Flux Of Nuclei Research Articles

The Host Galaxy Fluxes of Active Galaxy Nuclei Are Generally Overestimated by the Flux Variation Gradient Method

In terms of the variable nature of normal active galaxy nuclei (AGN) and luminous quasars, a so-called flux variation gradient (FVG) method has been widely utilized to estimate the underlying non-variable host galaxy fluxes. The FVG method assumes an invariable AGN color, but this assumption has been questioned by the intrinsic color variation of quasars and local Seyfert galaxies. Here, using an up-to-date thermal fluctuation model to simulate multi-wavelength AGN variability, we theoretically demonstrate that the FVG method generally overestimates the host galaxy flux; that is, it is more significant for brighter AGN/quasars. Furthermore, we observationally confirm that the FVG method indeed overestimates the host galaxy flux by comparing it to that estimated through other independent methods. We thus caution that applying the FVG method should be performed carefully in the era of time-domain astronomy.

The Silicon Charge Detector of the High Energy Cosmic Radiation Detection experiment

The High Energy Cosmic Radiation Detector (HERD) is an experiment designed for direct measurement of cosmic rays on the Chinese Space Station in 2027. Its goals include precise measurements of cosmic ray energy spectra, mass composition, electron/positron spectra, cosmic rays anisotropy, gamma ray astronomy and indirect searches for Dark Matter. HERD features a 55X0, homogeneous, 3D segmented imaging calorimeter and can detect particles from the top and four lateral sides, providing precise energy measurements and electron/proton separation for a wide field of view. A key detector in HERD is the Silicon Charge Detector (SCD). SCD measures the charge of particles before interaction with other materials, minimizing cosmic rays nuclei fragmentation and reducing systematics on nuclei flux measurement. Thorough studies, TCAD and/or SPICE simulations, and accelerator tests on prototypes have been conducted to evaluate the tracking and charge resolution capabilities of the SCD. Further testing with 300 μm detectors is planned in the coming months to fully characterize the SCD's performance. This paper presents the results of the simulation studies and of the measured performance with particles.

Fluxes and spectral indices of rare and abundant nuclei of cosmic rays according to the data of the NUCLEON satellite experiment

During the processing of the data obtained in the space experiment NUCLEON, results were obtained that were of significant astrophysical importance. Using the GALPROP package, the inverse problem of the propagation of cosmic rays from the source (close Supernovae) to the observer was solved, a component spectrum was calculated at the source. It was shown that a systematic change in the power index (slope of the spectrum) was observed at the source, which can be interpreted as incomplete ionization of cosmic rays now of acceleration at the front of the supernova shock wave. Magnetic rigidity spectra analysis was applied for nitrogen nuclei fluxes and the total spectrum of rare nuclei with odd charges from 9 to 19 (F, Na, Al, P, Cl, K). Ratios of odd and even nuclei fluxes are calculated. It turned out that the spectrum of rare, odd nuclei is more rigid than the spectrum of abundant even nuclei (Z = 10–20) at the magnetic rigidity area 300–10 000 GV.

CAVITATION IN LIQUID METHANE WITH SMALL HELIUM ADDITIVES

Cavitation in a viscous gas-saturated liquid has been considered taking into account the diffusive supply of a volatile component to a bubble within the framework of the classical nucleation theory (CNT). An expression has been obtained for the steady-state flux of new phase nuclei. The method of simultaneous pulse stretching and heating has been employed to determine the limiting stretchings of pure methane and methane–helium solutions with helium contents of up to 0.2 mol %. The data obtained on nucleation rate of (1020–1022) m–3 s–1, have been compared with the results of calculations by the CNT. The peculiarities of new phase nucleation in weak solutions and the reasons for the discrepancy between the theoretical and experimental data have been discussed.

