Abstracts of Interest
Selected by:
Abstract: 1908.06073
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Title:Studying Cosmic-ray Interactions in Giant Molecular Clouds with the HAWC Gamma-ray Observatory
(Submitted on 16 Aug 2019)
Abstract: The cosmic-ray flux in the Galaxy can be characterized by combining the knowledge of the distribution of gas in the Galaxy and the observation of gamma rays. We analyze the data from the HAWC Observatory to look for gamma rays in three galactic giant molecular clouds, that are outside the galactic plane ($|b|>5^{\circ}$). We can then test the paradigm that the measured local cosmic-ray flux is the same as the "sea" of Galactic cosmic rays. Due to its large field of view, and high duty cycle, HAWC is suitable to search for gamma rays from large structures in the TeV gamma-ray regime. We present here preliminary results from measurements of the Aquila Rift, Hercules and Taurus molecular clouds.
Abstract: 1908.06048
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Full Text: [ PostScript, PDF]
Title:Statistical analysis on X-ray flares from the nucleus and HST-1 knot in the M87 jet
(Submitted on 16 Aug 2019)
Abstract: The statistical properties of X-ray flares from two separate locations (nucleus and HST-1) in the M87 jet are investigated to reveal the physical origin of the flares. We analyse the archival \textit{Chandra} data for M87, and identify 14 flares in the nucleus and 9 flares in HST-1. The peak intensity ($I_{\rm{P}}$) and the flaring duration time ($T_{\rm{fl}}$) for each flare are obtained. It is found that the distributions of both $I_{\rm{P}}$ and $T_{\rm{fl}}$ for the nucleus obey a power-law form with a similar index. A similar result is also obtained for HST-1, and no significant inconsistency between the nucleus and HST-1 is found for the indices. Similar to solar X-ray flares, the power-law distributions of the flare event parameters can be well explained by a self-organized criticality (SOC) system, which are triggered by magnetic reconnection. Our results suggest that the flares from nucleus and HST-1 are possibly triggered by magnetic reconnection process. The consistent indices for the distributions of $I_{\rm{P}}$ and $T_{\rm{fl}}$ in the CORE and HST-1 indicate that the dimensions of the energy dissipation of the magnetic reconnection is identical in the two regions. A strong correlation between the flares in the two regions also suggests a similar physical origin for the flares.
Abstract: 1908.05993
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Title:Ten years of All-sky Neutrino Point-Source Searches
(Submitted on 16 Aug 2019)
Abstract: These proceedings present the results of point-like neutrino source searches using ~10 yrs of IceCube data from Apr.~6, 2008 to Jul.~10, 2018. We evaluate the significance of an astrophysical signal from a point-like source looking for an excess of clustered neutrino events with energies above ~1 TeV among the background of atmospheric muons and neutrinos. We perform a full sky scan, a search based on a selected source catalog, and a catalog population study. The most significant location in the Northern hemisphere from the full-sky scan is compatible with the Seyfert galaxy NGC 1068. This object had also been identified in the source catalog search which finds a 2.9 $\sigma$ excess after accounting for statistical trials. The combination of this result along with excesses observed at the coordinates of three other sources, including TXS 0506+056, suggests that collectively correlations with sources in the Northern catalog are inconsistent with background at the level of 3.3 $\sigma$. These results motivate further interest in such point-like sources which should become observable or ruled out after accumulation of more data or with future detectors.
Abstract: 1908.05958
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Full Text: [ PostScript, PDF]
Title:The determination capability of potential neutrinos from gravitational wave sources and contributions of extra detector at the future reactor neutrino experiment
(Submitted on 16 Aug 2019)
Abstract: After several gravitational wave transients were discovered since 2015, studying neutrino signals coincident with the gravitational wave events now becomes an important mission for the existing neutrino experiments. Unfortunately, no candidate neutrinos have been found yet. This article introduces a method to find the neutrino excess to search for the potential neutrinos from gravitational wave sources at the future reactor neutrino experiment (such as JUNO and RENO-50). According to our calculations and simulations, the non-detection of $\bar\nu_e$ associated with gravitational waves at the nominal JUNO experiment gives rise to the $\bar\nu_e$ signal sensitivity at 90$\%$ confidence level (C.L.), $\mu_{90}$ = 2.44. This corresponds to the range of neutrino fluence on the Earth around 6 $\times$ 10$^{10}$ cm$^{-2}$ to 4 $\times$ 10$^{10}$ cm$^{-2}$ with neutrino energy range from 1.8 MeV to 120 MeV at monochromatic energy spectrum assumption. Based on certain popular models which describe the gravitational wave sources, we calculate the corresponding fluence ($F_{UL}^{90}$), which is around 1 - 3 $\times$ 10$^{8}$ cm$^{-2}$ for both monochromatic energy spectrum assumption and Fermi-Dirac energy spectrum assumption. Then we convert $F_{UL}^{90}$ into the detectable distance ($D_\text{UL}^{90}$), about 1 - 3 Mpc for two assumptions, with the predicted luminosities in these known models. To further improve the sensitivity, we discuss the potential benefits from an extra detector, with different target masses and baselines. Particularly, there will be around 38\% sensitivity improvement and around 28$\%$ detectable distance increasing if the extra detector is designed to be identical to the JUNO detector. On the other hand, instead of building an extra detector, if we combine the JUNO experiment with the RENO-50 experiment, the sensitivity will also be significantly improved.
