Direct detection of a break in the teraelectronvolt cosmic-ray spectrum of electrons and positrons

Direct Measurement of the Spectral Structure of Cosmic-Ray Electrons+Positrons in the TeV Region with CALET on the International Space Station

Detailed measurements of the spectral structure of cosmic-ray electrons and positrons from 10.6 GeV to 7.5 TeV are presented from over 7 years of observations with the CALorimetric Electron Telescope (CALET) on the International Space Station. The instrument, consisting of a charge detector, an imaging calorimeter, and a total absorption calorimeter with a total depth of 30 radiation lengths at normal incidence and a fine shower imaging capability, is optimized to measure the all-electron spectrum well into the TeV region. Because of the excellent energy resolution (a few percent above 10 GeV) and the outstanding e/p separation (10^{5}), CALET provides optimal performance for a detailed search of structures in the energy spectrum. The analysis uses data up to the end of 2022, and the statistics of observed electron candidates has increased more than 3 times since the last publication in 2018. By adopting an updated boosted decision tree analysis, a sufficient proton rejection power up to 7.5 TeV is achieved, with a residual proton contamination less than 10%. The observed energy spectrum becomes gradually harder in the lower energy region from around 30 GeV, consistently with AMS-02, but from 300 to 600 GeV it is considerably softer than the spectra measured by DAMPE and Fermi-LAT. At high energies, the spectrum presents a sharp break around 1 TeV, with a spectral index change from -3.15 to -3.91, and a broken power law fitting the data in the energy range from 30 GeV to 4.8 TeV better than a single power law with 6.9 sigma significance, which is compatible with the DAMPE results. The break is consistent with the expected effects of radiation loss during the propagation from distant sources (except the highest energy bin). We have fitted the spectrum with a model consistent with the positron flux measured by AMS-02 below 1 TeV and interpreted the electron+positron spectrum with possible contributions from pulsars and nearby sources. Above 4.8 TeV, a possible contribution from known nearby supernova remnants, including Vela, is addressed by an event-by-event analysis providing a higher proton-rejection power than a purely statistical analysis.

Searching for Afterglow: Light Dark Matter Boosted by Supernova Neutrinos

A novel analysis is performed, incorporating time-of-flight (TOF) information to study the interactions of dark matter (DM) with standard model particles. After supernova (SN) explosions, DM with mass m_{χ}≲O(MeV) in the halo can be boosted by SN neutrinos (SNν) to relativistic speed. The SNν boosted DM (BDM) arrives on Earth with TOF which depends only on m_{χ} and is independent of the cross section. These BDMs can interact with detector targets in low-background experiments and manifest as afterglow events after the arrival of SNν. The characteristic TOF spectra of the BDM events can lead to large background suppression and unique determination of m_{χ}. New cross section constraints on sqrt[σ_{χe}σ_{χν}] are derived from SN1987a in the Large Magellanic Cloud with data from the Kamiokande and Super-Kamiokande experiments. Potential sensitivities for the next galactic SN with Hyper-Kamiokande are projected. This analysis extends the existing bounds on sqrt[σ_{χe}σ_{χν}] over a broad range of r_{χ}=σ_{χν}/σ_{χe}. In particular, the improvement is by 1-3 orders of magnitude for m_{χ}<O(100  keV) for σ_{χe}∼σ_{χν}. Prospects of exploiting TOF information in other astrophysical systems to probe exotic physics with other DM candidates are discussed.

