Abstracts of Interest
Selected by:
Violet Harvey
Abstract: 1907.01676
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Title:Astro2020 APC White Paper: The Early Career Perspective on the Coming Decade, Astrophysics Career Paths, and the Decadal Survey Process
(Submitted on 2 Jul 2019 (v1), last revised 12 Jul 2019 (this version, v2))
Abstract: In response to the need for the Astro2020 Decadal Survey to explicitly engage early career astronomers, the National Academies of Sciences, Engineering, and Medicine hosted the Early Career Astronomer and Astrophysicist Focus Session (ECFS) on October 8-9, 2018 under the auspices of Committee of Astronomy and Astrophysics. The meeting was attended by fifty six pre-tenure faculty, research scientists, postdoctoral scholars, and senior graduate students, as well as eight former decadal survey committee members, who acted as facilitators. The event was designed to educate early career astronomers about the decadal survey process, to solicit their feedback on the role that early career astronomers should play in Astro2020, and to provide a forum for the discussion of a wide range of topics regarding the astrophysics career path.
This white paper presents highlights and themes that emerged during two days of discussion. In Section 1, we discuss concerns that emerged regarding the coming decade and the astrophysics career path, as well as specific recommendations from participants regarding how to address them. We have organized these concerns and suggestions into five broad themes. These include (sequentially): (1) adequately training astronomers in the statistical and computational techniques necessary in an era of "big data", (2) responses to the growth of collaborations and telescopes, (3) concerns about the adequacy of graduate and postdoctoral training, (4) the need for improvements in equity and inclusion in astronomy, and (5) smoothing and facilitating transitions between early career stages. Section 2 is focused on ideas regarding the decadal survey itself, including: incorporating early career voices, ensuring diverse input from a variety of stakeholders, and successfully and broadly disseminating the results of the survey.
Abstract: 1907.04388
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Title:The Origin of Elements Across Cosmic Time: Astro2020 Science White Paper
(Submitted on 9 Jul 2019)
Abstract: The problem of the origin of the elements is a fundamental one in astronomy and one that has many open questions. Prominent examples include (1) the nature of Type Ia supernovae and the timescale of their contributions; (2) the observational identification of elements such as titanium and potassium with the $\alpha$-elements in conflict with core-collapse supernova predictions; (3) the number and relative importance of r-process sites; (4) the origin of carbon and nitrogen and the influence of mixing and mass loss in winds; and (5) the origin of the intermediate elements, such as Cu, Ge, As, and Se, that bridge the region between charged-particle and neutron-capture reactions. The next decade will bring to maturity many of the new tools that have recently made their mark, such as large-scale chemical cartography of the Milky Way and its satellites, the addition of astrometric and asteroseismic information, the detection and characterization of gravitational wave events, 3-D simulations of convection and model atmospheres, and improved laboratory measurements for transition probabilities and nuclear masses. All of these areas are key for continued improvement, and such improvement will benefit many areas of astrophysics.
Abstract: 1907.04867
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Title:A better consensus: Changes to the Decadal process itself
(Submitted on 10 Jul 2019)
Abstract: The importance of the Decadal Survey in astrophysics is great; it deserves attention and revision. We make recommendations to increase the Survey's transparency and political legitimacy. The Astro2020 charge asks the Survey to "generate consensus recommendations". It is healthy to re-evaluate how to achieve consensus as the community and context evolve. Our recommendations are the following: (R1) Appoint the Decadal panel chairs and panel members through a transparent process, or even a democratic process. (R2) Don't make panel members sign any kinds of non-disclosure agreements, or strictly limit these. (R3) Educate the community about the Decadal's decision-making and consensus-building. (R4) Provide written documentation about how white papers will be read and used. (R5) Give the community an opportunity to comment on and vote to approve the final reports. (R6) Ask the AAAC to help the agencies make these changes.
