Abstracts of Interest
Selected by:
Tristan Sudholz
Abstract: 1808.07435
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Title: X-ray Structure between the Innermost Disk and Optical Broad Line Region in NGC 4151
(Submitted on 22 Aug 2018)
Abstract: We present an analysis of the narrow Fe K-alpha line in Chandra/HETGS observations of the Seyfert AGN, NGC 4151. The sensitivity and resolution afforded by the gratings reveal asymmetry in this line. Models including weak Doppler boosting, gravitational red-shifts, and scattering are generally preferred over Gaussians at the 5 sigma level of confidence, and generally measure radii consistent with R ~ 500-1000 GM/c^2. Separate fits to "high/unobscured" and "low/obscured" phases reveal that the line originates at smaller radii in high flux states; model-independent tests indicate that this effect is significant at the 4-5 sigma level. Some models and Delta t ~ 2 E+4 s variations in line flux suggest that the narrow Fe K-alpha line may originate at radii as small as R ~ 50-130 GM/c^2 in high flux states. These results indicate that the narrow Fe K-alpha line in NGC 4151 is primarily excited in the innermost part of the optical broad line region (BLR), or X-ray BLR. Alternatively, a warp could provide the solid angle needed to enhance Fe K-alpha line emission from intermediate radii, and might resolve an apparent discrepancy in the inclination of the innermost and outer disk in NGC 4151. Both warps and the BLR may originate through radiation pressure, so these explanations may be linked. We discuss our results in detail, and consider the potential for future observations with Chandra, XARM, and ATHENA to measure black hole masses and to study the intermediate disk in AGN using narrow Fe K-alpha emission lines.
Abstract: 1808.07361
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Full Text: [ PostScript, PDF]
Title: On X-ray emission of radio pulsars
(Submitted on 21 Aug 2018)
Abstract: The analysis of distributions of some parameters of radio pulsars emitting X-ray radiation was carried out. The majority of such pulsars has short spin periods with the average value $< P >$ = 133 msec. The distribution of period derivatives reveals a bimodality, dividing millisecond ($< log \dfrac{dP}{dt}>$ = -19.69) and normal ($< log \dfrac{dP}{dt}> $ = -13.29) pulsars. Magnetic fields at the surface of the neutron star are characterized by the bimodal distribution as well. The mean values of $<log B_s>$ are $8.48$ and $12.41$ for millisecond pulsars and normal ones, respectively. The distribution of magnetic fields near the light cylinder, it does not show the noticeable bimodality. The median value of $log B_{lc}$ = 4.43 is almost three orders higher comparing with this quantity ($<log B_{lc}>$ = 1.75) for radio pulsars without registered X-ray emission. Losses of rotational energy ($<log \dfrac{dE}{dt}>$ = 35.24) are also three orders higher than corresponding values for normal pulsars. There is the strong correlation between X-ray luminosities and losses of rotational energies. The dependence of the X-ray luminosity on the magnetic field at the light cylinder has been detected. It shows that the generation of the non-thermal X-ray emission takes place at the periphery of the magnetosphere and is caused by the synchrotron mechanism. We detected the positive correlations between luminosities in radio, X-ray and gamma -ray ranges. Such correlations give the possibility to carry out a purposeful search for pulsars in one of these ranges if they radiate in other one.