Attaining the PeV frontier of the cosmic ray spectrum in space with HERD

The High Energy cosmic-Radiation Detection facility (HERD) is a calorimetric experiment planned to be launched in 2027. It will be operational for at least 10 years on board the China Space Station. With HERD we will measure the energy flux of cosmic protons and heavier nuclei from 30 GeV up to, for the first time in space, a few PeV. We will search for signatures of annihilation and decay products of dark matter in the energy spectrum of cosmic electrons and gamma rays from 10 GeV to 100 TeV. A wide field of view monitoring of the gamma-ray full-sky from 100 MeV will also be performed. The five HERD subdetectors, the calorimeter (CALO), the scintillating fiber tracker (FIT), the plastic scintillator detector (PSD), the silicon charge detector (SCD) and the transition radiation detector (TRD), are currently under development. The design, prospects and expected performance of HERD, as well as its contribution to the multimessenger astronomy will be presented in this contribution.

Insight into History of GCR Heavy Nuclei Fluxes by Their Tracks in Meteorites

Insight into History of GCR Heavy Nuclei Fluxes by Their Tracks in Meteorites

Search for variability in the spectra cosmic ray protons

Search for global time variability in the energy spectra of cosmic rays protons was carried out using data 6 experiments: CALET [1], DAMPE [2], NUCLEON [3], CREAM-III [37], AMS-02 [35] (3 years of observation) and AMS-02 [60] (7 years of observation). Approximation of all spectra (in the energy range of ∼ 6 GeV - 300 TeV) was produced by an empirical model describing experimental data as the sum of three power components: constant background and two variables of the power components with various cuts off on high energies. It turned out that the “soft” power component has slope index αH≈3 and the cutting energy of ∼ 200 GeV, and the “hard” power component has slope index αL≈2.4, the cutting energy of ∼ 100 TeV. To find the variability of spectra of cosmic rays all experiments were compared in pairs. Reliable changes in spectral curves of different experiments were not found. The causes of lack of reliable variability are discussed. Nevertheless, it was found that the cutoff parameter of “hard” spectral components of some experiments may differ by more than 5σ. Since the global variability of the spectra is not detected, it makes sense to see how well our model describes the combined pairs of spectra. It turned out that the parameters of the fits of the combined spectra coincide with the accuracy to errors with the parameters of the fits of individual spectra. The significance of the differences between the average values of the power indexes of slope “soft” and “hard” component of more than 28σ. Consequently, the “soft” and “hard” components of the spectra of protons of CR really exist. The “hard” cutoff parameter EL_cut of the fit of the pair of experiments “AMS_(3y)+DAMPE” is significantly different by 8.6σ from the corresponding cutoff parameter of the pairs of experiments “AMS_(3y)+NUCLEON”. In the experiments “AMS_(7y)+DAMPE” and “AMS_(3y)+NUCLEON” parameter EL_cut reliably differ by 8.3σ. Consequently, the variability of the cutoff parameter of the “hard” component is real. In addition, our estimates show that the global variability of CR spectra (that is, the variability of the whole spectral curve) for nuclei of elements with large Z can be detected. The explanation of the difference in the fluxes of nuclei (C, O, Fe) of cosmic rays found in the AMS and CALET experiments is proposed.

On the perspectives for separating the radio flux variations of the nucleus and the jet of active galactic based on data from monitoring programs and VLBI observations

The subject and purpose of the work: the possibility of separating the spectral flux densities of the active core and the jet of sources (3C 120, 3C 273, 3C 345, 3C 454.3, 3C 446, Bl Lac, CTA 102, OJ 287, OT 081) is considered. The data of long-term monitoring of changes in the integral flux of extragalactic radio sources performed on the 26-meter telescope of the University of Michigan UMRAO (1969–2012) at frequencies of 14.5, 8, 4.8 GHz are used. Also, data on the core flux and images of active galactic nuclei at a frequency of 15–15.4 GHz VLBA monitoring MOJAVE are used. The subject of this work is to separate the jet flow from the integral flux from the source, as well as to compile the catalog of the quasi-periods of variability of nuclei and jets separately. Methods and methodology: Fourier-periodogram analysis is used to distinguish long-term and short-period variability of nuclei and jets of extragalactic sources. Autocorrelation calculations were carried out in order to confirm the periods of variability. Results: conclusions were made about the applicability of the described method for separating the jet flux, and a catalog of long-term and short-period variability of radio emission fluxes from nuclei and jets for the investigated radio sources was compiled.

