Supernova remnant evolution in an AGN environment

Astronomy & Astrophysics, 2017

Early-time observations of Type II supernovae (SNe) 2013cu and 2013fs have revealed an interaction of ejecta with material near the star surface. Unlike Type IIn SN 2010jl, which interacts with a dense wind for ∼1 yr, the interaction ebbs after 2-3 d, suggesting a dense and compact circumstellar envelope. Here, we use multi-group radiation hydrodynamics and non-local-thermodynamic-equilibrium radiative transfer to explore the properties of red-supergiant (RSG) star explosions embedded in a variety of dense envelopes. We consider the cases of an extended static atmosphere or a steady-state wind, adopting a range of mass loss rates. The shock breakout signal, luminosity and color evolution up to 10 d, and ejecta dynamics are strongly influenced by the properties of this nearby environment. This compromises the use of early-time observations to constrain R. For dense circumstellar envelopes, the time-integrated luminosity over the first 10−15 d can be boosted by a factor of a few. The presence of narrow lines for 2-3 d in 2013fs and 2013cu require a cocoon of material of ∼0.01 M out to 5−10 R. Spectral lines evolve from electron scattering to Doppler broadened with a growing blueshift of their emission peaks. Recent studies propose a super-wind phase with a mass loss rate from 0.001 up to 1 M yr −1 in the last months or years of the life of a RSG, although there is no observational constraint that this external material is a steady-state outflow. Alternatively, observations may be explained by the explosion of a RSG star inside its complex atmosphere. Indeed, spatially resolved observations reveal that RSG stars have extended atmospheres, with the presence of downflows and upflows out to several R , even in a standard RSG such as Betelgeuse. Mass loading in the region intermediate between star and wind can accommodate the 0.01 M needed to explain the observations of 2013fs. Signatures of interaction in early-time spectra of RSG star explosions may therefore be the norm, not the exception, and a puzzling super-wind phase prior to core collapse may be superfluous.

… de Astronomia y …, 2009

Damos una reseña de los efectos de explosiones de supernovas (SNe) sobre el medio ambiente de galaxias con formación estelar. Explosiones de SNe en cúmulos distribuidos al azar producen super burbujas calientes que impulsan fuentes galácticas o vientos supersónicos que salen del disco galáctico, dependiendo de la cantidad y concentración de la energía que inyecten. En una fuente galáctica, el gas eyectado es recapturado por el potencial gravitacional, y vuelve a caer sobre el disco. Con simulaciones 3D de dinámica de gases radiativos fuera de equilibrio de estas fuentes galácticas, encontramos que pueden llegar a alturas menores a 5 kpc en el halo, y de esta manera explicar las nubes de velocidad intermedia (IVCs) frecuentemente observadas sobre los discos de estas galaxias. Por otro lado, las nubes de alta velocidad (HVCs) observadas a mayores alturas (hasta de 1 kpc) requieren de otro mecanismo para explicar su producción. Argumentamos que podrían ser formadas por captura de gas del medio intergaláctico y/o por la acción de campos magnéticos llevados hacia el halo con el gas de las fuentes galácticas. Debido a pérdidas de momento angular (de 10-15%) al halo, encontramos que el material de las fuentes cae sobre radios menores, y no es esparcido sobre el disco, como era esperado, cayendo en vez cerca de la región donde está la fuente. Este resultado es consistente con la distribución de metales de recientes modelos químicos de la galaxia. Tambien encontramos que despues de aproximadamente 150 Myr la circulación del gas entre el halo y el disco en las fuentes llega a un estado estacionario, el cual es poco sensible a la distancia de las fuentes al centro galáctico. El material que vuelve a caer sobre el disco lleva a la formación de nuevas generaciones de estructuras complejas que alimentan la turbulencia supersónica del disco.