Abstract: 1907.04880
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Title:Increasing Gender Diversity and Inclusion in Scientific Committees and Related Activities at STScI
(Submitted on 10 Jul 2019)
Abstract: We present a new initiative by the Women in Astronomy Forum at Space Telescope Science Institute (STScI) to increase gender diversity and inclusion in STScI's scientific committees and the activities they generate. This initiative offers new and uniform guidelines on binary gender representation goals for each committee and recommendations on how to achieve them in a homogeneous way, as well as metrics and tools to track progress towards defined goals. While the new guidelines presented in the paper focus on binary gender representation, they can be adapted and implemented to support all minority groups. By creating diverse committees and making them aware of, and trained on implicit bias, we expect to create a diverse outcome in the activities they generate, which, in turn, will advance science further and faster.
Abstract: 1907.04893
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Title:The Nonbinary Fraction: Looking Towards the Future of Gender Equity in Astronomy
(Submitted on 10 Jul 2019)
Abstract: Gender equity is one of the biggest issues facing the field of astrophysics, and there is broad interest in addressing gender disparities within astronomy. Many studies of these topics have been performed by professional astronomers who are relatively unfamiliar with research in fields such as gender studies and sociology. As a result, they adopt a normative view of gender as a binary choice of 'male' or 'female', leaving astronomers whose genders do not fit within that model out of such research entirely. Reductive frameworks of gender and an overemphasis on quantification as an indicator of gendered phenomena are harmful to people of marginalized genders, especially those who live at the intersections of multiple axes of marginalization such as race, disability, and socioeconomic status. In order for the astronomy community to best serve its marginalized members as we move into the next decade, a new paradigm must be developed. This paper aims to address the future of gender equity in astronomy by recommending better survey practices and institutional policies based on a more complex approach to gender.
Abstract: 1907.04943
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Title:Astro2020 APC White Paper: Accessible Astronomy: Policies, Practices, and Strategies to Increase Participation of Astronomers with Disabilities
(Submitted on 10 Jul 2019)
Abstract: (Abridged) In this white paper, we outline the major barriers to access within the educational and professional practice of astronomy. We present current best practices for inclusivity and accessibility, including classroom practices, institutional culture, support for infrastructure creation, hiring processes, and outreach initiatives. We present specific ways--beyond simple compliance with the ADA--that funding agencies, astronomers, and institutions can work together to make astronomy as a field more accessible, inclusive, and equitable. In particular, funding agencies should include the accessibility of institutions during proposal evaluation, hold institutions accountable for inaccessibility, and support efforts to gather data on the status and progress of astronomers and astronomy students with disabilities.
Abstract: 1907.05261
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Title:(Un)conscious Bias in the Astronomical Profession: Universal Recommendations to improve Fairness, Inclusiveness, and Representation
(Submitted on 10 Jul 2019)
Abstract: (Un)conscious bias affects every aspect of the astronomical profession, from scientific activities (e.g., invitations to join collaborations, proposal selections, grant allocations, publication review processes, and invitations to attend and speak at conferences) to activities more strictly related to career advancement (e.g., reference letters, fellowships, hiring, promotion, and tenure). For many, (un)conscious bias is still the main hurdle to achieving excellence, as the most diverse talents encounter bigger challenges and difficulties to reach the same milestones than their more privileged colleagues. Over the past few years, the Space Telescope Science Institute (STScI) has constructed tools to raise awareness of (un)conscious bias and has designed guidelines and goals to increase diversity representation and outcome in its scientific activities, including career-related matters and STScI sponsored fellowships, conferences, workshops, and colloquia. STScI has also addressed (un)conscious bias in the peer-review process by anonymizing submission and evaluation of Hubble Space Telescope (and soon to be James Webb Space Telescope) observing proposals. In this white paper we present a plan to standardize these methods with the expectation that these universal recommendations will truly increase diversity, inclusiveness and fairness in Astronomy if applied consistently throughout all the scientific activities of the Astronomical community.
