontres de Moriond
12 January 2019

8. Milagro All Sky Survey December 2000 to November 2003
Raw Significance (standard deviations)
3EG J ?
RA=79.90, Dec=26.80
4.9 s
Mrk 421
Crab
Astrophysical Journal 608, 680 (2004)
Pablo Saz Parkinson, Recontres de Moriond
12 January 2019

9. Extended source search
Apply standard event selection
Vary source bin size from 2.1o (optimal for point sources) to 5.9o in steps of 0.2o
Data set June 2000 to May 2004
1269 days live time
Two sources appear with high significance:
3EG J and Cygnus Region
Pablo Saz Parkinson, Recontres de Moriond
12 January 2019

10. 3EG J0520+2556? Preliminary RA = 79.8o±0.4o±0.15o J0520+2556
DEC = 26.0o±0.4o±0.10o
Consistent with EGRET location
For Gaussian source profile s = 0.8o±0.4o
5.9s excess for 2.9o bin size. Probability of excess anywhere in sky at any bin size 7 x 10-3
Flux ~0.85 x Crab
Compatible with Whipple limit given source extent
Accumulation of excess consistent
with steady source J
Crab
Smoothed with 0.75o Gaussian
Pablo Saz Parkinson, Recontres de Moriond
12 January 2019

11. Pablo Saz Parkinson, Recontres de Moriond
Cygnus Region
Preliminary
5.5s excess for 5.9o bin size (2% chance for whole sky at any bin size)
RA ~ 308o, Dec ~ 42o, consistent with steady source
Consistent with diffuse emission from region of high density matter
Brightest GeV EGRET source in the northern sky
Galactic plane emission still significant with this region excluded
Flux ~2 x Crab Nebula flux
significance (s)
Pablo Saz Parkinson, Recontres de Moriond
12 January 2019

12. Pablo Saz Parkinson, Recontres de Moriond
Milagro GRB Search
Evidence for TeV emission from GRB a seen by Milagrito
37 satellite detected GRBs have been within 45 degrees of zenith at Milagro from 2000 to 2005
Fewer than Milagrito because of BATSE’s demise
No high energy emission is detected from any of the bursts
Analysis of the most recent bursts still preliminary
Constraints on TeV emission are most interesting for GRB with known redshift
5 have measured redshift z = 0.45, 0.859,1.01, 2.03, 2.04
Pablo Saz Parkinson, Recontres de Moriond
12 January 2019

13. GRB 010921 First afterglow detected from HETE-localised burst
Spectrum of the host galaxy measured by Palomar —> z = 0.45
Closest burst to fall in Milagro field of view
Zenith angle of 10 degrees at Milagro
astro-ph/
HETE spectrum
Milagro 99% c.l. upper limits
Stecker & de Jager 1998
Primack et al. 2004
Pablo Saz Parkinson, Recontres de Moriond
12 January 2019

14. Search for VHE GRB emission
Swift launched in November 2004
It will detect ~100 bursts/year
Already 2 Swift bursts in Milagro field of view. Analysis is ongoing.
Redshift determination should be possible for most Swift bursts
We expect ~15-20 GRBs per year in Milagro FOV with redshift information
Larger sample by factor of ~4
Flux (even if limit) will be meaningful on each burst
Pablo Saz Parkinson, Recontres de Moriond
12 January 2019

15. Pablo Saz Parkinson, Recontres de Moriond
Summary and Future
Milagro has been operational since 2000
Operating with “outriggers” since 2003
Crab and Mkn 421 detected
Galactic Plane observed at VHE for first time
Two diffuse source candidates reported
Ongoing search for Gamma-ray burst emission for the next two years of Swift mission
Proposing move to higher altitude (~4500 m) site with O(10) increase in sensitivity
Longer term — HAWC (astro-ph/ )
Pablo Saz Parkinson, Recontres de Moriond
12 January 2019

16. EXTRA SLIDES EXTRA SLIDES
Pablo Saz Parkinson, Recontres de Moriond
12 January 2019

17. Bkg Rejection – “Compactness”
Data
Proton (MC)
Gammas (MC)
Compactness
PMTs > 2 PE
Maximum PE
C =
using just bottom layer PMTs
C > 2.5 removes 90% of the protons and keeps 50% of the gammas
Astrophysical Journal 595, 803–811 (2003)
Pablo Saz Parkinson, Recontres de Moriond
12 January 2019

18. Most significant locations
Pablo Saz Parkinson, Recontres de Moriond
12 January 2019

19. Pablo Saz Parkinson, Recontres de Moriond
Milagro Outriggers
175 black plastic tanks deployed over 20,000 m2
Each lined with Tyvek and filled with filtered water
A single 8” PMT in each
Operating since 2003
Pablo Saz Parkinson, Recontres de Moriond
12 January 2019

20. Pablo Saz Parkinson, Recontres de Moriond
EGRET source
Pablo Saz Parkinson, Recontres de Moriond
12 January 2019