The Astrophysical Journal, 2015

The expanding ejecta from a classical nova remains hot enough (∼ 10 4 K) to be detected in thermal radio emission for up to years after the cessation of mass loss triggered by a thermonuclear instability on the underlying white dwarf (WD). Nebular spectroscopy of nova remnants confirms the hot temperatures observed in radio observations. During this same period, the unstable thermonuclear burning transitions to a prolonged period of stable burning of the remnant hydrogen-rich envelope, causing the WD to become, temporarily, a super-soft X-ray source. We show that photoionization heating of the expanding ejecta by the hot WD maintains the observed nearly constant temperature of (1 − 4) × 10 4 K for up to a year before an eventual decline in temperature due to either the cessation of the supersoft phase or the onset of a predominantly adiabatic expansion. We simulate the expanding ejecta using a one-zone model as well as the Cloudy spectral synthesis code, both incorporating the time-dependent WD effective temperatures for a range of masses from 0.60 M to 1.10 M. We show that the duration of the nearly isothermal phase depends most strongly on the velocity and mass of the ejecta and that the ejecta temperature depends on the WD's effective temperature, and hence its mass.

The Astrophysical Journal, 1999

We show that many observations of W44, a supernova remnant in the galactic plane at a distance of about 2500 pc, are remarkably consistent with the simplest realistic model. The model remnant is evolving in a smooth ambient medium of fairly high density, about 6 cm −3 on average, with a substantial density gradient. At the observed time it has an age of about 20,000 years, consistent with the age of the associated pulsar, and a radius of 11 to 13 pc. Over most of the outer surface, radiative cooling has become important in the post shock gas; on the denser end there has been sufficient compression of the cooled gas to develop a very thin dense half shell of about 450 M⊙ , supported against further compression by nonthermal pressure. The half shell has an expansion velocity of about 150 km s −1 , and is bounded on the outer surface by a radiative shock with that speed. The deep interior of the remnant has a substantial and fairly uniform pressure, as expected from even highly idealized adiabatic models; our model, however, is never adiabatic. Thermal conduction, while the remnant is young and hot, reduces the need for expansion cooling, and prevents formation of the intensely vacuous cavity characteristic of adiabatic evolution. It radically alters the interior structure from what one might expect from familiarity with the Sedov solution. At the time of observation, the temperature in the center is about 6×10 6 K, the density about 1 cm −3. The temperature decreases gradually away from the center, while the density rises. Farther out where cooling is becoming important, the pressure drops precipitously and the temperature in the denser gas there is quite low. Our model is similar to but more comprehensive than the recent one by Harrus et al. (1997). Because their model lacked thermal conduction, ours is more successful in providing the thermal x-rays from the hot interior, including a better match to the spectrum, but neither provides the sharpness of the central peaking without further complications. By using a 2d hydrocode to follow the evolution in a density gradient, we are able to verify that the spatial and velocity structure of the HI shell are a good match to the observations, without the complications suggested by Koo and Heiles (1995), and to demonstrate that the remnant's asymmetry does not substantially affect the distribution of x-ray emitting material. A 1d hydrocode model is then used to explore the effects of nonequilibrium ionization on the x-ray spectrum and intensity. We calculate the radio continuum emission expected from the compression of the ambient magnetic field and cosmic rays into the dense shell (the van der Laan mechanism, 1962a) and find it to be roughly consistent with observation, though the required density of ambient cosmic ray electrons is about 4 times greater than that estimated for the solar neighborhood. We estimate the optical emission that should be present from fluorescence of UV, emitted by the forming shell and the radiative shock and absorbed in the cold shell and the ambient medium, and the associated 63 µm [OI] emission. Both are in agreement with the intensity and spatial structures found in recent observations. Neither requires interaction with a dense molecular cloud for its generation. We calculate the gamma rays that should be emitted by cosmic ray electrons and ions in the shell, interacting with the cold material, and find each capable of generating about 25% of the flux reported by EGRET for the vicinity. We provide several analytic tools for the assembly of models of this type. We review the early evolution and shell formation analyses and their generalizations to evolution in a density gradient. We also calculate the density and temperature that should be present in the hot interior of a remnant with thermal conduction. We supply the van der Laan mechanism in a particularly useful form for the calculation of radio continuum from radiative remnants. Finally, we demonstrate a simple technique for estimating the optical emission expected. These tools are employed to choose parameters of models which we then explore with our 1d and 2d hydrocodes, providing, respectively, the detailed x-ray spectra and dynamical characteristics. supernova remnants-W44-cosmic ray acceleration-x-rays-gamma rays-masers-radio continuum-interstellar matter affiliations:

The Astrophysical Journal, 1999

We examine the relation between presupernova stellar structure and the distribution of ejecta in core-collapse supernovae of types Ib, Ic and II, under the approximations of adiabatic, spherically symmetric flow. We develop a simple yet accurate analytical formula for the velocity of the initial forward shock that traverses the stellar envelope. For material that does not later experience a strong reverse shock, the entropy deposited by this forward shock persists into the final, freely-expanding state. We demonstrate that the final density distribution can be approximated with simple models for the final pressure distribution, in a way that matches the results of simulations. Our results indicate that the distribution of density and radiation pressure in a star's ejecta depends on whether the outer envelope is radiative or convective, and if convective, on the composition structure of the star.

The Astrophysical Journal, 2013

We present observations with the Very Large Telescope and Hubble Space Telescope (HST) of the broad emission lines from the inner ejecta and reverse shock of SN 1987A from 1999 February until 2012 January (days 4381-9100 after explosion). We detect broad lines from Hα, Hβ, Mg i], Na i, [O i], [Ca ii], and a feature at ∼9220 Å. We identify the latter line with Mg ii λλ9218, 9244, which is most likely pumped by Lyα fluorescence. Hα and Hβ both have a centrally peaked component extending to ∼4500 km s −1 and a very broad component extending to 11,000 km s −1 , while the other lines have only the central component. The low-velocity component comes from unshocked ejecta, heated mainly by X-rays from the circumstellar environment, whereas the very broad component comes from faster ejecta passing through the reverse shock, created by the collision with the circumstellar ring. The flux in Hα from the reverse shock has increased by a factor of four to six from 2000 to 2007. After that there is a tendency of flattening of the light curve, similar to what may be seen in the optical lines from the shocked ring. The core component seen in Hα, [Ca ii], and Mg ii has experienced a similar increase, which is consistent with that found from HST photometry. The energy deposition of the external X-rays is calculated using explosion models for SN 1987A and we predict that the outer parts of the unshocked ejecta will continue to brighten because of this. The external X-ray illumination also explains the edge-brightened morphology of the ejecta seen in the HST images. We finally discuss evidence for dust in the ejecta from line asymmetries.

Eight X-ray observations of V4743 Sgr (2002), observed with Chan-dra and XMM-Newton, are presented, covering three phases: Early optically thin hard emission (day 50.2), photospheric emission from the ejecta (days 180.4, 196.1, 301.9, 371, 526), and faint post-outburst emission (days 742 and 1286). The flux level at Earth during the first and last phase is of order 10 −12 erg cm −2 s −1 over the energy range 0.3-2.5 keV. These values are higher than an upper limit obtained in September 1990 with ROSAT. The nova thus continued fading in the soft band (0.1-2.4 keV). The nova turned off some time between days 301.9 and 371, and the X-ray flux subsequently decreased from day 301.9 to 526, following an exponential decline time scale of (96 ± 3) days. We use the absorption lines present in the SSS spectrum for diagnostic purposes, and characterize the physics and the dynamics of the expanding atmosphere during the explosion of the nova. The information extracted from this first stage is then used as input for computing full photoion-ization models of the ejecta in V4743 Sgr. The SSS spectrum is modeled with a simple black-body and multiplicative Gaussian lines, which provides us of a general kinematical picture of the system, before it decays to its faint phase (Ness et al. 2003). In the grating spectra taken between days 180.4 and 370, we can resolve the line profiles of absorption lines arising from H-like and He-like C, N, and O, including transitions involving higher principal quantum numbers. Except for a few interstellar lines, all lines are significantly blue-shifted, yielding velocities between 1000 and 6000 km s −1 which implies an ongoing mass loss. It is shown that significant expansion and mass loss occur during this phase of the explosion, at a rate ˙ M ≈ (3 − 5) × 10 −4 (L/L 38) M /yr. Our measurements show that the efficiency of the amount of energy used for the motion of the ejecta, defined as the ratio between the kinetic luminosity L kin and the radiated luminosity L rad , is of the order of one.