Abstract: 1808.07101
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Full Text: [ PostScript, PDF]
Title: A multi-wavelength view of the neutron star binary 1FGL J1417.7--4402: A progenitor to canonical millisecond pulsars
(Submitted on 21 Aug 2018)
Abstract: The Fermi $\gamma$-ray source 1FGL J1417.7--4407 (J1417) is a compact X-ray binary with a neutron star primary and a red giant companion in a $\sim$5.4 day orbit. This initial conclusion, based on optical and X-ray data, was confirmed when a 2.66 ms radio pulsar was found at the same location (and with the same orbital properties) as the optical/X-ray source. However, these initial studies found conflicting evidence about the accretion state and other properties of the binary. We present new optical, radio, and X-ray observations of J1417 that allow us to better understand this unusual system. We show that one of the main pieces of evidence previously put forward for an accretion disk---the complex morphology of the persistent H$\alpha$ emission line---can be better explained by the presence of a strong, magnetically driven stellar wind from the secondary and its interaction with the pulsar wind. The radio spectral index derived from VLA/ATCA observations is broadly consistent with that expected from a millisecond pulsar, further disfavoring an accretion disk scenario. X-ray observations show evidence for a double-peaked orbital light curve, similar to that observed in some redback millisecond pulsar binaries and likely due to an intrabinary shock. Refined optical light curve fitting gives a distance of 3.1$\pm$0.6 kpc, confirmed by a Gaia DR2 parallax measurement. At this distance the X-ray luminosity of J1417 is (1.0$^{+0.4}_{-0.3}$) $\times 10^{33}$ erg s$^{-1}$, which is more luminous than all known redback systems in the rotational-powered pulsar state, perhaps due to the wind from the giant companion. The unusual phenomenology of this system and its differing evolutionary path from redback millisecond pulsar binaries points to a new eclipsing pulsar "spider" subclass that is a possible progenitor of normal field millisecond pulsar binaries.
Abstract: 1808.07091
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Title: Scaling of X-ray spectral properties of a black hole in the Seyfert 1 galaxy NGC~7469
(Submitted on 21 Aug 2018)
Abstract: We present our analysis of X-ray spectral properties observed from the Seyfrert 1 galactic nucleus NGC~7469 using the RXTE and ASCA observations. We demonstrate strong observational evidence that NGC~7469 undergoes spectral transitions from the low hard state (LHS) to the intermediate state (IS) during these observations. The RXTE observations (1996--2009) show that the source was in the IS ~ 75 % of the time only, ~ 25 % of the time in the LHS. The spectra of NGC~7469 are well fitted by the so-called bulk motion Comptonization (BMC) model for all spectral states. We have established the photon index saturation level, Gamma_{sat}+2.1+/-0.1, in the Gamma versus mass accretion rate, Mdot correlation. This Gamma- Mdot correlation allows us to estimate the black hole (BH) mass in NGC~7469 to be M__BH> 3 x 10^6 solar masses assuming the distance to NGC~7469 of 70 Mpc. For this BH mass estimate, we use the scaling method taking Galactic BHs, GRO~J1655--40, Cyg~ X--1 and an extragalactic BH source, NGC~4051 as reference sources. The Gamma versus Mdot correlation revealed in NGC~7469 is similar to those in a number of Galactic and extragalactic BHs and it clearly shows the correlation along with the strong Gamma saturation at ~2.1. This is robust observational evidence for the presence of a BH in NGC~7469. We also find that the seed photon temperatures are quite low, of the order of 140-200 eV, which are consistent with a high BH mass in NGC~7469 that is more than 3x10^6 solar masses.
Abstract: 1808.06978
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Full Text: [ PostScript, PDF]
Title: Macro detection using fluorescence detectors
(Submitted on 21 Aug 2018)
Abstract: Macroscopic dark matter (aka macros) constitutes a broad class of alternatives to particulate dark matter. We calculate the luminosity produced by the passage of a single macro as a function of its physical cross section. A general detection scheme is developed for measuring the fluorescence caused by a passing macro in the atmosphere that is applicable to any ground based or space based Fluorescence Detecting (FD) telescopes. In particular, we employ this scheme to constrain the parameter space ($\sigma_{x} \mbox{ vs} \mbox{ M}_{x}$) of macros than can be probed by the Pierre Auger Observatory and by the Extreme Universe Space Observatory onboard the Japanese Experiment Module (JEM-EUSO). It is of particular significance that both detectors are sensitive to macros of nuclear density, since most candidates that have been explored (excepting primordial black holes) are expected to be of approximately nuclear density.
Abstract: 1808.06916
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Full Text: [ PostScript, PDF]
Title: The Evolution of X-ray Bursts in the "Bursting Pulsar" GRO J1744-28
(Submitted on 21 Aug 2018)
Abstract: GRO J1744-28, commonly known as the `Bursting Pulsar', is a low mass X-ray binary containing a neutron star and an evolved giant star. This system, together with the Rapid Burster (MXB 1730-33), are the only two systems that display the so-called Type II X-ray bursts. These type of bursts, which last for 10s of seconds, are thought to be caused by viscous instabilities in the disk; however the Type II bursts seen in GRO J1744-28 are qualitatively very different from those seen in the archetypal Type II bursting source the Rapid Burster. To understand these differences and to create a framework for future study, we perform a study of all X-ray observations of all 3 known outbursts of the Bursting Pulsar which contained Type II bursts, including a population study of all Type II X-ray bursts seen by RXTE. We find that the bursts from this source are best described in four distinct phenomena or `classes' and that the characteristics of the bursts evolve in a predictable way. We compare our results with what is known for the Rapid Burster and put out results in the context of models that try to explain this phenomena.
