We report a search for a magnetic monopole component of the cosmic-ray flux in a 95-day exposure of the NOvA experiment's Far Detector, a 14 kt segmented liquid scintillator detector designed ...primarily to observe GeV-scale electron neutrinos. No events consistent with monopoles were observed, setting an upper limit on the flux of 2 × 10−14 cm−2 s−1 sr−1 at 90% C.L. for monopole speed 6 × 10−4 < β < 5 × 10−3 and mass greater than 5 × 108 GeV . Because of NOvA's small overburden of 3 meters-water equivalent, this constraint covers a previously unexplored low-mass region.
Cross sections for the interaction νμA → μ-π0X with neutrino energies between 1 and 5 GeV are measured using a sample of 165,000 selected events collected in the NOvA experiment’s near detector, a ...hydrocarbon-based detector exposed to the Neutrinos from the Main Injector beam at the Fermi National Accelerator Laboratory. Results are presented as a flux-averaged total cross section and as differential cross sections in the momenta and angles of the outgoing muon and π0 , the total four-momentum transfer, and the invariant mass of the hadronic system. Comparisons are made with predictions from a reference version of the genie neutrino interaction generator. The measured total cross section of ( 3.57±0.44 ) ×10-39 cm2 is 7.5% higher than the genie prediction, but is consistent within experimental errors.
In this work, we report the discovery with Fermi/LAT of γ-ray emission from three radio-loud narrow-line Seyfert 1 galaxies: PKS 1502+036 (z = 0.409), 1H 0323+342 (z = 0.061), and PKS 2004 – 447 (z = ...0.24). In addition to PMN J0948+0022 (z = 0.585), the first source of this type to be detected in γ rays, they may form an emerging new class of γ-ray active galactic nuclei (AGNs). Lastly, these findings can have strong implications on our knowledge about relativistic jets and the unified model of the AGN.
Using the NOvA neutrino detectors, a broad search has been performed for any signal coincident with 28 gravitational wave events detected by the LIGO/Virgo Collaboration between September 2015 and ...July 2019. For all of these events, NOvA is sensitive to possible arrival of neutrinos and cosmic rays of GeV and higher energies. For five (seven) events in the NOvA Far (Near) Detector, timely public alerts from the LIGO/Virgo Collaboration allowed recording of MeV-scale events. No signal candidates were found.
It is widely accepted that strong and variable radiation detected over all accessible energy bands in a number of active galaxies arises from a relativistic, Doppler-boosted jet pointing close to our ...line of sight. The size of the emitting zone and the location of this region relative to the central supermassive black hole are, however, poorly known, with estimates ranging from light-hours to a light-year or more. Here we report the coincidence of a gamma (gamma)-ray flare with a dramatic change of optical polarization angle. This provides evidence for co-spatiality of optical and gamma-ray emission regions and indicates a highly ordered jet magnetic field. The results also require a non-axisymmetric structure of the emission zone, implying a curved trajectory for the emitting material within the jet, with the dissipation region located at a considerable distance from the black hole, at about 10(5) gravitational radii.
Using two years of data from the NOvA Near Detector at Fermilab, we report a seasonal variation of cosmic ray induced multiple-muon (Nμ≥2) event rates which has an opposite phase to the seasonal ...variation in the atmospheric temperature. The strength of the seasonal multiple-muon variation is shown to increase as a function of the muon multiplicity. However, no significant dependence of the strength of the seasonal variation of the multiple-muon variation is seen as a function of the muon zenith angle, or the spatial or angular separation between the correlated muons.
Millisecond pulsars, old neutron stars spun up by accreting matter from a companion star, can reach high rotation rates of hundreds of revolutions per second. Until now, all such "recycled" ...rotation-powered pulsars have been detected by their spin-modulated radio emission. In a computing-intensive blind search of gamma-ray data from the Fermi Large Area Telescope (with partial constraints from optical data), we detected a 2.5-millisecond pulsar, PSR J1311—3430. This unambiguously explains a formerly unidentified gamma-ray source that had been a decade-long enigma, confirming previous conjectures. The pulsar is in a circular orbit with an orbital period of only 93 minutes, the shortest of any spin-powered pulsar binary ever found.
The contribution of unresolved sources to the diffuse gamma-ray background could induce anisotropies in this emission on small angular scales. We analyze the angular power spectrum of the diffuse ...emission measured by the Fermi Large Area Telescope at Galactic latitudes b > 30degrees in four energy bins spanning 1-50 GeV. At multipoles l > or = 155, corresponding to angular scales <, ~ 2degrees, angular power above the photon noise level is detected at > 99.99% confidence level in the 1-2 GeV, 2-5 GeV, and 5-10 GeV energy bins, and at > 99% confidence level at 10-50 GeV. Within each energy bin the measured angular power takes approximately the same value at all multipoles l > or = 155, suggesting that it originates from the contribution of one or more unclustered source populations. The amplitude of the angular power normalized to the mean intensity in each energy bin is consistent with a constant value at all energies, C sub(P)/left angle bracketIright angle bracket super(2) = 9.05 + or - 0.84 X 10 super(-6) sr, while the energy dependence of C sub(P) is consistent with the anisotropy arising from one or more source populations with power-law photon spectra with spectral index Gamma sub(s) = 2.40 + or - 0.07. We discuss the implications of the measured angular power for gamma-ray source populations that may provide a contribution to the diffuse gamma-ray background.
Pulsars are rapidly rotating, highly magnetized neutron stars emitting radiation across the electromagnetic spectrum. Although there are more than 1800 known radio pulsars, until recently only seven ...were observed to pulse in gamma rays, and these were all discovered at other wavelengths. The Fermi Large Area Telescope (LAT) makes it possible to pinpoint neutron stars through their gamma-ray pulsations. We report the detection of 16 gamma-ray pulsars in blind frequency searches using the LAT. Most of these pulsars are coincident with previously unidentified gamma-ray sources, and many are associated with supernova remnants. Direct detection of gamma-ray pulsars enables studies of emission mechanisms, population statistics, and the energetics of pulsar wind nebulae and supernova remnants.
We present the detections of 18 solar flares detected in high-energy gamma-rays (above 100 MeV) with the Fermi Large Area Telescope (LAT) during its first 4 yr of operation. This work suggests that ...particle acceleration up to very high energies in solar flares is more common than previously thought, occurring even in modest flares, and for longer durations. We then describe the detailed temporal, spatial, and spectral characteristics of the first two long-lasting events; the 2011 March 7 flare, a moderate (M3.7) impulsive flare followed by slowly varying gamma-ray emission over 13 hr, and the 2011 June 7 M2.5 flare. We compare the Fermi LAT data with X-ray and proton data measurements from GOES and RHESSI. We argue that the gamma-rays are more likely produced through pion decay than electron bremsstrahlung, and we find that flic energy spectrum of the proton distribution softens during the extended emission of the 2011 March 7 flare.
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