We present high angular resolution (∼80 mas) ALMA continuum images of the SN 1987A system, together with CO J=2→1, J=6 → 5, and SiO J=5→4 to J=7 → 6 images, which clearly resolve the ejecta (dust continuum and molecules) and ring (synchrotron continuum) components. Dust in the ejecta is asymmetric and clumpy, and overall the dust fills the spatial void seen in Hα images, filling that region with material from heavier elements. The dust clumps generally fill the space where CO J=6→5 is fainter, tentatively indicating that these dust clumps and CO are locationally and chemically linked. In these regions, carbonaceous dust grains might have formed after dissociation of CO. The dust grains would have cooled by radiation, and subsequent collisions of grains with gas would also cool the gas, suppressing the CO J=6→5 intensity. The data show a dust peak spatially coincident with the molecular hole seen in previous ALMA CO J=2→1 and SiO J=5→4 images. That dust peak, combined with CO and SiO line spectra, suggests that the dust and gas could be at higher temperatures than the surrounding material, though higher density cannot be totally excluded. One of the possibilities is that a compact source provides additional heat at that location. Fits to the far-infraredmillimeter spectral energy distribution give ejecta dust temperatures of 18-23K. We revise the ejecta dust mass to M dust = 0.2 − 0.4M for carbon or silicate grains, or a maximum of < 0.7M for a mixture of grain species, using the predicted nucleosynthesis yields as an upper limit. ciganp@cardiff.ac.uk

The nearby SN 1987A offers a spatially resolved view of the evolution of a young supernova (SN) remnant. Here we precent recent Hubble Space Telescope imaging observations of SN 1987A, which we use to study the evolution of the ejecta, the circumstellar equatorial ring (ER) and the increasing emission from material outside the ER. We find that the inner ejecta have been brightening at a gradually slower rate and that the western side has been brighter than the eastern side since ∼ 7000 days. This is expected given that the X-rays from the ER are most likely powering the ejecta emission. At the same time the optical emission from the ER continues to fade linearly with time. The ER is expanding at 680 ± 50 km s −1 , which reflects the typical velocity of transmitted shocks in the dense hotspots. A dozen spots and a rim of diffuse Hα emission have appeared outside the ER since 9500 days. The new spots are more than an order of magnitude fainter than the spots in the ER and also fade faster. We show that the spots and diffuse emission outside the ER may be explained by fast ejecta interacting with high-latitude material that extends from the ER toward the outer rings. Further observations of this emission will make it possible to determine the detailed geometry of the high-latitude material and provide insight into the formation of the rings and the mass-loss history of the progenitor.

Despite more than 30 years of searches, the compact object in Supernova (SN) 1987A has not yet been detected. We present new limits on the compact object in SN 1987A using millimeter, near-infrared, optical, ultraviolet, and X-ray observations from ALMA, VLT, HST, and Chandra. The limits are approximately 0.1 mJy (0.1×10 −26 erg s −1 cm −2 Hz −1 ) at 213 GHz, 1 L (6×10 −29 erg s −1 cm −2 Hz −1 ) in optical if our line-of-sight is free of ejecta dust, and 10 36 erg s −1 (2 × 10 −30 erg s −1 cm −2 Hz −1 ) in 2-10 keV X-rays. Our X-ray limits are an order of magnitude less constraining than previous limits because we use a more realistic ejecta absorption model based on three-dimensional neutrino-driven SN explosion models (Alp et al. 2018). The allowed bolometric luminosity of the compact object is 22 L Corresponding author: Dennis Alp dalp@kth.se arXiv:1805.04526v2 [astro-ph.HE] 30 Jul 2018 2 Alp et al.if our line-of-sight is free of ejecta dust, or 138 L if dust-obscured. Depending on assumptions, these values limit the effective temperature of a neutron star to < 4-8 MK and do not exclude models, which typically are in the range 3-4 MK. For the simplest accretion model, the accretion rate for an efficiency η is limited to < 10 −11 η −1 M yr −1 , which excludes most predictions. For pulsar activity modeled by a rotating magnetic dipole in vacuum, the limit on the magnetic field strength (B) for a given spin period (P ) is B 10 14 P 2 G s −2 , which firmly excludes pulsars comparable to the Crab. By combining information about radiation reprocessing and geometry, it is likely that the compact object is a dustobscured thermally-emitting neutron star, which may appear as a region of higher-temperature ejecta dust emission.

The first electromagnetic signal from a supernova (SN) is released when the shock crosses the progenitor surface. This shock breakout (SBO) emission provides constraints on progenitor and explosion properties. Observationally, SBOs appear as minute- to hour-long extragalactic X-ray transients. They are challenging to detect and only one SBO has been observed to date. Here, we search the XMM-Newton archive and find 12 new SN SBO candidates. We identify host galaxies to nine of these at estimated redshifts of 0.1–1. The SBO candidates have energies of ∼1046 erg, timescales of 30–3000 s, and temperatures of 0.1–1 keV. They are all consistent with being SN SBOs, but some may be misidentified Galactic foreground sources or other extragalactic objects. SBOs from blue supergiants agree well with most of the candidates. However, a few could be SBOs from Wolf–Rayet stars surrounded by dense circumstellar media, whereas two are more naturally explained as SBOs from red supergiants. The observations tentatively support non-spherical SBOs and are in agreement with asymmetries predicted by recent three-dimensional SN explosion simulations. eROSITA may detect ∼2 SBOs per year, which could be detected in live analyses and promptly followed up.