Abstract: 1808.06618
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Full Text: [ PostScript, PDF]
Title: Collisional triggering of fast flavor conversions of supernova neutrinos
(Submitted on 20 Aug 2018)
Abstract: Fast flavor conversions of supernova neutrinos, possible near the neutrinosphere, depends on an interesting interplay of collisions and neutrino oscillations. Contrary to naive expectations, the rate of self-induced neutrino oscillations, due to neutrino-neutrino forward scattering, comfortably exceeds the rate of collisions even deep inside the supernova core. Consistently accounting for collisions and oscillations, we present the first calculations to show that collisions can create the conditions for fast flavor conversions of neutrinos, but become subdominant thereafter, and oscillations can continue without significant damping. This may have interesting consequences for supernova explosions and the nature of its associated neutrino emission.
Abstract: 1808.06426
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Full Text: [ PostScript, PDF]
Title: The problem of the height dependence of magnetic fields in sunspots
(Submitted on 20 Aug 2018)
Abstract: To understand the physics of sunspots, it is important to know the properties of their magnetic field, and especially its height stratification plays a substantial role. There are mainly two methods to assess this stratification, but they yield different magnetic gradients in the photospheric layers. Determinations based on the different origin of several spectral lines and the slope of their profiles result in gradients of -2 to -3G/km, or even steeper. This is similar for the total magnetic field strength and for the vertical component of the magnetic field. The other option is to determine the horizontal partial derivatives of the magnetic field, and with the condition divB=0, also the vertical derivative is known. With this method, gradients of -0.5 G/km and shallower are obtained. Obviously, these results do not agree. If chromospheric spectral lines are included, only shallow gradients around -0.5G/km are encountered. Shallow gradients are also found from gyro-resonance measurements in the radio wave range 300 - 2000GHz. Some indirect methods are also considered, but they cannot clarify the total picture. An analysis of a numerical simulation of a sunspot indicates a shallow gradient over a wide height range, but with slightly steeper gradients in deep layers. Several ideas to explain the discrepancy are also discussed. With no doubts cast on Maxwell's equations, the first one is to look at the uncertainties of the formation heights of spectral lines, but a wider range of these heights would require an extension of the solar photosphere that is incompatible with observations and the theory of stellar atmospheres. The problem of the height gradient of the magnetic field in sunspots is still not solved.
Abstract: 1808.06295
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Full Text: [ PostScript, PDF]
Title: Space Weather Prediction from the Ground: Case of CHAIN
(Submitted on 20 Aug 2018)
Abstract: In this article, we insist on the importance and the challenges of the prediction of solar eruptive phenomena including flares, coronal mass ejections (CME), and filament eruptions fully based on the ground-based telescopes. It is true that satellites' data are indispensable for the space weather prediction, but they are vulnerable to the space weather effects. Therefore, the ground-based telescopes can be complementary to them from the viewpoint of space weather prediction. From this view point, one possible new flare prediction method that makes use of H-alpha, red wings, and blue wings images obtained by the SDDI/SMART, the ground-based telescope at Hida Observatory, is presented. And in order to show the possibility for the actual operation based on that method, the recent progress of CHAIN project, the international observation network, is mentioned in terms of their outcomes and capacity buildings.
