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The photospheric emission in the prompt phase is the natural prediction of the original fireball model for gamma-ray burst (GRB) due to the large optical depth ($\tau >1$) at the base of the outflow, which is supported by the quasi-thermal components detected in several Fermi GRBs. However, which radiation mechanism (photosphere or synchrotron) dominates in most GRB spectra is still under hot debate. The shape of the observed photosphere spectrum from a pure hot fireball or a pure Poynting-flux-dominated outflow has been investigated before. In this work, we further study the photosphere spectrum from a hybrid outflow containing both a thermal component and a magnetic component with moderate magnetization ($\sigma_{0}=L_{P}/L_{\text{Th}}\sim 1-10$), by invoking the probability photosphere model. The high-energy spectrum from such a hybrid outflow is a power law rather than an exponential cutoff, which is compatible with the observed Band function in large amounts of GRBs. Also, the distribution of the low-energy indices (corresponding to the peak-flux spectra) is found to be quite consistent with the statistical result for the peak-flux spectra of GRBs best-fitted by the Band function, with similar angular profiles of structured jet in our previous works. Finally, the observed distribution of the high-energy indices can be well understood after considering the different magnetic acceleration (due to magnetic reconnection and kink instability) and the angular profiles of dimensionless entropy with the narrower core., Comment: 14 pages, 10 figures, published in MNRAS

Black-hole (BH) accretion disks formed in compact-object mergers or collapsars may be major sites of the rapid-neutron-capture (r-)process, but the conditions determining the electron fraction (Y_e) remain uncertain given the complexity of neutrino transfer and angular-momentum transport. After discussing relevant weak-interaction regimes, we study the role of neutrino absorption for shaping Y_e using an extensive set of simulations performed with two-moment neutrino transport and again without neutrino absorption. We vary the torus mass, BH mass and spin, and examine the impact of rest-mass and weak-magnetism corrections in the neutrino rates. We also test the dependence on the angular-momentum transport treatment by comparing axisymmetric models using the standard alpha-viscosity with viscous models assuming constant viscous length scales (l_t) and three-dimensional magnetohydrodynamic (MHD) simulations. Finally, we discuss the nucleosynthesis yields and basic kilonova properties. We find that absorption pushes Y_e towards ~0.5 outside the torus, while inside increasing the equilibrium value Y_e^eq by ~0.05-0.2. Correspondingly, a substantial ejecta fraction is pushed above Y_e=0.25, leading to a reduced lanthanide fraction and a brighter, earlier, and bluer kilonova than without absorption. More compact tori with higher neutrino optical depth, tau, tend to have lower Y_e^eq up to tau~1-10, above which absorption becomes strong enough to reverse this trend. Disk ejecta are less (more) neutron-rich when employing an l_t=const. viscosity (MHD treatment). The solar-like abundance pattern found for our MHD model marginally supports collapsar disks as major r-process sites, although a strong r-process may be limited to phases of high mass-infall rates, Mdot>~ 2 x 10^(-2) Msun/s., 37 pages, 22 figures, 5 tables, accepted to MNRAS, minor changes compared to previous version

The first generation (Pop-III) stars can ionize 1-10% of the universe by $z=15$, when the metal-enriched (Pop-II) stars may contribute negligibly to the ionization. This low ionization tail might leave detectable imprints on the large-scale CMB E-mode polarization. However, we show that physical models for reionization are unlikely to be sufficiently extended to detect any parameter beyond the total optical depth through reionization. This result is driven in part by the total optical depth inferred by Planck, indicating a reionization midpoint around $z=8$, which in combination with the requirement that reionization completes by $z\approx 5.5$ limits the amplitude of an extended tail. To demonstrate this, we perform semi-analytic calculations of reionization including Pop-III star formation in minihalos with Lyman-Werner feedback. We find that standard Pop-III models need to produce very extended reionization at $z>15$ to be distinguishable at 2-$��$ from Pop-II-only models, assuming a cosmic variance-limited measurement of the low-$\ell$ EE power spectrum. However, we show that unless there is (1) a late-time quenching mechanism such as from strong X-ray feedback or (2) some other extreme Pop-III scenario, structure formation makes it quite challenging to produce high enough Thomson scattering optical depth from $z>15$, $��(z>15)$, and still be consistent with other observational constraints on reionization., 11 pages 4 figures + appendix

We present a new release of the RELTRANS model to fit the complex cross-spectrum of accreting black holes as a function of energy. The model accounts for continuum lags and reverberation lags self-consistently in order to consider the widest possible range of X-ray variability timescales. We introduce a more self-consistent treatment of the reverberation lags, accounting for how the time variations of the illuminating flux change the ionisation level of the accretion disc. This process varies the shape of the reflection spectrum in time causing an additional source of lags besides the light crossing delay. We also consider electron densities in the accretion disc up to $10^{20}$ cm$^{-3}$, which are found in most of the stellar mass black holes and in some AGN. These high densities increase the amplitude of the reverberation lags below $1$ keV since the reflection flux enhances in the same energy range. In addition, we investigate the properties of hard lags produced by variations in the power-law index of the continuum spectrum, which can be interpreted as due to roughly $3\%$ variability in the corona's optical depth and temperature. As a test case, we simultaneously fit the lag energy spectra in a wide range of Fourier frequency for the black hole candidate MAXI J1820+070 observed with NICER. The best fit shows how the reverberation lags contribute even at the longer timescales where the hard lags are important. This proves the importance of modelling these two lags together and self-consistently in order to constrain the parameters of the system., Accepted for publication in MNRAS

We present results of phase- and time-resolved study of iron spectral features in the emission of the Be/X-ray transient pulsar V0332+53, during its type II outburst in 2004 using archival RXTE/PCA data. Coherent pulsations of both fluorescent iron line at {\approx}6.4 keV and neutral iron K-edge at {\approx}7.1 keV have been detected throughout the entire outburst. The pulsating iron K-edge is reported for the first time for this object. Near the peak of the outburst, the 3-12 keV pulse profile shows two deep, F_max / F_min ~ 2, and narrow dips of nearly identical shape, separated by exactly {\Delta}{\phi}=0.5 in phase. The dip spectra are nearly identical to each other and very similar in shape to the spectra outside the dips. The iron K-edge peaks at the phase intervals corresponding to the dips, although its optical depth {\tau}_K ~ 0.05 is by far insufficient to explain the dips. The iron line shows pulsations with a complex pulse profile without any obvious correlation with the total flux or optical depth of the K-edge. Accounting for the component associated with reprocessing of the pulsar emission by the surface of the donor star and circumstellar material, we find a very high pulsation amplitude of the iron line flux, F_max / F_min ~ 10. We demonstrate that these properties of V0332+53 can not be explained by contemporary emission models for accreting X-ray pulsars and speculate about the origin of the observed iron spectral features., Comment: 16 pages, 6 figures. Monthly Notices of the Royal Astronomical Society Main Journal Accepted

In this article, we study the effect of various environmental factors on intra-atomic frequency comb (I-AFC) based quantum memory. The effect of the environment is incorporated as random fluctuations and non-uniformity in the parameters such as comb spacing and the optical depth, of the frequency comb. We found that the I-AFC is viable for photon storage even for very large fluctuations in the parameters of the frequency comb, which makes I-AFC a robust platform for photon storage. Furthermore, we show that the non-uniform frequency combs without any fluctuations in the comb parameters can also yield efficient quantum memory. Since the intra-atomic frequency combs found in natural atomic systems are often non-uniform, our results suggest that a large class of these systems can be used for I-AFC based efficient quantum memory.

