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Tea Temim

Publications and source records attributed to Tea Temim.

At least 55 records · Page 3Linked to original sources
arXiv2022

The Eel Pulsar Wind Nebula: a PeVatron-Candidate Origin for HAWC J1826-128 and HESS J1826-130

HAWC J1826-128 is one of the brightest Galactic TeV gamma-ray sources detected by the High Altitude Water Cherenkov (HAWC) Observatory, with photon energies extending up to nearly $\sim$100 TeV. This HAWC source spatially coincides with the H.E.S.S. TeV source HESS J1826-130 and the "Eel" pulsar wind nebula (PWN), which is associated with the GeV pulsar PSR J1826-1256. In the X-ray band, Chandra and XMM-Newton revealed that the Eel PWN is composed of both a compact nebula ($\sim$15") and diffuse X-ray emission ($\sim$6'$\times$2') extending away from the pulsar. Our NuSTAR observation detected hard X-ray emission from the compact PWN up to $\sim$20 keV and evidence of the synchrotron burn-off effect. In addition to the spatial coincidence between HESS J1826-130 and the diffuse X-ray PWN, our multi-wavelength spectral energy distribution (SED) analysis using X-ray and gamma-ray data establishes a leptonic origin of the TeV emission associated with the Eel PWN. Furthermore, our evolutionary PWN SED model suggests (1) a low PWN B-field of $\sim$1 $μ$G, (2) a significantly younger pulsar age ($t \sim5.7$ kyr) than the characteristic age ($τ= 14.4$ kyr) and (3) a maximum electron energy of $E_{max} = 2$ PeV. The low B-field as well as the putative supersonic motion of the pulsar may account for the asymmetric morphology of the diffuse X-ray emission. Our results suggest that the Eel PWN may be a leptonic PeVatron particle accelerator powered by the $\sim$6-kyr-old pulsar PSR J1826-1256 with a spin-down power of $3.6 \times 10^{36}$ erg s$^{-1}$.

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arXiv2020

Element Abundances in the Unshocked Ejecta of Cassiopeia A

We analyze and model the infrared spectrum of the Cassiopeia A supernova remnant, with the aim of determining the masses of various elements in the unshocked ejecta. In this way we complement the survey of the X-ray emitting ejecta of Hwang & Laming (2012) to provide a complete census of the elemental composition of the Cas A ejecta. We calculate photoionization-recombination equilibria to determine the ionization balance of various elements in the ejecta as a function of density, using the X-ray and UV emission from the forward and reverse shocks as the ionizing radiation. With the assumption that all emission lines are principally excited at the ejecta density that maximizes their emission, we can convert observed line intensities into element masses. We find that the majority of the $\sim 3 $M_sun ejecta have already been through the reverse shock and are seen today in X-rays. A minority, $\sim 0.47\pm 0.05$ M_sun, with uncertainties quoted here coming from the data fitting procedure only, are still expanding inside the reverse shock and emitting in the infrared. This component is comprised mainly of O, Si, and S, with no Fe readily detectable. Incorporating uncertainties estimated to come from our modeling, we quote $0.47 \pm {0.47\atop 0.24}$ M_sun. We speculate that up to a further 0.07 M_sun of Fe may be present in diffuse gas in the inner ejecta, depending on the Fe charge state.

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arXiv2020

The Nonstandard Properties of a "Standard" PWN: Unveiling the Mysteries of PWN G21.5-0.9 Using its IR and X-ray emission

The evolution of a pulsar wind nebula (PWN) depends on properties of the progenitor star, supernova, and surrounding environment. As some of these quantities are difficult to measure, reproducing the observed dynamical properties and spectral energy distribution (SED) with an evolutionary model is often the best approach in estimating their values. G21.5-0.9, powered by the pulsar J1833-1034, is a well observed PWN for which previous modeling efforts have struggled to reproduce the observed SED. In this study, we reanalyze archival infrared (IR; Herschel, Spitzer) and X-ray (Chandra, NuSTAR, Hitomi) observations. The similar morphology observed between IR line and continuum images of this source indicates that a significant portion of this emission is generated by surrounding dust and gas, and not synchrotron radiation from the PWN. Furthermore, we find the broadband X-ray spectrum of this source is best described by a series of power laws fit over distinct energy bands. For all X-ray detectors, we find significant softening and decreasing unabsorbed flux at higher energy bands. Our model for the evolution of a PWN is able to reproduce the properties of this source when the supernova ejecta has a low initial kinetic energy $E_{\mathrm{sn}} \approx 1.2 \times 10^{50}\,\mathrm{ergs}$ and the spectrum of particles injected into the PWN at the termination shock is softer at low energies. Lastly, our hydrodynamical modeling of the SNR can reproduce its morphology if there is a significant density increase of the ambient medium ${\sim} 1.8$ pc north of the explosion center.

