Improvements to aerosol attenuation measurements at the Pierre Auger Observatory Max Malacari 1 for the Pierre Auger Collaboration 2 [Photo by S. Saffi, Univ. of Adelaide] 1 Kavli Institute for Cosmological Physics, University of Chicago, Chicago, IL, USA 2 Observatorio Pierre Auger, Av. San Martín Norte 304, 5613 Malargüe, Argentina Email: auger_spokespersons@fnal.gov Full author list: http://www.auger.org/archive/authors_icrc_2017.html 35 th International Cosmic Ray Conference, July 12 – 20 2017, Busan, South Korea
Improvements to aerosol attenuation measurements at the Pierre Auger Observatory Max Malacari The Pierre Auger Observatory Fluorescence detector (FD) Measurement of the longitudinal shower profile Ø Used to calibrate the Observatory’s energy scale. Ø Sensitive to the atmospheric aerosol transmission. Key observables: Energy (integral → calorimetric energy) • • Depth of maximum development, X max [The Pierre Auger Collaboration, NIM A 798 (2015) 172-213] 35 th International Cosmic Ray Conference, July 12 – 20 2017, Busan, South Korea 2 3,000 km 2 array in western Argentina
Improvements to aerosol attenuation measurements at the Pierre Auger Observatory Max Malacari Aerosol attenuation measurements Z h Ø Quantity of interest is the Vertical 0.07 α A ( h 0 ) dh 0 VAOD( h ) = Aerosol Optical Depth (VAOD) . 0.06 0 Ø Measured with an hourly time resolution 0.05 via two complementary techniques. VAOD Ø Inferred from observations of the 355 nm 0.04 vertically-fired laser of the Central and 0.03 eXtreme Laser Facilities ( CLF / XLF ). 0.02 0.01 0 0 2000 4000 6000 8000 10000 Height [m a.g.l] 700 600 Los Leones < > = 0.040 τ a 500 Los Morados < > = 0.042 τ a Entries 400 Entries Coihueco < > = 0.038 τ a 300 Quality cut for data T > 90 % a 200 Clear nights Dirty nights 100 0 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 VAOD(3.5 km a.g.l, 355 nm) (3.5 km,355 nm) τ [The Pierre Auger Collaboration, Astropart. Phys. 33 (2010) 108-129] 35 th International Cosmic Ray Conference, July 12 – 20 2017, Busan, South Korea 3
Improvements to aerosol attenuation measurements at the Pierre Auger Observatory Max Malacari Aerosol attenuation measurements Data Normalized (DN) analysis 300 2 ~ 90% of aerosol Normalized Photons at Aperture profiles 250 3 200 r e s 1 FD a h 150 L 100 2 1 50 ~25 km 0 0 2000 4000 6000 8000 10000 12000 14000 Height [m a.g.l.] − 1 ✓ N aer ◆ Laser Simulation (LS) analysis VAOD( h ) = ln 1 + 1 / sin φ 2 N ref Measured light flux relative to that on a nominally aerosol free reference night ~1 0% of aerosol profiles Assumptions § Atmosphere horizontally uniform. § Laser light scattered towards the detector by molecules only (DN only). § No multiple scattering of laser light. [The Pierre Auger Collaboration, JINST 8 (2013) P04009] 35 th International Cosmic Ray Conference, July 12 – 20 2017, Busan, South Korea 4
Improvements to aerosol attenuation measurements at the Pierre Auger Observatory Max Malacari Aerosol scattering correction Assumptions 1 § Atmosphere horizontally uniform. ∆ VAOD( h ) = ln(1 + S A /S M ) 1 + 1 / sin φ 2 § Laser light scattered towards the detector by molecules only (DN only). Aerosol volume ✓ § No multiple scattering of laser light. scattering coefficient ✓ 1 d σ ◆ e, S A = α A ( h ) · d Ω σ A ✓ 1 d 0.012 ◆ VAOD = 0.02 VAOD = 0.04 0.01 Aerosol scattering phase VAOD = 0.06 function VAOD = 0.1 0.008 AS VAOD Ø Correction is iterative in nature. 0.006 Ø Increases the VAOD low in the ∆ atmosphere. 0.004 Ø Sensitive to the shape of the aerosol 0.002 scattering phase function . 0 0 2 4 6 8 10 12 Height [km a.g.l] 35 th International Cosmic Ray Conference, July 12 – 20 2017, Busan, South Korea 5
Improvements to aerosol attenuation measurements at the Pierre Auger Observatory Max Malacari Aerosol scattering phase function Ø Aerosol scattering phase function Modified shape measured hourly . Henyey-Greenstein phase function Ø APF monitor beam fired ✓ 1 ( 1 + g 2 − 2 g cos θ ) 3/2 + f 3 cos 2 θ − 1 = 1 − g 2 ◆ ✓ ◆ d σ 1 horizontally across the FD field- 2 ( 1 + g 2 ) 3/2 σ d Ω 4 π of-view @ 350 nm. A 𝒉 – asymmetry parameter Ø Angular distribution of 𝒈 – backscattering parameter measured signal fit to 4- parameter function. χ χ χ 2 2 2 / ndf / ndf / ndf 5.433 / 18 5.433 / 18 5.433 / 18 5 10 ± ± ± A A A 5893 5893 5893 142.6 142.6 142.6 ± ± ± B B B 6283 6283 6283 141.7 141.7 141.7 Phase function [arb. units] ± ± ± g g g 0.52 0.52 0.52 0.01937 0.01937 0.01937 ± ± ± f f f 0.2496 0.2496 0.2496 0.084 0.084 0.084 30 25 4 10 20 Total PF (fit) 15 Aerosol PF 10 Molecular PF 5 20 40 60 80 100 120 140 160 180 0 Scattering angle [deg] 40 60 80 100 120 140 [S.Y. BenZvi et al., Astropart. Phys. 28 (2007) 312-320] azimuth [deg] 35 th International Cosmic Ray Conference, July 12 – 20 2017, Busan, South Korea 6
