Search

We report on Chandra X-ray observations of SN 2016jae and SN 2018cqj, both low luminosity Type Ia supernova that showed the presence of a H line in their early optical spectrum. No X-ray emission is detected at the location of either SN. Upper limits to the luminosity of up to 2 $\times 10^{40}\,$ erg s$^{-1}$ are calculated for each SN, depending on the assumed spectral model, temperature and column density. This luminosity is comparable to that of another low-luminosity Type Ia SN, SN 2018fhw, that was observed with Chandra. It is generally lower than upper limits calculated for Type Ia-CSM SNe observed in X-rays, and also below that of SN 2012ca, the only Type Ia-CSM SN to have been detected in X-rays. Comparisons are made to other Type Ia SN with a H line observed in X-rays. The observations suggest that while the density into which the SN is expanding may have been high at the time the H$\alpha$ line was detected, it had decreased considerably by the time of X-ray observations., Comment: 9 pages, 4 figures and 3 Tables. Accepted to MNRAS. arXiv admin note: text overlap with arXiv:2211.09274

The detection of gravitational waves from a binary neutron star merger by Advanced LIGO and Advanced Virgo (GW170817), along with the discovery of the electromagnetic counterparts of this gravitational wave event, ushered in a new era of multimessenger astronomy, providing the first direct evidence that BNS mergers are progenitors of short gamma-ray bursts (GRBs). Such events may also produce very-high-energy (VHE, > 100GeV) photons which have yet to be detected in coincidence with a gravitational wave signal. The Cherenkov Telescope Array (CTA) is a next-generation VHE observatory which aims to be indispensable in this search, with an unparalleled sensitivity and ability to slew anywhere on the sky within a few tens of seconds. New observing modes and follow-up strategies are being developed for CTA to rapidly cover localization areas of gravitational wave events that are typically larger than the CTA field of view. This work will evaluate and provide estimations on the expected number of of gravitational wave events that will be observable with CTA, considering both on- and off-axis emission. In addition, we will present and discuss the prospects of potential follow-up strategies with CTA., Comment: Presented at the 38th International Cosmic Ray Conference (ICRC 2023), 2023 (arXiv:2309.08219)

I report on Chandra X-ray observations of SN 2018cqj, a low luminosity Type Ia supernova that showed an H$\alpha$ line in its optical spectrum. No X-ray emission was detected at the location of the SN, with an upper limit to the X-ray luminosity of 2 $\times 10^{39}$ erg s$^{-1}$., Comment: 3 pages, 1 table. Published in RNAAS

The structure and evolution of wind-blown bubbles (WBBs) around massive stars has primarily been investigated using an energy-conserving model of wind-blown bubbles. While this model is useful in explaining the general properties of the evolution, several problems remain, including inconsistencies between observed wind luminosities and those derived using this formulation. Major difficulties include the low X-ray temperature and X-ray luminosity, compared to the model. In this paper, we re-examine the evolution, dynamics, and kinematics of WBBs around massive stars, using published ionization gasdynamic simulations of wind-blown bubbles. We show that WBBs can cool efficiently due to the presence of various instabilities and turbulence within the bubble. The expansion of WBBs is more consistent with a momentum-conserving solution, rather than an energy-conserving solution. This compares well with the dynamics and kinematics of observed wind bubbles. Despite the cooling of the bubble, the shocked wind temperature is not reduced to the observed values. We argue that the X-ray emission arise mainly from clumps and filaments within the hot shocked wind region, with temperatures just above 10$^6$ K. The remainder of the plasma can contribute to a lesser extent., Comment: 22 pages, 7 figures. Published in Galaxies. Only low-resolution figures are included due to size requirements; original high-resolution figures, especially Figure 1, can be obtained from the published paper in the journal

We report on Chandra X-ray observations of ASASSN-18tb/SN 2018fhw, a low luminosity Type Ia supernova that showed a H line in its optical spectrum. No X-ray emission was detected at the location of the SN. Upper limits to the luminosity of up to 3 $\times 10^{39}$ erg s$^{-1}$ are calculated, depending on the assumed spectral model, temperature and column density. These are compared to two Type Ia-CSM SNe, SN 2005gj and SN 2002ic, that have been observed with Chandra in the past. The upper limits are lower than the X-ray luminosity found for the Type Ia-CSM SN 2012ca, the only Type Ia SN to have been detected in X-rays. Consideration of various scenarios for the H$\alpha$ line suggests that the density of the surrounding medium at the time of H$\alpha$ line detection could have been as high as 10$^8$ cm$^{-3}$, but must have decreased below 5 $\times\, 10^6$ cm$^{-3}$ at the time of X-ray observation. Continual X-ray observations of SNe which show a H line in their spectrum are necessary in order to establish Type Ia SNe as an X-ray emitting class., Comment: 9 pages, 1 figure, 3 tables. Accepted to MNRAS