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arXiv2020

Turbulent model of Crab nebula radiation

We construct a turbulent model of the Crab Nebula's non-thermal emission. The present model resolves a number of long-standing problems of the Kennel-Coroniti (1984) model: (i) the sigma problem; (ii) the hard spectrum of radio electrons; (iii) the high peak energy of gamma-ray flares; (iv) and the spacial evolution of the infrared (IR) emission. The Nebula contains two populations of injected particles: Component-I accelerated at the wind termination shock via Fermi-I mechanism, and Component-II accelerated in reconnecting turbulence in highly magnetized ($σ$ $\gg 1$) plasma in the central part of the Crab Nebula. The reconnecting turbulence Component-II extends from radio to gamma rays: it accelerate radio electrons with a hard spectrum, destroy the large scale magnetic flux (and thus resolves the sigma-problem), and occasionally produces gamma-ray flares (from the largest scale reconnection events). The model reproduces the broad-band spectrum of the Crab Nebula, from low-frequency synchrotron emission in radio to inverse-Compton emission at TeV energies, as well as spatially resolved evolution of the spectral indices in IR and optical bands.

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arXiv2019

Interpreting Crab Nebula synchrotron spectrum: two acceleration mechanisms

We outline a model of the Crab Pulsar Wind Nebula with two different populations of synchrotron emitting particles, arising from two different acceleration mechanisms: (i) Component-I due to Fermi-I acceleration at the equatorial portion of the termination shock, with particle spectral index $p_I \approx 2.2$ above the injection break corresponding to $γ_{wind} σ_{wind} \sim 10^5$, peaking in the UV ($γ_{wind} \sim 10^2$ is the bulk Lorentz factor of the wind, $σ_{wind} \sim 10^3$ is wind magnetization); (ii) Component-II due to acceleration at reconnection layers in the bulk of the turbulent Nebula, with particle index $p_{II} \approx 1.6$. The model requires relatively slow but highly magnetized wind. For both components the overall cooling break is in the infra-red at $\sim 0.01$ eV, so that the Component-I is in the fast cooling regime (cooling frequency below the peak frequency). In the optical band Component-I produces emission with the cooling spectral index of $α_o \approx 0.5$, softening towards the edges due to radiative losses. Above the cooling break, in the optical, UV and X-rays, Component-I mostly overwhelms Component-II. We hypothesize that acceleration at large-scale current sheets in the turbulent nebula (Component-II) extends to the synchrotron burn-off limit of $ε_s \approx 100$ MeV. Thus in our model acceleration in turbulent reconnection (Component-II) can produce both hard radio spectra and occasional gamma-ray flares. This model may be applicable to a broader class of high energy astrophysical objects, like AGNe and GRB jets, where often radio electrons form a different population from the high energy electrons.

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arXiv2019

Increasing Gender Diversity and Inclusion in Scientific Committees and Related Activities at STScI

We present a new initiative by the Women in Astronomy Forum at Space Telescope Science Institute (STScI) to increase gender diversity and inclusion in STScI's scientific committees and the activities they generate. This initiative offers new and uniform guidelines on binary gender representation goals for each committee and recommendations on how to achieve them in a homogeneous way, as well as metrics and tools to track progress towards defined goals. While the new guidelines presented in the paper focus on binary gender representation, they can be adapted and implemented to support all minority groups. By creating diverse committees and making them aware of, and trained on implicit bias, we expect to create a diverse outcome in the activities they generate, which, in turn, will advance science further and faster.