Abstract: 1808.08215
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Full Text: [ PostScript, PDF]
Title: Beyond sunspots: Studies using the McIntosh Archive of global solar magnetic field patterns
(Submitted on 24 Aug 2018)
Abstract: In 1964 (Solar Cycle 20; SC 20), Patrick McIntosh began creating hand-drawn synoptic maps of solar magnetic features, based on H$\alpha$ images. These synoptic maps were unique in that they traced magnetic polarity inversion lines, and connected widely separated filaments, fibril patterns, and plage corridors to reveal the large-scale organization of the solar magnetic field. Coronal hole boundaries were later added to the maps, which were produced, more or less continuously, into 2009 (i.e., the start of SC 24). The result was a record of $\sim45$ years ($\sim570$ Carrington rotations), or nearly four complete solar cycles of synoptic maps. We are currently scanning, digitizing and archiving these maps, with the final, searchable versions publicly available at NOAA's National Centers for Environmental Information. In this paper we present preliminary scientific studies using the archived maps from SC 23. We show the global evolution of closed magnetic structures (e.g., sunspots, plage, and filaments) in relation to open magnetic structures (e.g., coronal holes), and examine how both relate to the shifting patterns of large-scale positive and negative polarity regions.
Abstract: 1808.08226
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Full Text: [ PostScript, PDF]
Title: Towards the next generation of CORSIKA: A framework for the simulation of particle cascades in astroparticle physics
(Submitted on 24 Aug 2018)
Abstract: A large scientific community depends on the precise modelling of complex processes in particle cascades in various types of matter. These models are used most prevalently in cosmic-ray physics, astrophysical-neutrino physics, and gamma-ray astronomy. In this white paper, we summarize the necessary steps to ensure the evolution and future availability of optimal simulation tools. The purpose of this document is not to act as a strict blueprint for next-generation software, but to provide guidance for the vital aspects of its design. The topics considered here are driven by physics and scientific applications. Furthermore, the main consequences of implementation decisions on performance are outlined. We highlight the computational performance as an important aspect guiding the design since future scientific applications will heavily depend on an efficient use of computational resources.
Abstract: 1808.08082
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Full Text: [ PostScript, PDF]
Title: New constraints on inelastic dark matter from IceCube
(Submitted on 24 Aug 2018)
Abstract: We study the capture and subsequent annihilation of inelastic dark matter (DM) in the Sun, placing constraints on the DM-nucleon scattering cross section from the null result of the IceCube neutrino telescope. We then compare such constraints with exclusion limits on the same cross section that we derive from XENON1T, PICO and CRESST results. We calculate the cross section for inelastic DM-nucleon scattering within an extension of the effective theory of DM-nucleon interactions which applies to the case of inelastic DM models characterised by a mass splitting between the incoming and outgoing DM particle. We find that for values of the mass splitting parameter larger than about 200 keV, neutrino telescopes place limits on the DM-nucleon scattering cross section which are stronger than the ones from current DM direct detection experiments. The exact mass splitting value for which this occurs depends on whether DM thermalises in the Sun or not. This result applies to all DM-nucleon interactions that generate DM-nucleus scattering cross sections which are independent of the nuclear spin, including the "canonical" spin-independent interaction. We explicitly perform our calculations for a DM candidate with mass of 1 TeV, but our conclusions qualitatively also apply to different masses. Furthermore, we find that exclusion limits from IceCube on the coupling constants of this family of spin-independent interactions are more stringent than the ones from a (hypothetical) reanalysis of XENON1T data based on an extended signal region in nuclear recoil energy. Our results should be taken into account in global analyses of inelastic DM models.
Abstract: 1808.08035
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Full Text: [ PostScript, PDF]
Title: A beam of ultrahigh energy particles of the same magnetic rigidity
(Submitted on 24 Aug 2018)
Abstract: Two EAS arrays during a day have recorded 3 particles with energies above 30 EeV arriving from the same sky region. Two events were registered by the Yakutsk array and one - by the Telescope Array. Two Yakutsk events were estimated to be same energy and the Telescope Array shower's energy was almost 2 times higher. This indicates the same magnetic rigidity of all three particles, if the charge differs by a factor of 2. The relatively short sequence of all three events and their "monochromaticity" in rigidity can be due to the magnetic separation of particles in the acceleration process and propagation of the beam.
