Broken Power Law Research Articles

Success and failure of the spreading law for large drops of dense granular suspensions

The spreading of large viscous drops of density-matched suspensions of non-Brownian spheres on a smooth solid surface is investigated experimentally at the global drop scale. The focus is on dense suspensions with a solid volume fraction equal to or greater than $40\,\%$ , and for drops larger than the capillary length, i.e. for which the spreading is governed by the balance of gravitational and viscous forces. Our findings indicate that all liquids exhibit a power-law behaviour typical of gravity-driven dynamics, albeit with an effective suspension viscosity that is smaller than the bulk value. When the height of the drop is of the order of the particle size, the power law breaks down as the particles freeze while the contact line continues to advance.

Origin of the break in the cosmic-ray electron plus positron spectrum at ∼1 TeV

Recent measurements of the cosmic-ray electron plus positron spectrum in several experiments have confirmed the presence of a break at ∼1 TeV. The origin of the break is still not clearly understood. In this work, we explored different possibilities for the origin, which include an electron source spectrum with a broken power law, a power law with an exponential or super-exponential cutoff, and the absence of potential nearby cosmic-ray sources. Based on the observed electron plus positron data from the DAMPE and the H.E.S.S experiments, and considering supernova remnants as the main sources of cosmic rays in the Galaxy, we find statistical evidence in favor of the scenario with a broken power-law source spectrum, with the best-fit source parameters obtained as Γ = 2.39 for the source spectral index, E0 ≈ 1.6 TeV for the break energy, and f = 1.59 × 1048 ergs for the amount of supernova kinetic energy injected into cosmic-ray electrons. This power-law break in the spectrum has been predicted for electrons confined inside supernova remnants after acceleration via diffusive shock acceleration process, and also indicated by the multi-wavelength study of supernova remnants. All of this evidence shows that the observed spectral break provides a strong indication of a direct link between cosmic-ray electrons and their sources. Our findings further show that electrons must undergo spectral changes while escaping the source region in order to reconcile the difference between the spectral index of electrons observed inside supernova remnants and that obtained from Galactic cosmic-ray propagation studies.

Evidence for hybrid gamma-ray emission from the supernova remnant G150.3+4.5

The supernova remnant (SNR) G150.3+4.5 was first identified in radio, exhibiting a hard GeV spectrum and a ~1.5º radius. Radio observations revealed a bright arc with an index of ~−0.40, which stands in contrast to the index of ~−0.69 for the rest. This arc is coincident with the point-like Fermi source 4FGL J0426.5+5434 and KM2A source 1LHAASO J0428+5531. The rest of the SNR has a hard GeV spectrum and a soft TeV spectrum, implying a spectral cut-off or break near 1 TeV. Since there is no X-ray counterpart and no pulse signal detected, the gamma-ray (γ-ray) emission mechanism from the SNR and the point-like source appear puzzling. In this work, we reanalyse the γ-ray emission using 14 yr data recorded by Fermi Large Area Telescope and find that the spectrum of the northern half-sphere is compatible with a broken power law with a break at 146 ± 11 eV and photon indices of ΓNorthlobe = 1.54 ± 0.04stat ± 0.07syst (2.28 ± 0.08stat ± 0.12syst) below (above) the break. In addition, the southern half-sphere can be described well with a single power law with ΓSouthlobe =1.95 ± 0.07stat ± 0.09syst. Since the southern half-sphere is well correlated with CO emission, we propose that the γ-ray emission of the northern half-sphere could be dominated by relativistic electrons via inverse-Compton processes, while the southern half-sphere is dominated by cosmic rays via hadronic processes. 4FGL J0426.5+5434 may result from the illumination of a cloud by escaping cosmic rays or recent shock-cloud interaction. Observations from LHAASO-KM2A thus favour the possibility of a cosmic-ray PeVatron candidate, however, leptonic scenarios cannot be ruled out. Further multi-wavelength observations are warranted to confirm the hadronic nature of 1LHAASO J4028+5531.