We present the results of our spectral and timing analysis of the emission from the transient X-ray pulsar XTE J1946+274 based on the simultaneous NuSTAR and Swift/XRT observations in the broad energy range 0.3-79 keV carried out in June 2018 during a bright outburst. Our spectral analysis has confirmed the presence of a cyclotron absorption line at an energy $\sim38$ keV in both averaged and phase-resolved spectra of the source. Phase-resolved spectroscopy has also allowed the variation in spectral parameters with neutron star rotation phase, whose period is $\simeq15.755$ s, to be studied. The energy of the cyclotron line is shown to change significantly (from $\simeq34$ to $\simeq39$ keV) on the scale of a pulse, with the line width and optical depth also exhibiting variability. The observed behavior of the cyclotron line parameters can be interpreted in terms of the model of the reflection of emission from a small accretion column (the source's luminosity at the time of its observations was $\sim 3 \times 10^{37}$ erg s$^{-1}$) off the neutron star surface. The equivalent width of the iron line has been found to also change significantly with pulse phase. The time delay between the pulse and equivalent width profiles can be explained by the reflection of neutron star emission from the outer accretion disk regions., 19 pages, 7 figures, 1 table

We examine general relativistic radiatively-driven spherical winds, using the basic equations for relativistic radiation hydrodynamics under the moment formalism. Moment equations are often closed, using the equilibrium diffusion approximation, which has an acausal problem, and furthermore, gives nodal-type critical points. Instead, we use the nonequilibrium diffusion approximation with a closure relation of a variable Eddington factor, $f(\tau,\beta)$, where $\tau$ is the optical depth and $\beta$ is the flow speed normalized by the speed of light. We then analyze the critical properties in detail for several parameters, and found that there appear saddle-type critical points as well as nodal type and spiral one. The most suitable type is the saddle one, which appears in a region close to a black hole. We also calculate transonic solutions with typical parameters, and show that the luminosity is almost comparable to the Eddington luminosity, the gas is quickly accelerated in the vicinity of the black hole, and wind terminal speeds are on the order of 0.1$-$0.3$~c$. These results of radiatively-driven black hole winds can be applied, e.g., to ultra-fast outflows (UFOs), which are supposed to be fast outflows from the vicinity of super massive black holes., Comment: 12 pages, 15 figures, published in MNRAS, some typos in equation (10) of the published article have been corrected

Using the latest upper limits on the 21-cm power spectrum at $z\approx9.1$ from the Low Frequency Array (LOFAR), we explore regions of parameter space which are inconsistent with the data. We use 21CMMC, a Monte Carlo Markov Chain sampler of 21cmFAST which directly forward models the 3D cosmic 21-cm signal in a fully Bayesian framework. We use the astrophysical parameterisation from 21cmFAST, which includes mass-dependent star formation rates and ionising escape fractions as well as soft-band X-ray luminosities to place limits on the properties of the high-$z$ galaxies. Further, we connect the disfavoured regions of parameter space with existing observational constraints on the Epoch of Reionisation such as ultra-violet (UV) luminosity functions, background UV photoionisation rate, intergalactic medium (IGM) neutral fraction and the electron scattering optical depth. We find that all models exceeding the 21-cm signal limits set by LOFAR at $z\approx9.1$ are excluded at $\gtrsim2\sigma$ by other probes. Finally, we place limits on the IGM spin temperature from LOFAR, disfavouring at 95 per cent confidence spin temperatures below $\sim2.6$ K across an IGM neutral fraction range of $0.15 \lesssim \bar{x}_{H{\scriptscriptstyle I}} \lesssim 0.6$. Note, these limits are only obtained from 141 hrs of data in a single redshift bin. With tighter upper limits, across multiple redshift bins expected in the near future from LOFAR, more viable models will be ruled out. Our approach demonstrates the potential of forward modelling tools such as 21CMMC in combining 21-cm observations with other high-$z$ probes to constrain the astrophysics of galaxies., Comment: 12 pages, 4 pages, 1 table. Submitted to MNRAS, comments welcome

Understanding the persistent emission is crucial for studying type I X-ray bursts, which provide insight into neutron star properties. Although accretion disc coronae appear to be common in many accreting systems, their fundamental properties remain insufficiently understood. Recent work suggests that Type I X-ray bursts from accreting neutron stars provide an opportunity to probe the characteristics of coronae. Several studies have observed hard X-ray shortages from the accretion disk during an X-ray burst implying strong coronal cooling by burst photons. Here, we use the plasma emission code EQPAIR to study the impact of X-ray bursts on coronae, and how the coronal and burst properties affect the coronal electron temperatures and emitted spectra. Assuming a constant accretion rate during the burst, our simulations show that soft photons can cool coronal electrons by a factor of $\gtrsim 10$ and cause a reduction of emission in the $30$-$50$ keV band to $\lesssim 1\%$ of the pre-burst emission. This hard X-ray drop is intensified when the coronal optical depth and aspect ratio is increased. In contrast, depending on the properties of the burst and corona, the emission in the $8$-$24$ keV band can either increase, by a factor of $\gtrsim20$, or decrease, down to $\lesssim 1\%$ of the pre-burst emission. An increasing accretion rate during the X-ray burst reduces the coronal cooling effects and the electron temperature drop can be mitigated by $\gtrsim60\%$. These results indicate that changes of the hard X-ray flux during an X-ray burst probe the geometrical properties of the corona., 12 pages, 7 figures, MNRAS in press

We present new measurements of the spatial distribution and kinematics of neutral hydrogen in the circumgalactic and intergalactic medium surrounding star-forming galaxies at z ~ 2. Using the spectra of ~ 3000 galaxies with redshifts +/- 0.4 from the Keck Baryonic Structure Survey (KBSS), we assemble a sample of more than 200,000 distinct foreground-background pairs with projected angular separations of 3 - 500 arcsec and spectroscopic redshifts, with = 2.23 and = 2.57. The ensemble of sightlines and foreground galaxies is used to construct a 2D map of the mean excess Ly$\alpha$ optical depth relative to the intergalactic mean as a function of projected galactocentric distance (20 < $D_{tran}$/pkpc < 4000) and line-of-sight velocity. We provide information on the line-of-sight kinematics of H I gas as a function of projected distance $D_{tran}$. We compare the map with cosmological zoom-in simulation, finding qualitative agreement between them. A simple two-component (accretion, outflow) analytical model generally reproduces the observed line-of-sight kinematics and projected spatial distribution of H I. The best-fitting model suggests that galaxy-scale outflows with initial velocity $v_{out}$ ~ 600 km/s dominate the kinematics of circumgalactic H I out to $D_{tran}$ ~ 50 kpc, while H I at $D_{tran}$ > 100 kpc is dominated by infall with characteristic $v_{in}$ < $v_c$, where $v_c$ is the circular velocity of the host halo ($M_h$ ~ $10^{12} M_\odot$). Over the impact parameter range 80 < $D_{tran}$/pkpc < 200, the H I line-of-sight velocity range reaches a minimum, with a corresponding flattening in the rest-frame Ly$\alpha$ equivalent width. These observations can be naturally explained as the transition between outflow-dominated and accretion-dominated flows. Beyond $D_{tran}$ ~ 300 kpc, the line of sight kinematics are dominated by Hubble expansion., Comment: 27 pages, 24 figures, 3 tables, accepted by MNRAS. Additional data at http://ramekin.caltech.edu/KBSS/

We present simulations of cosmic reionization and reheating from $z=18$ to $z=5$, investigating the role of stars (emitting soft UV-photons), nuclear black holes (BHs, with power-law spectra), X-ray binaries (XRBs, with hard X-ray dominated spectra), and the supernova-associated thermal bremsstrahlung of the diffuse interstellar medium (ISM, with soft X-ray spectra). We post-process the hydrodynamical simulation Massive-Black II (MBII) with multifrequency ionizing radiative transfer. The source properties are directly derived from the physical environment of MBII, and our only real free parameter is the ionizing escape fraction $f_{\rm esc}$. We find that, among the models explored here, the one with an escape fraction that decreases with decreasing redshift yields results most in line with observations, such as of the neutral hydrogen fraction and the Thomson scattering optical depth. Stars are the main driver of hydrogen reionization and consequently of the thermal history of the intergalactic medium (IGM). We obtain $\langle x_{\rm HII} \rangle = 0.99998$ at $z=6$ for all source types, with volume averaged temperatures $\langle T \rangle \sim 20,000~{\rm K}$. BHs are rare and negligible to hydrogen reionization, but conversely they are the only sources which can fully ionize helium, increasing local temperatures by $\sim 10^4~{\rm K}$. The thermal and ionization state of the neutral and lowly ionized hydrogen differs significantly with different source combinations, with ISM and (to a lesser extent) XRBs, playing a significant role and, as a consequence, determining the transition from absorption to emission of the 21 cm signal from neutral hydrogen., Comment: 17 pages, 19 figures, accepted for publication in MNRAS

