The properties of the population of compact objects created in core-collapse supernovae (SNe) are uncertain. X-ray observations years to decades after the explosions offer a way to gain insight into this, as hard X-ray emission from the central regions will emerge as the ejecta absorption decreases. Here, we analyze and place upper limits on late-time X-ray emission in 242 nearby SNe, using 607 observations from Chandra, XMM-Newton, Swift, and NuSTAR. We use absorption models based on 3D simulations of neutrino-driven explosions to account for absorption of emission from the compact objects by the asymmetric ejecta. We detect X-ray emission from 12 SNe, including 4 for the first time (SN 1982R, SN 1984J, SN 1992bu, and SN 2003gk), and several of the others at later epochs than before. The X-ray spectra of these SNe are consistent with interaction with the circumstellar medium (CSM), with the possible exception of SN 1979C, which shows an additional hard component, as also noted in previous studies at earlier epochs. This emission may be due to a pulsar wind nebula. Using the upper limits in the full sample, we also perform a population synthesis to constrain the fraction of SNe that produce pulsars and the properties of the pulsars themselves. We find that pulsar populations with mean initial spin periods ≳100 ms are favored. Finally, we note that the high luminosities of several of the SNe with CSM interaction imply interactions with dense shells.

Aims. The accurate positional measurement of Supernova (SN) 1987A is important for determining the kick velocity of its compact object and the velocities of the ejecta and various shock components. In this work, we perform absolute astrometry to determine the position of SN 1987A. Methods. We used multi-epoch Hubble Space Telescope imaging to model the early ejecta and the equatorial ring (ER). We combined our measurements and obtained the celestial coordinates in the International Celestial Reference System (ICRS) by registering the observations onto Gaia Data Release 3. Results. The final average position of the different measurements is α = 5h35m27⋅s9884(30),δ = −69∘16′11⋅′′1134(136) (ICRS J2016). The early ejecta position is located 14 mas south and 16 mas east of the ER center, with the offset being significant at 96% confidence. The offset may be due to instrument and/or filter-dependent systematics and registration uncertainties, though an intrinsic explosion offset relative to the ER remains possible. Image registration with proper motion corrections yields similar astrometry and a source proper motion of μ east(≡ PMα*) = 1.60 ± 0.15 mas yr−1 and μ north(≡ PMδ ) = 0.44 ± 0.09 mas yr−1, in agreement with the typical local motion of the Large Magellanic Cloud. Conclusions. The absolute positional uncertainty of 21 mas adds a systematic uncertainty to the sky-plane kick velocity of 123 (t/40 yr−1 km s−1, where t is the time since the explosion. Comparing the location of the compact source observed with JWST to our updated position implies a sky-plane kick of 399 ± 148 km s−1 and a 3D kick of 472 ± 126 km s−1, which is consistent with previous estimates.

JWST/NIRCam obtained high angular resolution (0.05-0.1 arcsec), deep near-infrared 1-5 μm imaging of Supernova (SN) 1987A taken 35 yr after the explosion. In the NIRCam images, we identify: (1) faint H2 crescents, which are emissions located between the ejecta and the equatorial ring, (2) a bar, which is a substructure of the ejecta, and (3) the bright 3-5 μm continuum emission exterior to the equatorial ring. The emission of the remnant in the NIRCam 1-2.3 μm images is mostly due to line emission, which is mostly emitted in the ejecta and in the hotspots within the equatorial ring. In contrast, the NIRCam 3-5 μm images are dominated by continuum emission. In the ejecta, the continuum is due to dust, obscuring the centre of the ejecta. In contrast, in the ring and exterior to the ring, synchrotron emission contributes a substantial fraction to the continuum. Dust emission contributes to the continuum at outer spots and diffuse emission exterior to the ring, but little within the ring. This shows that dust cooling and destruction time-scales are shorter than the synchrotron cooling time-scale, and the time-scale of hydrogen recombination in the ring is even longer than the synchrotron cooling time-scale. With the advent of high sensitivity and high angular resolution images provided by JWST/NIRCam, our observations of SN 1987A demonstrate that NIRCam opens up a window to study particle-acceleration and shock physics in unprecedented details, probed by near-infrared synchrotron emission, building a precise picture of how an SN evolves.