Photometric classification of stars around the Milky Way’s central black hole

Context. The presence of young massive stars in the Galactic Centre (GC) raises questions about how such stars could form near the massive black hole Sagittarius A* (Sgr A*). Furthermore, the shape of the initial mass function (IMF) in this region seems to differ from its standard Salpeter/Kroupa law. Due to observational challenges such as extreme extinction and crowding, our understanding of the stellar population in this region remains limited, with spectroscopic data available only for selected small and comparably bright sources. Aims. We aim to improve our knowledge about the distribution and the IMF of young, massive, stars in the vicinity of Sgr A*. Methods. We used intermediate band (IB) photometry to identify candidates for massive young stars. To ensure robust classification, we applied three different, but complementary methods: Bayesian inference, a basic neural network, and a fast gradient-boosted trees algorithm. Results. We obtain spectral energy distributions for 6590 stars, 1181 of which have been previously classified spectroscopically. We identify 351 stars that are classified as early types by all three classification methods, with 155 of them being newly identified candidates. The radial density profiles for late and early-type stars fit well with broken power laws, revealing a break radius of 9.2 ± 0.6″ for early-type stars. The late-type stars show a core-like distribution around Sgr A* while the density of the early-type stars increases steeply towards the black hole, consistent with previous work. We infer a top-heavy IMF of the young stars near Sgr A* (R < 9″), with a power-law of 1.6 ± 0.1. At greater distances from Sgr A* a standard Salpeter/Kroupa IMF can explain the data. Additionally, we demonstrate that IB photometry can also constrain the metallicities of late-type stars, estimating metallicities for over 600 late-type stars. Conclusions. The variation of the IMF with radial distance from Sgr A* suggests that different mechanisms of star formation may have been at work in this region. The top-heavy IMF in the innermost region is consistent with star formation in a disc around Sgr A*.

Concurrent Particle Acceleration and Pitch-angle Anisotropy Driven by Magnetic Reconnection: Ion-electron Plasmas

Particle acceleration and pitch-angle anisotropy resulting from magnetic reconnection are investigated in highly magnetized ion-electron plasmas. By means of fully kinetic particle-in-cell simulations, we demonstrate that magnetic reconnection generates anisotropic particle distributions fs∣cosα∣,ε , characterized by broken power laws in the particle energy spectrum f s (ε) ∝ ε −p and pitch angle 〈sin2α〉∝εm . The characteristics of these distributions are determined by the relative strengths of the magnetic field’s guide and reconnecting components (B g /B 0) and the plasma magnetization (σ 0). Below the injection break energy ε 0, ion and electron energy spectra are extremely hard (p < ≲ 1) for any B g /B 0 and σ 0 ≳ 1, while above ε 0 the spectral index steepens (p > ≳ 2), displaying high sensitivity to both B g /B 0 and σ 0. The pitch angle displays power-law ranges with negative slopes (m <) below and positive slopes (m >) above εminα , steepening with increasing B g /B 0 and σ 0. The ratio B g /B 0 regulates the redistribution of magnetic energy between ions (ΔE i ) and electrons (ΔE e ), with ΔE i ≫ ΔE e for B g /B 0 ≪ 1, ΔE i ∼ ΔE e for B g /B 0 ∼ 1, and ΔE i ≪ ΔE e for B g /B 0 ≫ 1, with ΔE i /ΔE e approaching unity when σ 0 ≫ 1. The anisotropic distribution of accelerated particles results in an optically thin synchrotron power spectrum F ν (ν) ∝ ν (2−2p+m)/(4+m) and a linear polarization degree Πlin = (p + 1)/(p + 7/3 + m/3) for a uniform magnetic field. Pitch-angle anisotropy also induces temperature anisotropy and eases synchrotron cooling, along with producing beamed radiation aligned with the magnetic field, which is potentially responsible for rapid frequency-dependent variability.

Statistical Analysis of Pulsar Flux Density Distribution

This study presents a comprehensive analysis of the spectral properties of 886 pulsars across a wide frequency range from 20 MHz–343.5 GHz, including a total of 86 millisecond pulsars (MSPs). The majority of the pulsars exhibit power-law behavior in their spectra, although some exceptions are observed. Five different spectral models, namely, simple power law, broken power law, low-frequency turnover, high-frequency cutoff, and double turnover, were employed to explore the spectral behaviors. The average spectral index for pulsars modeled with a simple power law is found to be −1.64 ± 0.80, consistent with previous studies. Additionally, significant correlations between the spectral index and characteristic parameters are observed, particularly in MSPs, while no strong correlation is observed in normal pulsars. Different models show variations in the most influential characteristic parameters associated with the spectral index, indicating diverse dominant radiation mechanisms in MSPs. Finally, this study identifies 22 pulsars of the gigahertz-peaked spectra type for the first time based on the Akaike information criterion.