The 21-cm signal of neutral hydrogen is a sensitive probe of the Epoch of Reionization (EoR) and Cosmic Dawn. Currently operating radio telescopes have ushered in a data-driven era of 21-cm cosmology, providing the first constraints on the astrophysical properties of sources that drive this signal. However, extracting astrophysical information from the data is highly non-trivial and requires the rapid generation of theoretical templates over a wide range of astrophysical parameters. To this end emulators are often employed, with previous efforts focused on predicting the power spectrum. In this work we introduce 21cmGEM - the first emulator of the global 21-cm signal from Cosmic Dawn and the EoR. The smoothness of the output signal is guaranteed by design. We train neural networks to predict the cosmological signal using a database of ~30,000 simulated signals which were created by varying seven astrophysical parameters: the star formation efficiency and the minimal mass of star-forming halos; the efficiency of the first X-ray sources and their spectrum parameterized by spectral index and the low energy cutoff; the mean free path of ionizing photons and the CMB optical depth. We test the performance with a set of ~2,000 simulated signals, showing that the relative error in the prediction has an r.m.s. of 0.0159. The algorithm is efficient, with a running time per parameter set of 0.16 sec. Finally, we use the database of models to check the robustness of relations between the features of the global signal and the astrophysical parameters that we previously reported., Comment: 17 pages, 13 figures, accepted for publication in MNRAS

High-$z$ AGNs hosted in gas rich galaxies are expected to grow through significantly obscured accretion phases. This may limit or bias their observability. In this work, we use \textsc{BlueTides}, a large volume cosmological simulation of galaxy formation to examine quasar obscuration for the highest-redshift ($z \geq 7$) supermassive black holes residing in the center of galaxies. We find that for the bright quasars, most of the high column density gas ($>90\%$) resides in the innermost regions of the host galaxy, (typically within $< 10$ ckpc), while the gas in the outskirts is a minor contributor to the $N_\mathrm H$. The brightest quasars can have large angular variations in galactic obscuration, over 2 orders of magnitude, where the lines of sight with the lowest obscuration are those formed via strong gas outflows driven by AGN feedback. We find that for the overall AGN population, the mean $N_\mathrm H$ is generally larger for high luminosity and BH mass, while the $N_\mathrm H$ distribution is significantly broadened, developing a low $N_\mathrm H $ wing due to the angular variations driven by the AGN outflows/feedback. The obscured fraction P($N_{\rm H} > 10^{23} {\rm cm}^{-2}$) typically range from 0.6 to 1.0 for increasing $L_{X}$ (with $L_X > 10^{43} \rm{ergs/s}$), with no clear trend of redshift evolution. With respect to the galaxy host property, we find a linear relation between $N_{\rm H}$, $M_*$ and $M_{\rm H_2}$ with $\log N_{\rm H} = (0.24 \pm 0.03) \log M_{*} + (20.7 \pm 0.3)$ and $\log N_{\rm H} = (0.47 \pm 0.03) \log M_{\rm H_2} + (18.4 \pm 0.3)$. The dust optical depth in the UV band $��_{\mathrm UV}$ has tight positive correlation with $N_{\rm H}$. Our dust extincted UVLF is about 1.5 dex lower than the intrinsic UVLF, implying that more than 99\% of the $z \sim 7$ AGNs are heavily dust extincted and therefore would be missed by the UV band observation.

I explore the origin of an asymmetry of the H$\alpha$ emission from a circumstellar (CS) shell around type IIP supernova SN 2013fs in the spectrum taken 10.3\,h after the shock breakout. A spherical model of the H$\alpha$ emission from the CS shell that takes into account a preshock gas acceleration by the supernova radiation permits us to successfully reproduce the \ha H$\alpha$ profile. Principal factors responsible for the H$\alpha$ asymmetry are the high velocity of the accelerated CS preshock gas ($\sim 3000$\,km s$^{-1}$) and a low H$\alpha$ Sobolev optical depth in a combination with an occultation of the H$\alpha$ emission by the photosphere., Comment: accepted by Astronomy Letters

We evolve stellar models with zero-age main sequence (ZAMS) mass of $M_{\rm ZAMS} \gtrsim 18 M_\odot$ under the assumption that they experience an enhanced mass-loss rate when crossing the instability strip at high luminosities and conclude that most of them end as type Ibc supernovae (SNe Ibc) or dust-obscured SNe II. We explore what level of enhanced mass-loss rate during the instability strip would be necessary to explain the `red supergiant (RSG) problem'. This problem refers to the dearth of observed core-collapse supernovae progenitors with $M_{\rm ZAMS} \gtrsim 18 M_\odot$. Namely, we examine what enhanced mass loss rate could make it possible for all these stars actually to explode as CCSNe. We find that the mass-loss rate should increase by a factor of at least about ten. We reach this conclusion by analyzing the hydrogen mass in the stellar envelope and the optical depth of the dusty wind at the explosion, and crudely estimate that under our assumptions only about a fifth of these stars explode as unobscured SNe II and SNe IIb. About 10-15 per cent end as obscured SNe II that are infrared-bright but visibly very faint, and the rest, about 65-70 per cent, end as SNe Ibc. However, the statistical uncertainties are still too significant to decide whether many stars with $M_{\rm ZAMS} \gtrsim 18M_\odot$ do not explode as expected in the neutrino driven explosion mechanism, or whether all of them explode as CCSNe, as expected by the jittering jets explosion mechanism., Accepted for publication in MNRAS

Here we present the study on chemical properties of massive star forming clumps using N $ _2 $ H $ ^+ $ (1-0), H $ ^{13} $ CO $ ^+ $ (1-0), HCN(1-0) and HN $ ^{13} $ C(1-0) data from the literature [Astron. Astrophys. 563, A97 (2014)]. We found that abundances of H $ ^{13} $ CO $ ^+ $ and HN $ ^{13} $ C are affected by H $ _2 $ column densities. As the median values of these two abundances increase by nearly 10 times from stages A to B, H $ ^{13} $ CO $ ^+ $ and HN $ ^{13} $ C are suitable for tracing the evolution of massive star forming clumps. The order of rapidity in growth of abundances of all the four studied molecules from stages A to B, is H $ ^{13} $ CO $ ^+ $ , HCN, HN $ ^{13} $ C, and N $ _2 $ H $ ^+ $ , from the highest to the lowest. Our results suggest that the observing optically thin molecular lines with high angular resolution are necessary to study the chemical evolution of massive star forming clumps.

The hard X-ray spectral index of some AGN has been observed to steepen with the source flux. This has been interpreted in a Comptonization scenario, where an increase in the soft flux decreases the temperature of the corona, leading to steepening of the photon index. However, the variation of the coronal temperature with flux has been difficult to measure due to the presence of complex reflection component in the hard X-rays and the lack of high-quality data at that energy band. Recently, a 200 ks {\it NuSTAR} observation of Ark 564 in 3--50 keV band, revealed the presence of one of the coolest coronae with temperature $kT_e \sim 15$ keV in the time-averaged spectrum. Here, we re-analyse the data and examined the spectra in four flux levels. Our analysis shows that the coronal temperature decreased from $\sim 17$ to $\sim 14$ keV as the flux increased. The high energy photon index $\Gamma \sim 2.3$ varied by less than $0.1$, implying that the optical depth of the corona increased by about 10\% as the flux increased. This first reporting of coronal temperature variation with flux shows that further long observation by {\it NuSTAR} of this and other sources would shed light on the geometry and dynamics of the inner regions of the accretion flow., Comment: Accepted for Publication in MNRAS, 6 Pages, 5 Figures, 2 Tables

We examine the properties of damped Lyman-$\alpha$ absorbers (DLAs) emerging from a single set of cosmological initial conditions in two state-of-the-art cosmological hydrodynamic simulations: {\sc Simba} and {\sc Technicolor Dawn}. The former includes star formation and black hole feedback treatments that yield a good match with low-redshift galaxy properties, while the latter uses multi-frequency radiative transfer to model an inhomogeneous ultraviolet background (UVB) self-consistently and is calibrated to match the Thomson scattering optical depth, UVB amplitude, and Ly-$\alpha$ forest mean transmission at $z>5$. Both simulations are in reasonable agreement with the measured stellar mass and star formation rate functions at $z\geq 3$, and both reproduce the observed neutral hydrogen cosmological mass density, $\Omega_{\rm HI}(z)$. However, the DLA abundance and metallicity distribution are sensitive to the galactic outflows' feedback and the UVB amplitude. Adopting a strong UVB and/or slow outflows under-produces the observed DLA abundance, but yields broad agreement with the observed DLA metallicity distribution. By contrast, faster outflows eject metals to larger distances, yielding more metal-rich DLAs whose observational selection may be more sensitive to dust bias. The DLA metallicity distribution in models adopting an ${\rm H}_2$-regulated star formation recipe includes a tail extending to $[M/H] \ll -3$, lower than any DLA observed to date, owing to curtailed star formation in low-metallicity galaxies. Our results show that DLA observations play an imporant role in constraining key physical ingredients in galaxy formation models, complementing traditional ensemble statistics such as the stellar mass and star formation rate functions., Comment: Accepted for publication in MNRAS