Abstract: 1908.05948
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Title:Modeling of rigidity dependent CORSIKA simulations for GRAPES-3
(Submitted on 16 Aug 2019)
Abstract: The GRAPES-3 muon telescope located in Ooty, India records 4x10^9 muons daily. These muons are produced by interaction of primary cosmic rays (PCRs) in the atmosphere. The high statistics of muons enables GRAPES-3 to make precise measurement of various sun-induced phenomenon including coronal mass ejections (CME), Forbush decreases, geomagnetic storms (GMS) and atmosphere acceleration during the overhead passage of thunderclouds. However, the understanding and interpretation of observed data requires Monte Carlo (MC) simulation of PCRs and subsequent development of showers in the atmosphere. CORSIKA is a standard MC simulation code widely used for this purpose. However, these simulations are time consuming as large number of interactions and decays need to be taken into account at various stages of shower development from top of the atmosphere down to ground level. Therefore, computing resources become an important consideration particularly when billion of PCRs need to be simulated to match the high statistical accuracy of the data. During the GRAPES-3 simulations, it was observed that over 60% of simulated events don't really reach the Earth's atmosphere. The geomagnetic field (GMF) creates a threshold to PCRs called cutoff rigidity Rc, a direction dependent parameter below which PCRs can't reach the Earth's atmosphere. However, in CORSIKA there is no provision to set a direction dependent threshold. We have devised an efficient method that has taken into account of this Rc dependence. A reduction by a factor ~3 in simulation time and ~2 in output data size was achieved for GRAPES-3 simulations. This has been incorporated in CORSIKA version v75600 onwards. Detailed implementation of this along the potential benefits are discussed in this work.
Abstract: 1908.05779
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Full Text: [ PostScript, PDF]
Title:Probing Massive Black Hole Binary Populations with LISA
(Submitted on 15 Aug 2019)
Abstract: ESA and NASA are moving forward with plans to launch LISA around 2034. With data from the Illustris cosmological simulation, we provide analysis of LISA detection rates accompanied by characterization of the merging massive black hole population. Massive black holes of total mass $\sim10^5-10^{10} M_\odot$ are the focus of this study. We evolve Illustris massive black hole mergers, which form at separations on the order of the simulation resolution ($\sim$kpc scales), through coalescence with two different treatments for the binary massive black hole evolutionary process. The coalescence times of the population, as well as physical properties of the black holes, form a statistical basis for each evolutionary treatment. From these bases, we Monte Carlo synthesize many realizations of the merging massive black hole population to build mock LISA detection catalogs. We analyze how our massive black hole binary evolutionary models affect detection rates and the associated parameter distributions measured by LISA. Additionally, we evaluate the impact of the low-frequency shape of the LISA sensitivity curve on the measurements of our massive black hole binary population. With our models and two LISA detector configurations, we find MBH binary detection rates with LISA of $\sim0.5-1$ yr$^{-1}$ for massive black holes with masses greater than $10^5M_\odot$. We suggest reasons why we predict lower detection rates compared to much of the literature.
Abstract: 1908.05526
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Full Text: [ PostScript, PDF]
Title:Searching for Time-Dependent Neutrino Emission from Blazars with IceCube
(Submitted on 15 Aug 2019)
Abstract: In 2017, IceCube detected a high energy neutrino in coincidence with the blazar TXS 0506+056. In a follow up analysis of archival data, evidence for previous neutrino emission from the blazar during 2014-15 was found. In this analysis, we investigate whether other blazars might have had episodes of neutrino emission. We use a 5-year sample of muon-neutrino data and the same timedependent algorithm that was used for the archival analysis of TXS 0506+056, applying it to all of the objects in the northern sky listed in the Fermi 3LAC catalog. We fit for the most significant neutrino flare from each direction, without assuming any correlation with electromagnetic light curves. To search for an excess of significant flares which could indicate a small population of neutrino emitters, we apply a binomial test. This binomial test does not find a significant excess of flares relative to the results expected for background coincidences from atmospheric neutrinos. The final significance of the analysis is p=0.244 when TXS 0506+056 is excluded, consistent with the background-only hypothesis. We report the parameters of the individual fits for the most significant objects which contributed to the final result.