Compound models and Pearson residuals for single-cell RNA-seq data without UMIs.

Recent work employed Pearson residuals from Poisson or negative binomial models to normalize UMI data. To extend this approach to non-UMI data, we model the additional amplification step with a compound distribution: we assume that sequenced RNA molecules follow a negative binomial distribution, and are then replicated following an amplification distribution. We show how this model leads to compound Pearson residuals, which yield meaningful gene selection and embeddings of Smart-seq2 datasets. Further, we suggest that amplification distributions across several sequencing protocols can be described by a broken power law. The resulting compound model captures previously unexplained overdispersion and zero-inflation patterns in non-UMI data.

Evidence for particle acceleration approaching PeV energies in the W51 complex

The γ-ray emission from the W51 complex is widely acknowledged to be attributed to the interaction between the cosmic rays (CRs) accelerated by the shock of supernova remnant (SNR) W51C and the dense molecular clouds in the adjacent star-forming region, W51B. However, the maximum acceleration capability of W51C for CRs remains elusive. Based on observations conducted with the Large High Altitude Air Shower Observatory (LHAASO), we report a significant detection of γ rays emanating from the W51 complex, with energies from 2 to 200 TeV. The LHAASO measurements, for the first time, extend the γ-ray emission from the W51 complex beyond 100 TeV and reveal a significant spectrum bending at tens of TeV. By combining the “π0-decay bump” featured data from Fermi-LAT, the broadband γ-ray spectrum of the W51 region can be well-characterized by a simple pp-collision model. The observed spectral bending feature suggests an exponential cutoff at ∼400 TeV or a power-law break at ∼200 TeV in the CR proton spectrum, most likely providing the first evidence of SNRs serving as CR accelerators approaching the PeV regime. Additionally, two young star clusters within W51B could also be theoretically viable to produce the most energetic γ rays observed by LHAASO. Our findings strongly support the presence of extreme CR accelerators within the W51 complex and provide new insights into the origin of Galactic CRs.

A Systematic Analysis of the X-Ray Emission in Optically Selected Tidal Disruption Events: Observational Evidence for the Unification of the Optically and X-Ray-selected Populations

We present a systematic analysis of the X-ray emission of a sample of 17 optically selected, X-ray-detected tidal disruption events (TDEs) discovered between 2014 and 2021. The X-ray light curves show a diverse range of temporal behaviors, with most sources not following the expected power-law decline. The X-ray spectra are mostly extremely soft and consistent with thermal emission from the innermost region of an accretion disk, which cools as the accretion rate decreases. Three sources show formation of a hard X-ray corona at late times. The spectral energy distribution shape, probed by the ratio (L BB/L X) between the UV/optical and X-ray, shows a wide range of L BB/L X ∈ (0.5, 3000) at early times and converges to disklike values of L BB/L X ∈ (0.5, 10) at late times. We estimate the fraction of optically discovered TDEs with L X ≥ 1042 erg s−1 to be at least 40% and show that X-ray loudness is independent of black hole mass. We argue that distinct disk formation timescales are unlikely to be able to explain the diverse range of X-ray evolution. We combine our sample with X-ray-discovered ones to construct an X-ray luminosity function, best fit by a broken power law, with a break at L X ≈ 1044 erg s−1. We show that there is no dichotomy between optically and X-ray-selected TDEs; instead, there is a continuum of early-time L BB/L X, at least as wide as L BB/L X ∈ (0.1, 3000), with optical/X-ray surveys selecting preferentially, but not exclusively, from the higher/lower end of the distribution. Our findings are consistent with unification models for the overall TDE population.