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arXiv2019

Probing the Innermost Ejecta Layers in SNR Kes 75: Implications for the Supernova Progenitor

Supernova remnants (SNRs) that contain pulsar wind nebulae (PWNe) are characterized by distinct evolutionary stages. In very young systems, the PWN drives a shock into the innermost supernova (SN) material, giving rise to low-excitation lines and an infrared (IR) continuum from heated dust grains. These observational signatures make it possible to cleanly measure the properties of the deepest SN ejecta layers that can, in turn, provide constraints on the SN progenitor. We present Herschel Space Observatory far-IR observations of the PWN in the Galactic SNR Kes 75, containing the youngest known pulsar that exhibited magnetar-like activity. We detect highly-broadened oxygen and carbon line emission that arises from the SN ejecta encountered by the PWN. We also detect a small amount (a few thousandths of a solar mass) of shock-heated dust that spatially coincides with the ejecta material and was likely formed in the SN explosion. We use hydrodynamical models to simulate the evolution of Kes 75 and find that the PWN has so far swept up 0.05-0.1 solar masses of SN ejecta. Using explosion and nucleosynthesis models for different progenitor masses in combination with shock models, we compare the predicted far-IR emission with the observed line intensities and find that lower mass and explosion energy SN progenitors with mildly mixed ejecta profiles and comparable abundance fractions of carbon and oxygen are favored over higher mass ones. We conclude that Kes 75 likely resulted from an 8-12 solar-mass progenitor, providing further evidence that lower energy explosions of such progenitors can give rise to magnetars.

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arXiv2019

Astro2020 Science White Paper: Probing the Structure of Interstellar Dust from Micron to Kpc Scales with X-ray Imaging

The X-ray regime is a largely underused resource for constraining interstellar dust grain models and improving our understanding of the physical processes that dictate how grains evolve over their lifetimes. This is mostly due to current detectors' relatively low sensitivity and high background, limiting the targets to the brightest sources. The improved sensitivity of the next generation of X-ray detectors will allow studies of much fainter sources, at much higher angular resolution, expanding our sampled sightlines in both quality and quantity.

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arXiv2019

Astro 2020: Astromineralogy of interstellar dust with X-ray spectroscopy

X-ray absorption fine structure (XAFS) in the 0.2-2 keV band is a crucial component in multi-wavelength studies of dust mineralogy, size, and shape -- parameters that are necessary for interpreting astronomical observations and building physical models across all fields, from cosmology to exoplanets. Despite its importance, many fundamental questions about dust remain open. What is the origin of the dust that suffuses the interstellar medium (ISM)? Where is the missing interstellar oxygen? How does iron, predominantly produced by Type Ia supernovae, become incorporated into dust? What is the main form of carbon in the ISM, and how does it differ from carbon in stellar winds? The next generation of X-ray observatories, employing microcalorimeter technology and $R \equiv λ/Δλ\geq 3000$ gratings, will provide pivotal insights for these questions by measuring XAFS in absorption and scattering. However, lab measurements of mineralogical candidates for astrophysical dust, with R > 1000, are needed to fully take advantage of the coming observations.

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arXiv2019

Supernova Remnants in High Definition

Supernova remnants (SNRs) offer the means to study SN explosions, dynamics, and shocks at sub-parsec scales. X-ray observations probe the hot metals synthesized in the explosion and the TeV electrons accelerated by the shocks, and thus they are key to test recent, high-fidelity three-dimensional SN simulations. In this white paper, we discuss the major advances possible with X-ray spectro-imaging at arcsecond scales, with a few eV spectral resolution and a large effective area. These capabilities would revolutionize SN science, offering a three-dimensional view of metals synthesized in explosions and enabling population studies of SNRs in Local Group galaxies. Moreover, this future X-ray mission could detect faint, narrow synchrotron filaments and shock precursors that will constrain the diffusive shock acceleration process.