Cosmic antihelium-3 nuclei sensitivity of the GAPS experiment

The General Antiparticle Spectrometer (GAPS) is an Antarctic balloon experiment designed for low-energy (0.1–0.3 GeV/n) cosmic antinuclei as signatures of dark matter annihilation or decay. GAPS is optimized to detect low-energy antideuterons, as well as to provide unprecedented sensitivity to low-energy antiprotons and antihelium nuclei. The novel GAPS antiparticle detection technique, based on the formation, decay, and annihilation of exotic atoms, provides greater identification power for these low-energy antinuclei than previous magnetic spectrometer experiments. This work reports the sensitivity of GAPS to detect antihelium-3 nuclei, based on full instrument simulation, event reconstruction, and realistic atmospheric influence simulations. The report of antihelium nuclei candidate events by AMS-02 has generated considerable interest in antihelium nuclei as probes of dark matter and other beyond the Standard Model theories. GAPS is in a unique position to detect or set upper limits on the cosmic antihelium nuclei flux in an energy range that is essentially free of astrophysical background. In three 35-day long-duration balloon flights, GAPS will be sensitive to an antihelium flux on the level of 1.3−1.2+4.5·10−6 m-2sr-1s-1(GeV/n)-1 (95% confidence level) in the energy range of 0.11–0.3 GeV/n, opening a new window on rare cosmic physics.

Fresh insights on properties of particle fluxes in cosmic rays measured with the Alpha Magnetic Spectrometer on the international space station

The Alpha Magnetic Spectrometer is a particle physics detector focusing on the search for dark matter, the existence of antimatter, the origin and composition of cosmic rays from primordial sources in the universe and the exploration of new physics in space. Important features of the elementary particle (proton, antiproton, positron and election) fluxes in cosmic rays are presented: (1) The proton spectrum has a smooth hardening from 200 GeV; (2) antiproton and positron spectra show excess from traditional physics background; (3) in particular, the positron flux shows a source term with a cutoff energy of 810 GeV, which raises the question of its source; (4) the origin of the energetic electrons is different from that of positrons and (5) the identical momentum dependence of primary and secondary cosmic ray nuclei fluxes are also reviewed.

Implications of current nuclear cross sections on secondary cosmic rays with the upcoming DRAGON2 code

Current measurements of cosmic-ray fluxes have reached unprecedented accuracy thanks to the new generation of experiments, and in particular the AMS-02 mission. At the same time, significant progress has been made in the propagation models of galactic cosmic rays. These models include several propagation parameters, which are usually inferred from the ratios of secondary to primary cosmic rays, and which depend on the cross sections describing the collisions among the various species of cosmic-ray nuclei. At present, our knowledge of these cross sections in the energy range where cosmic-ray interactions occur is limited, and this is a source of uncertainties in the predicted fluxes of secondary cosmic-ray nuclei. In this work we study the impact of the cross section uncertainties on the fluxes of light secondary nuclei (Li, Be, B) using a preliminary version of the upcoming DRAGON2 code. We first present a detailed comparison of the secondary fluxes computed by implementing different parameterizations for the network of spallation cross sections. Then, we discuss the use of secondary-over-secondary cosmic-ray flux ratios as a tool to improve the consistency of cross sections parameterizations and give insight of the overall uncertainties coming from the cross sections parametrisations. We show that the uncertainties inferred from the cross section data are enough to explain the discrepancies in the Be and Li fluxes with respect to the AMS-02 data, with no need of a primary component in their spectra. In addition, we show that the fluxes of B, Be and Li can be simultaneously reproduced by rescaling their cross sections within the experimental uncertainty. Finally, we also revisit the diffusive estimation of the halo size, obtaining good agreement with previous works and a best fit value of 6.8 ± 1 kpc from the most updated cross sections parametrisations.