Improvements to aerosol attenuation measurements at the Pierre Auger Observatory Max Malacari Aerosol scattering phase function Aerosol scattering correction to the VAOD is sensitive to the asymmetry parameter. Analysis of ~ 2,100 hours of APF monitor data taken between 2011 and 2015. 1 Entries Entries 2151 2151 𝒉 = 𝟏. 𝟔𝟖 ± 𝟏. 𝟐𝟏 350 0.9 Mean 0.5688 Mean 0.5688 RMS 0.1013 RMS 0.1013 0.8 Asymmetry parameter g 300 0.7 250 0.6 Counts 200 0.5 0.4 150 0.3 100 0.2 50 0.1 0 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 2 4 6 8 10 12 Asymmetry parameter g Month Ø ~ 0.6 , consistent with expectation Ø Seasonal variation in less than the for a dry desert atmosphere. RMS spread in a given month. 35 th International Cosmic Ray Conference, July 12 – 20 2017, Busan, South Korea 7
Improvements to aerosol attenuation measurements at the Pierre Auger Observatory Max Malacari Multiple scattering correction Assumptions § Atmosphere horizontally uniform. ✓ 1 − f aer ◆ − 1 ∆ VAOD( h ) = ln § Laser light scattered towards the detector 1 + 1 / sin φ 2 1 − f ref by molecules only (DN only). § No multiple scattering of laser light. 𝒈 - the fraction of the detected light originating from height ℎ 0.006 attributed to MS VAOD = 0.02 VAOD = 0.04 0.005 VAOD = 0.08 0.004 VAOD = 0.1 Ø Sensitive to the shape of the aerosol VAOD scattering phase function . 0.003 Ø Correction is iterative in nature. ∆ 0.002 Ø Increases the VAOD low in the atmosphere. 0.001 0 0 2 4 6 8 10 12 Height [km a.g.l] 35 th International Cosmic Ray Conference, July 12 – 20 2017, Busan, South Korea 8
Improvements to aerosol attenuation measurements at the Pierre Auger Observatory Max Malacari Multiple scattering correction 30 Ø Multiply scattered fraction 𝑔 parametrized from Monte Carlo Photons at aperture 25 Elevation [deg] raytracing simulations. 4 10 Ø Simulations performed under various 20 aerosol attenuation conditions. 15 3 10 10 30 5 Height [km a.g.l] 2 10 25 0 20 − − − 15 10 5 0 5 10 15 Azimuth [deg] 15 10 5 𝑔 𝜂 ℎ = MS photons 0 Total photons y [km] 20 10 Beam 20 0 x [km] For observations of the CLF/XLF 𝜂 = 1.5° 10 -10 0 SS -10 -20 -20 MS [M. Malacari and B.R. Dawson, Astropart. Phys. 93 (2017) 38-45] 35 th International Cosmic Ray Conference, July 12 – 20 2017, Busan, South Korea 9
Improvements to aerosol attenuation measurements at the Pierre Auger Observatory Max Malacari Multiple scattering correction Ø Multiply scattered fraction 𝑔 parametrized from Monte Carlo raytracing simulations. Ø Simulations performed under various aerosol attenuation conditions. 𝜼 30 Height [km a.g.l] 25 20 15 10 5 𝑔 𝜂 ℎ = MS photons 0 Total photons y [km] 20 10 Beam 20 0 x [km] For observations of the CLF/XLF 𝜂 = 1.5° 10 -10 0 SS -10 -20 -20 MS [M. Malacari and B.R. Dawson, Astropart. Phys. 93 (2017) 38-45] 35 th International Cosmic Ray Conference, July 12 – 20 2017, Busan, South Korea 10
Improvements to aerosol attenuation measurements at the Pierre Auger Observatory Max Malacari Multiple scattering correction 𝜼~𝟐. 𝟔° for CLF/XLF observations Total optical depth f ζ ( α , τ ) = k · α A · τ (aerosol + molecular) Total attenuation coefficient (aerosol + molecular) 35 th International Cosmic Ray Conference, July 12 – 20 2017, Busan, South Korea 11
Improvements to aerosol attenuation measurements at the Pierre Auger Observatory Max Malacari Effect of the corrections ~50,000 hours of aerosol profiles 2004 – 2015. Example reconstructed VAOD profile 0.07 0.06 0.05 VAOD 0.04 0.03 Original VAOD + aerosol scattering correction 0.02 + multiple scattering correction Smoothed result 0.01 0 0 2000 4000 6000 8000 10000 Height [m a.g.l] 35 th International Cosmic Ray Conference, July 12 – 20 2017, Busan, South Korea 12
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