Abstract: 1908.05506
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Full Text: [ PostScript, PDF]
Title:First Double Cascade Tau Neutrino Candidates in IceCube and a New Measurement of the Flavor Composition
(Submitted on 15 Aug 2019)
Abstract: The IceCube Neutrino Observatory at the South Pole, which detects Cherenkov light from charged particles produced in neutrino interactions, firmly established the existence of an astrophysical high-energy neutrino component. The expected neutrino flavor composition on Earth is $\nu_e:\nu_{\mu}:\nu_{\tau}$ of about 1:1:1 for neutrinos produced in astrophysical sources through pion decay. A measurement of the flavor composition on Earth can provide important constraints on sources and production mechanisms within the standard model, and can also constrain various beyond-standard-model processes. Here the measurement of the flavor composition performed on IceCube's High-Energy Starting Events sample with a livetime of about 7.5 years is presented. IceCube is directly sensitive to each neutrino flavor via the single cascade, track and double cascade event topologies. In IceCube, $\nu_{\tau}$-CC interactions above $\sim$ 100 TeV can produce resolvable double cascades, breaking the degeneracy between $\nu_e$ and $\nu_{\tau}$ present at lower energies. IceCube's first two identified double cascades are presented and the properties of the two $\nu_{\tau}$ candidates are discussed.
Abstract: 1908.05458
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Full Text: [ PostScript, PDF]
Title:The Baikal-GVD detector calibration
(Submitted on 15 Aug 2019)
Abstract: In April 2019, the Baikal-GVD collaboration finished the installation of the fourth and fifth clusters of the neutrino telescope Baikal-GVD. Momentarily, 1440 Optical Modules (OM) are installed in the largest and deepest freshwater lake in the world, Lake Baikal, instrumenting 0.25 cubic km of sensitive volume. The Baikal-GVD is thus the largest neutrino telescope on the Northern Hemisphere. The first phase of the detector construction is going to be finished in 2021 with 9 clusters, 2592 OMs in total, however the already installed clusters are stand-alone units which are independently operational and taking data from their commissioning.
Huge number of channels as well as strict requirements for the precision of the time and charge calibration (ns, p.e.) make calibration procedures vital and very complex tasks. The inter cluster time calibration is performed with numerous calibration systems. The charge calibration is carried out with a Single Photo-Electron peak. The various data acquired during the last three years in regular and special calibration runs validate successful performance of the calibration systems and of the developed calibration techniques. The precision of the charge calibration has been improved and the time dependence of the obtained calibration parameters have been cross-checked. The multiple calibration sources verified a 1.5 - 2.0 ns precision of the in-situ time calibrations. The time walk effect has been studied in detail with in situ specialized calibration runs.
Abstract: 1908.05450
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Full Text: [ PostScript, PDF]
Title:The Baikal-GVD neutrino telescope: First results of multi-messenger studies
(Submitted on 15 Aug 2019)
Abstract: Multi-messenger astronomy is a powerful tool to study the physical processes driving the non-thermal Universe. A combination of observations in cosmic rays, neutrinos, photons of all wavelengths and gravitational waves is expected. The alert system of the Baikal-GVD detector under construction will allow for a fast, on-line reconstruction of neutrino events recorded by the Baikal-GVD telescope and - if predefined conditions are satisfied - for the formation of an alert message to other communities. The preliminary results of searches for high-energy neutrinos in coincidence with GW170817/GRB170817A using the cascade mode of neutrino detection are discussed. Two Baikal-GVD clusters were operating during 2017. The zenith angle of NGC 4993 at the detection time of the GW170817 was 93.3 degrees. No events spatially coincident with GRB170817A were found. Given the non-detection of neutrino events associated with GW170817, upper limits on the neutrino fluence were established.