Supernova 1987A offers a unique opportunity to study an evolving supernova in unprecedented detail over several decades. The X-ray emission is dominated by interactions between the ejecta and the circumstellar medium, primarily the equatorial ring (ER). We analyze 3.3 Ms of NuSTAR data obtained between 2012 and 2020, and two decades of XMM-Newton data. Since ∼2013, the flux below 2 keV has declined, the 3–8 keV flux has increased but has started to flatten, and the emission above 10 keV has remained nearly constant. The spectra are well described by a model with three thermal shock components. Two components at 0.3 and 0.9 keV are associated with dense clumps in the ER, and a 4 keV component may be a combination of emission from diffuse gas in the ER and the surrounding low-density H ii region. We disfavor models that involve nonthermal X-ray emission and place constraints on nonthermal components, but cannot firmly exclude an underlying power law. Radioactive lines show a 44 Ti redshift of 670 − 380 + 520 km s − 1 , 44 Ti mass of 1.73 − 0.29 + 0.27 × 10 − 4 M ⊙ , and 55 Fe mass of < 4.2 × 10 − 4 M ⊙ . The 35–65 keV luminosity limit on the compact object is 2 × 10 34  erg s−1, and < 15 % of the 10–20 keV flux is pulsed. Considering previous limits, we conclude that there are currently no indications of a compact object, aside from a possible hint of dust heated by a neutron star in recent ALMA images.

The material expelled by core-collapse supernova (SN) explosions absorbs X-rays from the central regions. We use SN models based on three-dimensional neutrino-driven explosions to estimate optical depths to the center of the explosion, compare different progenitor models, and investigate the effects of explosion asymmetries. The optical depths below 2 keV for progenitors with a remaining hydrogen envelope are expected to be high during the first century after the explosion due to photoabsorption. A typical optical depth is 100 t −2 4 E −2 , where t 4 is the time since the explosion in units of 10 000 days (∼27 years) and E the energy in units of keV. Compton scattering dominates above 50 keV, but the scattering depth is lower and reaches unity already at ∼1000 days at 1 MeV. The optical depths are approximately an order of magnitude lower for hydrogen-stripped progenitors. The metallicity of the SN ejecta is much higher than in the interstellar medium, which enhances photoabsorption and makes absorption edges stronger. These results are applicable to young SN remnants in general, but we explore the effects on observations of SN 1987A and the compact object in Cas A in detail. For SN 1987A, the absorption is high and the X-ray upper limits of ∼100 L on a compact object are approximately an order of magnitude less constraining than previous estimates using other absorption models. The details are presented in an accompanying paper (Alp et al. 2018). For the central compact object in Cas A, we find no significant effects of our more detailed absorption model on the inferred surface temperature.

Comparison of theoretical line profiles to observations provides important tests for supernova explosion models. We study the shapes of radioactive decay lines predicted by current 3D core-collapse explosion simulations, and compare these to observations of SN 1987A and Cas A. Both the widths and shifts of decay lines vary by several thousand kilometers per second depending on viewing angle. The line profiles can be complex with multiple peaks. By combining observational constraints from 56 Co decay lines, 44 Ti decay lines, and Fe IR lines, we delineate a picture of the morphology of the explosive burning ashes in SN 1987A. For M ZAMS = 15 − 20 M ⊙ progenitors exploding with ∼ 1.5 × 10 51 erg, ejecta structures suitable to reproduce the observations involve a bulk asymmetry of the 56 Ni of at least ∼400 km s −1 and a bulk velocity of at least 1500 km s −1 . By adding constraints to reproduce the UVOIR bolometric light curve of SN 1987A up to 600d, an ejecta mass around 14 M ⊙ is favoured. We also investigate whether observed decay lines can constrain the neutron star (NS) kick velocity. The model grid provides a constraint V NS > V redshift , and applying this to SN 1987A gives a NS kick of at least 500 km s −1 . For Cas A, our single model provides a satisfactory fit to the NuSTAR observations and reinforces the result that current neutrino-driven core-collapse SN models achieve enough bulk asymmetry in the explosive burning material. Finally, we investigate the internal gamma-ray field and energy deposition, and compare the 3D models to 1D approximations.

During the first few hundred days after the explosion, core-collapse supernovae (SNe) emit downscattered X-rays and gamma-rays originating from radioactive line emissions, primarily from the 56 Ni → 56 Co → 56 Fe chain. We use SN models based on three-dimensional neutrino-driven explosion simulations of single stars and mergers to compute this emission and compare the predictions with observations of SN 1987A. A number of models are clearly excluded, showing that high-energy emission is a powerful way of discriminating between models. The best models are almost consistent with the observations, but differences that cannot be matched by a suitable choice of viewing angle are evident. Therefore, our self-consistent models suggest that neutrino-driven explosions are able to produce, in principle, sufficient mixing, although remaining discrepancies may require small changes to the progenitor structures. The soft X-ray cutoff is primarily determined by the metallicity of the progenitor envelope. The main effect of asymmetries is to vary the flux level by a factor of ∼3. For the more asymmetric models, the shapes of the light curves also change. In addition to the models of SN 1987A, we investigate two models of Type II-P SNe and one model of a stripped-envelope Type IIb SN. The Type II-P models have similar observables as the models of SN 1987A, but the stripped-envelope SN model is significantly more luminous and evolves faster. Finally, we make simple predictions for future observations of nearby SNe.