A dozen X-ray supernova shock breakout (SN SBO) candidates were reported recently based on XMM-Newton archival data, which increased the X-ray-selected SN SBO sample by an order of magnitude. Assuming that they are genuine SN SBOs, we study the luminosity function (LF) by improving on the method used in our previous work. The light curves and the spectra of the candidates were used to derive the maximum volume within which these objects could be detected with XMM-Newton by simulation. The results show that the SN SBO LF can be described by either a broken power law (BPL) with indices (at the 68% confidence level) of 0.48 +/- 0.28 and 2.11 +/- 1.27 before and after the break luminosity at log(L-b/erg s(-1)) = 45.32 +/- 0.55 or a single power law (SPL) with an index of 0.80 +/- 0.16. The local event rate densities of SN SBOs above 5 x 10(42) erg s (-1) are consistent for two models, i.e., 4.6(-1.3)(+1.7) x 10(4) Gpc(-3) yr(-1) and 4.9(-1.4)(+1.9 )x 10(4) Gpc(-3) yr(-1) for BPL and SPL models, respectively. The number of fast X-ray transients of SN SBO origin can be significantly increased by wide-field X-ray telescopes such as the Einstein Probe.

A core-collapse supernova (CCSN) is an astronomical explosion that indicates the death of a massive star. From observations, it is clear that a large fraction of all massive stars undergoes supernova (SN) explosions, but describing how SNe explode has remained a challenge for many decades. A key piece of the puzzle is the properties of the progenitor star.

The attached papers focus on comparing theoretical predictions with observations, primarily observations of SN 1987A. It is the closest observed SN in more than four centuries, allowing for more detailed studies than for any other SN. The papers investigate different aspects of the SN phenomenon. These individual studies are observationally diverse, but all attempt to answer different questions that are important for our understanding of the SN process.

The properties of the progenitor star set the stage for the SN. Paper III compares SN models based on different progenitor stars with early X-ray and gamma-ray observations of SN 1987A. The results help constrain the evolution of the progenitor. In Paper IV, we searched for SN shock breakouts (SBOs), which are the first electromagnetic signals from CCSNe. The discovered candidates convey information about the progenitors, test the SBO theory, and indicate the presence of other types of X-ray transients.

The SN explosion mechanism itself is also integral to the analysis in Paper III. The explosion models used in Paper III rely on some of the most recent three-dimensional neutrino-driven SN models. The results lend further support to the hypothesis that delayed neutrino heating is sufficient to explode the vast majority of all CCSNe.

Much can also be learned about SNe by studying their remnants. The remains of the core, the compact remnant, in SN 1987A has not yet been detected. We have investigated how a compact object can remain hidden in the ejecta in Paper I, using an absorption model from Paper II. We favor a scenario where the compact object is a neutron star that is quiescent, dust-obscured, and only emitting thermal emission. Paper V is another study of SN 1987A, but focuses on the X-ray emission from the ongoing interactions between the ejecta and circumstellar medium (CSM). The X-ray emission is primarily generated by thermal processes in shocks produced by collisions between the ejecta and the CSM. We found no evidence for any contribution from relativistic particles or a neutron star.

Our description of CCSNe continues to improve but many questions remain unanswered. Future observations will further our knowledge and the models we have studied can be used for continued analyses. The next generation of X-ray missions is very promising and a Galactic SN, which would greatly accelerate the entire research field, could occur at any time.

En kärnkollapssupernova (CCSN) är en astronomisk explosion som indikerar slutet av en massiv stjärnas liv. Från observationer är det tydligt att en stor andel av alla massiva stjärnor exploderar som supernovor (SN:or), men att förklara hur SN:or exploderar har kvarstått som en utmaning under flera decennier. En viktig del av pusslet är föregångarstjärnans egenskaper.