Explaining the GeV Antiproton Excess, GeV γ-Ray Excess, and W-Boson Mass Anomaly in an Inert Two Higgs Doublet Model

For the newly discovered W-boson mass anomaly, one of the simplest dark matter (DM) models that can account for the anomaly without violating other astrophysical and experimental constraints is the inert two Higgs doublet model, in which the DM mass (m_{S}) is found to be within ∼54-74  GeV. In this model, the annihilation of DM via SS→bb[over ¯] and SS→WW^{*} would produce antiprotons and gamma rays, and may account for the excesses identified previously in both particles. Motivated by this, we reanalyze the AMS-02 antiproton and Fermi-LAT Galactic center γ-ray data. For the antiproton analysis, the novel treatment is the inclusion of the charge-sign-dependent three-dimensional solar modulation model as constrained by the time-dependent proton data. We find that the excess of antiprotons is more distinct than previous results based on the force-field solar modulation model. The interpretation of this excess as the annihilation of SS→WW^{*} (SS→bb[over ¯]) requires a DM mass of ∼40-80 (40-60) GeV and a velocity-averaged cross section of O(10^{-26})  cm^{3} s^{-1}. As for the γ-ray data analysis, besides adopting the widely used spatial template fitting, we employ an orthogonal approach with a data-driven spectral template analysis. The fitting to the GeV γ-ray excess yields DM model parameters overlapped with those to fit the antiproton excess via the WW^{*} channel. The consistency of the DM particle properties required to account for the W-boson mass anomaly, the GeV antiproton excess, and the GeV γ-ray excess suggests a common origin of them.

Galactic Cosmic Rays Throughout the Heliosphere and in the Very Local Interstellar Medium

We review recent observations and modeling developments on the subject of galactic cosmic rays through the heliosphere and in the Very Local Interstellar Medium, emphasizing knowledge that has accumulated over the past decade. We begin by highlighting key measurements of cosmic-ray spectra by Voyager, PAMELA, and AMS and discuss advances in global models of solar modulation. Next, we survey recent works related to large-scale, long-term spatial and temporal variations of cosmic rays in different regimes of the solar wind. Then we highlight new discoveries from beyond the heliopause and link these to the short-term evolution of transients caused by solar activity. Lastly, we visit new results that yield interesting insights from a broader astrophysical perspective.

Deep Ensemble Learning with Atrous Spatial Pyramid Networks for Protein Secondary Structure Prediction

The secondary structure of proteins is significant for studying the three-dimensional structure and functions of proteins. Several models from image understanding and natural language modeling have been successfully adapted in the protein sequence study area, such as Long Short-term Memory (LSTM) network and Convolutional Neural Network (CNN). Recently, Gated Convolutional Neural Network (GCNN) has been proposed for natural language processing. It has achieved high levels of sentence scoring, as well as reduced the latency. Conditionally Parameterized Convolution (CondConv) is another novel study which has gained great success in the image processing area. Compared with vanilla CNN, CondConv uses extra sample-dependant modules to conditionally adjust the convolutional network. In this paper, we propose a novel Conditionally Parameterized Convolutional network (CondGCNN) which utilizes the power of both CondConv and GCNN. CondGCNN leverages an ensemble encoder to combine the capabilities of both LSTM and CondGCNN to encode protein sequences by better capturing protein sequential features. In addition, we explore the similarity between the secondary structure prediction problem and the image segmentation problem, and propose an ASP network (Atrous Spatial Pyramid Pooling (ASPP) based network) to capture fine boundary details in secondary structure. Extensive experiments show that the proposed method can achieve higher performance on protein secondary structure prediction task than existing methods on CB513, Casp11, CASP12, CASP13, and CASP14 datasets. We also conducted ablation studies over each component to verify the effectiveness. Our method is expected to be useful for any protein related prediction tasks, which is not limited to protein secondary structure prediction.

Structured Scintillators for Efficient Radiation Detection

Scintillators, which can convert high-energy ionizing radiation into visible light, have been serving as the core component in radiation detectors for more than a century of history. To address the increasing application demands along with the concern on nuclear security, various strategies have been proposed to develop a next-generation scintillator with a high performance in past decades, among which the novel approach via structure control has received great interest recently due to its high feasibility and efficiency. Herein, the concept of "structure engineering" is proposed for the exploration of this type of scintillators. Via internal or external structure design with size ranging from micro size to macro size, this promising strategy cannot only improve scintillator performance, typically radiation stopping power and light yield, but also extend its functionality for specific applications such as radiation imaging and therapy, opening up a new range of material candidates. The research and development of various types of structured scintillators are reviewed. The current state-of-the-art progresses on structure design, fabrication techniques, and the corresponding applications are discussed. Furthermore, an outlook focusing on the current challenges and future development is proposed.