Abstract: 1908.05430
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Title:Search for cascade events with Baikal-GVD
(Submitted on 15 Aug 2019)
Abstract: Baikal-GVD is a next generation, kilometer-scale neutrino telescope currently under construction in Lake Baikal. GVD is formed by multi-megaton sub-arrays (clusters) and is designed for the detection of astrophysical neutrino fluxes at energies from a few TeV up to 100 PeV. The design of the Baikal-GVD allows one to search for astrophysical neutrinos with flux values measured by IceCube already at early phases of the array construction. We present here preliminary results of the search for high-energy neutrinos via the cascade mode with the Baikal-GVD neutrino telescope.
Abstract: 1908.05427
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Title:Neutrino Telescope in Lake Baikal: Present and Future
(Submitted on 15 Aug 2019)
Abstract: A significant progress in the construction and operation of the Baikal Gigaton Volume Detector in Lake Baikal, the largest and deepest freshwater lake in the world, is reported. The effective volume of the detector for neutrino initiated cascades of relativistic particles with energy above 100 TeV has been increased up to about 0.25 cubic kilometer. This unique scientific facility, the largest operating neutrino telescope in Northern Hemisphere, allows already to register two to three events per year from astrophysical neutrinos with energies exceeding 100 TeV. Preliminary results obtained with data recorded in 2016-2018 are announced. Multimessenger approach is used to relate finding of cosmic neutrinos with those of classical astronomers, with X-ray or gamma-ray observations and the gravitational wave events.
Abstract: 1908.05282
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Full Text: [ PostScript, PDF]
Title:Changes in the solar rotation over two solar cycles
(Submitted on 14 Aug 2019)
Abstract: We use helioseismic data from ground and space-based instruments to analyze how solar rotation has changed since the beginning of solar Cycle 23 with emphasis on studying the differences between Cycles 23 and 24. We find that the nature of solar rotation is indeed different for the two cycles. While the changes in the latitudinally independent component follows solar-cycle indices, some of the other components have a more complicated behavior. There is a substantial change in the behavior of the solar zonal flows and their spatial gradients too. While the zonal flows are in general weaker in Cycle 24 than those in Cycle 23, there are clear signs of the emergence of Cycle 25. We have also investigated the properties of the solar tachocline, in particular, its position, width, and the change (or jump) in the rotation rate across it. We find significant temporal variation in the change of the rotation rate across the tachocline. We also find that the changes in solar Cycle 24 were very different from those of Cycle 23. We do not find any statistically significant change in the position or the width of the tachocline.
Abstract: 1908.05215
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Full Text: [ PostScript, PDF]
Title:A new sample of X-ray selected Swift/SDSS faint blazars and blazar candidates
(Submitted on 13 Aug 2019)
Abstract: Our present knowledge of the properties of blazars mostly comes from small samples of bright objects, especially regarding studies on their cosmological evolution. Statistically well defined and completely identified samples of faint blazars are very difficult to obtain. We present a new X-ray selected sample of 62 blazars and blazar candidates reaching deep X-ray fluxes. We relied on the availability of large catalogs of astronomical objects combined with on-line services offering simple access to finding charts and magnitude estimates. We built the sample cross-matching X-ray sources in the Swift Serendipitous Survey in deep XRT GRB Fields catalog with data from deep radio and optical surveys. Our sample can probe populations of sources 10 times weaker in the X-ray flux with respect previous studies, thus allowing for a more detailed comparison between data and simulated counts. We use the sample to calculate the radio and X-ray LogN-LogS of blazars down to fluxes at least one order of magnitude fainter than previous studies. We show that, considering that our sample may be somewhat contaminated by sources other than blazars, we are in agreement with previous observational and theoretical estimations.
Abstract: 1908.04600
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Full Text: [ PostScript, PDF]
Title:Cosmic ray ensembles from ultra-high energy photons propagating in the galactic and intergalactic space
(Submitted on 13 Aug 2019)
Abstract: Propagation of ultra-high energy photons in the galactic and intergalactic space gives rise to cascades comprising thousands of photons. Using Monte Carlo simulations, we investigate the development of such cascades in the solar magnetosphere, and find that the photons in the cascades are distributed over hundreds of kilometers as they arrive at the top of the Earth's atmosphere. We also perform similar study for cascades starting as far as 10 Mpc away from us using relevant magnetic field models. A few photons correlated in time are expected to arrive at the Earth from the latter type of cascade. We present our simulation results and discuss the prospects for detection of these cascades with the Cosmic-Ray Extremely Distributed Observatory.
