C. R. A. Augusto

Muon excess at sea level from solar flares in association with the Fermi GBM spacecraft detector

This paper presents results of an ongoing survey on the associations between muon excesses at ground level registered by the Tupi telescopes and transient solar events, two solar flares whose gamma-ray and X-ray emissions were reported by, respectively, the Fermi GBM and the GOES 14. We show that solar flares of small scale, those with prompt X-ray emission classified by GOES as C-Class (power 10 to 10 W m at 1 AU) may give rise to muon excess probably associated with solar protons and ions emitted by the flare and arriving at the Earth as a coherent particle pulse. The Tupi telescopes are within the central region of the South Atlantic Anomaly (SAA), which allows particle detectors to achieve a low rigidity of response to primary and secondary charged particles (≥ 0.1 GV). Here we argue for the possibility of a “scale-free” energy distribution of particles accelerated by solar flares. Large and small scale flares have the same energy spectrum up to energies exceeding the pion production, the difference between them is only the intensity. If this hypothesis is correct, the Tupi telescope is registering muons produced by protons (ions)

Search for muon enhancement at sea level from transient solar activity

This paper presents first results of an ongoing study of a possible association between muon enhancements at ground observed by the TUPI telescope and transient events such as the Suns X-ray activity. The analysis of the observed phenomenon by using the GOES satellite archive data seems to indicate that on most cases the Ground Level Enhancements (GLEs) could potentially be associated with solar flares. We show that small-scale solar flares, those with prompt X-ray emission classified as C class (power above 10{sup -6} Watts m{sup -2} at 1 AU) may give rise to GLEs, probably associated with solar protons and ions arriving to the Earth as a coherent particle pulse. The TUPI telescopes high performance with these energetic solar particles arises mainly from: (i) its high counting rate (up to {approx}100 KHz). This value in most cases is around 100 times higher than other detectors at ground and (ii) due to its tracking system. The telescope is always looking near the direction of the IMF lines. The GLEs delay in relation of the X-ray prompt emission suggest that shock driven by corona mass ejection (CME) is an essential requirement for the particle acceleration efficiency.

Muon enhancements at sea level in association with Swift-BAT and MILAGRO triggers

Recently, triggers occurring during high background rate intervals have been reporter by the Swift-BAT gamma-ray burst detector. Among them, there were two on January 24, two on January 25, and two on February 13 and 18, all in 2008. These Swift-BAT triggers in most cases are probably noise triggers that occurred while Swift was entering the South Atlantic Anomaly (SAA). In fact, we show that they happen during a plentiful precipitation of high energy particles in the SAA, producing muons in the atmosphere detected by two directional telescopes at sea level, inside the SAA region (Tupi experiment). They look like sharp peaks in the muon counting rate. In the same category are two triggers from the MILAGRO ground-based detector, on January 25 and 31, 2008, respectively. In addition, the trigger coordinates are close to (and, in two cases, inside) the field of view of the telescopes. From an additional analysis in the behavior of the muon counting rate, it is possible to conclude that the events are produced by precipitation of high energy charged particles in the SAA region. Thus, due to its localization, the Tupi experiment constitutes a new sensor of high energy particle precipitation in the SAA, and it can be useful in the identification of some triggers of gamma-ray burst detectors.

OBSERVATION OF MUON EXCESS AT GROUND LEVEL IN RELATION TO GAMMA-RAY BURSTS DETECTED FROM SPACE

In this paper we examine the possibility of the ground observation of the gigaelectronvolt counterparts associated with the Monitor of All-sky X-ray Image transient event (trigger 58072727) and the Swift GRB140512A event. In both cases, there was a muon excess with a statistical significance above 4σ. The coordinates of the events were located in the field of view (FOV) of the Tupi muon telescopes at the time of the occurrence. Since 2013 August, the Tupi experiment has been operating a new extended array of five muon telescopes, located at ground level at (, 3 m above sea level). This location coincides with the South Atlantic Anomaly central region. We consider a hypothesis that the muon excess could be due to photonuclear reactions in the Earths atmosphere induced by gamma rays with energies above 10 GeV. We describe a data analysis for candidate events identified by internally triggered (by the Tupi experiment) as well as untriggered (dependent on external observations) modes of search. In light of the Fermi LAT () gamma-ray bursts (GRBs) catalog, we examine the possibility of the ground observation of similar transient events within the FOV of the extended Tupi array and perform a systematic analysis of the Tupi data. Using a Monte Carlo simulation, we discuss the experimental conditions that allow the detection of signals from GRBs at ground level.