Constraining the axion-photon coupling using radio data of the Bullet cluster

Axion is one of the most popular candidates of the cosmological dark matter. Recent studies considering the misalignment production of axions suggest some benchmark axion mass ranges near [Formula: see text] μeV. For such axion mass, the spontaneous decay of axions can give photons in radio band frequency [Formula: see text] GHz, which can be detected by radio telescopes. In this article, we show that using radio data of galaxy clusters would be excellent to constrain axion dark matter. Specifically, by using radio data of the Bullet cluster (1E 0657-55.8), we find that the upper limit of the axion-photon coupling constant can be constrained to [Formula: see text] GeV[Formula: see text] for [Formula: see text] μeV, which is tighter than the limit obtained by the CERN Axion Solar Telescope (CAST).

Measurement of the Cosmic Ray Helium Energy Spectrum from 70 GeV to 80 TeV with the DAMPE Space Mission

The measurement of the energy spectrum of cosmic ray helium nuclei from 70 GeV to 80 TeV using 4.5 years of data recorded by the Dark Matter Particle Explorer (DAMPE) is reported in this work. A hardening of the spectrum is observed at an energy of about 1.3 TeV, similar to previous observations. In addition, a spectral softening at about 34 TeV is revealed for the first time with large statistics and well controlled systematic uncertainties, with an overall significance of 4.3σ. The DAMPE spectral measurements of both cosmic protons and helium nuclei suggest a particle charge dependent softening energy, although with current uncertainties a dependence on the number of nucleons cannot be ruled out.

The Discovery of a Low-energy Excess in Cosmic-Ray Iron: Evidence of the Past Supernova Activity in the Local Bubble

Since its launch, the Alpha Magnetic Spectrometer-02 (AMS-02) has delivered outstanding quality measurements of the spectra of cosmic-ray (CR) species ( p ¯ , e ±, and nuclei, 1H-8O, 10Ne, 12Mg, 14Si) which resulted in a number of breakthroughs. One of the latest long-awaited surprises is the spectrum of 26Fe just published by AMS-02. Because of the large fragmentation cross section and large ionization energy losses, most of CR iron at low energies is local and may harbor some features associated with relatively recent supernova (SN) activity in the solar neighborhood. Our analysis of the new AMS-02 results, together with Voyager 1 and ACE-CRIS data, reveals an unexpected bump in the iron spectrum and in the Fe/He, Fe/O, and Fe/Si ratios at 1-2 GV, while a similar feature in the spectra of He, O, and Si and in their ratios is absent, hinting at a local source of low-energy CRs. The found excess extends the recent discoveries of radioactive 60Fe deposits in terrestrial and lunar samples and in CRs. We provide an updated local interstellar spectrum (LIS) of iron in the energy range from 1 MeV nucleon-1 to ~10 TeV nucleon-1. Our calculations employ the GALPROP-HELMOD framework, which has proved to be a reliable tool in deriving the LIS of CR p ¯ , e -, and nuclei Z ⩽ 28.

Gamma Rays as Probes of Cosmic-Ray Propagation and Interactions in Galaxies

Continuum gamma-ray emission produced by interactions of cosmic rays with interstellar matter and radiation fields is a probe of non-thermal particle populations in galaxies. After decades of continuous improvements in experimental techniques and an ever-increasing sky and energy coverage, gamma-ray observations reveal in unprecedented detail the properties of galactic cosmic rays. A variety of scales and environments are now accessible to us, from the local interstellar medium near the Sun and the vicinity of cosmic-ray accelerators, out to the Milky Way at large and beyond, with a growing number of gamma-ray emitting star-forming galaxies. Gamma-ray observations have been pushing forward our understanding of the life cycle of cosmic rays in galaxies and, combined with advances in related domains, they have been challenging standard assumptions in the field and have spurred new developments in modelling approaches and data analysis methods. We provide a review of the status of the subject and discuss perspectives on future progress.