Taking the pulse of the outer Milky Way with the Halo Outskirts With Variable Stars (HOWVAST) survey: an RR Lyrae density profile out to &amp;gt;200 kpc

ABSTRACT In order to constrain the evolutionary history of the Milky Way, we hunt for faint RR Lyrae stars (RRLs) using Dark Energy Camera data from the High cadence Transient Survey and the Halo Outskirts With Variable Stars survey. We report the detection of $\sim$500 RRLs, including previously identified stars and $\sim$90 RRLs not yet reported. We identify nine new RRLs beyond 100 kpc from the Sun, most of which are classified as fundamental-mode pulsators. The periods and amplitudes of the distant RRLs do not place them in either one of the two classical Oosterhoff groups, but in the Oosterhoff intermediate region. We detect two groups of clumped distant RRLs with similar distances and equatorial coordinates, which we interpret as an indication of their association with undiscovered bound or unbound satellites. We study the halo density profile using spheroidal and ellipsoidal ($q=0.7$) models, following a Markov chain Monte Carlo methodology. For a spheroidal halo, our derived radial profile is consistent with a broken power law with a break at $18.1^{+2.1}_{-1.1}$ kpc separating the inner and the outer halo, and an outer slope of $-4.47^{+0.11}_{-0.18}$. For an ellipsoidal halo, the break is located at $24.3^{+2.6}_{-3.2}$ kpc and the outer slope is $-4.57^{+0.17}_{-0.25}$. The break in the density profile is a feature visible in different directions of the halo. The similarity of these radial distributions with previous values reported in the literature seems to depend on the regions of the sky surveyed (direction and total area) and halo tracer used. Our findings are compatible with simulations and observations that predict that the outer regions of Milky Way-like galaxies are mainly composed of accreted material.

The On-axis Jetted Tidal Disruption Event AT2022cmc: X-Ray Observations and Broadband Spectral Modeling

AT2022cmc was recently reported as the first on-axis jetted tidal disruption event (TDE) discovered in the last decade, and the fourth on-axis jetted TDE candidate known so far. In this work, we present NuSTAR hard X-ray (3–30 keV) observations of AT2022cmc, as well as soft X-ray (0.3–6 keV) observations obtained by NICER, Swift, and XMM-Newton. Our analysis reveals that the broadband X-ray spectra can be well described by a broken power law with f ν ∝ ν −0.5 (f ν ∝ ν −1) below (above) the rest-frame break energy of E bk ∼ 10 keV at the observer frame t obs = 7.8 and 17.6 days since discovery. At t obs = 36.2 days, the X-ray spectrum is consistent with either a single power law or a broken power law. By modeling the spectral energy distribution from radio to hard X-ray across the three NuSTAR observing epochs, we find that the submillimeter/radio emission originates from external shocks at large distances ≳1017 cm from the black hole, the UV/optical light comes from a thermal envelope with radius ∼1015 cm, and the X-ray emission is consistent with synchrotron radiation powered by energy dissipation at intermediate radii within the (likely magnetically dominated) jet. We constrain the bulk Lorentz factor of the jet to be of the order 10–100. Our interpretation differs from the model proposed by Pasham et al. where both the radio and X-rays come from the same emitting zone in a matter-dominated jet. Our model for the jet X-ray emission has broad implications on the nature of relativistic jets in other sources such as gamma-ray bursts.

The Initial Conditions of Clustered Core Collapse: Multiwavelength Analysis of Oph A SM1N and N6 at 100 au Resolution

We present new Atacama Large Millimeter/submillimeter Array (ALMA) continuum and NH2D, N2D+, and H2D+ line emission at matched, ∼100 au resolution toward the dense star-forming cores SM1N and N6 within the Ophiuchus molecular cloud. We determine the density and temperature structure of SM1N based on radiative transfer modeling and simulated observations of the multiwavelength continuum emission at 0.8, 2, and 3 mm. We show that SM1N is best fit by either a broken power-law or Plummer-like density profile with high central densities (n ∼ 108 cm−3), and an inner transition radius of only ∼80–300 au. The free-fall time of the inner region is only a few ×103 yr. The continuum modeling rules out the presence of an embedded first hydrostatic core (FHSC) or protostar. SM1N is therefore a dynamically unstable but still starless core. We find that NH2D is likely depleted at high densities within SM1N. The nonthermal velocity dispersions increase from NH2D to N2H+ and H2D+, possibly tracing increasing (but still subsonic) infall speeds at higher densities as predicted by some models of starless core contraction. Toward N6, we confirm the previous ALMA detection of a faint, embedded point source (N6-mm) in 0.8 mm continuum emission. NH2D and N2D+ avoid N6-mm within ∼100 au, while H2D+ is not strongly detected toward N6. The distribution of these tracers is consistent with heating by a young, warm object. N6-mm thus remains one of the best candidate FHSCs detected so far, although its observed (sub)millimeter luminosity remains below predictions for FHSCs.

