Supernova remnants (SNRs) are thought to be one of the major acceleration sites of galactic cosmic rays and an important class of objects for high-energy astrophysics. SNRs produce multiwavelength, ...nonthermal emission via accelerated particles at collisionless shocks generated by the interactions between the SN ejecta and the circumstellar medium (CSM). Although it is expected that the rich diversities observed in supernovae (SNe) and their CSM can result in distinct very high energy (VHE) electromagnetic signals in the SNR phase, there are only a handful of SNRs observed in both GeV and TeV γ-rays so far. A systematic understanding of particle acceleration at SNRs in different ambient environments is therefore limited. Here we explore nonthermal emission from SNRs in various circumstellar environments up to 5000 yr from explosion using hydrodynamical simulations coupled with efficient particle acceleration. We find that time evolution of emission characteristics in the VHE regime is mainly dictated by two factors: the number density of the target particles and the amplified magnetic field in the shocked medium. We also predict that the Cherenkov Telescope Array (CTA) will have sufficient sensitivity to detect VHE γ-rays from most young SNRs at distances 5.0 kpc. Future SNR observations with CTA will thus be promising for probing the CSM environment of SNe and hence their progenitor properties, including the mass-loss history of massive stars.
Abstract
We present the results of Atacama Large Millimeter/submillimeter Array (ALMA) band 3 observations of the nearby type Ic supernova (SN) 2020oi. Under the standard assumptions on the ...SN-circumstellar medium (CSM) interaction and the synchrotron emission, the data indicate that the CSM structure deviates from a smooth distribution expected from the steady-state mass loss in the very vicinity of the SN (≲10
15
cm), which is then connected to the outer smooth distribution (≳10
16
cm). This structure is further confirmed through the light-curve modeling of the whole radio data set as combined with the previously reported data at lower frequency. Because this is an explosion of a bare carbon-oxygen (C+O) star with a fast wind, we can trace the mass-loss history of the progenitor of SN 2020oi in the final year. The inferred nonsmooth CSM distribution corresponds to fluctuations on the subyear timescale in the mass-loss history toward the SN explosion. Our finding suggests that the pre-SN activity is likely driven by the accelerated change in the nuclear burning stage in the last moments just before the massive star’s demise. The structure of the CSM derived in this study is beyond the applicability of the other methods at optical wavelengths, highlighting the importance and uniqueness of quick follow-up observations of SNe by ALMA and other radio facilities.
Recent high-cadence transient surveys and rapid follow-up observations indicate that some massive stars may dynamically lose their own mass within decades before supernovae (SNe). Such a mass-loss ...forms "confined" circumstellar medium (CSM); a high-density material distributed only within a small radius ( 1015 cm with the mass-loss rate of 0.01 ∼ 10−4 M yr−1). While the SN shock should trigger particle acceleration and magnetic field amplification in the "confined" CSM, synchrotron emission may be masked in centimeter wavelengths due to free-free absorption; the millimeter range can, however, be a potential new window. We investigate the time evolution of synchrotron radiation from the system of a red supergiant surrounded by the "confined" CSM, relevant to typical Type II-P SNe. We show that synchrotron millimeter emission is generally detectable, and that the signal can be used as a sensitive tracer of the nature of the "confined" CSM; it traces different CSM density parameter space than in the optical. Furthermore, our simulations show that the "confined" CSM efficiently produces secondary electrons and positrons through proton inelastic collisions, which can become main contributors to the synchrotron emission in several ten days since the SN. We predict that the synchrotron emission is detectable by ALMA, and suggest that it will provide a robust evidence of the existence of the "confined" CSM.
Abstract
We discuss the acceleration and escape of secondary cosmic-ray (CR) nuclei, such as lithium, beryllium, and boron, produced by spallation of primary CR nuclei like carbon, nitrogen, and ...oxygen accelerated at the shock in supernova remnants (SNRs) surrounded by the interstellar medium (ISM) or a circumstellar medium (CSM). We take into account the energy-dependent escape of CR particles from the SNR shocks, which is supported by gamma-ray observations of SNRs, to calculate the spectra of primary and secondary CR nuclei running away into the ambient medium. We find that if the SNR is surrounded by a CSM with a wind-like density distribution (i.e.,
n
CSM
∝
r
−2
), the spectra of the escaping secondary nuclei are harder than those of the escaping primary nuclei, while if the SNR is surrounded by a uniform ISM, the spectra of the escaping secondaries are always softer than those of the escaping primaries. Using this result, we show that if there was a past supernova surrounded by a dense wind-like CSM (∼2.5 × 10
−3
M
⊙
yr
−1
), which happened ∼1.6 × 10
5
yr ago at a distance of ∼1.6 kpc, we can simultaneously reproduce the spectral hardening of primary and secondary CRs above ∼200 GV that have recently been reported by AMS-02.
Abstract
Among Type Ia supernova remnants (SNRs), Tycho’s SNR has been considered as a typical object from the viewpoints of its spectroscopic, morphological, and environmental properties. A recent ...reanalysis of Chandra data showed that its forward shock is experiencing a substantial deceleration since around 2007, which suggests recent shock interactions with a dense medium as a consequence of a cavity-wall environment inside a molecular cloud. Such a nonuniform environment can be linked back to the nature and activities of its progenitor. In this study, we perform hydrodynamic simulations to characterize Tycho’s cavity-wall environment using the latest multiepoch proper motion measurements of the forward shock. A range of parameters for the environment is explored in the hydrodynamic models to fit with the observational data for each azimuthal region. Our results show that a wind-like cavity with
ρ
(
r
) ∝
r
−2
reconciles with the latest data better than a uniform medium with a constant density. In addition, our best-fit model favors an anisotropic wind with an azimuthally varying wind parameter. The overall result indicates a mass-loss rate which is unusually high for the conventional single-degenerate explosion scenario.