Abstract: 1808.07887
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Full Text: [ PostScript, PDF]
Title: Black Hole Pulsar
(Submitted on 23 Aug 2018)
Abstract: In anticipation of a LIGO detection of a black hole/neutron star merger, we expand on the intriguing possibility of an electromagnetic counterpart. Arguing against common lore, we consider the electric charge of the black hole as an overlooked source of electromagnetic radiation. Relying on the well-known Wald mechanism by which a spinning black hole immersed in an external magnetic field acquires a stable net charge, we remark on the fact that a strongly magnetized neutron star companion in such a binary system may thus give rise to a large enough charge on the black hole to allow for potentially observable effects. In turn, a spinning charged black hole itself creates a magnetic field --- a black hole pulsar. Another promising signal is provided by the continuous acceleration of charges that we show to be present even when the black hole's charge has reached its stable value. Additionally, we show that even in a force-free magnetosphere, as in the Blandford-Znajek description, the black hole is in fact charged. This suggests that charged solutions could be important in force-free astrophysical settings, as well as in vacuum.
Abstract: 1808.07877
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Full Text: [ PostScript, PDF]
Title: X-Ray Reverberation From Black Hole Accretion Disks with Realistic Geometric Thickness
(Submitted on 23 Aug 2018)
Abstract: X-ray reverberation in AGN, believed to be the result of the reprocessing of corona photons by the underlying accretion disk, has allowed us to probe the properties of the inner-most regions of the accretion flow and the central black hole. This process is modeled via raytracing in the Kerr metric, with the disk thickness almost ubiquitously assumed to be negligible (razor-thin) and the corona commonly approximated as a point source located along the polar axis (a lamppost). In this work, we use the new raytracing suite, Fenrir, to explore the effect that accretion disk geometry has on reverberation signatures, assuming a lamppost configuration but allowing for a finite scale height. We characterize the signatures of finite disk thickness in the reverberation transfer-function and calculate how they might manifest in observed lag-frequency spectra. We also show that a disk-hugging corona (approximated by off-axis point-like flares) exhibits characteristics that are qualitatively different from observation, thus providing further evidence for a flaring corona that is separated from the underlying disk material.
Abstract: 1808.07875
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Full Text: [ PostScript, PDF]
Title: ASASSN-18ey: The Rise of a New Black-Hole X-ray Binary
(Submitted on 23 Aug 2018)
Abstract: We present the discovery of ASASSN-18ey, a new black hole low-mass X-ray binary discovered by the All-Sky Automated Survey for SuperNovae (ASAS-SN). A week after ASAS-SN discovered ASASSN-18ey as an optical transient, it was detected as an X-ray transient by MAXI/GCS. Here, we analyze ASAS-SN and Asteroid Terrestrial-impact Last Alert System (ATLAS) pre-outburst optical light curves, finding evidence of intrinsic variability for several years prior to the outburst. While there was no long-term rise leading to outburst, as has been seen in several other systems, the start of the outburst in the optical preceded that in the X-rays by $7.20\pm0.97~\rm days$. We analyze the spectroscopic evolution of ASASSN-18ey from pre-maximum to $> 100~\rm days$ post-maximum. The spectra of ASASSN-18ey exhibit broad, asymmetric, double-peaked H$\alpha$ emission. The Bowen blend ($\lambda \approx 4650$\AA) in the post-maximum spectra shows highly variable double-peaked profiles, likely arising from irradiation of the companion by the accretion disk, typical of low-mass X-ray binaries. The optical and X-ray luminosities of ASASSN-18ey are consistent with black hole low-mass X-ray binaries, both in outburst and quiescence.
Abstract: 1808.07837
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Full Text: [ PostScript, PDF]
Title: Interactions between Ultra-High-Energy Particles and Protogalactic Environments
(Submitted on 23 Aug 2018)
Abstract: We investigate the interactions of energetic hadronic particles (cosmic ray protons) with photons and baryons in protogalactic environments, where the target photons are supplied by the first generations of stars to form in the galaxy and the cosmological microwave background, while the target baryons are the interstellar and circumgalactic medium. We show that pair-production and photo-pion processes are the dominant interactions at particle energies above $10^{19}\;\! {\rm eV}$, while ${\rm pp}$-interaction pion-production dominates at the lower energies in line with expectations from, for example $\gamma$-ray observations of star-forming galaxies and dense regions of our own galaxy's interstellar medium. We calculate the path lengths for the interaction channels and determine the corresponding rates of energy deposition. We have found that protogalactic magnetic fields and their evolution can significantly affect the energy transport and energy deposition processes of cosmic rays. Within a Myr after the onset of star-formation the magnetic field in a protogalaxy could attain a strength sufficient to confine all but the highest energy particles within the galaxy. This enhances the cosmic ray driven self-heating of the protogalaxy to a rate of around $10^{-24}\;\! {\rm erg} \;\!{\rm cm}^{-3}\;\! {\rm s}^{-1}$ for a galaxy with strong star-forming activity that yields 1 core collapse SN event per year. This heating power exceeds even that due to radiative emission from the protogalaxy's stellar populations. However, in a short window before the protogalaxy is fully magnetised, energetic particles could stream across the galaxy freely, delivering energy into the circumgalactic and intergalactic medium.