Abstract: 1907.06485
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Title:CMB constraints on ultra-light primordial black holes with extended mass distributions
(Submitted on 15 Jul 2019)
Abstract: We examine the effects ultra-light primordial black holes (PBHs) have on the anisotropies of the cosmic microwave background (CMB). PBHs in the mass range of $10^{15}$ to $10^{17}$ g emit Hawking radiation in the early Universe, modifying the standard recombination history. This leads to a damping of small-scale temperature and polarisation anisotropies and enhances large-scale polarisation fluctuations. As some models of inflation predict PBHs with a range of masses, we investigate the impacts of extended mass distributions on PBH abundance constraints. We model PBH energy injection using a ground-up approach incorporating species-dependent deposition efficiencies. By allowing the $\Lambda$CDM parameters to vary simultaneously with the PBH fraction and mass, we show that exclusion bounds on the PBH fraction of DM $f_\text{PBH}$ are relaxed by up to an order of magnitude, compared to the case of fixed $\Lambda$CDM parameters. We also give 95% exclusion regions for $f_\text{PBH}$ for a variety of mass distributions. In particular, for a uniform mass distribution between $10^{15}$ and $10^{17}$ g, we find $f_\text{PBH} < 1.6 \times 10^{-5}$ when allowing $\Lambda$CDM parameters to vary.
Abstract: 1906.12240
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Title:Cosmic ray acceleration by shocks: spectral steepening due to turbulent magnetic field amplification
(Submitted on 28 Jun 2019)
Abstract: We show that the energy required to turbulently amplify magnetic field during cosmic ray (CR) acceleration by shocks extracts energy from the CR and steepens the CR energy spectrum.
Abstract: 1906.12257
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Title:The origin of spin in binary black holes: Predicting the distributions of the main observables of Advanced LIGO
(Submitted on 28 Jun 2019)
Abstract: We study the formation of coalescing binary black holes via the evolution of isolated field binaries that go through the common envelope phase in order to obtain the combined distributions of the main observables of Advanced LIGO. We use a hybrid technique that combines the parametric binary population synthesis code COMPAS with detailed binary evolution simulations performed with the MESA code. We then convolve our binary evolution calculations with the redshift- and metallicity-dependent star-formation rate and the selection effects of gravitational-wave detectors to obtain predictions of observable properties. By assuming efficient angular momentum transport, we are able to present a model capable of predicting simultaneously the three main gravitational-wave observables: the effective inspiral spin parameter $\chi_{eff}$, the chirp mass $M_{chirp}$ and the cosmological redshift of merger $z_{merger}$. We find an excellent agreement between our model and the ten events from the first two advanced detector observing runs. We make predictions for the third observing run O3 and for Advanced LIGO design sensitivity. We expect 59% of events with $\chi_{eff} < 0.1$, while the remaining 41% of events with $\chi_{eff} \ge 0.1$ are split into 9% with $M_{chirp} < 15$ M$_\odot$ and 32% with $M_{chirp} \ge 15$ M$_\odot$. In conclusion, the favorable comparison of the existing LIGO/Virgo observations with our model predictions gives support to the idea that the majority, if not all of the observed mergers, originate from the evolution of isolated binaries. The first-born black hole has negligible spin because it lost its envelope after it expanded to become a giant star, while the spin of the second-born black hole is determined by the tidal spin up of its naked helium star progenitor by the first-born black hole companion after the binary finished the common-envelope phase.
Abstract: 1906.12258
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Title:Astrophysical neutrinos: theory
(Submitted on 28 Jun 2019)
Abstract: In the era of multi-messenger astronomy, neutrinos are among the most important astronomical messengers, due to their interaction properties. In these lessons I briefly review the main issues concerning the theory on astrophysical neutrinos.