We report on the development of a polarization-sensitive dichroic (150/220 GHz) detector array for the Cosmology Large Angular Scale Surveyor (CLASS) delivered to the telescope site in June 2019. In concert with existing 40 and 90 GHz telescopes, the 150/220 GHz telescope will make observations of the cosmic microwave background over large angular scales aimed at measuring the primordial B-mode signal, the optical depth to reionization, and other fundamental physics and cosmology. The 150/220 GHz focal plane array consists of three detector modules with 1020 transition edge sensor (TES) bolometers in total. Each dual-polarization pixel on the focal plane contains four bolometers to measure the two linear polarization states at 150 and 220 GHz. Light is coupled through a planar orthomode transducer (OMT) fed by a smooth-walled feedhorn array made from an aluminum-silicon alloy (CE7). In this work, we discuss the design, assembly, and in-lab characterization of the 150/220 GHz detector array. The detectors are photon-noise limited, and we estimate the total array noise-equivalent power (NEP) to be 2.5 and 4 aW$\sqrt{\mathrm{s}}$ for 150 and 220 GHz arrays, respectively., Comment: 8 pages, 5 figures, Published in J Low Temp Phys

$$UBVJHKLM$$ photometry for the carbon Mira star V CrB are presented. The infrared observations were carried out in the time interval 1989–2018, while the $$U$$ , $$B$$ , and $$V$$ data were obtained in 2001–2014. The light and color curves are analyzed. The pulsation period of V CrB has been found to be $$355\overset{\textrm{d}}{.}2$$ in the infrared $$JHKLM$$ bands and $$352^{\textrm{d}}$$ for the optical $$BV$$ band. In the $$JHK$$ bands, apart from periodic pulsations, there are distinct sinusoidal variations in the average brightness level with a characteristic period of $${\sim}8300$$ days. Color–magnitude relationships have been revealed for the infrared and optical bands. The phase curves exhibit the wavelength dependence of the brightness variability amplitude. The light curves for various bands and colors are discussed. We have constructed the model of a spherically symmetric circumstellar dust envelope that allows the observed spectral energy distribution at both maximum and minimum light to be reproduced equally well (within the model assumptions) and is consistent with the observations of V CrB by differential speckle polarimetry. The model is characterized by the following parameters: the optical depth is $$\tau_{K}=0.33$$ , the inner and outer radii of the envelope are 8 and 40 000 AU, respectively. The envelope contains spherical carbon dust grains ( $$3/4$$ by mass) and silicon carbide dust grains. Dust grains with a radius of 0.5 $$\mu$$ m account for $$90\%$$ of the envelope mass. The remaining $$10\%$$ of the mass is accounted for by finer dust with a grain radius of 0.1 $$\mu$$ m. Based on the observational data, we have estimated the bolometric flux from V CrB: $$2.6\times 10^{-7}$$ and $$5.1\times 10^{-7}$$ erg cm $${}^{-2}$$ s $${}^{-1}$$ at minimum and maximum light, respectively. The effective temperature of the star is $$T_{\textrm{max}}=3000$$ K at maximum light and $$T_{\textrm{min}}=2400$$ K at minimum light.

We report the SOFIA/HAWC+ band D (154$\,\mu$m) and E (214$\,\mu$m) polarimetric observations of the filamentary structure OMC-3 that is part of the Orion molecular cloud. The polarization pattern is uniform for both bands and parallel to the filament structure. The polarization degree decreases toward regions with high intensity for both bands, revealing a so called "polarization hole." We identified an optical depth effect in which polarized emission and extinction act as counteracting mechanisms as a potential contributor to this phenomenon. Assuming that the detected polarization is caused by the emission of magnetically aligned non-spherical dust grains, the inferred magnetic field is uniform and oriented perpendicular to the filament. The magnetic field strength derived from the polarization patterns at 154$\,\mu$m and 214$\,\mu$m amounts to 202$\,\mu$G and 261$\,\mu$G, respectively. The derived magnetic field direction is consistent with that derived from previous polarimetric observations in the far infrared and submillimeter (submm) wavelength range. Investigating the far-infrared polarization spectrum derived from the SOFIA/HAWC+ observations, we do not find a clear correlation between the polarization spectrum and cloud properties, namely, the column density, $N(H_2$), and temperature, $T$., Comment: Accepted for publication in A&A, 13 pages, 13 figures

The HI 21-cm optical depth ($\tau_b$) can be considerably large as the kinetic and spin temperature of the inter-galactic medium (IGM) is expected to be very low during cosmic dawn. It will be particularly higher at regions with HI over-density. We revisit the validity of the widely used linearized equation for estimating the HI 21-cm differential brightness temperature ($T_b$) which assumes $\tau_b << 1$ and approximates $[1-\exp({-\tau_b})]$ as $\tau_b$. We consider two scenarios, one without any additional cooling mechanism or radio background (referred as the standard scenario) and the other (referred as the excess-cooling} scenario) assumes the EDGES-like absorption profile and an excess cooling mechanism. We find that given a measured global absorption signal, consistent with the standard (excess-cooling) scenario, the linearized equation overestimates the spin temperature by $\sim 5\%(10\%)$. Further, using numerical simulations, we study the impact that the large optical depth has on various signal statistics. We observe that the variance, skewness and kurtosis, calculated at simulation resolution ($\sim 0.5 h^{-1} \, {\rm Mpc}$), are over-predicted up to $\sim 30\%$, $30\%$ and $15\%$ respectively for the standard and up to $\sim 90\%$, $50\%$ and $50\%$ respectively for the excess-cooling scenario. Moreover, we find that the probability distribution function of $T_b$ is squeezed and becomes more Gaussian in shape if no approximation is made. The spherically averaged HI power spectrum is overpredicted by up to $\sim 25 \%$ and $80\%$ at all scales for the standard and excess-cooling scenarios respectively., Comment: 9 pages, 6 figures. Accepted for publication in the MNRAS

We explore the potential of an artificial neural network (ANN) based method intelligence to probe the propagation of cosmic $\gamma$-ray photons in the extragalactic Universe. The journey of $\gamma$-rays emitted from a distant source like blazar to the observer at the Earth is impeded by the absorption through the interaction with the extragalactic background light (EBL), leading to an electron-positron pair production. This process dominates for gamma ray photons with energy above 10 GeV propagating over the cosmological distances. The effect of $\gamma$-ray attenuation is characterized by a physical quantity called \emph{optical depth}, which strongly depends on the $\gamma$-ray photon energy, redshift of the source, and density of the EBL photons. We estimate the optical depth values for $\gamma$-ray energies above 10 GeV emitted from the sources at redshifts in the range 0.01 to 1 using three different and most promising EBL models. These optical depth estimates are randomly divided into two data sets for training and testing of the ANN using energy, redshift as inputs and optical depth as output. The optimization of ANN-performance for each EBL model employs standard back-propagation (BP) and radial-basis function (RBF) algorithms. The performance of the ANN model using the RBF is found to be superior to the BP method. In particular, the RBF-ANN with 40 neurons in the hidden layer corresponding to the EBL model proposed by Finke et al. (2010) shows the best performance for the propagation of $\gamma$-rays in the Universe., Comment: 23 Pages, 6 Tables, 6 Figures, Accepted for Publication in New Astronomy Journal

A concise and powerful method for dual-wavelength digital holography (DWDH) is proposed. By designing a new algorithm, this proposed method bypasses the phase synthesis process and directly obtains the thickness distribution of the object. This method can enlarge the range of measurement with strong noise resistance. For example, noise analysis results show that the proposed method reduces the reconstruction error from 101 nm to 9 nm when the signal-to-noise ratio is equal to 30. Therefore, this method would prove useful for DWDH, and its effectiveness is verified by both numerical simulations and experimental results.