Monthly Notices of the Royal Astronomical Society

Supernova explosions and their remnants (SNRs) drive important feedback mechanisms that impact considerably the galaxies that host them. Then, the knowledge of the SNRs evolution is of paramount importance in the understanding of the structure of the interstellar medium and the formation and evolution of galaxies. Here, we study the evolution of SNRs in homogeneous ambient media from the initial, ejecta-dominated phase, to the final, momentum-dominated stage. The numerical model is based on the Thin-Shell approximation and takes into account the configuration of the ejected gas and radiative cooling. It accurately reproduces well-known analytic and numerical results and allows one to study the SNR evolution in ambient media with a wide range of densities n0. It is shown that in the high-density cases, strong radiative cooling alters noticeably the shock dynamics and inhibits the Sedov-Taylor stage, thus limiting significantly the feedback that SNRs provide to such environments. For ...

Astronomy and Astrophysics, 2005

We model the hydrodynamic interaction of a shock wave of an evolved supernova remnant with a small interstellar gas cloud like the ones observed in the Cygnus loop and in the Vela SNR. We investigate the interplay between radiative cooling and thermal conduction during cloud evolution and their effect on the mass and energy exchange between the cloud and the surrounding medium. Through the study of two cases characterized by different Mach numbers of the primary shock ( ¤ and 50, corresponding to a post-shock temperature ¤ !" $ # % & ¤ ' K and ) ( 0 !" $ # % 1 ¤ ' K, respectively), we explore two very different physical regimes: for 2 3 , the radiative losses dominate the evolution of the shocked cloud which fragments into cold, dense, and compact filaments surrounded by a hot corona which is ablated by the thermal conduction; instead, for 4 6 5 7 , the thermal conduction dominates the evolution of the shocked cloud, which evaporates in a few dynamical timescales. In both cases we find that the thermal conduction is very effective in suppressing the hydrodynamic instabilities that would develop at the cloud boundaries.

The Astrophysical Journal, 2010

We present a grid of nonequilibrium ionization models for the X-ray spectra from supernova remnants undergoing efficient diffusive shock acceleration. The calculation follows the hydrodynamics of the blast wave as well as the time-dependent ionization of the plasma behind the shock. The ionization state is passed to a plasma emissivity code to compute the thermal X-ray emission, which is combined with the emission from nonthermal synchrotron emission to produce a self-consistent model for the thermal and nonthermal emission from cosmic-ray dominated shocks. We show how plasma diagnostics such as the G'-ratio of He-like ions, defined as the ratio of the sum of the intercombination, forbidden, and satellite lines to the resonance line, can vary with acceleration efficiency, and discuss how the thermal X-ray emission, when the time-dependent ionization is not calculated self-consistently with the hydrodynamics, can differ from the thermal X-ray emission from models which do account for the hydrodynamics. Finally, we compare the thermal X-ray emission from models which show moderate acceleration (~35%) to the thermal X-ray emission from test-particle models.