Abstract: 1806.01839
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Title:Observing small-scale $γ$-ray anisotropies with the Cherenkov Telescope Array
(Submitted on 5 Jun 2018 (v1), last revised 22 Aug 2018 (this version, v2))
Abstract: Disentangling the composition of the diffuse gamma-ray background (DGRB) is a major challenge in gamma-ray astronomy. It is presumed that at the highest energies, the DGRB is dominated by relatively few, still unresolved point sources. This conjecture has recently been supported by the measurement of small-scale anisotropies in the DGRB by the Fermi Large Area Telescope (LAT) up to energies of 500 GeV. We show how such anisotropies can be searched for with the forthcoming Earth-bound Cherenkov Telescope Array (CTA) up to the TeV range. We investigate different observation modes to analyse CTA data for small-scale anisotropies and propose the projected extragalactic large-area sky survey as the most promising data set. Relying on an up-to-date model of the performance of the southern CTA, we find that CTA will be able to probe anisotropies in the DGRB from unresolved point sources at a relative amplitude of $C_{\rm P}^I/I^2_{\rm DGRB}\gtrsim 4\times 10^{-3}\,{\rm sr}$ at energies above 30 GeV and angular scales $\lesssim 1.5^{\circ}$. Such DGRB anisotropies have not yet been ruled out by the Fermi-LAT. The proposed analysis would primarily clarify the contribution from blazars and misaligned active galactic nuclei to the very-high-energy regime of the DGRB, as well as provide insight into dark matter annihilation in Galactic and extragalactic density structures. Finally, it constitutes a measurement with complementary systematic uncertainties compared to the Fermi-LAT.
Abstract: 1907.00640
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Title:High-energy atmospheric muon flux calculations in comparison with recent measurements
(Submitted on 1 Jul 2019)
Abstract: Recently the atmospheric muon spectra at high energies were reconstructed for two ranges of zenith angles, basing on the events collected with the IceCube detector. These measurements reach high energies at which the contribution to atmospheric muon fluxes from decays of short-lived hadrons is expected. Latest IceCube measurements of the high-energy atmospheric muon spectrum indicate the presence of prompt muon component at energies above 500 TeV. In this work, the atmospheric conventional muon flux in the energy range 10 GeV - 10 PeV is calculated using a set of hadronic models in combination with known parameterizations of the cosmic ray spectrum by Zatsepin $\&$ Sokolskaya and by Hillas $\&$ Gaisser. The calculation of the prompt muons with use of the quark-gluon string model (QGSM) reproduces the muon data of the IceCube experiment. Nevertheless, an additional contribution to the prompt muon component is required to describe the IceCube muon spectra in case if a charm production model predicts the appreciably lower prompt lepton flux as compared with QGSM. This addition, apparently originating from rare decay modes of the short-lived unflavored mesons $\eta, \eta^\prime, \rho, \omega, \phi$, might ensure the competing contribution to the high-energy atmospheric muon flux.
Abstract: 1907.01090
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Title:A Genetic Algorithm for Astroparticle Physics Studies
(Submitted on 1 Jul 2019)
Abstract: Precision measurements of charged cosmic rays have recently been carried out by space-born (e.g. AMS-02), or ground experiments (e.g. HESS). These measured data are important for the studies of astro-physical phenomena, including supernova remnants, cosmic ray propagation, solar physics and dark matter. Those scenarios usually contain a number of free parameters that need to be adjusted by observed data. Some techniques, such as Markov Chain Monte Carlo and MultiNest, are developed in order to solve the above problem. However, it is usually required a computing farm to apply those tools. In this paper, a genetic algorithm for finding the optimum parameters for cosmic ray injection and propagation is presented. We find that this algorithm gives us the same best fit results as the Markov Chain Monte Carlo but consuming less computing power by nearly 2 orders of magnitudes.
Abstract: 1907.01443
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Title:Search for gravitational-wave signals associated with gamma-ray bursts during the second observing run of Advanced LIGO and Advanced Virgo
(Submitted on 2 Jul 2019)
Abstract: We present the results of targeted searches for gravitational wave transients associated with gamma-ray bursts during the second observing run of Advanced LIGO and Advanced Virgo, which took place from November 2016 to August 2017. We have analyzed 98 gamma-ray bursts using an unmodeled search method that searches for generic transient gravitational waves and 42 with a modeled search method that targets compact-binary mergers as progenitors of short gamma-ray bursts. Both methods clearly detect the previously reported binary merger signal GW170817, with p-values of $<9.38 \times 10^{-6}$ (modeled) and $3.1 \times 10^{-4}$ (unmodeled). We find no evidence of associated gravitational-wave signals for any of the other gamma-ray bursts analyzed, and therefore report lower bounds on the distance to each of these, assuming various source types and signal morphologies. Using our final modeled search results, short gamma-ray burst observations, and assuming binary neutron star progenitors, we place bounds on the rate of short gamma-ray bursts as a function of redshift for $z \leq 1$ and estimate 0.07-1.80 detections for the 2019-20 LIGO-Virgo observing run and 0.15-3.90 joint detections per year when current gravitational-wave detectors are operating at design sensitivities.