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arXiv2018

A Deep X-ray View of the Synchrotron-Dominated Supernova Remnant G330.2+1.0

We present moderately deep (125 ks) {\it XMM-Newton} observations of supernova remnant G330.2$+$1.0. This remnant is one of only a few known that fall into "synchrotron-dominated" category, with the emission almost entirely dominated by a nonthermal continuum. Previous X-ray observations could only characterize the spectra of a few regions. Here, we examine the spectra from fourteen regions surrounding the entire rim, finding that the spectral properties of the nonthermal emission do not vary significantly in any systematic way from one part of the forward shock to another, unlike several other remnants of this class. We confirm earlier findings that the power-law index, $Γ$, ranges from about 2.1-2.5, while the absorbing column density is generally between 2.0-2.6 $\times 10^{22}$ cm$^{-2}$. Fits with the {\it srcut} model find values of the roll-off frequency in the range of 10$^{17.1} - 10^{17.5}$ Hz, implying energies of accelerated electrons of $\sim 100$ TeV. These values imply a high shock velocity of $\sim 4600$ km s$^{-1}$, favoring a young age of the remnant. Diffuse emission from the interior is nonthermal in origin as well, and fits to these regions yield similar values to those along the rim, also implying a young age. Thermal emission is present in the east, and the spectrum is consistent with a $\sim 650$ km s$^{-1}$ shock wave encountering interstellar or circumstellar material with a density of $\sim 1$ cm$^{-3}$.

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arXiv2017

Proper Motion of the High-Velocity Pulsar in SNR MSH 15-56

We present a measurement of the proper motion of the presumed pulsar in the evolved composite supernova remnant (SNR) MSH 15-56 whose pulsar wind nebula (PWN) has been disrupted by the supernova (SN) reverse shock. Using Chandra X-ray observations acquired over a baseline of 15 years, we measure a pulsar velocity of 720 (+290/-215) km/s and a direction of motion of 14 +/- 22 degrees west of south. We use this measurement to constrain a hydrodynamical model for the evolution of this system and find that its morphology is well-described by an SNR expanding in an ambient density gradient that increases from east to west. The effect of the density gradient and the pulsar's motion is an asymmetric interaction between the SN reverse shock and the PWN that displaces the bulk of the PWN material away from the pulsar, towards the northeast. The simulation is consistent with an SNR age of 11,000 years, an SN ejecta mass of 10 solar masses, and an average surrounding density of 0.4 cm^-3. However, a combination of a higher SN ejecta mass and ambient density can produce a similar SNR morphology at a later age.

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arXiv2017

Infrared Emission from Supernova Remnants: Formation and Destruction of Dust

We review the observations of dust emission in supernova rem- nants (SNRs) and supernovae (SNe). Theoretical calculations suggest that SNe, particularly core-collapse, should make significant quantities of dust, perhaps as much as a solar mass. Observations of extragalactic SNe have yet to find anywhere near this amount, but this may be the result of observa- tional limitations. SN 1987A, in the process of transitioning from a SN to an SNR, does show signs of a significant amount of dust forming in its ejecta, but whether this dust will survive the passage of the reverse shock to be injected into the ISM is unknown. IR observations of SNRs have not turned up significant quantities of dust, and the dust that is observed is generally swept-up by the forward shock, rather than created in the ejecta. Because the shock waves also destroy dust in the ISM, we explore the question of whether SNe might be net destroyers, rather than net creators of dust in the universe.

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arXiv2017

Evolution of a Pulsar Wind Nebula within a Composite Supernova Remnant

The interaction between a pulsar wind nebula (PWN) and its host supernova remnant (SNR) can produce a vast array of observable structures. Asymmetry present within these structures derives from the complexity of the composite system, where many factors take turns playing a dominating hand throughout the stages of composite SNR evolution. Of particular interest are systems characterized by blastwave expansion within a nonuniform interstellar medium (ISM), which contain an active pulsar having a substantial "kick" velocity (upward of 300 km s$^{-1}$ ), because these systems tend to produce complex morphologies. We present a numerical model that employs these and several other factors in an effort to generate asymmetry similar to that seen in various X-ray and radio observations. We find that the main parameters driving structure are ISM uniformity and total pulsar spin- down energy, with secondary contributions from factors such as pulsar trajectory and initial spin-down luminosity. We also investigate the dynamics behind PWN "tails," which may form to link active pulsars to a crushed, relic nebula as the reverse shock passes. We find that the directions of such tails are not good indicators of pulsar motion, but direction does reveal the flow of ejecta created by the passage of a reverse shock.