Antideuterons and antihelium nuclei from annihilating dark matter

Recent studies of the cosmic-ray antiproton-to-proton ratio have identified an excess of $\sim$10-20 GeV antiprotons relative to the predictions of standard astrophysical models. Intriguingly, the properties of this excess are consistent with the same range of dark matter models that can account for the long-standing excess of $\gamma$-rays observed from the Galactic Center. Such dark matter candidates can also produce significant fluxes of anti-deuterium and anti-helium nuclei. Here we study the production and transport of such particles, both from astrophysical processes as well as from dark matter annihilation. Importantly, in the case of AMS-02, we find that Alfv\'{e}nic reacceleration (i.e., diffusion in momentum space) can boost the expected number of $\bar{\rm d}$ and ${}^{3}\overline{\textrm{He}}$ events from annihilating dark matter by an order of magnitude or more. For relatively large values of the Alfv\'{e}n speed, and for dark matter candidates that are capable of producing the antiproton and $\gamma$-ray excesses, we expect annihilations to produce a few anti-deuteron events and about one anti-helium event in six years of AMS-02 data. This is particularly interesting in light of recent reports from the AMS-02 Collaboration describing the detection of a number of anti-helium candidate events.

Universal properties of primary and secondary cosmic ray energy spectra

Atomic nuclei appearing in cosmic rays (CRs) are typically classified as primary or secondary. However, a better understanding of their origin and propagation properties is still necessary. We analyse the flux of primary (He, C, O) and secondary nuclei (Li, Be, B) detected with rigidity (momentum/charge) between 2 GV and 3 TV by the alpha magnetic spectrometer on the International Space Station. We show that q-exponential distribution functions, as motivated by generalized versions of statistical mechanics with temperature fluctuations, provide excellent fits for the measured flux of all nuclei considered. Primary and secondary fluxes reveal a universal dependence on kinetic energy per nucleon for which the underlying energy distribution functions are solely distinguished by their effective degrees of freedom. All given spectra are characterized by a universal mean temperature parameter ∼200 MeV which agrees with the Hagedorn temperature. Our analysis suggests that QCD scattering processes together with nonequilibrium temperature fluctuations imprint universally onto the measured CR spectra, and produce a similar shape of energy spectra as high energy collider experiments on the Earth.

Nuclei charge measurement by the Alpha Magnetic Spectrometer silicon tracker

The Alpha Magnetic Spectrometer (AMS) is a high energy particle detector aboard the International Space Station. AMS precisely measures the fluxes of all cosmic-ray nuclei with charge from Z=1 to Z=28 and beyond. The AMS silicon tracker measures energy deposition of charged particles traversing over nine-layer silicon sensors, from L1 to L9. In this paper, the details of the AMS silicon tracker charge measurement method are presented. The obtained charge resolution of the AMS inner tracker (L2 to L8 combined) is 0.1 charge units for carbon, 0.15 charge units for silicon, and 0.3 charge units for iron nuclei.

Optical variability of Active Galactic Nuclei from Catalina Surveys data

The Catalina Real-Time Transients Survey (CRTS) has observed a large fraction of the sky (∼33000 deg2), detecting more than 500 million objects several times, so providing a statistically consistent database of multi-epoch observations of various Galactic and extragalactic sources. Therefore, it is particularly suitable to perform variability studies over different timescales. The analysis of active galactic nuclei (AGN) flux variations provides an invaluable insight on these sources since variability encodes the underlying physics of the emitting regions. In this context, we present an optical variability analysis based on a statistical sample of AGN derived from the crossmatching of a preexistent multi-wavelength based catalogue (Multi-Epoch X-ray Serendipitous AGN Sample 2, or MEXSAS2) with the Catalina Surveys Data Release 2 (CSDR2). Visual inspection of the light curves and a novel estimate of the photometric error associated to the Catalina Sky Surveys have been mandatory to obtain a refined sample of 400 quasars widespread over a large interval of redshift (0.1 < z < 3.4) and bolometric luminosity (1045 erg/s ≲ LBoi ≲ 1048 erg/s). We exploit the structure function (SF) method, which works in the time domain, to investigate the short (few days) to long term (up to ∼ 10 years) variability properties of our sample. Our variability analysis suggests a possible underestimate of the photometric errors, which strongly affect the structure functions.