We propose a new reionization probe that uses cosmic microwave background (CMB) observations; the cross-correlation between fluctuations in the CMB optical depth which probes the integrated electron density, $\delta\tau$, and the Compton $y$-map which probes the integrated electron pressure. This cross-correlation is much less contaminated than the $y$-map power spectrum by late-time cluster contributions. In addition, this cross-correlation can constrain the temperature of ionized bubbles while the optical-depth fluctuations and kinetic SZ effect can not. We measure this new observable using a Planck $y$-map as well as a map of optical-depth fluctuations that we reconstruct from Planck CMB temperature data. We use our measurements to derive a first CMB-only upper limit on the temperature inside ionized bubbles, $T_{\rm b}\lesssim 7.0\times10^5\,$K ($2\,\sigma$). We also present future forecasts, assuming a fiducial model with characteristic reionization bubble size $R_{\rm b}=5\,$Mpc and $T_{\rm b}=5\times10^4\,$K. The signal-to-noise ratio of the fiducial cross-correlation using a signal dominated PICO-like $y$-map becomes $\simeq7$ with CMB-S4 $\delta\tau$ and $\simeq13$ with CMB-HD $\delta\tau$. For the fiducial model, we predict that the CMB-HD $-$ PICO cross-correlation should achieve an accurate measurement of the reionization parameters; $T_{\rm b}\simeq 49800^{+4500}_{-5100}\,$K and $R_{\rm b}\simeq 5.09^{+0.66}_{-0.79}\,$Mpc. Since the power spectrum of the electron density fluctuations is constrained by the $\delta\tau$ auto spectrum, the temperature constraints should be only weakly model-dependent on the details of the electron distributions and should be statistically representative of the temperature in ionized bubbles during reionization. This cross-correlation could, therefore, become an important observable for future CMB experiments., Comment: 13 pages, 9 figures, Accepted for publication in PRD

We release relike (reionization effective likelihood), a fast and accurate effective likelihood code based on the latest Planck 2018 data that allows one to constrain any model for reionization between $6lzl30$ using five constraints from the CMB reionization principal components (PC). We tested the code on two example models which showed excellent agreement with sampling the exact Planck likelihoods using either a simple Gaussian PC likelihood or its full kernel density estimate. This code enables a fast and consistent means for combining Planck constraints with other reionization data sets, such as kinetic Sunyaev-Zeldovich effects, line-intensity mapping, luminosity function, star formation history, quasar spectra, etc., where the redshift dependence of the ionization history is important. Since the PC technique tests any reionization history in the given range, we also derive model-independent constraints for the total Thomson optical depth ${\ensuremath{\tau}}_{\mathrm{PC}}={0.0619}_{\ensuremath{-}0.0068}^{+0.0056}$ and its $15\ensuremath{\le}z\ensuremath{\le}30$ high redshift component ${\ensuremath{\tau}}_{\mathrm{PC}}(15,30)l0.020$ (95% C.L.). The upper limits on the high-redshift optical depth is a factor of $\ensuremath{\sim}3$ larger than those reported in the Planck 2018 cosmological parameter paper using the FlexKnot method and we validate our results with a direct analysis of a two-step model which permits this small high-$z$ component.

We report flux-resolved spectroscopic analysis of the active galactic nucleus (AGN) ESO 103--035 using \textit{NuSTAR} observations. Following an earlier work, we fit the spectra using a thermal Comptonization model with a relativistic reflection component to obtain estimates of the coronal temperature for two flux levels. The coronal temperature was found to increase from 24.0$^{+6.8}_{-3.4}$ to 55.3$^{+54.6}_{-7.2}$ keV (errors at 1-$\sigma$ confidence level) as the flux increased from $9.8$ to $11.9 \times 10^{-11}$ erg cm$^{-2}$ s$^{-1}$ in the 3--78 keV band. A marginal variation in the high energy photon index allows for both, a non-varying optical depth and for the optical depth to have varied by a factor of $\sim$2. This is in contrast to a previous work on \textit{NuSTAR} flux resolved spectroscopy of the AGN, Ark 564, where the temperature was found to decrease with flux along with a $10$\% variation in the optical depth. The results maybe understood in a framework where AGN variability is either dominated by coronal heating variation leading to correlated increase of temperature with flux and the opposite effect being seen when the variability is dominated by changes in the seed photon flux., Comment: Accepted for Publication in ApJ, 8 Pages, 4 Figures, 2 Tables

Primordial black holes (PBHs) may form in the early stages of the Universe via the collapse of large density perturbations. Depending on the formation mechanism, PBHs may exist and populate today the galactic halos and have masses in a wide range, from about 10^{-14}Msun up to thousands, or more, of solar masses. Gravitational microlensing is the most robust and powerful method to constrain primordial black holes (PBHs), since it does not require that the lensing objects be directly visible. We calculate the optical depth and the rate of microlensing events caused by PBHs eventually distributed in the Milky Way halo, towards some selected directions of observation. Then we discuss the capability of Euclid, a space-based telescope which might perform microlensing observations at the end of its nominal mission, to probe the PBH populations in the Galactic halo.

We present a systematic analysis of the effects of orbital inclination angle on the non-linear variability properties of type-B and type-C QPOs from black hole binaries. We use the bicoherence, a measure of phase coupling at different Fourier frequencies for our analysis. We find that there is a likely inclination dependent change in the non-linear properties of type-C QPOs as the source transitions from a hard intermediate state to a soft intermediate state. High inclination (edge-on) sources show a change from a `web' to a `cross' pattern, while the low inclination (face-on) sources show a change from a `web' to a `hypotenuse' pattern. We present a scenario of a moderate increase in the optical depth of the Comptonising region as a possible explanation of these effects. The bicoherence of type-B QPOs do not exhibit any measurable inclination dependence., 13 pages, Accepted for publication in MNRAS

Modelling reionization often requires significant assumptions about the properties of ionizing sources. Here, we infer the total output of hydrogen-ionizing photons (the ionizing emissivity, $\dot{N}_\textrm{ion}$) at $z=4-14$ from current reionization constraints, being maximally agnostic to the properties of ionizing sources. We use a Bayesian analysis to fit for a non-parametric form of $\dot{N}_\textrm{ion}$, allowing us to flexibly explore the entire prior volume. We infer a declining $\dot{N}_\textrm{ion}$ with redshift at $z>6$, which can be used as a benchmark for reionization models. Model-independent reionization constraints from the CMB optical depth and Ly$\alpha$ and Ly$\beta$ forest dark pixel fraction produce $\dot{N}_\textrm{ion}$ evolution ($d\log_{10}\dot{N}_\textrm{ion}/dz|_{z=6\rightarrow8} = -0.31\pm0.35$ dex) consistent with the declining UV luminosity density of galaxies, assuming constant ionizing photon escape fraction and efficiency. Including measurements from Ly$\alpha$ damping of galaxies and quasars produces a more rapid decline: $d\log_{10}\dot{N}_\textrm{ion}/dz|_{z=6\rightarrow8} =-0.44\pm0.22$ dex, steeper than the declining galaxy luminosity density (if extrapolated beyond $M_\mathrm{UV} \lesssim -13$), and constrains the mid-point of reionization to $z = 6.93\pm0.14$., Comment: submitted to MNRAS

Over the last few years instruments such as VLT/SPHERE and Subaru/HiCIAO have been able to take detailed scattered light images of protoplanetary discs. Many of the features observed in these discs are generally suspected to be caused by an embedded planet, and understanding the cause of these features requires detailed theoretical models. In this work we investigate disc-planet interactions using the PLUTO code to run 2D and 3D hydrodynamic simulations of protoplanetary discs with embedded 30 M$_{\oplus}$ and 300 M$_{\oplus}$ planets on both an inclined ($i = 2.86^{\circ}$) and non-inclined orbit, using an $\alpha$-viscosity of $4 \times 10^{-3}$. We produce synthetic scattered-light images of these discs at \emph{H-band} wavelengths using the radiative transfer code RADMC3D. We find that while the surface density evolution in 2D and 3D simulations of inclined and non-inclined planets remain fairly similar, their observational appearance is remarkably different. Most of the features seen in the synthetic \emph{H-band} images are connected to density variations of the disc at around 3.3 scale heights above and below the midplane, which emphasizes the need for 3D simulations. Planets on sustained orbital inclinations disrupt the disc's upper-atmosphere and produce radically different observable features and intensity profiles, including shadowing effects and intensity variation in the order of 10-20 times the surrounding background. The vertical optical depth to the disc midplane for \emph{H-band} wavelengths is $\tau \approx 20$ in the disc gap created by the high-mass planet. We conclude that direct imaging of planets embedded in the disc remains difficult to observe, even for massive planets in the gap.