First Detection of sub-PeV Diffuse Gamma Rays from the Galactic Disk: Evidence for Ubiquitous Galactic Cosmic Rays beyond PeV Energies

We report, for the first time, the long-awaited detection of diffuse gamma rays with energies between 100 TeV and 1 PeV in the Galactic disk. Particularly, all gamma rays above 398 TeV are observed apart from known TeV gamma-ray sources and compatible with expectations from the hadronic emission scenario in which gamma rays originate from the decay of π^{0}'s produced through the interaction of protons with the interstellar medium in the Galaxy. This is strong evidence that cosmic rays are accelerated beyond PeV energies in our Galaxy and spread over the Galactic disk.

Radio Constraints of Dark Matter: A Review and Some Future Perspectives

In the past few decades, many studies have analyzed the data of gamma-rays, X-rays, radio waves, electrons, positrons, anti-protons, and neutrinos to search for the signal of dark matter annihilation. In particular, analyzing radio data has been one of the most important and effective ways to constrain dark matter. In this article, we review the physics and the theoretical framework of using radio data to constrain annihilating dark matter. We also review some important radio constraints of annihilating dark matter and discuss the future perspectives of using radio detection to reveal the nature of dark matter.

Status, Challenges and Directions in Indirect Dark Matter Searches

Indirect searches for dark matter are based on detecting an anomalous flux of photons, neutrinos or cosmic-rays produced in annihilations or decays of dark matter candidates gravitationally accumulated in heavy cosmological objects, like galaxies, the Sun or the Earth. Additionally, evidence for dark matter that can also be understood as indirect can be obtained from early universe probes, like fluctuations of the cosmic microwave background temperature, the primordial abundance of light elements or the Hydrogen 21-cm line. The techniques needed to detect these different signatures require very different types of detectors: Air shower arrays, gamma- and X-ray telescopes, neutrino telescopes, radio telescopes or particle detectors in balloons or satellites. While many of these detectors were not originally intended to search for dark matter, they have proven to be unique complementary tools for direct search efforts. In this review we summarize the current status of indirect searches for dark matter, mentioning also the challenges and limitations that these techniques encounter.

Inference of the Local Interstellar Spectra of Cosmic-Ray Nuclei Z ⩽ 28 with the GalProp-HelMod Framework

Composition and spectra of Galactic cosmic rays (CRs) are vital for studies of high-energy processes in a variety of environments and on different scales, for interpretation of γ-ray and microwave observations, for disentangling possible signatures of new phenomena, and for understanding of our local Galactic neighborhood. Since its launch, AMS-02 has delivered outstanding-quality measurements of the spectra of p ¯ , e ±, and nuclei: 1H-8O, 10Ne, 12Mg, 14Si. These measurements resulted in a number of breakthroughs; however, spectra of heavier nuclei and especially low-abundance nuclei are not expected until later in the mission. Meanwhile, a comparison of published AMS-02 results with earlier data from HEAO-3-C2 indicates that HEAO-3-C2 data may be affected by undocumented systematic errors. Utilizing such data to compensate for the lack of AMS-02 measurements could result in significant errors. In this paper we show that a fraction of HEAO-3-C2 data match available AMS-02 measurements quite well and can be used together with Voyager 1 and ACE-CRIS data to make predictions for the local interstellar spectra (LIS) of nuclei that are not yet released by AMS-02. We are also updating our already-published LIS to provide a complete set from 1H-28Ni in the energy range from 1 MeV nucleon-1 to ~100-500 TeV nucleon-1, thus covering 8-9 orders of magnitude in energy. Our calculations employ the GalProp-HelMod framework, which has proved to be a reliable tool in deriving the LIS of CR p ¯ , e -, and nuclei 1H-8O.

