Gamma-Ray Observatory Gamma-Ray Observatory HAWC response to the atmospheric electric field activity 1 , Alejandro Lara 2 and Olivia Enríquez 1 Graciela Binimelis de Raga 1 Instituto de Geofísica, UNAM 2 Centro de Ciencias de la Atmósfera, UNAM ICRC 2017 Busan, Korea alara@igeofisica.unam.mx ICRC 2017, Busan Alejandro Lara 1
Outline Gamma-Ray Observatory Gamma-Ray Observatory Motivation HAWC TDC and Hardware scaler systems The HAWC site Electric field measurements Response of HAWC to the atmospheric electricity activity low high medium Two examples of atmospheric electric field and counting rate correlation ICRC 2017, Busan Alejandro Lara 2
Motivation HAWC low energy (scaler) rates during the FD of Jun 22, 2015 HAWC HAWC is able to observe heliospheric IMF disturbances as Forbush decreases (FDs) and ground level enhancements SW density (GLEs) In order to study these phenomena we SW velocity need to correct the data by taking into account the atmospheric e ff ects on the counting rates Neutron monitor rates
Motivation HAWC low energy (scaler) rates during the FD of Jun 22, 2015 HAWC HAWC is able to observe heliospheric IMF disturbances as Forbush decreases (FDs) and ground level enhancements SW density (GLEs) In order to study these phenomena we SW velocity need to correct the data by taking into account the atmospheric e ff ects on the counting rates Neutron monitor rates In this work we focus in the e ff ects of the atmospheric electricity on the counting rates
HAWC ● 22,000 m 2 air shower array ● 300 Water Cherenkov detectors (WCD) - 4.5m high, 7.3m diameter Water Cherenkov Detectors ● 200,000 liters of purified water per WCD ● 4 sensors (photo-multiplier tubes) per WCD 5
HAWC Scaler Systems Gamma-Ray Observatory Gamma-Ray Observatory HAWC scaler data are collected by two data acquisition systems (DAQs).: - The time to digital converters ( TDC ) or main DAQ system, has a scaler system which counts the hits, inside a time window of 30 ns, of each PMT and the coincidences of 2, 3 and 4 PMT in each detector, these coincidences are called multiplicity 2, 3 and 4 , respectively. multiplicity ~energy Mult 2 Mult 4 6 Mult 3 ICRC 2017, Busan Alejandro Lara
HAWC Scaler Systems Gamma-Ray Observatory Gamma-Ray Observatory HAWC scaler data are collected by two data acquisition systems (DAQs).: - The time to digital converters ( TDC ) or main DAQ system, has a scaler system which counts the hits, inside a time window of 30 ns, of each PMT and the coincidences of 2, 3 and 4 PMT in each detector, these coincidences are called multiplicity 2, 3 and 4 , respectively. -The second scaler system independently records the hits of each PMT and we call it hardware (HW) scaler system . In this study, we use the percentage of the scaler rates referenced to the mean rate value during one hour before the event. ICRC 2017, Busan Alejandro Lara 7
The HAWC site Gamma-Ray Observatory Gamma-Ray Observatory Average spatial distribution of cloud-to-ground lightning density in flashes per square kilometer per year for the period 2006-2012 (Raga et al 2014).. HAWC HAWC is at a privileged site to study the e ff ects of atmospheric electricity It is at the border of one of the highest lighting incidence areas in Mexico ICRC 2017, Busan Alejandro Lara 8
The HAWC site Gamma-Ray Observatory Gamma-Ray Observatory Sierra Negra 4640m HAWC Site Pico de Orizaba 4100m 5636m HAWC is at a privileged site to study the e ff ects of atmospheric electricity Is at the border of one of the highest lighting incidence areas The orography forces the formation of thunder-clouds at the site The high altitude makes us able to measure the electric field very close to the clouds ICRC 2017, Busan Alejandro Lara 9
Electric Field Measurements Gamma-Ray Observatory Gamma-Ray Observatory We use the EFM-100 for this work ICRC 2017, Busan Alejandro Lara 10
Gamma-Ray Observatory Gamma-Ray Observatory HAWC response to the atmospheric electricity changes Low electric activity Mean count rate of the TDC scaler Multiplicities M - 2 M - 3 M - 4 8” PMTs 10” PMTs The counting rates are not a ff ected by positive fields neither by low-amplitude negative electric field ICRC 2017, Busan Alejandro Lara 11
Gamma-Ray Observatory Gamma-Ray Observatory HAWC response to the atmospheric electricity changes Mean counting rate of High electric activity the TDC scaler Multiplicities M - 2 M - 3 M - 4 8” PMTs 10” PMTs lightning activity: cloud to ground (red squares) inter-cloud (purple triangles) The response of the scaler systems during strong electric activity, with close cloud to ground and cloud to cloud discharges, is unstable. We discard this kind of events ICRC 2017, Busan Alejandro Lara 12
Gamma-Ray Observatory Gamma-Ray Observatory HAWC response to the atmospheric electricity changes Moderated electric activity Spikes Mean counting rate of the HW scaler system, each available channel is plotted in different color. lightning activity: cloud to ground (red squares) inter-cloud (purple triangles) There is a clear distinction between the spikes due to the lightning discharges and the slow and well correlated, scaler enhancements due to the negative electric field increases. ICRC 2017, Busan Alejandro Lara 13
HAWC slow response to atmospheric negative Gamma-Ray Observatory Gamma-Ray Observatory electric field increases example 1, rate enhancement of 6% Mean counting rate of the TDC scaler Multiplicities during May 26, 2015 Two examples of scaler enhancement during increases of electric field where selected due to the good (not saturation) measurement of the electric field. Mean counting rate of the HW scaler system during May 26, 2015. ICRC 2017, Busan Alejandro Lara 14
HAWC slow response to atmospheric negative Gamma-Ray Observatory Gamma-Ray Observatory electric field increases example 2 - rate enhancement of 1 % Mean counting rate of the TDC scaler Multiplicities during Sep 3, 2015. It is important to note the correlated behaviour of all available channels. Mean counting rate of the HW scaler system during Sep 3, 2015. . ICRC 2017, Busan Alejandro Lara 15
HAWC slow response to increases of the Gamma-Ray Observatory Gamma-Ray Observatory atmospheric negative electric field and the atmospheric variables (example 1) The electric field changes significantly during the enhancement The ambient pressure has not e ff ect in this enhancement The ambient temperature has not e ff ect in this enhancement There were humidity at the site There were rain close to the time of the enhancement The solar irradiance was low, showing the presence . of clouds ICRC 2017, Busan Alejandro Lara 16
HAWC slow response to increases of the Gamma-Ray Observatory Gamma-Ray Observatory atmospheric negative electric field and the atmospheric variables (example 2) The electric field changes significantly during the enhancement The ambient pressure has not e ff ect in this enhancement The ambient temperature has not e ff ect in this enhancement There were humidity at the site There were rain close to the time of the enhancement The solar irradiance was low, showing the presence . of clouds ICRC 2017, Busan Alejandro Lara 17
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