We develop a physically motivated, spherical corona model to investigate the frequency-dependent time lags in AGN. The model includes the effects of Compton up-scattering between the disc UV photons and coronal electrons, and the subsequent X-ray reverberation from the disc. The time lags are associated with the time required for multiple scatterings to boost UV photons up to soft and hard X-ray energies, and the light crossing time the photons take to reach the observer. This model can reproduce not only low-frequency hard and high-frequency soft lags, but also the clear bumps and wiggles in reverberation profiles which should explain the wavy-residuals currently observed in some AGN. Our model supports an anti-correlation between the optical depth and coronal temperatures. In case of an optically thin corona, time delays due to propagating fluctuations may be required to reproduce observed time lags. We fit the model to the lag-frequency data of 1H0707-495, Ark 564, NGC 4051 and IRAS 13224-3809 estimated using the minimal bias technique so that the observed lags here are highest-possible quality. We find their corona size is ~7-15 r_g having the constrained optical depth ~2-10. The coronal temperature is ~150-300 keV. Finally, we note that the reverberation wiggles may be signatures of repeating scatters inside the corona that control the distribution of X-ray sources., Comment: 15 pages, 10 figures, accepted for publication in MNRAS

The infrared signatures of polycyclic aromatic hydrocarbons (PAHs) are observed in a variety of astrophysical objects, including the circumnuclear medium of active galactic nuclei (AGNs). These are sources of highly energetic photons (0.2 to 10 keV), exposing the PAHs to a harsh environment. In this work, we examined experimentally the photoionization and photostability of naphthalene (C$_{10}$H$_{8}$), anthracene (C$_{14}$H$_{10}$), 2-methyl-anthracene (C$_{14}$H$_{9}$CH$_{3}$) and pyrene (C$_{16}$H$_{10}$) upon interaction with photons of 275, 310 and 2500 eV. The measurements were performed at the Brazilian Synchrotron Light Laboratory using time-of-flight mass-spectrometry (TOF-MS). We determined the absolute photoionization and photodissociation cross sections as a function of the incident photon energy; the production rates of singly, doubly and triply charged ions; and the molecular half-lives in regions surrounding AGNs. Even considering moderate X-ray optical depth values ($\tau = 4.45$) due to attenuation by the dusty torus, the half-lives are not long enough to account for PAH detection. Our results suggest that a more sophisticated interplay between PAHs and dust grains should be present in order to circumvent molecular destruction. We could not see any significant difference in the half-life values by increasing the size of the PAH carbon backbone, N$_C$, from 10 to 16. However, we show that the multiple photoionization rates are significantly greater than the single ones, irrespective of the AGN source. We suggest that an enrichment of multiply charged ions caused by X-rays can occur in AGNs., Comment: 20 pages (appendix: 3 pages), 10 figures, 4 tables. Accepted for publication in the Montly Notices of the Royal Astronomical Society (MNRAS). Accepted 2019 April 4

We consider future cosmological tests based on observations of Fast Radio Bursts (FRBs). We use Illustris Simulation to realistically estimate the scatter in the dispersion measure (DM) of FRBs caused by the inhomogeneous distribution of ionized gas in the Intergalactic Medium (IGM). We find ~13% scatter in DM to a source at z=1 and ~7% at z=3 (one sigma). The distribution of DM is close to Gaussian. We simulate samples of FRBs and examine their applicability to simple cosmological tests. Our calculations show that using a sample of 100 FRBs and fixing cosmological model one can find the redshift and sample averaged fraction of ionized gas with ~1% uncertainty. Finding the ionized fraction with ~1% accuracy at few different epochs would require ~10 000 FRBs with known redshifts. Because DM is proportional to the product of ionized fraction, baryon density and the Hubble constant it is impossible to constrain these parameters separately with FRBs. Constraints on cosmological densities are possible in a flat LCDM model but give uninterestingly low accuracy. Using FRBs with other type of data improves the constraints, but the role of FRBs is not crucial. Thus constraints on the distribution of ionized gas are probably the most promising application of FRBs which allow for "tomography" if sources redshifts are known, as opposed to measuring electron scattering optical depth or S-Z y parameters with CMB observations., 8 pages, 5 figures, accepted by MNRAS

The detection of an unexpectedly large number of faint candidate quasars (QSO) at $z \gtrsim 4$ has motivated Madau and Haardt to investigate a reionization scenario in which active galactic nuclei dominate the photon budget at all times. Their analytical study reveals that this picture is in agreement with the evolution of the HI volume fraction in the intergalactic medium (IGM) and the optical depth to Thomson scattering of the cosmic microwave background. We employ a suite of hydrodynamical simulations post-processed with a radiative transfer code to further investigate the properties of such a reionization history. In particular, we generate synthetic absorption-line spectra for HI and HeII that we compare with observational data. Although we confirm the analytical results mentioned above, we also find that the evolution of the IGM temperature and of the HeII optical depth are at odds with current observational constraints. Nevertheless, the QSO-dominated scenario presents the attractive feature that it naturally generates an inhomogeneous IGM and thus produces an extended tail at high values in the distribution function of the HI effective optical depth, in agreement with recent observations. We find tentative evidence that considering some QSO emission at redshift $z \gtrsim 5$ could reconcile such observations with numerical simulations that have so far failed to reproduce this feature. Finally, we show that collecting more HeII-absorption spectra at $z \gtrsim 3$ and studying their distinctive characteristics will be key to precisely constraining the QSO contribution to reionization., 15 pages, 13 figures, published on MNRAS

We present a detailed spectral analysis of the joint XMM-Newton and NuSTAR observations of the active galactic nuclei (AGN) in the Seyfert 1.5 Galaxy ESO 362-G18. The broadband ($0.3\mbox{--}79$ keV) spectrum shows the presence of a power-law continuum with a soft excess below $2$ keV, iron K$\alpha$ emission ($\sim 6.4$ keV), and a Compton hump (peaking at $\sim 20$ keV). We find that the soft excess can be modeled by two different possible scenarios: a warm ($kT_\mathrm{e}\sim0.2$ keV) and optically thick ($\tau\sim34$) Comptonizing corona; or with relativistically-blurred reflection off a high-density ($\log{[n_\mathrm{e}/\mathrm{cm}^{-3}]}>18.3$) inner disk. These two models cannot be easily distinguished solely from their fit statistics. However, the low temperature ($kT_\mathrm{e}\sim20$ keV) and the thick optical depth ($\tau\sim5$) of the hot corona required by the warm corona scenario are uncommon for AGNs. We also fit a 'hybrid' model, which includes both disk reflection and a warm corona. Unsurprisingly, as this is the most complex of the models considered, this provides the best fit, and more reasonable coronal parameters. In this case, the majority of the soft excess flux arises in the warm corona component. However, based on recent simulations of warm coronae, it is not clear whether such a structure can really exist at the low accretion rates relevant for ESO 362-G18 ($\dot{m}\sim0.015$). This may therefore argue in favor of a scenario in which the soft excess is instead dominated by the relativistic reflection. Based on this model, we find that the data would require a compact hot corona ($h\sim3\,R_\mathrm{Horizon}$) around a highly spinning ($a_\star>0.927$) black hole., Comment: 18 pages, 9 figures, Accepted by ApJ

We present a detailed study of the longitudinal proximity effect using a sample of 85 quasars spanning an emission redshift range of $3.5 \leq z_{em} \leq 4.5$ and Lyman continuum luminosity ($L_{912}$) ranging from 1.06$\times 10^{31}$ to 2.24$\times 10^{32}$ erg s$^{-1}$ Hz$^{-1}$. We use the high-quality spectra of these quasars obtained at a spectral resolution of $R\sim$ 5100 and S/N $\sim$ 30 using X-SHOOTER spectrograph mounted on the Very Large Telescope (VLT). In our analysis, we compared the transmitted flux and pixel optical depth of the Ly$\alpha$ absorption originating from the vicinity of quasars to those from the general intergalactic medium by using a redshift matched control sample. The longitudinal proximity effect is found up to $r \leq 12$ Mpc (proper) from quasars. By appropriately scaling up the pixel optical depth in the vicinity of quasars to account for the excess ionization by quasars, we constrain the ratio of median HI optical depth in the vicinity of the quasar to that of the IGM ($R_\tau(r)$). The $R_\tau (r)$ is found to be significantly higher than unity up to 6 Mpc from the quasar with a typical radial profile of the form $R_\tau(r) = 1+A \times exp(-r/r_0)$ with $A=9.16\pm 0.68$ and $r_0= 1.27\pm 0.08$ Mpc. The integrated value of the scaled pixel optical depth over the radial bin of 0-6 Mpc is found to be higher by a factor of $2.55 \pm 0.17$ than the corresponding integrated value of the median pixel optical depth of the IGM. We also found $R_\tau (r)$ to be luminosity dependent., Comment: 14 pages, 8 figures, accepted for publication in MNRAS