Measurements of nuclear interaction cross sections with the Alpha Magnetic Spectrometer on the International Space Station

Precise knowledge of nuclear interactions with the detector materials is crucial for the accurate measurements of cosmic-ray nuclei fluxes. We have measured the interaction cross sections on carbon target for various nuclear species with charge 2≤Z≤16 in a wide rigidity (momentum/charge) range from a few GV to TV, using cosmic-ray nuclei events collected by the Alpha Magnetic Spectrometer. The properties of the measured nuclear interaction cross sections are discussed.

AMS-02 beryllium data and its implication for cosmic ray transport

The flux of unstable secondary cosmic ray nuclei, produced by spallation processes in the interstellar medium, can be used to constrain the residence time of cosmic rays inside the Galaxy. Among them, $^{10}$Be is especially useful because of its relatively long half-life of 1.39 Myr. In the framework of the diffusive halo model we describe cosmic ray transport taking into account all relevant interaction channels and accounting for the decay of unstable secondary nuclei. We then compare our results with the data collected by the Alpha Magnetic Spectrometer (AMS-02) on board the International Space Station for the flux ratios Be/C, B/C, Be/O, B/O, C/O and Be/B as well as C, N and O absolute fluxes. These measurements, and especially the Be/B ratio, allow us to single out the flux of $^{10}$Be and infer a best fit propagation time of CRs in the Galaxy. Our results show that, if the cross sections for the production of secondary elements through spallation are taken at face value, AMS-02 measurements are compatible with the standard picture based on CR diffusion in a halo of size $H \gtrsim 5$ kpc. Taking into account the uncertainties in the cross sections, this conclusion becomes less reliable, although still compatible with the standard picture. Implications of our findings for alternative models of CR transport are discussed.

Journey through the birth, growth and maturity of X-ray astronomy

In this biographical account, I recall my scientific journey that began in 1961 when I joined as a Physics Trainee in the BARC Training School and after one year course was admitted in TIFR as a Research Associate. During 1962–1967, I worked on determination of the He3/He4 ratio in cosmic rays using a gas Cerenkov counter and also used a scintillation + solid Cerenkov detector to measure flux of protons and helium nuclei in primary cosmic rays. I also developed a large area scintillation-Cerenkov detector with a spark chamber between them for measuring charge composition of primary cosmic rays. I joined the X-ray astronomy programme in 1967 initiated by Prof. B. V. Sreekantan and played a leading role in developing a balloon borne hard X-ray instrument for studying time variability and energy spectra of cosmic X-ray sources. We carried out a series of balloon experiments and studied temporal intensity variation and energy spectra of X-ray objects like Sco X-1, Cyg X-1, etc. Results on rapid intensity changes and spectra appeared in a series of publications based on which I obtained a Ph.D. degree in 1972. Immediately afterwards, I joined Prof. Gordon Garmire at Caltech as a Research Fellow (a post-doctoral position) to work with him on the low energy component of HEAO A-2 experiment. The instrument was developed and successfully realised. Working on this satellite experiment was a thrilling experience which exposed me to the technical complexities of space instruments. The HEAO-1 satellite was launched in 1978. During 1978–1979, Guenter Riegler and I, working at JPL, reported detection of intense soft X-rays from several classes of extragalactic and Galactic objects like new BL Lacs, a new AM Her binary, coronal X-rays from active stars, etc. After returning to TIFR, I developed a rocket experiment with K. P. Singh to map the spatial and spectral distribution of the Soft Diffuse X-ray Background. At the same time, I also designed 15 cm deep Xenon filled Proportional Counters (XPCs) of ∼ 2500 cm2 area for balloon experiments which were done during 1983–1990 and produced new results on several X-ray binaries. During this period I also developed a proportional counter (PC) based satellite instrument and submitted a proposal jointly with the astronomy group at the Indian Space Research Organization (ISRO) for an Indian X-ray Astronomy Experiment (IXAE). After success of the Polar Satellite Launch Vehicle (PSLV), the IXAE instrument was included on the top deck of the IRS-P3 satellite that was launched in March 1996. Despite the severe limitation of a polar orbit, the IXAE observed a good number of X-ray binaries and produced interesting results, with the most notable being quasi-regular bursts from a new transient, GRS 1915+105, which turned out to be an enigmatic black hole source. Following success of the IXAE, a proposal for an ambitious multiwavelength astronomy satellite, named ASTROSAT, with broad spectral coverage in the optical, NUV, FUV, soft X-ray and hard X-ray by a suite of instruments, was submitted to ISRO and finally approved by the Govt. of India in 2004. Over the next 10 years, the development and fabrication of the five ASTROSAT instruments were accomplished and a PSLV launch on Sept. 28, 2015 placed ASTROSAT in a 650 km circular orbit with 6 degree inclination. The ASTROSAT instruments have been performing well for ∼ 4 years and have observed more than 500 cosmic sources. Results from ASTROSAT have appeared in a large number of journal publications. Successful realization and performance of ASTROSAT marks culmination of my research career. I formally retired as a Senior Professor from TIFR on 2006 April 30 on attaining the age of superannuation. However by agreement with TIFR, ISRO designated me ‘ISRO Chair Professor’, which was later renamed as ISRO Satish Dhawan Professor, and asked me to continue to lead ASTROSAT as PI. At the end of my tenure as ISRO Professor on 2011 April 30, I relinquished the PI position. I am at present affiliated with the MU-DAE Centre of Excellence for Basic Sciences, Mumbai University Campus at Mumbai as an Emeritus Professor.

