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Core-collapse Supernovae: Theory vs. Observations
KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. (Particle and Astroparticle)
2019 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Abstract [sv]

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.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2019. , p. 62
Series
TRITA-SCI-FOU ; 2019:01
Keywords [en]
Astrophysics, Supernovae
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Physics
Identifiers
URN: urn:nbn:se:kth:diva-241431ISBN: 978-91-7873-062-9 (print)OAI: oai:DiVA.org:kth-241431DiVA, id: diva2:1280986
Presentation
2019-02-14, FB52, AlbaNova Universitetscentrum, Roslagstullsbacken 21, Stockholm, 15:00 (English)
Opponent
Supervisors
Note

QC 20190121

Available from: 2019-01-21 Created: 2019-01-21 Last updated: 2019-01-21Bibliographically approved
List of papers
1. The 30 Year Search for the Compact Object in SN 1987A
Open this publication in new window or tab >>The 30 Year Search for the Compact Object in SN 1987A
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2018 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 864, no 2, article id 174Article in journal (Refereed) Published
Abstract [en]

Despite more than 30 years of searching, 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 x 10(-26) erg s(-1) cm(-2) Hz(-1)) at 213 GHz, 1 L-circle dot (6 x 10(-29) erg s(-1) cm(-2) Hz(-1)) in the optical if our line of sight is free of ejecta dust, and 10(36) erg s(-1) (2 x 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. The allowed bolometric luminosity of the compact object is 22 L-circle dot if our line of sight is free of ejecta dust, or 138L(circle dot) if dust-obscured. Depending on assumptions, these values limit the effective temperature of a neutron star (NS) 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 77 is limited to <10(-11) eta(-1) M-circle dot 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 less than or similar to 10(14) P-2 G s(-2), which firmly excludes pulsars comparable to the Crab. By combining information about radiation reprocessing and geometry, we infer that the compact object is a dust-obscured thermally emitting NS, which may appear as a region of higher-temperature ejecta dust emission.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2018
Keywords
stars: black holes, stars: neutron, supernovae: individual (SN 1987A)
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-235442 (URN)10.3847/1538-4357/aad739 (DOI)000444645600011 ()2-s2.0-85053411220 (Scopus ID)
Funder
Knut and Alice Wallenberg FoundationSwedish Research CouncilEU, European Research Council, 341157-COCO2CASA
Note

QC 20180927

Available from: 2018-09-27 Created: 2018-09-27 Last updated: 2019-01-21Bibliographically approved
2. X-Ray Absorption in Young Core-collapse Supernova Remnants
Open this publication in new window or tab >>X-Ray Absorption in Young Core-collapse Supernova Remnants
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2018 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 864, no 2, article id 175Article in journal (Refereed) Published
Abstract [en]

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(4)(-2 )E(-2), where t(4) is the time since the explosion in units of 10,000 days (similar to 27 years) and E is the energy in units of keV. Compton scattering dominates above 50 keV, but the scattering depth is lower and reaches unity at similar to 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 that 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 similar to 100 L-circle dot 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. For the central compact object in Cas A, we find no significant effects of our more detailed absorption model on the inferred surface temperature.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2018
Keywords
stars: neutron, supernova remnants, supernovae: general, supernovae: individual (SN 1987A, Cas A), X-rays: ISM
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-235443 (URN)10.3847/1538-4357/aad737 (DOI)000444645600012 ()2-s2.0-85053387396 (Scopus ID)
Note

QC 20180927

Available from: 2018-09-27 Created: 2018-09-27 Last updated: 2019-01-21Bibliographically approved
3. Early X-Ray and Gamma-Ray Emission from 3D Neutrino-Driven SN Simulations and Comparisons With Observations of SN 1987A
Open this publication in new window or tab >>Early X-Ray and Gamma-Ray Emission from 3D Neutrino-Driven SN Simulations and Comparisons With Observations of SN 1987A
(English)Manuscript (preprint) (Other academic)
Abstract [en]

During the first few hundred days, core-collapse supernovae (CCSNe) strongly emit X-rays and gamma-rays originating from radioactive elements, primarily the 56Ni chain. We use SN models based on three-dimensional (3D) neutrino-driven explosion simulations to compute this early emission and compare the predictions to observations of SN 1987A. The agreement between the models and observations is good but small differences that cannot be matched by a suitable choice of viewing angle are evident. The discrepancies indicate that the models need to be slightly more mixed and the bulk of the 56Ni should be moving away from us at higher velocities than can be found in the models. Asymmetries and 3D structures vary the flux by a factor of a few but do not affect the emission qualitatively. The emission also shows similar properties for qualitatively similar progenitors. The only major difference is that stripped-envelope SNe evolve faster and are more than an order of magnitude more luminous. The soft X-ray cutoff is primarily determined by the metallicity of the progenitor. Future NuSTAR observations should detect the down-scattered continuum and low-energy cutoff of (non-)stripped SNe at distances of (3)10 Mpc. INTEGRAL/SPI can detect the direct line emission at distances of (0.2)2 Mpc.

Keywords
Astrophysics, Supernovae
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Physics
Identifiers
urn:nbn:se:kth:diva-241430 (URN)
Note

QC 20190121

Available from: 2019-01-21 Created: 2019-01-21 Last updated: 2019-01-21Bibliographically approved

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