Astrophysical Journal, 2003

The explosion mechanism behind Type Ia supernovae is a matter of continuing debate. The diverse attempts to identify or at least constrain the physical processes involved in the explosion have been only partially successful so far. In this paper we propose to use the thermal X-ray emission from young supernova remnants originated in Type Ia events to extract relevant information concerning the explosions themselves. We have produced a grid of thermonuclear supernova models representative of the paradigms currently under debate: pure deflagrations, delayed detonations, pulsating delayed detonations and sub-Chandrasekhar explosions, using their density and chemical composition profiles to simulate the interaction with the surrounding ambient medium and the ensuing plasma heating, non-equilibrium ionization and thermal X-ray emission of the ejecta. Key observational parameters such as electron temperatures, emission measures and ionization time scales are presented and discussed. We find that not only is it possible to identify the explosion mechanism from the spectra of young Type Ia Supernova Remnants, it is in fact necessary to take the detailed ejecta structure into account if such spectra are to be modeled in a self-consistent way. Neither element line flux ratios nor element emission measures are good estimates of the true ratios of ejected masses, with differences of as much as two or three orders of magnitude for a given model. Comparison with observations of the Tycho SNR suggests a delayed detonation as the most probable explosion mechanism. Line strengths, line ratios, and the centroid of the Fe Kalpha line are reasonably well reproduced by a model of this kind.

arXiv (Cornell University), 2021

Aims. To investigate the structure, elemental abundances, physical conditions and the immediate surroundings of supernova remnant 0540-69.3 in the Large Magellanic Cloud. Methods. Imaging in [O iii] and spectroscopic studies through various slits were utilized using European Souther Observatory's Very Large and New Technology Telescopes. Densities, temperatures and abundances were estimated applying nebular analysis for various parts of the remnant. Results. Several new spectral lines are identified, both in the pulsar-wind nebula part of the remnant, and in interstellar clouds shocked by the supernova blast wave. In the pulsar-wind nebula, all lines are redshifted by 440 ± 80 km s −1 with respect to the rest frame of the host galaxy, and a 3D-representation of the [O iii] emission displays a symmetry axis of ring-like structures which could indicate that the pulsar shares the same general redshift as the central supernova ejecta. [O ii], [S ii], [Ar iii] and Hβ share a common more compact structure than [O iii], and possibly [Ne iii]. The average [O iii] temperature in the pulsar-wind nebula is 23 500 ± 1 800 K, and the electron density derived from [S ii] is typically ∼ 10 3 cm −3. By mass, the relative elemental abundances of the shocked ejecta in the pulsar-wind nebula are O : Ne : S : Ar ≈ 1 : 0.07 : 0.10 : 0.02, consistent with explosion models of 13 − 20 M progenitors, and similar to that of SN 1987A, as is also the explosive mixing of hydrogen and helium into the center. From Hβ and He i λ5876, the mass ratio of He/H in the center is estimated to be in excess of ∼ 0.8. The rapid cooling of the shocked ejecta could potentially cause variations in the relative abundances if the ejecta are not fully microscopically mixed, and this is highlighted for S/O for the period 1989-2006. [O iii] is also seen in presumably freely coasting photoionized ejecta outside the pulsar-wind nebula at inferred velocities out to well above 2 000 km s −1 , and in projection [O iii] is seen out to ∼ 10 from the pulsar. This is used to estimate that the pulsar age is ≈ 1 200 years. The freely coasting [O iii]-emitting ejecta have a strictly non-spherical distribution, and their mass is estimated to be ∼ 0.12 M. A possible outer boundary of oxygen-rich ejecta is seen in [O ii] λλ3726,3729 at ∼ 2 000 − 2 100 km s −1. Four filaments of shocked interstellar medium are identified, and there is a wide range in degree of ionization of iron, from Fe + to Fe 13+. One filament belongs to a region also observed in X-rays, and another one has a redshift of 85 ± 30 km s −1 relative to the host. From this we estimate that the electron density of the [O iii]-emitting gas is ∼ 10 3 cm −3 , and that the line of the most highly ionized ion, [Fe xiv] λ5303, come from an evaporation zone in connection with the radiatively cooled gas emitting, e.g., [O iii], and not from immediately behind the blast wave. We do not find evidence for nitrogen-enriched ejecta in the southwestern part of the remnant, as was previously suggested. Emission in this region is instead from a severely reddened H ii-region.