Cosmic-Ray Database Update: Ultra-High Energy, Ultra-Heavy, and Antinuclei Cosmic-Ray Data (CRDB v4.0)

We present an update on CRDB, the cosmic-ray database for charged species. CRDB is based on MySQL, queried and sorted by jquery and table-sorter libraries, and displayed via PHP web pages through the AJAX protocol. We review the modifications made on the structure and outputs of the database since the first release (Maurin et al., 2014). For this update, the most important feature is the inclusion of ultra-heavy nuclei (Z>30), ultra-high energy nuclei (from 1015 to 1020 eV), and limits on antinuclei fluxes (Z≤−1 for A>1); more than 100 experiments, 350 publications, and 40,000 data points are now available in CRDB. We also revisited and simplified how users can retrieve data and submit new ones. For questions and requests, please contact crdb@lpsc.in2p3.fr.

Heat-resistant Pb(ii)-based X-ray scintillating metal–organic frameworks for sensitive dosage detection via an aggregation-induced luminescent chromophore

Unusual X-aggregation induced luminescent chromophores in heat-resistant Pb(ii)-based metal–organic frameworks facilitate excellent scintillation for X-ray dosage detection.

AMS-100: The Next Generation Magnetic Spectrometer in Space - An International Science Platform for Physics and Astrophysics at Lagrange Point 2

The next generation magnetic spectrometer in space, AMS-100, is designed to have a geometrical acceptance of 100 m2 sr and to be operated for at least ten years at the Sun-Earth Lagrange Point 2. Compared to existing experiments, it will improve the sensitivity for the observation of new phenomena in cosmic rays, and in particular in cosmic antimatter, by at least a factor of 1000. The magnet design is based on high temperature superconductor tapes, which allow the construction of a thin solenoid with a homogeneous magnetic field of 1 Tesla inside. The inner volume is instrumented with a silicon tracker reaching a maximum detectable rigidity of 100 TV and a calorimeter system that is 70 radiation lengths deep, equivalent to four nuclear interaction lengths, which extends the energy reach for cosmic-ray nuclei up to the PeV scale, i.e. beyond the cosmic-ray knee. Covering most of the sky continuously, AMS-100 will detect high-energy gamma rays in the calorimeter system and by pair conversion in the thin solenoid, reconstructed with excellent angular resolution in the silicon tracker.

Measurement of the cosmic ray proton spectrum from 40 GeV to 100 TeV with the DAMPE satellite

The precise measurement of the spectrum of protons, the most abundant component of the cosmic radiation, is necessary to understand the source and acceleration of cosmic rays in the Milky Way. This work reports the measurement of the cosmic ray proton fluxes with kinetic energies from 40 GeV to 100 TeV, with 2 ¹/₂ years of data recorded by the DArk Matter Particle Explorer (DAMPE). This is the first time that an experiment directly measures the cosmic ray protons up to ~100 TeV with high statistics. The measured spectrum confirms the spectral hardening at ~300 GeV found by previous experiments and reveals a softening at ~13.6 TeV, with the spectral index changing from ~2.60 to ~2.85. Our result suggests the existence of a new spectral feature of cosmic rays at energies lower than the so-called knee and sheds new light on the origin of Galactic cosmic rays.

Spectrum of Electrons Accelerated in Supernova Remnants

Using a semianalytic model of nonlinear diffusive shock acceleration, we model the total spectrum of cosmic ray (CR) electrons accelerated by supernova remnants (SNRs). Because electrons experience synchrotron losses in the amplified magnetic fields characteristic of SNRs, they exhibit substantially steeper spectra than protons. In particular, we find that the difference between the electron and proton spectral index (power law slope) ranges from 0.1 to 0.4. Our findings must be reckoned with theories of Galactic CR transport, which often assume that electrons and protons are injected with the same slope, and may especially have implications for the observed "positron excess".