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arXiv2017

Comparing Neutron Star Kicks to Supernova Remnant Asymmetries

Supernova explosions are inherently asymmetric and can accelerate new-born neutron stars (NSs) to hundreds of km/s. Two prevailing theories to explain NS kicks are ejecta asymmetries (e.g., conservation of momentum between NS and ejecta) and anisotropic neutrino emission. Observations of supernova remnants (SNRs) can give us insights into the mechanism that generates these NS kicks. In this paper, we investigate the relationship between NS kick velocities and the X-ray morphologies of 18 SNRs observed with the Chandra X-ray Observatory and the Rontgen Satellite (ROSAT). We measure SNR asymmetries using the power-ratio method (a multipole expansion technique), focusing on the dipole, quadrupole, and octupole power-ratios. Our results show no correlation between the magnitude of the power-ratios and NS kick velocities, but we find that for Cas A and G292.0+1.8, whose emission traces the ejecta distribution, their NSs are preferentially moving opposite to the bulk of the X-ray emission. In addition, we find a similar result for PKS 1209-51, CTB 109, and Puppis A; however their emission is dominated by circumstellar/interstellar material, so their asymmetries may not reflect their ejecta distributions. Our results are consistent with the theory that NS kicks are a consequence of ejecta asymmetries as opposed to anisotropic neutrino emission. In the future, additional observations to measure NS proper motions within ejecta-dominated SNRs are necessary to constrain robustly the NS kick mechanism.

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arXiv2017

A Massive Shell of Supernova-formed Dust in SNR G54.1+0.3

While theoretical dust condensation models predict that most refractory elements produced in core-collapse supernovae (SNe) efficiently condense into dust, a large quantity of dust has so far only been observed in SN 1987A. We present the analysis of Spitzer Space Telescope, Herschel Space Observatory, Stratospheric Observatory for Infrared Astronomy (SOFIA), and AKARI observations of the infrared (IR) shell surrounding the pulsar wind nebula in the supernova remnant G54.1+0.3. We attribute a distinctive spectral feature at 21 $μ$m to a magnesium silicate grain species that has been invoked in modeling the ejecta-condensed dust in Cas A, which exhibits the same spectral signature. If this species is responsible for producing the observed spectral feature and accounts for a significant fraction of the observed IR continuum, we find that it would be the dominant constituent of the dust in G54.1+0.3, with possible secondary contributions from other compositions, such as carbon, silicate, or alumina grains. The smallest mass of SN-formed dust required by our models is 1.1 $\pm$ 0.8 $\rm M_{\odot}$. We discuss how these results may be affected by varying dust grain properties and self-consistent grain heating models. The spatial distribution of the dust mass and temperature in G54.1+0.3 confirms the scenario in which the SN-formed dust has not yet been processed by the SN reverse shock and is being heated by stars belonging to a cluster in which the SN progenitor exploded. The dust mass and composition suggest a progenitor mass of 16$-$27 $\rm M_{\odot}$ and imply a high dust condensation efficiency, similar to that found for Cas A and SN 1987A. The study provides another example of significant dust formation in a Type IIP SN and sheds light on the properties of pristine SN-condensed dust.

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arXiv2016

Deep Chandra Observations of the Pulsar Wind Nebula Created by PSR B0355+54

We report on Chandra X-ray Observatory (CXO) observations of the pulsar wind nebula (PWN) associated with PSR B0355+54 (eight observations with a 395 ks total exposure, performed over an 8 month period). We investigated the spatial and spectral properties of the emission coincident with the pulsar, compact nebula (CN), and extended tail. We find that the CN morphology can be interpreted in a way that suggests a small angle between the pulsar spin axis and our line-of-sight, as inferred from the radio data. On larger scales, emission from the 7' (2 pc) tail is clearly seen. We also found hints of two faint extensions nearly orthogonal to the direction of the pulsar's proper motion. The spectrum extracted at the pulsar position can be described with an absorbed power-law + blackbody model. The nonthermal component can be attributed to magnetospheric emission, while the thermal component can be attributed to emission from either a hot spot (e.g., a polar cap) or the entire neutron star surface. Surprisingly, the spectrum of the tail shows only a slight hint of cooling with increasing distance from the pulsar. This implies either a low magnetic field with fast flow speed, or particle re-acceleration within the tail. We estimate physical properties of the PWN and compare the morphologies of the CN and the extended tail with those of other bow shock PWNe observed with long CXO exposures.

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