Abstract The nature of Type Ia supernova (SN Ia) explosions remains an open issue, with several contending progenitor scenarios actively being considered. One such scenario involves an SN Ia ...explosion inside a planetary nebula (PN) in the aftermath of a stellar merger triggered by a common envelope (CE) episode. We examine this scenario using hydrodynamic and nonequilibrium ionization simulations of the interaction between the SN ejecta and the PN cocoon into the supernova remnant (SNR) phase, focusing on the impact of the delay between the CE episode and the SN explosion. We compare the bulk dynamics and X-ray spectra of our simulated SNRs to the observed properties of known Type Ia SNRs in the Milky Way and the Magellanic Clouds. We conclude that models where the SN explosion happens in the immediate aftermath of the CE episode (with a delay ≲1000 yr) are hard to reconcile with the observations, because the interaction with the dense PN cocoon results in ionization timescales much higher than those found in any known Type Ia SNR. Models with a longer delay between the CE episode and the SN explosion (∼10,000 yr) are closer to the observations, and may be able to explain the bulk properties of some Type Ia SNRs.
Abstract While various methods have been proposed to disentangle the progenitor system for Type Ia supernovae, their origin is still unclear. A circumstellar environment is key to distinguishing ...between the double-degenerate and single-degenerate (SD) scenarios since a dense wind cavity is expected only in the case of the SD system. We perform spatially resolved X-ray spectroscopy of Tycho’s supernova remnant (SNR) with XMM-Newton and reveal the three-dimensional velocity structure of the expanding shock-heated ejecta measured from Doppler-broadened lines of intermediate-mass elements. Obtained velocity profiles are fairly consistent with those expected from a uniformly expanding ejecta model near the center, whereas we discover a rapid deceleration (∼4000 to ∼1000 km s −1 ) near the edge of the remnant in almost every direction. The result strongly supports the presence of a dense wall entirely surrounding the remnant, which is confirmed also by our hydrodynamical simulation. We thus conclude that Tycho’s SNR is likely of SD origin. Our new method will be useful for understanding progenitor systems of Type Ia SNRs in the era of high-angular/energy-resolution X-ray astronomy with microcalorimeters.
Abstract
The dynamics and spectral characteristics of supernova ejecta reveal details of the supernova energetics, explosive nucleosynthesis, and evolution of the progenitor. However, in practice, ...this important diagnostic information is only derived from CCD-resolution X-ray spectra of shock-heated material. If the spectra were to be observed at higher resolution, then important clues to the explosion energetics would be obvious through measurements of bulk Doppler motions and turbulence in the ejecta. Likewise, the unshocked ejecta in supernovae and young remnants are responsible for obscuring the emission from ejecta on the back side of the remnant. In light of these important effects, we present line-of-sight spectral maps of core-collapse supernova remnant models. We explore the bulk Doppler broadening of spectral lines, including line-of-sight effects. We also explore the time-dependent absorption from both shocked and unshocked ejecta. Finally, we discuss how future X-ray missions such as XRISM and Athena will be able to resolve these effects in nearby and extragalactic supernovae and their remnants.
Abstract
One of the outstanding mysteries surrounding the rich diversity found in supernova remnants (SNRs) is the recent discovery of over-ionized or recombining plasma from a number of dynamically ...evolved objects. To help decipher its formation mechanism, we have developed a new simulation framework capable of modeling the time evolution of the ionization state of the plasma in an SNR. The platform is based on a one-dimensional hydrodynamics code coupled to a fully time-dependent nonequilibrium ionization calculation, accompanied by a spectral synthesis code to generate space-resolved broadband X-ray spectra for SNRs at arbitrary ages. We perform a comprehensive parametric survey to investigate the effects of different circumstellar environments on the ionization state evolution in SNRs up to a few 10
4
yr. A two-dimensional parameter space, spanned by arrays of interstellar medium (ISM) densities and mass-loss rates of the progenitor, is used to create a grid of models for the surrounding environment, in which a core-collapse explosion is triggered. Our results show that a recombining plasma can be successfully reproduced in the case of a young SNR (a few 100 to 1000 yr old) expanding fast in a spatially extended low-density wind, an old SNR (>a few 1000 yr) expanding in a dense ISM, or an old SNR broken out from a confined dense wind region into a tenuous ISM. Finally, our models are confronted with observations of evolved SNRs, and an overall good agreement is found except for a couple of outliers.
Abstract
In spite of their importance as standard candles in cosmology and as major major sites of nucleosynthesis in the universe, the kinds of progenitor systems that lead to Type Ia supernovae ...(SNe Ia) remains a subject of considerable debate in the literature. This is true even for the case of Tycho’s supernova (SN) that exploded in 1572, although it has been deeply studied both observationally and theoretically. Analyzing X-ray data of Tycho’s supernova remnant (SNR) obtained with Chandra in 2003, 2007, 2009, and 2015, we discover that the expansion before 2007 was substantially faster than radio measurements reported in the past decades and then rapidly decelerated during the last ∼15 yr. The result is well explained if the shock waves recently hit a wall of dense gas surrounding the SNR. In fact, such a gas structure is expected in the so-called single-degenerate scenario, in which the progenitor is a binary system consisting of a white dwarf and a stellar companion, whereas it is not generally predicted by a competing scenario, the double-degenerate scenario, which has a binary of two white dwarfs as the progenitor. Our result thus favors the former scenario. This work also demonstrates a novel technique to probe gas environments surrounding SNRs and thus disentangle the two progenitor scenarios for SNe Ia.
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