Abstract: 1808.07809
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Full Text: [ PostScript, PDF]
Title: Verifying and Reporting Fast Radio Bursts
(Submitted on 23 Aug 2018)
Abstract: Fast Radio Bursts (FRBs) are a class of short-duration transients at radio wavelengths with inferred astrophysical origin. The prototypical FRB is a broadband signal that occurs over the extent of the receiver frequency range, is narrow in time, and is highly dispersed, following a $\nu^{-2}$ relation. However, some FRBs appear band-limited, and show apparent scintillation, complex frequency-dependent structure, or multi-component pulse shapes. While there is sufficient evidence that FRBs are indeed astrophysical, their one-off nature necessitates extra scrutiny when reporting a detection as bona fide and not a false positive. Currently, there is no formal validation framework for FRBs, rather a set of community practices. In this article, we discuss potential sources of false positives, and suggest a framework in which FRB-like events can be evaluated as real or otherwise. We present examples of false-positive events in data from the Arecibo, LOFAR, and Nanshan telescopes, which while FRB-like, are found to be due to instrumental variations, noise, and radio-frequency interference. Differentiating these false-positive detections from astrophysical events requires knowledge and tests beyond thresholded single-pulse detection. We discuss post-detection analyses, verification tests, and datasets which should be provided when reporting an FRB detection.
Abstract: 1808.07616
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Full Text: [ PostScript, PDF]
Title: The advection-dominated accretion flow for the origin of the thermal soft X-ray component in low-level accreting neutron stars
(Submitted on 23 Aug 2018)
Abstract: A thermal soft X-ray component is often detected in low-level accreting neutron stars (NSs), but is not detected in low-level accreting stellar-mass black holes (BHs). In this paper, we investigate the origin of such a thermal soft X-ray component in the framework of the self-similar solution of the advection-dominated accretion flow (ADAF) around NSs. It is assumed that a fraction, $f_{\rm th}$, of the energy transferred onto the surface of the NS is thermalized at the surface of the NS as the soft photons to be scattered in the ADAF. We self-consistently calculate the structure and the corresponding emergent spectrum of the ADAF by considering the radiative coupling between the soft photons from the surface of the NS and the ADAF itself. We show that the Compton $y$-parameter of the ADAF for NSs is systematically lower than that of BHs. Meanwhile, we find that the temperature of the thermal soft X-ray component in NSs decreases with decreasing mass accretion rate, which is qualitatively consistent with observations. We test the effect of $f_{\rm th}$ on the structure, as well as the emergent spectrum of the ADAF. It is found that a change of $f_{\rm th}$ can significantly change the temperature of the thermal soft X-ray component as well as the spectral slope in hard X-rays. Finally, it is suggested that the value of $f_{\rm th}$ can be constrained by fitting the high-quality X-ray data, such as the $\it XMM$-$\it Newton$ spectrum between 0.5-10 keV in the future work.