Radio spectra of pulsars fitted with the spectral distribution function of the emission from their current sheet

ABSTRACT In their catalogue of pulsars’ radio spectra, Swainston et al. distinguish between five different forms of these spectra: those that can be fitted with (i) a simple power law, (ii) a broken power law, (iii) a low-frequency turn-over, (iv) a high-frequency turn-over or (v) a double turn-over spectrum. Here, we choose two examples from each of these categories and fit them with the spectral distribution function of the caustics that are generated by the superluminally moving current sheet in the magnetosphere of a non-aligned neutron star. In contrast to the prevailing view that the curved features of pulsars’ radio spectra arise from the absorption of the observed radiation in high-density environments, our results imply that these features are intrinsic to the emission mechanism. We find that all observed features of pulsar spectra (including those that are normally fitted with simple or broken power laws) can be described by a single spectral distribution function and regarded as manifestations of a single emission mechanism. From the results of an earlier analysis of the emission from a pulsar’s current sheet and the values of the fit parameters for each spectrum, we also determine the physical characteristics of the central neutron star of each considered example and its magnetosphere.

Likelihood of white dwarf binaries to dominate the astrophysical gravitational wave background in the mHz band

Context. The astrophysical gravitational wave background (AGWB) is a collective signal of astrophysical gravitational wave sources dominated by compact binaries. One key science goal of current and future gravitational wave detectors is to obtain its measurement. Aims. We aim to determine the population of compact binaries dominating the AGWB in the mHz band. We revisit and update an earlier work by Farmer &amp; Phinney (2003, MNRAS, 346, 1197) to model the astrophysical gravitational wave background sourced by extragalactic white dwarf binaries in the mHz frequency band. Methods. We calculated the signal using a single-metallicity model for the white dwarf population in the Universe using the global star formation history. Results. We estimate the white dwarf AGWB amplitude to be ∼60% higher than the earlier estimate. We also find that the overall shape of the white dwarf AGWB shows a good fit with a broken power law combined with an exponential cut-off. Conclusions. We compare our results to present-day best estimates for the background due to black hole and neutron star binaries, finding that the white dwarf component is likely to dominate in the mHz band. We provide an order-of-magnitude estimate that explains this hierarchy and we comment on the implications for future missions that aim to detect the AGWB. We also note that the black hole AGWB may only be detectable at high frequency. We outline several improvements that can be made to our estimate, however, these points are unlikely to change our main conclusion, which posits that the white dwarf AGWB dominates the mHz band.

Impact of discontinuous grain size distributions on the spectral energy distribution of debris disks