We present broadband radio flux-density measurements supernova (SN) 1996cr, made with MeerKAT, ATCA and ALMA, and images made from very long baseline interferometry (VLBI) observations with the Australian Long Baseline Array. The spectral energy distribution of SN 1996cr in 2020, at age, $t \sim$8700 d, is a power-law, with flux density, $S \propto \nu^{-0.588 \pm 0.011}$ between 1 and 34 GHz, but may steepen at $>35$ GHz. The spectrum has flattened since $t = 5370$ d (2010). Also since $t = 5370$ d, the flux density has declined rapidly, with $S_{\rm 9 \, GHz} \propto t^{-2.9}$. The VLBI image at $t = 8859$ d shows an approximately circular structure, with a central minimum reminiscent of an optically-thin spherical shell of emission. For a distance of 3.7 Mpc, the average outer radius of the radio emission at $t = 8859$ d was $(5.1 \pm 0.3) \times 10^{17}$ cm, and SN 1996cr has been expanding with a velocity of $4650 \pm 1060$ km s$^{-1}$ between $t=4307$ and 8859 d. It must have undergone considerable deceleration before $t = 4307$ d. Deviations from a circular shell structure in the image suggest a range of velocities up to $\sim$7000 km s$^{-1}$, and hint at the presence of a ring- or equatorial-belt-like structure rather than a complete spherical shell., Comment: 10 Pages, 5 figures; Accepted for publication in MNRAS; this version (3) differs from version 2 by further minor revision

We probe the environmental properties of X-ray supernova remnants (SNRs) at various points along their evolutionary journey, especially the S-T phase, and their conformance with theoretically derived models of SNR evolution. The remnant size is used as a proxy for the age of the remnant. Our data set includes 34 Milky Way, 59 Large Magellanic Cloud (LMC), and 5 Small Magellanic Cloud (SMC) SNRs. We select remnants that have been definitively typed as either core-collapse (CC) or Type Ia supernovae, with well-defined size estimates, and a thermal X-ray flux measured over the entire remnant. A catalog of SNR size and X-ray luminosity is presented and plotted, with ambient density and age estimates from the literature. Model remnants with a given density, in the Sedov-Taylor (S-T) phase, are overplotted on the diameter-vs-luminosity plot, allowing the evolutionary state and physical properties of SNRs to be compared to each other, and to theoretical models. We find that small, young remnants are predominantly Type Ia remnants or high luminosity CCs, suggesting that many CC SNRs are not detected until after they have emerged from the progenitor's wind-blown bubble. An examination of the distribution of SNR diameters in the Milky Way and LMC reveals that LMC SNRs must be evolving in an ambient medium which is 30% as dense as that in the Milky Way. This is consistent with ambient density estimates for the Galaxy and LMC., Comment: 22 pages, 6 figures. Accepted to MNRAS. Online version of Fig 2 with all SNR names is available at https://voices.uchicago.edu/vikramvd/snrspaper/

SN 2014C was originally classified as a Type Ib supernova, but at phase {\phi} = 127 d post-explosion strong H{\alpha} emission was observed. SN 2014C has since been observed in radio, infrared, optical and X-ray bands. Here we present new optical spectroscopic and photometric data spanning {\phi} = 947 - 2494 d post-explosion. We address the evolution of the broadened H{\alpha} emission line, as well as broad [O III] emission and other lines. We also conduct a parallel analysis of all publicly available multi-wavelength data. From our spectra, we find a nearly constant H{\alpha} FWHM velocity width of {\sim}2000 km/s that is significantly lower than that of other broadened atomic transitions ({\sim}3000 - 7000 km/s) present in our spectra ([O I] {\lambda}6300; [O III] {\lambda}{\lambda}4959,5007; He I {\lambda}7065; [Ca II] {\lambda}{\lambda}7291,7324). The late radio data demand a fast forward shock ({\sim}10,000 km/s at {\phi} = 1700 d) in rarified matter that contrasts with the modest velocity of the H{\alpha}. We propose that the infrared flux originates from a toroidal-like structure of hydrogen surrounding the progenitor system, while later emission at other wavelengths (radio, X-ray) likely originates predominantly from the reverse shock in the ejecta and the forward shock in the quasi-spherical progenitor He wind. We propose that the H{\alpha} emission arises in the boundary layer between the ejecta and torus. We also consider the possible roles of a pulsar and a binary companion., Comment: 33 pages, 12 figures