Abstract: 1907.01542
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Title:A fast radio burst localised to a massive galaxy
(Submitted on 2 Jul 2019)
Abstract: Intense, millisecond-duration bursts of radio waves have been detected from beyond the Milky Way [1]. Their extragalactic origins are evidenced by their large dispersion measures, which are greater than expected for propagation through the Milky Way interstellar medium alone, and imply contributions from the intergalactic medium and potentially host galaxies [2]. Although several theories exist for the sources of these fast radio bursts, their intensities, durations and temporal structures suggest coherent emission from highly magnetised plasma [3,4]. Two sources have been observed to repeat [5,6], and one repeater (FRB 121102) has been localised to the largest star-forming region of a dwarf galaxy at a cosmological redshift of 0.19 [7, 8]. However, the host galaxies and distances of the so far non-repeating fast radio bursts are yet to be identified. Unlike repeating sources, these events must be observed with an interferometer with sufficient spatial resolution for arcsecond localisation at the time of discovery. Here we report the localisation of a fast radio burst (FRB 190523) to a few-arcsecond region containing a single massive galaxy at a redshift of 0.66. This galaxy is in stark contrast to the host of FRB 121102, being a thousand times more massive, with a greater than hundred times lower specific star-formation rate. The properties of this galaxy highlight the possibility of a channel for FRB production associated with older stellar populations.
Abstract: 1907.01981
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Title:The Karl G. Jansky Very Large Array Sky Survey (VLASS). Science case, survey design and initial results
(Submitted on 3 Jul 2019)
Abstract: The Very Large Array Sky Survey (VLASS) is a synoptic, all-sky radio sky survey with a unique combination of high angular resolution ($\approx$2.5"), sensitivity (a 1$\sigma$ goal of 70 $\mu$Jy/beam in the coadded data), full linear Stokes polarimetry, time domain coverage, and wide bandwidth (2-4 GHz). The first observations began in September 2017, and observing for the survey will finish in 2024. VLASS will use approximately 5500 hours of time on the Karl G. Jansky Very Large Array (VLA) to cover the whole sky visible to the VLA (Declination $>-40^{\circ}$), a total of 33,885 deg$^2$. The data will be taken in three epochs to allow the discovery of variable and transient radio sources. The survey is designed to engage radio astronomy experts, multi-wavelength astronomers, and citizen scientists alike. By utilizing an "on the fly" interferometry mode, the observing overheads are much reduced compared to a conventional pointed survey. In this paper, we present the science case and observational strategy for the survey, and also results from early survey observations.
Abstract: 1907.02107
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Title:Solar cycle prediction
(Submitted on 2 Jul 2019)
Abstract: A review of solar cycle prediction methods and their performance is given, including early forecasts for cycle 25. The review focuses on those aspects of the solar cycle prediction problem that have a bearing on dynamo theory. The scope of the review is further restricted to the issue of predicting the amplitude (and optionally the epoch) of an upcoming solar maximum no later than right after the start of the given cycle.
In their overall performance during the course of the last few solar cycles, precursor methods have clearly been superior to extrapolation methods. One method that has yielded predictions consistently in the right range during the past few solar cycles is the polar field precursor. Nevertheless, some extrapolation methods may still be worth further study. Model based forecasts are quickly coming into their own, and, despite not having a long proven record, their predictions are received with increasing confidence by the community.