The largest moon of Neptune, Triton, possess a cold and hazy atmosphere. Since the discovery of near-surface haze layer during the Voyager fly in 1989, the haze formation mechanism has not been investigated in detail. Here, we provide the first haze microphysical model on Triton. Our model solves the evolution of both size and porosity distributions of haze particles in a self-consistent manner. We simulated the formation of sphere and aggregate hazes with and without condensation of the C$_2$H$_4$ ice. The haze particles can grow into fractal aggregates with mass-equivalent sphere sizes of $\sim0.1$--$1~{\rm {\mu}m}$ and fractal dimension of $D_{\rm f} = 1.8$--$2.2$. The ice-free hazes cannot simultaneously explain both UV and visible observations of Voyager 2, while including the condensation of C$_2$H$_4$ ices provides two better solutions. For ice aggregates, the required total haze mass flux is $\sim2\times{10}^{-15}~{\rm g~{cm}^{-2}~s^{-1}}$. For the icy sphere scenario, the column integrated C$_2$H$_4$ production rate is $\sim8\times{10}^{-15}~{\rm g~{cm}^{-2}~s^{-1}}$, and the ice-free mass flux of $\sim6\times{10}^{-17}~{\rm g~{cm}^{-2}~s^{-1}}$. The UV occultation observations at short wavelength $, Comment: 29 pages, 14 figures, accepted for publication in ApJ, several typos had been amended in the proof of correction

This paper explores methods for constructing low multipole temperature and polarisation likelihoods from maps of the cosmic microwave background anisotropies that have complex noise properties and partial sky coverage. We use Planck 2018 High Frequency Instrument (HFI) and updated SRoll2 temperature and polarisation maps to test our methods. We present three likelihood approximations based on quadratic cross spectrum estimators: (i) a variant of the simulation-based likelihood (SimBaL) techniques used in the Planck legacy papers to produce a low multipole EE likelihood; (ii) a semi-analytical likelihood approximation (momento) based on the principle of maximum entropy; (iii) a density-estimation `likelihood-free' scheme (DELFI). Approaches (ii) and (iii) can be generalised to produce low multipole joint temperature-polarisation (TTTEEE) likelihoods. We present extensive tests of these methods on simulations with realistic correlated noise. We then analyse the Planck data and confirm the robustness of our method and likelihoods on multiple inter- and intra-frequency detector set combinations of SRoll2 maps. The three likelihood techniques give consistent results and support a low value of the optical depth to reoinization, tau, from the HFI. Our best estimate of tau comes from combining the low multipole SRoll2 momento (TTTEEE) likelihood with the CamSpec high multipole likelihood and is tau = 0.0627+0.0050-0.0058. This is consistent with the SRoll2 team's determination of tau, though slightly higher by 0.5 sigma, mainly because of our joint treatment of temperature and polarisation., 20 pages, 15 figures; published in MNRAS

Dust attenuation of an inclined galaxy can cause additional asymmetries in observations, even if the galaxy has a perfectly symmetric structure. {Taking advantage of the integral field spectroscopic data observed by the SDSS-IV MaNGA survey, we investigate the asymmetries of the emission-line and continuum maps of star-forming disk galaxies.} We define new parameters, $A_a$ and $A_b$, to estimate the asymmetries of a galaxy about its major and minor axes, respectively. Comparing $A_a$ and $A_b$ in different inclination bins, we attempt to detect the asymmetries caused by dust. For the continuum images, we find that $A_a$ increases with the inclination, while the $A_b$ is a constant as inclination changes. Similar trends are found for $g-r$, $g-i$ and $r-i$ color images. The dependence of the asymmetry on inclination suggests a thin dust layer with a scale height smaller than the stellar populations. For the H$\alpha$ and H$\beta$ images, neither $A_a$ nor $A_b$ shows a significant correlation with inclination. Also, we do not find any significant dependence of the asymmetry of $E(B-V)_g$ on inclination, implying that the dust in the thick disk component is not significant. Compared to the SKIRT simulation, the results suggest that the thin dust disk has an optical depth $\tau_V\sim0.2$. This is the first time that the asymmetries caused by the dust attenuation and the inclination are probed statistically with a large sample. Our results indicate that the combination of the dust attenuation and the inclination effects is a potential indicator of the 3D disk orientation., Comment: Accepted for publication in ApJ

We investigate numerically the role of near-field dipole-dipole interactions on the late-emission dynamics of large disordered cold atomic samples driven by a weak field. Previous experimental and numerical studies of subradiance in macroscopic samples have focused on low-density samples of pure two-level atoms, without internal structure, which corresponds to a scalar representation of the light. The cooperative nature of the late emission of light is then governed by the resonant optical depth. Here, by considering the vectorial nature of the light, we show the detrimental role of the near-field terms on cooperativity in higher-density samples. The observed reduction in the subradiant lifetimes is interpreted as a signature of the inhomogeneous broadening due to the near-field contributions, in analogy with the van der Waals dephasing phenomenon for superradiance.

The accreting millisecond X-ray pulsar Swift J1756.9$-$2508 went into outburst in April 2018 and June 2019, 8.7 yr after the previous activity period. We investigated the temporal, timing and spectral properties of these two outbursts using data from NICER, XMM-Newton, NuSTAR, INTEGRAL, Swift and Insight-HXMT. The two outbursts exhibited similar broad-band spectra and X-ray pulse profiles. For the first time, we report the detection of the pulsed emission up to $\sim100$ keV observed by Insight-HXMT during the 2018 outburst. We also found the pulsation up to $\sim60$ keV observed by NICER and NuSTAR during the 2019 outburst. We performed a coherent timing analysis combining the data from two outbursts. The binary system is well described by a constant orbital period over a time span of $\sim12$ years. The time-averaged broad-band spectra are well fitted by an absorbed thermal Comptonization model in a slab geometry with the electron temperature $kT_{\rm e}=40$-50 keV, Thomson optical depth $\tau\sim 1.3$, blackbody seed photon temperature $kT_{\rm bb,seed}\sim $0.7-0.8 keV and hydrogen column density of $N_{\rm H}\sim 4.2\times10^{22}$ cm$^{-2}$. We searched the available data for type-I (thermonuclear) X-ray bursts, but found none, which is unsurprising given the estimated low peak accretion rate ($\approx0.05$ of the Eddington rate) and generally low expected burst rates for hydrogen-poor fuel. Based on the history of four outbursts to date, we estimate the long-term average accretion rate at roughly $5\times10^{-12}\ M_\odot\,{\rm yr}^{-1}$ for an assumed distance of 8 kpc. The expected mass transfer rate driven by gravitational radiation in the binary implies the source can be no closer than 4 kpc., Comment: Accepted for publication in A&A

The progenitors of Type Ia supernovae (SNe Ia) are debated, particularly the evolutionary state of the binary companion that donates mass to the exploding carbon-oxygen white dwarf. In previous work, we presented hydrodynamic models and optically thin radio synchrotron light-curves of SNe Ia interacting with detached, confined shells of CSM, representing CSM shaped by novae. In this work, we extend these light-curves to the optically thick regime, considering both synchrotron self-absorption and free-free absorption. We obtain simple formulae to describe the evolution of optical depth seen in the simulations, allowing optically thick light-curves to be approximated for arbitrary shell properties. We then demonstrate the use of this tool by interpreting published radio data. First, we consider the non-detection of PTF11kx - an SN Ia known to have a detached, confined shell - and find that the non-detection is consistent with current models for its CSM, and that observations at a later time would have been useful for this event. Secondly, we statistically analyze an ensemble of radio non-detections for SNe Ia with no signatures of interaction, and find that shells with masses $(10^{-4}-0.3)~M_\odot$ located $(10^{15}-10^{16})$ cm from the progenitor are currently not well constrained by radio datasets, due to their dim, rapidly-evolving light-curves., 16 pages, 7 figures, ApJ accepted; companion Python tools available on github (see text)

In this paper we test if the ∼0.3–15 keV XMM-Newton EPIC pn spectral continuum of IPs can be described by the thermal Comptonization compTT model. We used publicly observations of 12 IPs (AE Aqr, EX Hya, V1025 Cen, V2731 Oph, RX J2133.7+5107, PQ Gem, NY Lup, V2400 Oph, IGR J00234+6141, IGR J17195-4100, V1223 Sgr, and XY Ari). We find that our modeling is capable of fitting well the average spectral continuum of these sources. In this framework, UV/soft X-ray seed photons (with 〈kT s〉 of 0.096 ± 0.013 keV) coming presumably from the star surface are scattered off by electrons present in an optically thick plasma (with 〈kT e〉 of 3.05 ± 0.16 keV and optical depth 〈τ〉 of 9.5 ± 0.6 for plane geometry) located nearby (on top) to the more central seed photon emission regions. A soft blackbody (bbody) component is observed in 5 out of the 13 observations analyzed, with a mean temperature 〈kT bb 〉 of 0.095 ± 0.004 keV. We observed that the spectra of IPs show in general two photon indices Γ, which are driven by the source luminosity and optical depth. Low luminosity IPs show 〈Γ〉 of 1.83 ± 0.19, whereas high luminosity IPs show lower 〈Γ〉 of 1.34 ± 0.02. Moreover, the good spectral fits of PQ Gem and V2400 Oph indicate that the polar subclass of CVs may be successfully described by the thermal Comptonization as well.