Interpretation of the excess of antiparticles within a modified paradigm of galactic cosmic rays

We argue that the anomalously high fluxes of positrons and antiprotons found in cosmic rays (CR) can be satisfactorily explained by introducing two additional elements to the current "standard" paradigm of Galactic CRs. First, we propose that the antiparticles are effectively produced in interactions of primary CRs with the surrounding gas not only in the interstellar medium (ISM) but also inside the accelerators. Secondly, we postulate the existence of two source populations injecting CRs into the ISM with different, (1) soft (close to $FI \propto E^{-2.3}$) and (2) hard ($FII \propto E^{-1.8}$ or harder), energy distributions. Assuming that CRs in the 2nd population of accelerators accumulate "grammage" of the order of $1 \ \rm g/cm^2$ before their leakage into ISM, we can explain the energy distributions and absolute fluxes of both positrons and antiprotons, as well as the fluxes of secondary nuclei of the (Li,Be,B) group. The superposition of contributions of two source populations also explains the reported hardening of the spectra of CR protons and nuclei above 200 GV. The 2nd source population accelerating CRs with a rate at the level below 10 percent of the power of the 1st source population, can be responsible for the highest energy protons and nuclei of Galactic CRs up to the "knee" around $10^{15} \ \rm eV$.

Breaks in interstellar spectra of positrons and electrons derived from time-dependent AMS data

Until fairly recently, it was widely accepted that local cosmic ray spectra were largely featureless power laws, containing limited information on their acceleration and transport. This viewpoint is currently being revised in the light of evidence for a variety of spectral breaks in the fluxes of cosmic ray nuclei. Here, we focus on cosmic ray electrons and positrons which at the highest energies must be of local origin due to strong radiative losses. We consider a pure diffusion model for their Galactic transport and determine its free parameters by fitting data in a wide energy range: measurements of the interstellar spectrum by Voyager at MeV energies, radio synchrotron data (sensitive to GeV electrons and positrons) and local observations by AMS up to ~ 1 TeV. For the first time, we also model the time-dependent fluxes of cosmic ray electrons and positrons at GeV energies recently presented by AMS, treating solar modulation in a simple extension of the widely used force-field approximation. We are able to reproduce all the available measurements to date. Our model of the interstellar spectrum of cosmic ray electrons and positrons requires the presence of a number of spectral breaks, both in the source spectra and the diffusion coefficients. While we remain agnostic as to the origin of these spectral breaks, their presence will inform future models of the microphysics of cosmic ray acceleration and transport.