The future of the high energy cosmic ray detection: HERD

The High Energy cosmic-Radiation Detection (HERD) facility will be one of the space astronomy payloads on board the future Chinese space station. The ambitious aim of HERD is the direct detection of cosmic rays towards the “knee” region (~ 1 PeV), with a detector able to measure electrons, photons and nuclei with an excellent energy resolution (1% for electrons and photons at 200 GeV and 20% for nuclei at 100 GeV - PeV), an acceptance 10 times the one of present generation missions (~ 1 m2 sr), and long life-time (> 10 years). The primary objectives of HERD are the indirect search for dark matter particles and the precise measurement of energy distribution and composition of cosmic rays from 30 GeV up to a few PeV, determining the origin of the “knee” structure of the spectrum. Furthermore, HERD will monitor the high energy gamma-ray sky from 500 MeV, observing gamma-ray bursts, active galactic nuclei, galactic microquasars, etc. HERD will be composed of a homogeneous calorimeter, surrounded by a particle tracker and a plastic scintillator detector. Two possible trackers are under study: a 5-side tracker made of silicon strip detectors and a 4-side scintillating fiber tracker with a silicon strip top tracker. The total volume of HERD will be (2.3 × 2.3 × 2.6) m3 with a weight of about 4 t. The HERD design, perspectives, expected performances in terms of energy sensitivity and acceptance will be presented in this contribution.

Towards Understanding the Origin of Cosmic-Ray Electrons

Precision results on cosmic-ray electrons are presented in the energy range from 0.5 GeV to 1.4 TeV based on 28.1×10^{6} electrons collected by the Alpha Magnetic Spectrometer on the International Space Station. In the entire energy range the electron and positron spectra have distinctly different magnitudes and energy dependences. The electron flux exhibits a significant excess starting from 42.1_{-5.2}^{+5.4}  GeV compared to the lower energy trends, but the nature of this excess is different from the positron flux excess above 25.2±1.8  GeV. Contrary to the positron flux, which has an exponential energy cutoff of 810_{-180}^{+310}  GeV, at the 5σ level the electron flux does not have an energy cutoff below 1.9 TeV. In the entire energy range the electron flux is well described by the sum of two power law components. The different behavior of the cosmic-ray electrons and positrons measured by the Alpha Magnetic Spectrometer is clear evidence that most high energy electrons originate from different sources than high energy positrons.

Cosmic ray e± at high energy

There is a commonly expressed opinion in the literature, that cosmic-ray (CR) e+ come from a primary source, which could be dark matter or pulsars. In these proceedings we review some evidence to the contrary: namely, that e+ come from secondary production due to CR nuclei scattering on interstellar matter. We show that recent measurements of the total e± flux at E ≲ 3 TeV are in good agreement with the predicted flux of secondary e±, that would be obtained if radiative energy losses during CR propagation do not play an important role. If the agreement between data and secondary prediction is not accidental, then the requirement of negligible radiative energy losses implies a very short propagation time for high energy CRs: tesc ≲. 105 yr at rigidities R ≳ 3 TV. Such short propagation history may imply that a recent, near-by source dominates the CRs at these energies. We review independent evidence for a transition in CR propagation, based on the spectral hardening of primary and secondary nuclei around R ~ 100 GV. The transition rigidity of the nuclei matches the rigidity at which the e+ flux saturates its secondary upper bound.

Main scientific results of the DAMPE mission

DAMPE (DArk Matter Particle Explorer) is a satellite-born experiment, resulting from the collaboration of Chinese, Italian, and Swiss institutions. Since December 2015, DAMPE flights at the altitude of 500 km and collects data smoothly. The detector is made of four sub-detectors: top layers of plastic scintillators, a silicon-tungsten tracker, a BGO calorimeter (32 radiation lengths), and a bottom boron-doped scintillator to detect delayed neutrons. The main goal of the experiment is the search for indirect signals of Dark Matter in the electron and photon spectra with energies up to 10 TeV. Furthermore DAMPE studies cosmic charged and gamma radiation. The calorimeter depth and the large acceptance allow to measure cosmic ray fluxes in the range from 20 GeV up to hundreds of TeV. An overview of the latest results about light component (p+He) of charged cosmic rays, gamma astronomy and electron and positron spectrum will be presented.