Abstract: 1907.02573
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Title:Global characteristics of the medium produced in ultra-high energy cosmic ray collisions
(Submitted on 4 Jul 2019)
Abstract: Estimations of some geometrical and bulk parameters are presented for the matter produced in various type collisions with ultra-high energy cosmic ray (UHECR) particles. Results for multiplicity density at midrapidity, decoupling time and energy density are discussed for small and larger collision systems. Based on the analytic functions suggested previously elsewhere, estimations for a wide set of space-time quantities are obtained for emission region created in various particle collisions at energies of UHECR. The space particle densities at freeze-out are derived also and allow the possibility of novel features for secondary particle production like Bose-Einstein condensation at least for nuclear interactions with UHECR particles. The estimations obtained for global and geometrical parameters indicate on the creation of deconfined quark-gluon matter with large enough volume and life time even in light nuclear collisions at UHECR energies. These quantitative results can be important for both the future collider experiments at center-of-mass energy frontier and the improvement of the phenomenological models for development of the cosmic ray cascades in ultra-high energy domain.
Abstract: 1907.02561
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Title:Neutron rich matter in heaven and on Earth
(Submitted on 4 Jul 2019)
Abstract: Despite a length-scale difference of 18 orders of magnitude, the internal structure of neutron stars and the spatial distribution of neutrons in atomic nuclei are profoundly connected.
Abstract: 1907.02853
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Title:V-shaped Cherenkov images of magnetically-separated gamma-rays
(Submitted on 5 Jul 2019)
Abstract: Cherenkov Telescope Array (CTA) is an upcoming instrument that will start a new generation of atmospheric Cherenkov telescopes. CTA is expected not only to provide an unprecedented sensitivity in the tens of GeV to hundreds of TeV range, but also to considerably improve the systematic uncertainties of the measurements. We study the images registered by Cherenkov telescopes from low energy gamma rays with its first interaction in the upper parts of the atmosphere. The images show a characteristic separation due to the deflection of the first e- e+ pair in the Geomagnetic Field. We evaluate the performance of the standard stereoscopic analysis for such events. We derive also a novel method for energy estimation of V-shaped events based purely on geometrical properties of the image. We investigate the potential of combining the classical energy estimation and the novel method for independent validation of the systematic shifts in the energy scale of Cherenkov telescopes and discuss the limitations of such analysis.
Abstract: 1907.04375
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Title:Using Muon Rings for the Calibration of the Cherenkov Telescope Array: A Systematic Review of the Method and its Potential Accuracy
(Submitted on 9 Jul 2019)
Abstract: The analysis of ring images produced by muons in an Imaging Atmospheric Cherenkov Telescope (IACT) provides a powerful and precise method to calibrate the IACT optical throughput and monitor its optical point-spread function (PSF). First proposed by the Whipple collaboration in the early 90's, this method has been refined by the so-called second generation of IACT experiments: H.E.S.S., MAGIC and VERITAS. We review here the progress made with these instruments and investigate the applicability of the method as the primary throughput calibration method for the different telescope types forming the future Cherenkov Telescope Array (CTA). We find several additional systematic effects not yet taken into account by previous authors and propose several new analytical methods to include these in the analysis. Slight modifications in hardware and analysis need to be made to ensure that such a calibration works as accurately as required for the CTA. We derive analytic estimates for the expected muon data rates for optical throughput calibration, camera pixel flat-fielding and monitoring of the optical PSF. The achievable statistical and systematic uncertainties of the method are also assessed.
Abstract: 1907.03102
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Title:Galactic Gamma Ray Background from Interactions of Cosmic Rays
(Submitted on 6 Jul 2019)
Abstract: Various studies firmly establish the fact that gamma-ray observations can act as a unique probe to detect the possible cosmic ray (CR) sources, study the CR density distribution and explore the average properties of interstellar medium (ISM) such as the gas density profile of ISM. We use the DRAGON code to study different propagation models by incorporating realistic source distribution, Galactic magnetic field (GMF) and gas density profile, and finally obtain the proton distribution (both spatial and energy) in the Galaxy by fitting the locally observed CR spectra. This distribution of protons is used to calculate the diffuse gamma-ray flux produced by proton-proton interactions in the Galactic halo. Our calculated diffuse gamma-ray flux is compared with the isotropic gamma-ray background (IGRB) at sub-TeV energy regime measured by Fermi-LAT. It is found to be much less than IGRB, which suggests IGRB is mostly of extragalactic origin.