Abstract: 1808.07596
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Full Text: [ PostScript, PDF]
Title: Galactic PeVatrons and helping to find them: Effects of Galactic absorption on the observed spectra of very high energy $γ$-ray sources
(Submitted on 23 Aug 2018)
Abstract: Identification of the cosmic-ray (CR) `PeVatrons', which are sources capable of accelerating particles to $\sim10^{15}$ eV energies and higher, may lead to resolving the long-standing question of the origin of the spectral feature in the all-particle CR spectrum known as the `knee'. Because CRs with these energies are deflected by interstellar magnetic fields identification of individual sources and determination of their spectral characteristics is more likely via very high energy $\gamma$-ray emissions, which provide the necessary directional information. However, pair production on the interstellar radiation field (ISRF) and cosmic microwave background leads to steepening of the high-energy tails of $\gamma$-ray spectra, and should be corrected for to enable true properties of the spectrum at source to be recovered. Employing recently developed three-dimensional ISRF models this paper quantifies the pair-absorption effect on spectra for sources in the Galactic centre direction at 8.5 kpc and 23.5 kpc distance, with the latter corresponding to the far side of the Galactic stellar disc where it is expected that discrimination of spectral features $>10$ TeV will be possible by the forthcoming Cherenkov Telescope Array. The estimates made suggest spectral cutoffs could be underestimated by factors of a few in the energy range so far sampled by TeV $\gamma$-ray telescopes. As an example to illustrate this, the recent HESS measurements of diffuse $\gamma$-ray emissions possibly associated with injection of CRs nearby Sgr A$^*$ are ISRF-corrected, and estimates of the spectral cutoff are re-evaluated. It is found that it could be higher by up to a factor $\sim 2$, indicating that these emissions may be consistent with a CR accelerator with a spectral cutoff of at least 1 PeV at the 95% confidence level.
Abstract: 1808.07629
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Full Text: [ PostScript, PDF]
Title: Measurements using the inelasticity distribution of multi-TeV neutrino interactions in IceCube
(Submitted on 23 Aug 2018)
Abstract: Inelasticity--the fraction of a neutrino's energy transferred to hadrons--is a quantity of interest in the study of astrophysical and atmospheric neutrino interactions at multi-TeV energies with IceCube. In this work, a sample of contained neutrino interactions in IceCube is obtained from 5 years of data and classified as 2650 tracks and 965 cascades. Tracks arise predominantly from charged-current $\nu_{\mu}$ interactions, and we demonstrate that we can reconstruct their energy and inelasticity. The inelasticity distribution is found to be consistent with the calculation of Cooper-Sarkar et al. across the energy range from $\sim$ 1 TeV to $\sim$ 100 TeV. Along with cascades from neutrinos of all flavors, we also perform a fit over the energy, zenith angle, and inelasticity distribution to characterize the flux of astrophysical and atmospheric neutrinos. The energy spectrum of diffuse astrophysical neutrinos is well-described by a power-law in both track and cascade samples, and a best-fit index $\gamma=2.62\pm0.07$ is found in the energy range from 3.5 TeV to 2.6 PeV. Limits are set on the astrophysical flavor composition that are compatible with a ratio of $\left(\frac{1}{3}:\frac{1}{3}:\frac{1}{3}\right)_{\oplus}$. Exploiting the distinct inelasticity distribution of $\nu_{\mu}$ and $\bar{\nu}_{\mu}$ interactions, the atmospheric $\nu_{\mu}$ to $\bar{\nu}_{\mu}$ flux ratio in the energy range from 770 GeV to 21 TeV is found to be $0.77^{+0.44}_{-0.25}$ times the calculation by Honda et al. Lastly, the inelasticity distribution is also sensitive to neutrino charged-current charm production. The data are consistent with a leading-order calculation, with zero charm production excluded at $91\%$ confidence level. Future analyses of inelasticity distributions may probe new physics that affects neutrino interactions both in and beyond the Standard Model.
Abstract: 1808.07464
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Full Text: [ PostScript, PDF]
Title: Massive Neutrinos Leave Fingerprints on Cosmic Voids
(Submitted on 22 Aug 2018)
Abstract: Massive neutrinos uniquely affect cosmic voids. We explore their impact on void clustering using both the DEMNUni and MassiveNuS simulations. For voids, neutrino effects depend on the observed void tracers. As the neutrino mass increases, the number of small voids traced by cold dark matter particles increases and the number of large voids decreases. Surprisingly, when massive, highly biased, halos are used as tracers, we find the opposite effect. How neutrinos impact the scale at which voids cluster and the void correlation is similarly sensitive to the tracers. This scale dependent trend is not due to simulation volume or halo density. The interplay of these signatures in the void abundance and clustering leaves a distinct fingerprint that could be detected with observations and potentially help break degeneracies between different cosmological parameters. This paper paves the way to exploit cosmic voids in future surveys to constrain the mass of neutrinos.
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