We model the near infrared SED of NGC 4151 with a 3-D radiative transfer SKIRT code, using which torus only (TO) and Ring And Torus (RAT) scenarios are studied. In the RAT models, a graphite ring-like structure (clumpy or smooth), is incorporated between the torus and the accretion disk. We vary the inclination angle $(i)$, inner radius (of the torus and the ring, $R_{\rm in, t}$ and $R_{\rm in, r}$ respectively), torus half-opening angle ($\sigma $), optical depth ($\tau_{9.7, \rm t} $ of the torus and $\tau_{9.7, \rm r} $ of the ring ) and the dust clump size ($R_{\rm clump}$). We perform a statistical analysis of the parameter space and find that all the models are able to explain the flat NIR SED of NGC 4151 with minor differences in the derived parameters. For the TO model, we get, $R_{\rm in, t}=0.1$ pc, $\sigma = 30^\circ $, $i = 53^\circ $, $\tau_{9.7, \rm t}=10$ and the clumpsize, $R_{\rm clump}$ =0.4 pc. For the smooth RAT model, $R_{\rm in, \rm r}=0.04$ pc, $\tau_{9.7, \rm total}$ = 11 and for the clumpy RAT model, $R_{\rm in, r} = 0.04$ pc/0.06 pc and $\tau_{9.7, \rm total}=20$. The $R_{\rm in, t}$ from the TO model does not agree with the NIR observations ($\sim 0.04$ pc). Hence, the most likely scenario is that a hot graphite ring is located at a distance 0.04 pc from the centre, composed of a smooth distribution of dust followed by a dusty torus at 0.1 pc with ISM type of grains., Comment: 21 pages, 24 figures, accepted for publication in MNRAS

We present the long-term X-ray spectral and temporal analysis of a 'bare-type AGN' Ark 120. We consider the observations from XMM-Newton, Suzaku, Swift, and NuSTAR from 2003 to 2018. The spectral properties of this source are studied using various phenomenological and physical models present in the literature. We report (a) the variations of several physical parameters, such as the temperature and optical depth of the electron cloud, the size of the Compton cloud, and accretion rate for the last fifteen years. The spectral variations are explained from the change in the accretion dynamics; (b) the X-ray time delay between 0.2-2 keV and 3-10 keV light-curves exhibited zero-delay in 2003, positive delay of 4.71 \pm 2.1 ks in 2013, and negative delay of 4.15 \pm 1.5 ks in 2014. The delays are explained considering Comptonization, reflection, and light-crossing time; (c) the long term intrinsic luminosities obtained using nthcomp, of the soft-excess and the primary continuum show a correlation with a Pearson Correlation Coefficient of 0.922. This indicates that the soft-excess and the primary continuum are originated from the same physical process. From a physical model fitting, we infer that the soft excess for Ark 120 could be due to a small number of scatterings in the Compton cloud. Using Monte-Carlo simulations, we show that indeed the spectra corresponding to fewer scatterings could provide a steeper soft-excess power-law in the 0.2-3 keV range. Simulated luminosities are found to be in agreement with the observed values., Communicated with MNRAS. The revised version will be updated soon. Comments are welcome

We present a thorough experimental investigation of the loading process of laser-cooled atoms from a magneto-optical trap into an optical dipole trap located inside a hollow-core photonic bandgap fiber, followed by propagation of the atoms therein. This, e.g., serves to identify limits to the loading efficiency and thus optical depth which is a key parameter for applications in quantum information technology. Although only limited access in 1D is available to probe atoms inside such a fiber, we demonstrate that a detailed spatially resolved characterization of the loading and trapping process along the fiber axis is possible by appropriate modification of probing techniques combined with theoretical analysis. Specifically, we demonstrate the loading of up to $2.1\ifmmode\times\else\texttimes\fi{}{10}^{5}$ atoms with a transfer efficiency of $2.1%$ during the course of 50 ms and a peak loading rate of $4.7\ifmmode\times\else\texttimes\fi{}{10}^{3}$ atoms ${\mathrm{ms}}^{\ensuremath{-}1}$ resulting in a peak atomic number density on the order of ${10}^{12}\phantom{\rule{0.16em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$. Furthermore, we determine the evolution of the spatial density (profile) and ensemble temperature as it approaches its steady-state value of $T=1400\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{K}$, as well as loss rates, axial velocity and acceleration. The spatial resolution along the fiber axis reaches a few millimeters, which is much smaller than the typical fiber length in experiments. We compare our results to other fiber-based as well as free-space optical dipole traps and discuss the potential for further improvements.

[Abridged] Planet formation is expected to be enhanced around snowlines in protoplanetary disks, in particular around the water snowline. However, the close proximity of the water snowline to the host star and water in the Earth's atmosphere makes a direct detection of the water snowline in protoplanetary disks challenging. Following earlier work on protostellar envelopes, the aim of this research is to investigate the validity of HCO$^+$ and H$^{13}$CO$^+$, as tracers of the water snowline in protoplanetary disks, as HCO$^+$ is destroyed by gas-phase water. Two small chemical networks are used to predict the HCO$^+$ abundance in a typical Herbig Ae disk. Subsequently, the corresponding emission profiles are modelled for H$^{13}$CO$^+$ and HCO$^+$ $J=2-1$, which provides the best balance between brightness and optical depth effects of the continuum emission. The HCO$^+$ abundance jumps by two orders of magnitude just outside the water snowline at 4.5 AU. We find that the emission of H$^{13}$CO$^+$ and HCO$^+$ is ring-shaped due to three effects: destruction of HCO$^+$ by gas-phase water, continuum optical depth, and molecular excitation effects. The presence of gas-phase water causes an additional drop of only $\sim$13% and 24% in the center of the disk, for H$^{13}$CO$^+$ and HCO$^+$, respectively. For the much more luminous outbursting source V883Ori, our models predict that the effect of dust and excitation are not limiting if the snowline is located outside $\sim$40 AU. Our analysis of ALMA observations of HCO$^+$ $J=3-2$ is consistent with the water snowline located around 100 AU. The HCO$^+$ abundance drops steeply around the water snowline, but dust and excitation can conceal the drop in HCO$^+$ emission due to the water snowline. Therefore, locating the water snowline with HCO$^+$ in Herbig disks is very difficult, but it is possible for outbursting sources like V883Ori., Accepted for publication in Astronomy and Astrophysics. 13 pages, 11 figures + appendices

We present optical and infrared (IR) light curves of NaSt1, also known as Wolf-Rayet (WR) 122, with observations from Palomar Gattini-IR (PGIR), the Zwicky Transient Facility (ZTF), the Katzman Automatic Imaging Telescope (KAIT), the Asteroid Terrestrial-impact Last Alert System (ATLAS), and the All-Sky Automated Survey for Supernovae (ASAS-SN). We identify a $P=309.7\pm0.7$ d photometric period from the optical and IR light curves that reveal periodic, sinusoidal variability between 2014 July and 2021 July. We also present historical IR light curves taken between 1983 July and 1989 May, which show variability consistent with the period of the present-day light curves. In the past, NaSt1 was brighter in the $J$ band with larger variability amplitudes than the present-day PGIR values, suggesting that NaSt1 exhibits variability on longer ($\gtrsim$ decade) timescales. Sinusoidal fits to the recent optical and IR light curves show that the amplitude of NaSt1's variability differs at various wavelengths and also reveal significant phase offsets of $17.0\pm2.5$ d between the ZTF $r$ and PGIR $J$ light curves. We interpret the $310$ d photometric period from NaSt1 as the orbital period of an enshrouded massive binary. We suggest that the photometric variability of NaSt1 may arise from variations in the line-of-sight optical depth toward circumstellar optical/IR emitting regions throughout its orbit due to colliding-wind dust formation. We speculate that past mass transfer in NaSt1 may have been triggered by Roche-lobe overflow (RLOF) during an eruptive phase of an Ofpe/WN9 star. Lastly, we argue that NaSt1 is no longer undergoing RLOF mass transfer., Comment: 20 Pages, 7 Figures, 5 Tables, 1 Table Attachment, Accepted to ApJ