Abstract: 1907.03127
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Full Text: [ PostScript, PDF]
Title:Spectroscopy with the Engineering Development Array: cold H$^{+}$ at 63 MHz towards the Galactic Centre
(Submitted on 6 Jul 2019)
Abstract: The Engineering Development Array (EDA) is a single test station for Square Kilometre Array (SKA) precursor technology. We have used the EDA to detect low-frequency radio recombination lines (RRLs) from the Galactic Centre region. Low-frequency RRLs are an area of interest for future low-frequency SKA work as these lines provide important information on the physical properties of the cold neutral medium. In this project we investigate the EDA, its bandpass and the radio frequency interference environment for low-frequency spectroscopy. We present line spectra from 30 to 325 MHz for the Galactic Centre region. The decrease in sensitivity for the EDA at the low end of the receiver prevents carbon and hydrogen RRLs to be detected below 40 and 60 MHz respectively. RFI strongly affects frequencies in the range 276-292, 234-270, 131-138, 95-102 and below 33 MHz. Cn$\alpha$ RRLs were detected in absorption for quantum levels n = 378 to 550 (39-121 MHz) and in emission for n = 272 to 306 (228-325 MHz). Cn$\beta$ lines were detected in absorption for n = 387 to 696 (39-225 MHz). Hn$\alpha$ RRLs were detected in emission for n = 272 to 480 (59-325 MHz). Hn$\beta$ lines were detected for n = 387 to 453 (141-225 MHz). The stacked Hn$\alpha$ detection at 63 MHz is the lowest frequency detection made for hydrogen RRLs and shows that a cold (partially) ionized medium exists along the line of sight to the Galactic Centre region. The size and velocity of this cold H$^{+}$ gas indicates that it is likely associated with the nearby Riegel-Crutcher cloud.
Abstract: 1907.03696
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Full Text: [ PostScript, PDF]
Title:Features in cosmic-ray lepton data unveil the properties of nearby cosmic accelerators
(Submitted on 8 Jul 2019)
Abstract: We present a comprehensive discussion about the origin of the features in the leptonic component of the cosmic-ray spectrum. Working in the framework of a up-to-date CR transport scenario tuned on the most recent AMS-02 and Voyager data, we show that the prominent features recently found in the positron and in the all-electron spectra by several experiments are explained in a scenario in which pulsar wind nebulae (PWNe) are the dominant sources of the positron flux, and nearby supernova remnants shape the high-energy peak of the electron spectrum. In particular we argue that the drop-off in positron spectrum found by AMS-02 at $\sim 300$ GeV can be explained --- under different assumptions --- in terms of a prominent PWN that provides the bulk of the observed positrons in the $\sim 100$ GeV domain, on top of the contribution from a large number of older objects. Finally, we turn our attention to the spectral softening at $\sim 1$ TeV in the all-lepton spectrum, recently reported by several experiments, showing that it requires the presence of a nearby supernova remnant at its final stage.
Abstract: 1907.04171
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Full Text: [ PostScript, PDF]
Title:A Surface Radio Array for the Enhancement of IceTop and its Science Prospects
(Submitted on 9 Jul 2019)
Abstract: Radio detection of air showers in the current era has progressed immensely to effectively extract the properties of these air showers. Primary cosmic rays with energies of hundreds of PeV have been successfully measured with the method of radio detection. There are also attempts to observe high-energy neutrinos with this technique. Current radio experiments measuring cosmic-ray air showers mostly operate in the frequency range of 30-80 MHz. An optimization of the frequency band of operation can be done for maximizing the signal-to-noise ratio that can be achieved by an array of radio antennas at the South Pole, operated along with IceTop. Such an array can improve the reconstruction of air showers performed with IceTop. The prospect of using such an optimized radio array for measuring gamma rays of PeV energies from the Galactic Center is discussed.
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