De bifogade artiklarna fokuserar på att jämföra teoretiska förutsägelser med observationer, primärt observationer av SN 1987A. Det är den närmsta observerade SN:an på över fyra århundraden, vilket möjliggör mer detaljerade studier än av någon annan SN. Artiklarna studerar olika aspekter av SN-fenomenet. Studierna är observationellt vitt skilda men adresserar alla frågor som är viktiga för vår förståelse av SN-processen.

Föregångarstjärnans egenskaper är avgörande för den efterföljande SN-explosionen. Paper III jämför modeller baserade på olika föregångarstjärnor med tidiga röntgen- och gamma-observationer av SN 1987A. Resultaten från studien begränsar föregångarstjärnans utveckling. I Paper IV söker vi SN chockutbrott (SBO:s), vilka är de första elektromagnetiska signalerna från CCSN:or. De upptäckta kandidaterna bär information om föregångarstjärnorna, testar SBO-teorin, och indikerar förekomsten av andra typer av röntgentransienter.

Själva SN-explosionsmekanismen är också kritisk för analysen i Paper III. Explosionsmodellerna som används i Paper III baseras på några av de senaste tre-dimensionella neutrinodrivna SN-modellerna. Resultaten ger ytterligare stöd för hypotesen att fördröjd neutrinoupphettning är tillräcklig för att explodera den överväldigande majoriteten av alla CCSN:or.

SN-rester ger också mycket information om SN-explosioner. Kvarlevorna av den centrala kärnan, det kompakta objektet, i SN 1987A har ännu inte blivit detekterad. Vi har undersökt hur ett kompakt objekt kan förbli dolt i ejektat i Paper I, med hjälp av en absorptionsmodell från Paper II. Den mest troliga förklaringen är att neutronstjärnan är passiv, stoftskymd, och bara har en termisk emissionskomponent. Paper V är ytterligare en studie av SN 1987A, men som specifikt fokuserar på röntgenemissionen som uppstår då ejektat interagerar med det cirkumstellära mediet (CSM:et). Röntgenstrålningen är primärt producerad av termiska processer i kollisionen mellan ejektat och CSM:et. Vi fann inget stöd för något bidrag från relativistiska partiklar eller en neutronstjärna.

Vår beskrivning av CCSN:or förbättras kontinuerligt men många frågor är ännu obesvarade. Framtida observationer kommer ge nya ledtrådar och de modeller vi har studerat kan användas för fortsatta analyser. Nästa generations röntgenteleskop kommer vara väldigt kraftfulla och en galaktisk SN, som skulle vara mycket värdefull för hela forskningsfältet, kan ske när som helst.

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 similar to 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 Ti-44 redshift of 670(+520) (-380) km s(-1), Ti-44 mass of ' 1.73(-0.29)(+0.27) 10(-4) M-circle dot, and Fe-55Y mass of <4.2 10(-4) M-circle dot. The 35-65.keV luminosity limit on the compact object is 2 ' 1034.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 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 similar to 10(46)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 similar to 2 SBOs per year, which could be detected in live analyses and promptly followed up.

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 kilometres per second depending on viewing angle. The line profiles can be complex with multiple peaks. By combining observational constraints from Co-56 decay lines, Ti-44 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-circle dot progenitors exploding with similar to 1.5 x 10(51) erg, ejecta structures suitable to reproduce the observations involve a bulk asymmetry of the Ni-56 of at least similar to 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 600 d, an ejecta mass around 14 M-circle dot 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.

A core-collapse supernova (CCSN) is an astronomical explosion that indicates the death of a massive star. The iron core of the star collapses into either a neutron star or a black hole while the rest of the material is expelled at high velocities. Supernovae (SNe) are important for the chemical evolution of the Universe because a large fraction of the heavier elements such as oxygen, silicon, and iron are liberated by CCSN explosions. Another important role of SNe is that the ejected material seed the next generation of stars and planets. From observations, it is clear that a large fraction of all massive stars undergoes SN explosions, but describing how SNe explode has remained a challenge for many decades.