Search for a simultaneous signal from small transient events in the Pierre Auger Observatory and the Tupi muon telescopes

We present results of a search for a possible signal from small scale solar transient events (such as flares and interplanetary shocks) as well as possible counterparts to Gamma-Ray Burst (GRB) observed simultaneously by the Tupi muon telescope Niteroi-Brazil, 22.90S, 43.20W, 3 m above sea level) and the Pierre Auger Observatory surface detectors (Malargue-Argentina, 69.30S, 35.30W, altitude 1400 m). Both cosmic ray experiments are located inside the South Atlantic Anomaly (SAA) region. Our analysis of several examples shows similarities in the behavior of the counting rate of low energy (above 100 MeV) particles in association with the solar activity (solar flares and interplanetary shocks). We also report an observation by the Tupi experiment of the enhancement of muons at ground level with a significance higher than 8 sigma in the 1-sec binning counting rate (raw data) in close time coincidence (T-184 sec) with the Swift-BAT GRB110928B (trigger=504307). The GRB 110928B coordinates are in the field of view of the vertical Tupi telescope, and the burst was close to the MAXI source J1836-194. The 5-min muon counting rate in the vertical Tupi telescope as well as publicly available data from Auger (15 minutes averages of the scaler rates) show small peaks above the background fluctuations at the time following the Swift-BAT GRB 110928B trigger. In accordance with the long duration trigger, this signal can possibly suggest a long GRB, with a precursor narrow peak at T-184 sec.

The 2015 Summer Solstice Storm: One of the Major Geomagnetic Storms of Solar Cycle 24 Observed at Ground Level

We report on the 22 – 23 June 2015 geomagnetic storm that occurred at the summer solstice. There have been fewer intense geomagnetic storms during the current solar cycle, Solar Cycle 24, than in the previous cycle. This situation changed after mid-June 2015, when one of the largest solar active regions (AR 12371) of Solar Cycle 24 that was located close to the central meridian, produced several coronal mass ejections (CMEs) associated with M-class flares. The impact of these CMEs on the Earth’s magnetosphere resulted in a moderate to severe G4-class geomagnetic storm on 22 – 23 June 2015 and a G2 (moderate) geomagnetic storm on 24 June. The G4 solstice storm was the second largest (so far) geomagnetic storm of Cycle 24. We highlight the ground-level observations made with the New-Tupi, Muonca, and the CARPET El Leoncito cosmic-ray detectors that are located within the South Atlantic Anomaly (SAA) region. These observations are studied in correlation with data obtained by space-borne detectors (ACE, GOES, SDO, and SOHO) and other ground-based experiments. The CME designations are taken from the Computer Aided CME Tracking (CACTus) automated catalog. As expected, Forbush decreases (FD) associated with the passing CMEs were recorded by these detectors. We note a peculiar feature linked to a severe geomagnetic storm event. The 21 June 2015 CME 0091 (CACTus CME catalog number) was likely associated with the 22 June summer solstice FD event. The angular width of CME 0091 was very narrow and measured ∼56∘

Signals at ground level of relativistic solar particles associated with a radiation storm on 2014 April 18

{\sim}\, 56^{\circ }

Search for GLAST gamma ray burst triggers due to particle precipitation in the South Atlantic Anomaly

degrees seen from Earth. In most cases, only CME halos and partial halos lead to severe geomagnetic storms. We perform a cross-check analysis of the FD events detected during the rise phase of Solar Cycle 24, the geomagnetic parameters, and the CACTus CME catalog. Our study suggests that narrow angular-width CMEs that erupt in a westward direction from the Sun–Earth line can lead to moderate and severe geomagnetic storms. We also report on the strong solar proton radiation storm that began on 21 June. We did not find a signal from this SEP at ground level. The details of these observations are presented.

Muon Excess at Sea Level during the Progress of a Geomagnetic Storm and High-Speed Stream Impact Near the Time of Earth’s Heliospheric Sheet Crossing

Far away from any sunspot, a bright flare erupted on November 1st, 2014, with onset at 4:44 UT and a duration of around three hours, causing a C2.7-class flare. The blast was associated with the sudden disappearance of a large dark solar filament. The rest of the filament flew out into space, forming the core of a massive CME. Despite the location of the explosion over the sun’s southeastern region (near the eastern edge of the sun) not be geoeffective, a radiation storm, that is, solar energetic particles (SEP) started to reach the Earth around 14:00 UT, reaching the condition of an S1 (minor) radiation storm level on Nov. 2th. In coincidence with onset of the S1 radiation storm (SEP above 5 MeV), the Tupi telescopes located at 22090′S; 43020′W, within the South Atlantic Anomaly (SAA) detected a muon enhancement caused by relativistic protons from this solar blast. In addition an increase in the particle intensity was found also at South Pole neutron monitor. This means that there was a transverse propagation to the interplanetary magnetic field of energetic solar particles. However, we show that perpendicular diffusion alone cannot explain these observations, it is necessary a combination with further processes as a very high speed, at least of a fraction the CME shocks, close to the ecliptic plane.

Connection among spacecrafts and ground level observations of small solar transient events

When GLAST is in the South Atlantic Anomaly (SAA), the rate of charged particles is too high to be efficiently filtered out. Moreover the high rate can cause saturation effects in the readout electronics and the sensors must be turned off. The SAA area relative to the total area of GLASTs orbit is approximately 12.5% and GLAST spends 18% of the time in it. In spite of these cares, we show in this work that, due to drift processes, particle precipitation can still trigger GLAST when it is close to the SAA region. Here, we report two GLAST gamma ray burst monitor (GBM) triggers, trigger 239895229 and trigger 239913100, on August, 08, 2008 whose characteristics are similar to the ones observed in the Swift-BAT noise triggers (due to particle precipitation in the SAA region). Both GLAST triggers happened during a plentiful particle precipitation in the SAA region, observed by Tupi telescopes at the ground with their trigger coordinates close to the field of view of the telescopes. Details of these results are reported.