Context. The collisional evolution of debris disks is expected to cause the characteristic wavy pattern, that is, an under- or overabundance of particles of specific sizes, of grain size distributions. This perturbed grain size distribution potentially leaves characteristic patterns in the spectral energy distribution (SED) of the disk system. Aims. We aim to quantify and understand the specific influence of discontinuous particle size distributions on the appearance of debris disks. For this purpose, we considered dust emission models based on two different grain size distributions, namely, one with a single power law and one with a broken power law. In particular, our study is focused on the impact of an overabundance of small grains and an underabundance of medium-sized grains on the far-IR and (sub-)millimeter regime on the dust reemission radiation and the potential to constrain discontinuities in the grain size distribution from (sub-)millimeter photometric measurements of debris disks. Methods. We compared the spectral index α (Fν ∝ να) in the case of a continuous grain size distribution with that of a discontinuous grain size distribution. We performed this comparison for central stars with different spectral types and two different disk structures (e.g., slim and broad debris dust rings). Results. Within the considered parameter space, we found a characteristic difference between the spectral slopes of the SED in the different scenarios. In particular, the overabundance of small grains resulting from collisional events and thus parameters defining the outcome of disk events in debris disks is potentially observable by comparison with the SED corresponding to a grain size distribution resulting from an ideal collisional cascade. More specifically, the overabundance of small grains leads to a steeper slope in the far-IR and sub-millimeter regime, while the spectral index in the millimeter regime is hardly affected. On the other hand, the underabundance of medium-sized grains results in a slight steepening of the far-IR slope of the SED, but its primary effect is on the millimeter slope of the SED, causing it to become shallower. We also found that the impact of an overabundance of small dust particles is more pronounced than that of an underabundance of medium-sized dust particles. We also found that the difference between the spectral indices for the two different grain size distributions is largest for debris disks around brighter central stars and broader disks. However, the impact of the considered spatial distributions described by the fractional width of the disk system is weak. Our results also show that the dust composition is not the sole physical mechanism responsible for the spectral inversion observed in the far-IR to millimeter part of the SED of debris disk systems. Furthermore, the location of the spectral break is placed at different wavelength regimes if the grain size distribution is considered as a function of blowout size and stellar type.

Observations of Nine Millisecond Pulsars at 8600 MHz Using the TMRT

We report detection results of nine millisecond pulsars (MSPs) at 8600 MHz using simultaneous 2250 and 8600 MHz observations conducted with the Shanghai Tian Ma Radio Telescope. Mainly benefiting from updated ephemerids with 2250 MHz observations, integrated profiles of all nine MSPs at 8600 MHz are successfully obtained by coherently adding multi-epoch (3–83 epochs) observation data spanning from 19–1210 days, which significantly increases the number of MSPs with published profiles (from 4 to 11) above 8000 MHz, as seven of our target MPSs had no related results previously. Combining our new flux density and pulse width measurements with previous low-frequency results, we study their integrated profile evolution and spectral behaviors in a wider frequency range. We find their component separations and pulse widths remain almost constant, which is consistent with previous findings. While dramatic evolution of integrated profiles exists at low frequencies, we observe a potential end of the related evolution around 5 GHz in eight MSPs. The spectra of four MSPs are found to deviate from a single power law, and we fit them with a broken power law. The change in the profile of PSR J1713+0747, which started around MJD 59320−59321, seems to be more prominent as the observation frequency increases. Compared with the effects of the interstellar medium, we prefer to explain this event as some changes in the magnetosphere. We also find its integrated profile possibly had not recovered to the pre-event state until MJD 59842–59857.

TeV Neutrinos and Hard X-Rays from Relativistic Reconnection in the Corona of NGC 1068

The recent discovery of astrophysical neutrinos from the Seyfert galaxy NGC 1068 suggests the presence of nonthermal protons within a compact “coronal” region close to the central black hole. The acceleration mechanism of these nonthermal protons remains elusive. We show that a large-scale magnetic reconnection layer, of the order of a few gravitational radii, may provide such a mechanism. In such a scenario, rough energy equipartition between magnetic fields, X-ray photons, and nonthermal protons is established in the reconnection region. Motivated by recent 3D particle-in-cell simulations of relativistic reconnection, we assume that the spectrum of accelerated protons is a broken power law, with the break energy being constrained by energy conservation (i.e., the energy density of accelerated protons is at most comparable to the magnetic energy density). The proton spectrum is dnp/dEp∝Ep−1 below the break and dnp/dEp∝Ep−s above the break, with IceCube neutrino observations suggesting s ≃ 3. Protons above the break lose most of their energy within the reconnection layer via photohadronic collisions with the coronal X-rays, producing a neutrino signal in good agreement with the recent observations. Gamma rays injected in photohadronic collisions are cascaded to lower energies, sustaining the population of electron–positron pairs that makes the corona moderately Compton thick.