The CALorimetric Electron Telescope (CALET) on the International Space Station: Results from the First Two Years of Operation

The CALorimetric Electron Telescope (CALET) space experiment, which has been developed by Japan in collaboration with Italy and the United States, is a high-energy astroparticle physics mission on the International Space Station (ISS). The primary goals of the CALET mission include investigation of possible nearby sources of high-energy electrons, detailed study of galactic cosmic-ray acceleration and propagation, and search for dark matter signatures. With a long-term observation onboard the ISS, the CALET experiment measures the flux of cosmic-ray electrons (including positrons) up to 20 TeV, gamma-rays to 10 TeV, and nuclei up to 1,000 TeV based on its charge separation capability from Z = 1 to 40. Since the start of science operation in mid-October, 2015, a continuous observation has been maintained without any major interruptions. The number of triggered events over 10 GeV is nearly 20 million per month. By using the data obtained during the first two-years, here we present a summary of the CALET observations: 1) Electron+positron energy spectrum, 2) Nuclei analysis, 3) Gamma-ray observation with a characterization of the on-orbit performance. The search results for the electromagnetic counterparts of LIGO/Virgo gravitational wave events are also discussed.

Undiscovered Pulsar in the Local Bubble as an Explanation of the Local High Energy Cosmic Ray All-Electron Spectrum

Cosmic ray electrons and positrons are tracers of particle propagation in the interstellar medium (ISM). A recent measurement performed using the High Energy Stereoscopic System extends the all-electron (electron+positron) spectrum up to 20 TeV, probing very local sources and transport due to the ∼10 kyr cooling time of these particles. An additional key local measurement was the recent estimation of the ISM diffusion coefficient around Geminga performed using the High-Altitude Water Cherenkov Observatory. The inferred diffusion coefficient is much lower than typically assumed values. It has been argued that if this diffusion coefficient is representative of the local ISM, pulsars would not be able to account for the all-electron spectrum measured at Earth. Here we show that a low diffusion coefficient in the local ISM is compatible with a pulsar wind nebula origin of the highest energy electrons, if a so-far-undiscovered pulsar with spin-down power ∼10^{33-34}  erg/s exists within 30-80 pc of Earth. The existence of such a pulsar is broadly consistent with the known population and may be detected in near future survey observations.

Extended Measurement of the Cosmic-Ray Electron and Positron Spectrum from 11 GeV to 4.8 TeV with the Calorimetric Electron Telescope on the International Space Station

Extended results on the cosmic-ray electron + positron spectrum from 11 GeV to 4.8 TeV are presented based on observations with the Calorimetric Electron Telescope (CALET) on the International Space Station utilizing the data up to November 2017. The analysis uses the full detector acceptance at high energies, approximately doubling the statistics compared to the previous result. CALET is an all-calorimetric instrument with a total thickness of 30 X_{0} at normal incidence and fine imaging capability, designed to achieve large proton rejection and excellent energy resolution well into the TeV energy region. The observed energy spectrum in the region below 1 TeV shows good agreement with Alpha Magnetic Spectrometer (AMS-02) data. In the energy region below ∼300  GeV, CALET's spectral index is found to be consistent with the AMS-02, Fermi Large Area Telescope (Fermi-LAT), and Dark Matter Particle Explorer (DAMPE), while from 300 to 600 GeV the spectrum is significantly softer than the spectra from the latter two experiments. The absolute flux of CALET is consistent with other experiments at around a few tens of GeV. However, it is lower than those of DAMPE and Fermi-LAT with the difference increasing up to several hundred GeV. The observed energy spectrum above ∼1  TeV suggests a flux suppression consistent within the errors with the results of DAMPE, while CALET does not observe any significant evidence for a narrow spectral feature in the energy region around 1.4 TeV. Our measured all-electron flux, including statistical errors and a detailed breakdown of the systematic errors, is tabulated in the Supplemental Material in order to allow more refined spectral analyses based on our data.