Abstract: 1908.04165
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Full Text: [ PostScript, PDF]
Title:X-ray and TeV gamma-ray emission from the 50-year period binary system PSR J2032+4127/MT91 213
(Submitted on 12 Aug 2019)
Abstract: We report on X-ray and TeV gamma-ray observations of the pulsar/Be star binary PSR J2032+4127/MT91 213. PSR J2032+4127 is a 143-ms gamma-ray pulsar which shares a long period (45-50 year) and highly eccentric orbit with the massive Be star MT91 213. TeV gamma-ray emission was detected from the binary following a coordinated observing campaign over the fall 2017 periastron with VERITAS, MAGIC, and X-ray monitoring with Swift-XRT. The discovery of this gamma-ray binary makes it just the second such source known to contain a pulsar as the compact object. We report on over 100 hours of extensive TeV observations across the periastron passage, which reveal variations in the TeV flux by an order of magnitude over time scales of days. The X-ray flux was also found to be highly variable, although it was not directly correlated with the TeV flux. These observations present serious challenges to existing models of the system, which will require significant revisions. We also discuss the steady and extended TeV source TeV J2032+4130, which lies in the same direction as the binary system, and its potential association with the pulsar.
Abstract: 1908.04163
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Full Text: [ PostScript, PDF]
Title:Measurement of the Extragalactic Background Light with VERITAS
(Submitted on 12 Aug 2019)
Abstract: The extragalactic background light records the history of infrared, optical and ultraviolet light radiation including re-radiation since the epoch of reionization. While challenging to measure directly, it can be measured indirectly via its impact on observed spectra of extragalactic gamma-ray emitters. VERITAS, a ground-based imaging atmospheric-Cherenkov telescope array sensitive to gamma rays above 100 GeV, has accrued 10 years of observations of hard-spectrum blazars. The energy and redshift range covered enables the measurement of the EBL in the range 0.56-56~$\mu$m, accessing the poorly constrained cosmic infrared background region. New constraints on the EBL resulting from the joint analysis using 16 spectra from 14 VERITAS-observed blazars will be presented. The method is independent of assumptions about the shape of the EBL spectrum, and includes a full treatment of systematic and statistical uncertainties. The measured spectrum is in good agreement with lower limits from galaxy counts, limiting the potential contribution from a diffuse component.
Abstract: 1908.04139
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Full Text: [ PostScript, PDF]
Title:Cosmic Ray Extremely Distributed Observatory: Status and perspectives of a global cosmic ray detection framework
(Submitted on 12 Aug 2019 (v1), last revised 19 Aug 2019 (this version, v3))
Abstract: The Cosmic-Ray Extremely Distributed Observatory (CREDO) is a project dedicated to global studies of extremely extended cosmic-ray phenomena, the cosmic-ray ensembles (CRE), beyond the capabilities of existing detectors and observatories. Up to date cosmic-ray research has been focused on detecting single air showers, while the search for ensembles of cosmic-rays, which may spread over a significant fraction of the Earth, is a scientific terra incognita. The key idea of CREDO is to combine existing cosmic-ray detectors (large professional arrays, educational instruments, individual detectors, such as smartphones, etc.) into a worldwide network, thus enabling a global analysis. The second goal of CREDO involves a large number of participants (citizen science!), assuring the geographical spread of the detectors and managing manpower necessary to deal with vast amount of data to search for evidence for cosmic-ray ensembles. In this paper the status and perspectives of the project are presented.
Abstract: 1908.05990
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Full Text: [ PostScript, PDF]
Title:AMON: TeV Gamma and Neutrino Coincidence Alerts from HAWC and IceCube subthreshold data
(Submitted on 16 Aug 2019)
Abstract: The era of multimessenger astrophysics has arrived with the simultaneous operation of large cosmic-ray, gamma-ray, neutrino, and gravitational-wave observatories. In just the past two years, an electromagnetic (EM) counterpart was detected for a gravitational wave event, and evidence for an EM counterpart of high energy neutrinos has been identified. These measurements have had a major impact on our view of the non-thermal universe, but understanding cosmic accelerators require a substantial increase in the number of multimessenger observations. The Astrophysical Multimessenger Observatory Network (AMON) is designed for high-statistics searches of sub-threshold transient alerts from gamma-ray and neutrino detectors. Within AMON, we have implemented a joint-likelihood analysis of TeV gamma-ray measurements from the High Altitude Water Cherenkov (HAWC) Observatory and neutrinos from the IceCube Neutrino Observatory. AMON is ready to produce real-time coincidence alerts using HAWC "hotspots" and IceCube astrophysical neutrino events. These alerts will be distributed to AMON follow-up partners with a median anticipated delay of six hours, which corresponds to a full transit in the field of view of HAWC. The alerts will have an angular resolution of ${\sim}0.2^{\circ}$, making them well-suited for deep electromagnetic follow-up observations.
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