The Astrophysical Journal, 2009

We present results of semi-analytic calculations which show clear evidence for changes in the nonequilibrium ionization behind a supernova remnant forward shock undergoing efficient diffusive shock acceleration (DSA). The efficient acceleration of particles (i.e., cosmic rays) lowers the shock temperature and raises the density of the shocked gas, thus altering the ionization state of the plasma in comparison to the test particle approximation where cosmic rays gain an insignificant fraction of the shock energy. The differences between the test particle and efficient acceleration cases are substantial and occur for both slow and fast temperature equilibration rates: in cases of higher acceleration efficiency, particular ion states are more populated at lower electron temperatures. We also present results which show that, in the efficient shock acceleration case, higher ionization fractions are reached noticeably closer to the shock front than in the test-particle case, clearly indicating that DSA may enhance thermal X-ray production. We attribute this to the higher postshock densities which lead to faster electron temperature equilibration and higher ionization rates. These spatial differences should be resolvable with current and future X-ray missions, and can be used as diagnostics in estimating the acceleration efficiency in cosmic-ray modified shocks.

The Astrophysical Journal, 2008

The serendipitous discovery of infrared echoes around the Cas A supernova remnant the Spitzer satellite has provided astronomers with a unique opportunity to study the properties of the echoing material and the history and nature of the outburst that generated these echoes. In retrospect, we find that the echoes are also clearly visible as infrared "hot spots" in IRAS images of the region. The spectra of the echoes are distinct from that of the dust in the general diffuse interstellar medium (ISM) revealing hot silicate grains that are either stochastically heated to temperatures in excess of ∼ 150 K, or radiating at an equilibrium temperature of this value. We show that the maximum luminosity that can be generated by the radioactive decay of 56 Ni is not capable of producing such spectra, and could therefore not have given rise to the echoes. Instead, we find that the echoes must have been generated by an intense and short burst of EUV-UV radiation associated with the breakout of the shock through the surface of the exploding star. The inferred luminosity of the burst depends on the amount of attenuation in the intervening medium to the clouds, and we derive a burst luminosity of ∼ 1.5 × 10 11 L ⊙ for an assumed H-column density of 1.5 × 10 19 cm −2. The average H-column density of the IR emitting region in the echoing clouds is about 5 × 10 17 cm −2. Derivation of their density requires knowledge of the width of the echo that is sweeping though the ISM, which in turn is determined by the duration of the burst. A burst time of ∼ 1 d gives a cloud density of ∼ 200 cm −3 , typical of dense IR cirrus.

The Astrophysical Journal Letters, 2010

We show that time variations in the UV ionizing continuum of quasars, on scales of ∼1 year, affect the dynamic structure of the plasmas responsible for low ionization broad absorption lines. Variations of the ionizing continuum produce non-equilibrium photoionization conditions over a significant fraction of the absorbing clouds and supersonically moving ionization fronts. When the flux drops the contraction of the ionized region drives a supersonic cooling front towards the radiation source and a rarefaction wave in the opposite direction. The pressure imbalance is compensated by an increased speed of the cool gas relative to the front. When the flux recovers the cool gas is re-ionized and re-heated by a supersonic ionization front traveling away from the radiation source and a forward shock is created. The reheated clouds equilibrate to a temperature of ∼ 10 4 K and are observed to have different radial velocities than the main cloud. Such fragmentation seems consistent with the multicomponent structure of troughs seen in some objects. The velocity differences measured among various components in the quasars QSO 2359-1241 and SDSS J0318-0600 can be reproduced by our model if strong magnetic fields (∼10 mG) are present within the clouds.