| 1. |
- Alp, Dennis, MSc, 1992-
(författare)
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An X-Ray View of Core-collapse Supernovae
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 2. |
- Milisavljevic, Dan, et al.
(författare)
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A JWST Survey of the Supernova Remnant Cassiopeia A
- 2024
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Ingår i: Astrophysical Journal Letters. - 2041-8205 .- 2041-8213. ; 965:2
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Tidskriftsartikel (refereegranskat)abstract
- We present initial results from a James Webb Space Telescope (JWST) survey of the youngest Galactic core-collapse supernova remnant, Cassiopeia A (Cas A), made up of NIRCam and MIRI imaging mosaics that map emission from the main shell, interior, and surrounding circumstellar/interstellar material (CSM/ISM). We also present four exploratory positions of MIRI Medium Resolution Spectrograph integral field unit spectroscopy that sample ejecta, CSM, and associated dust from representative shocked and unshocked regions. Surprising discoveries include (1) a weblike network of unshocked ejecta filaments resolved to ∼0.01 pc scales exhibiting an overall morphology consistent with turbulent mixing of cool, low-entropy matter from the progenitor's oxygen layer with hot, high-entropy matter heated by neutrino interactions and radioactivity; (2) a thick sheet of dust-dominated emission from shocked CSM seen in projection toward the remnant's interior pockmarked with small (∼1'') round holes formed by ≲01 knots of high-velocity ejecta that have pierced through the CSM and driven expanding tangential shocks; and (3) dozens of light echoes with angular sizes between ∼01 and 1' reflecting previously unseen fine-scale structure in the ISM. NIRCam observations place new upper limits on infrared emission (≲20 nJy at 3 μm) from the neutron star in Cas A's center and tightly constrain scenarios involving a possible fallback disk. These JWST survey data and initial findings help address unresolved questions about massive star explosions that have broad implications for the formation and evolution of stellar populations, the metal and dust enrichment of galaxies, and the origin of compact remnant objects.
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| 3. |
- Nymark, Tanja, 1971-
(författare)
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X-ray emission from supernova shock waves
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A theoretical study of the interaction between supernovae and their surroundings is presented.Supernovae are the endpoint of the life of massive stars, and are the dominant contributors to the chemical evolution of the Universe. During its life a massive star greatly modifies its environment. During and after the explosion of the star it interacts with its surroundings in a number of ways. A study of this interaction yields invaluable information about the late stages of stellar evolution and the physics of supernova explosions. Recent advances in observational facilities have given a wealth of observational data on interacting supernovae, and it is therefore essential to have good theoretical models for interpreting the data.This thesis presents an overview of the physics of supernovae and of their interaction with a circumstellar medium. In particular the reverse shock created by the interaction is investigated. In most Type IIL and Type IIn supernovae this shock is radiative, and due to the high temperature most of the radiation comes out as X-rays. A numerical model is presented which calculates the emission from the cooling region behind the reverse shock in a self-consistent way, by combining a hydrodynamic model with a time-dependent ionization balance and multilevel calculations. This has been applied to some of the best cases of circumstellar interaction.As a further application of the model the radio and X-ray emission from Type IIP supernovae is discussed. We estimate the mass loss rate of the progenitors of Type IIP supernovae, and find that a superwind phase is not required.VLT observations of the ring of SN 1987A show broad optical emission lines coming from a range of ionization stages, in particular optical coronal lines of Fe X-XIV. Models of the line emission indicate that the lines are formed by cooling shocks with shock velocities in the range 310-390 km/s, confirming the picture of shocks striking the protrusions from the ring obliquely.X-ray observations of the Type IIb SN 1993J and Type IIn SN 1998S are analyzed. For SN 1993J we find that the spectrum is best fit with a CNO-enriched composition. For SN 1998S we find that the high metal overabundance that has previously been claimed, is not necessary when a self-consistent model of the cooling region is applied.
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| 4. |
- Soffitta, Paolo, et al.
(författare)
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A polarized view of the hot and violent universe
- 2021
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Ingår i: Experimental astronomy. - : Springer Nature. - 0922-6435 .- 1572-9508. ; 51:3, s. 1109-1141
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Tidskriftsartikel (refereegranskat)abstract
- X-ray polarimetry has long been considered the 'holy grail' of X-ray astronomy. Fortunately, after a silence of more than 40 years, the field is now rejuvenating. In fact, an X-ray polarimeter onboard a Cube-sat nano-satellite has been recently successfully operated. IXPE, the Imaging X-ray Polarimetry Explorer, will be launched in 2021 while eXTP, containing a larger version of IXPE, is expected to be launched in 2027. Although at present it is difficult to predict the discoveries that, given their exploratory nature, IXPE and eXTP will obtain, the path for a follow-up mission can already be envisaged. In this paper we describe the scientific goals of such a follow-up mission, and present a medium-size mission profile that can accomplish this task.
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| 5. |
- Zane, Silvia, et al.
(författare)
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The on-board calibration system of the X-ray Imaging Polarimetry Explorer (XIPE)
- 2016
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Ingår i: SPACE TELESCOPES AND INSTRUMENTATION 2016. - : SPIE - International Society for Optical Engineering. - 9781510601895
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Konferensbidrag (refereegranskat)abstract
- The calibration system for XIPE is aimed at providing a way to check and correct possible variations of performance of the Gas Pixel Detector during the three years of operation in orbit (plus two years of possible extended operation), while facilitating the observation of the celestial sources. This will be performed by using a filter wheel with a large heritage having a set of positions for the calibration and the observation systems. In particular, it will allow for correcting possible gain variation, for measuring the modulation factor using a polarized source, for removing non interesting bright sources in the field of view and for observing very bright celestial sources. The on-board calibration system is composed of three filter wheels, one for each detector and it is expected to operate for a small number of times during the year. Moreover, since it operates once at a time, within the observation mode, it allows for simultaneous calibration and acquisition from celestial sources on different detectors. In this paper we present the scope and the requirements of the on-board calibration system, its design, and a description of its possible use in space.
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