The Structure Function of Mid-infrared Variability in Low-redshift Active Galactic Nuclei

Using the multi-epoch mid-infrared (MIR) photometry from the Wide-field Infrared Survey Explorer spanning a baseline of ∼10 yr, we extensively investigate the MIR variability of nearby active galactic nuclei (AGNs) at 0.15 < z < 0.4. We find that the ensemble structure function in the W1 band (3.4 μm) can be modeled with a broken power law. Type 1 AGNs tend to exhibit larger variability amplitudes than type 2 AGNs, possibly due to the extinction by the torus. The variability amplitude is inversely correlated with the AGN luminosity, consistent with a similar relation known in the optical. Meanwhile, the slope of the power law increases with AGN luminosity. This trend can be attributed to the fact that the inner radius of the torus is proportional to the AGN luminosity, as expected from the size−luminosity relation of the torus. Interestingly, low-luminosity type 2 AGNs, unlike low-luminosity type 1 AGNs, tend to exhibit smaller variability amplitude than do high-luminosity AGNs. We argue that either low-luminosity type 2 AGNs have distinctive central structures due to their low luminosity or their MIR brightness is contaminated by emission from the cold dust in the host galaxy. Our findings suggest that the AGN unification scheme may need to be revised. We find that the variability amplitude of dust-deficient AGNs is systematically larger than that of normal AGNs, supporting the notion that the hot and warm dust in dust-deficient AGNs may be destroyed and reformed according to the strength of the ultraviolet radiation from the accretion disk.

The Panchromatic Hubble Andromeda Treasury: Triangulum Extended Region (PHATTER). V. The Structure of M33 in Resolved Stellar Populations

We present a detailed analysis of the structure of the Local Group flocculent spiral galaxy M33, as measured using the Panchromatic Hubble Andromeda Treasury Triangulum Extended Region (PHATTER) survey. Leveraging the multiwavelength coverage of PHATTER, we find that the oldest populations are dominated by a smooth exponential disk with two distinct spiral arms and a classical central bar—completely distinct from what is seen in broadband optical imaging, and the first-ever confirmation of a bar in M33. We estimate a bar extent of ∼1 kpc. The two spiral arms are asymmetric in orientation and strength, and likely represent the innermost impact of the recent tidal interaction responsible for M33's warp at larger scales. The flocculent multiarmed morphology for which M33 is known is only visible in the young upper main-sequence population, which closely tracks the morphology of the interstellar medium. We investigate the stability of M33's disk, finding Q ∼ 1 over the majority of the disk. We fit multiple components to the old stellar density distribution and find that, when considering recent stellar kinematics, M33's bulk structure favors the inclusion of an accreted halo component, modeled as a broken power law. The best-fit halo has an outer power-law index of −3 and accurately describes observational evidence of M33's stellar halo from both resolved stellar spectroscopy in the disk and its stellar populations at large radius. Integrating this profile yields a total halo stellar mass of ∼5 × 108 M ⊙, for a stellar halo mass fraction of 16%, most of which resides in the innermost 2.5 kpc.

Injection Spectra of Different Species of Cosmic Rays from AMS-02, ACE-CRIS and Voyager-1

Precise measurements of energy spectra of different cosmic ray (CR) species have been obtained in recent years, by particularly the AMS-02 experiment on the International Space Station. It has been shown that apparent differences exist in different groups of the primary CRs. However, it is not straightforward to conclude that the source spectra of different particle groups are different since they will experience different propagation processes (e.g., energy losses and fragmentations) either. In this work, we study the injection spectra of different nuclear species using the measurements from Voyager-1 outside the solar system, and ACR-CRIS and AMS-02 on the top of atmosphere, in a physical framework of CR transportation. Two types of injection spectra are assumed, the broken power-law (BPL) form and the non-parametric spline interpolation form. The non-parametric form fits the data better than the BPL form, implying that potential structures beyond the constrained spectral shape of BPL may exist. For different nuclei the injection spectra are overall similar in shape but do show some differences among each other. For the non-parametric spectral form, the helium injection spectrum is the softest at low energies and the hardest at high energies. For both spectral shapes, the low-energy injection spectrum of neon is the hardest among all these species, and the carbon and oxygen spectra have more prominent bumps in 1–10 GV in the presentation. Such differences suggest the existence of differences in the sources or acceleration processes of various nuclei of CRs.