The attached papers focus on comparing theoretical predictions with observations, primarily observations of SN 1987A. The compact remnant in SN 1987A has not yet been detected and we have investigated how a compact object can remain hidden in the ejecta (Paper I and II). Because of the high opacity of the metal-rich ejecta, the direct X-ray observations are not very constraining even for potentially favorable viewing angles. However, the combined observations still strongly constrain fallback accretion and put a limit on possible pulsar wind activity. The thermal surface emission from a neutron star is consistent with the observations if our line of sight is dust-obscured, and only marginally consistent otherwise. Future observations provide promising opportunities for detecting the compact object.

We have also compared the most recent three-dimensional neutrino-driven SN models that are based on explosion simulations with early X-ray and gamma-ray observations of SN 1987A (Paper III). The models that are designed to match SN 1987A fit the data well, but not all tensions can be explained by choosing a suitable viewing angle. More generally, the asymmetries do not affect the early emission qualitatively and different progenitors of the same class result in similar early emission. We also find that the progenitor metallicity is important for the low-energy X-ray cuto↵. Current instruments should be able to detect this emission from SNe at distances of 3–10 Mpc, which correspond to distances slightly beyond the Local Group.

En kärnkollapssupernova (CCSN) är en astronomisk explosion som indikerar slutet av en massiv stjärnas liv. Stjärnans järnkärna kollapsar antingen till en neutronstjärna eller ett svart hål medan resten av materialet slungas iväg med höga hastigheter. Supernovor (SNe) är viktiga för Universums kemiska utveckling eftersom en stor andel av alla tyngre element såsom syre, kisel, och järn frigörs i CCSN-explosioner. Ytterligare en viktig roll för SNe är att nästa generations stjärnor och planeter bildas av det utkastade materialet. Från observationer är det tydligt att en stor andel av alla massiva stjärnor genomgår SN-explosioner, men att förklara hur SNe exploderar har kvarstått som en utmaning under flera decennier.

De bifogade artiklarna fokuserar på att jämföra teoretiska förutsägelser med observationer, primärt observationer av SN 1987A. Det kompakta objektet i SN 1987A har ännu inte blivit detekterat och vi har undersökt hur ett kompakt objekt kan förbli dolt i ejektat (Paper I och II). De direkta röntgenobservationerna är inte så begränsande även längs potentiellt gynsamma siktlinjer på grund av det metallrika ejektats höga opacitet. Däremot begränsar kombinationen av alla observationer starkt ackretion och sätter en gräns för möjlig pulsarvindsaktivitet. Den termiska ytstrålningen från en neutronstjärna är konsistent med observationerna om vår siktlinje är skymd av stoft, och bara marginellt konsistent annars. Framtida observationer utgör lovande möjligheter för att detektera det kompakta objektet.

Vi har också jämfört de senaste tredimensionella neutrinodrivna SN-modellerna, som är baserade på explosionssimuleringar, med tidiga röntgen- och gamma-observationer av SN 1987A (Paper III). SN 1987A-modellerna passar datan väl, men alla diskrepanser kan inte förklaras av ett lämpligt val av observationsvinkel. Generellt så påverkar inte asymmetrierna den tidiga emissionen kvalitativt och olika föregångarstjärnor av samma kategori resulterar i likartad strålning. Vi finner också att föregångarstjärnans metallisitet är viktig för egenskaperna av lågenergiröntgenstrålningen. Befintliga instrument borde kunna detektera denna emission på 3--10 Mpc, vilket motsvarar avstånd lite bortom den Lokala galaxhopen.

We present high angular resolution (similar to 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 H alpha 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-infrared-millimeter spectral energy distribution give ejecta dust temperatures of 18-23 K. We revise the ejecta dust mass to M-dust = 0.2-0.4 M-circle dot for carbon or silicate grains, or a maximum of <0.7 M-circle dot for a mixture of grain species, using the predicted nucleosynthesis yields as an upper limit.