Using a code that employs a self-consistent method for computing the effects of photo-ionization on circumstellar gas dynamics, we model the formation of wind-driven nebulae around massive stars. We take into account changes in stellar properties and mass-loss over the star's evolution. Our simulations show how various properties, such as the density and ionization fraction, change throughout the evolution of the star. The multi-dimensional simulations reveal the presence of strong ionization front instabilities in the main-sequence phase, similar to those seen in galactic ionization fronts. Hydrodynamic instabilities at the interfaces lead to the formation of filaments and clumps that are continually being stripped off and mixed with the low density interior. Even though the winds start out as completely radial, the spherical symmetry is quickly destroyed, and the shocked wind region is manifestly asymmetrical. The simulations demonstrate that it is important to include the effects of the photoionizing photons from the star, and simulations that do not include this may fail to reproduce the observed density profile and ionization structure of wind-blown bubbles around massive stars., Comment: 3 figures, 1 table. 13 pages. Author version of published paper, with reduced size figures 2 and 3. For full resolution figures see the published paper at https://www.mdpi.com/2075-4434/10/1/37. Accepted to Galaxies. This article belongs to the special issue of the conference Asymmetrical Post Main-Sequence Nebulae 8

We perform empirical fits to the \emph{Chandra} and \emph{XMM-Newton} spectra of three ultraluminous X-ray sources (ULXs) in the edge-on spiral galaxy NGC 891, monitoring the region over a seventeen year time window. One of these sources has been visible since the early 1990s with \emph{ROSAT} and has been observed multiple times with \emph{Chandra} and \emph{XMM-Newton}. Another has been visible since 2011. We build upon prior analyses of these sources by analyzing all available data at all epochs. Where possible \emph{Chandra} data is used, since its superior spatial resolution allows for more effective isolation of the emission from each individual source, thus providing a better determination of their spectral properties. We also identify a new transient ULX, CXOU J022230.1+421937, which faded from view over the course of a two month period from Nov 2016 to Jan 2017. Modeling of each source at every epoch was conducted using six different models ranging from thermal bremsstrahlung to accretion disk models. Unfortunately, but as is common with many ULXs, no single model yielded a much better fit than the others. The two known sources had unabsorbed luminosities that remained fairly consistent over five or more years. Various possibilities for the new transient ULX are explored., Comment: 23 pages, 4 tables, 5 figures. Accepted to Universe journal

The centroid energy of the Fe K$\alpha$ line has been used to identify the progenitors of supernova remnants (SNRs). These investigations generally considered the energy of the centroid derived from the spectrum of the entire remnant. Here we use {\it XMM-Newton} data to investigate the Fe K$\alpha$ centroid in 6 SNRs: 3C~397, N132D, W49B, DEM L71, 1E 0102.2-7219, and Kes 73. In Kes 73 and 1E 0102.2-7219, we fail to detect any Fe K$\alpha$ emission. We report a tentative first detection of Fe K$\alpha$ emission in SNR DEM L71, with a centroid energy consistent with its Type Ia designation. In the remaining remnants, the spatial and spectral sensitivity is sufficient to investigate spatial variations of the Fe K$\alpha$ centroid. We find in N132D and W49B that the centroids in different regions are consistent with that derived from the overall spectrum, although not necessarily with the remnant type identified via other means. However, in SNR 3C~397, we find statistically significant variation in the centroid of up to 100 eV, aligning with the variation in the density structure around the remnant. These variations span the intermediate space between centroid energies signifying core-collapse and Type Ia remnants. Shifting the dividing line downwards by 50 eV can place all the centroids in the CC region, but contradicts the remnant type obtained via other means. Our results show that caution must be used when employing the Fe K$\alpha$ centroid of the entire remnant as the sole diagnostic for typing a remnant., Comment: 10 pages, 3 figures. Accepted to the Astrophysical Journal

The transition from supernovae (SNe) to supernova remnants (SNRs) remains poorly understood, given the age gap between well-studied examples of the two. In order to bridge this gap, we analysed archival Chandra data for some of the oldest supernovae detected in X-rays, in order to extend their light curves out to late times. We fitted the spectra with thermal models. All the SNe with multiple X-ray data points were found to have similar X-ray luminosity, which was decreasing with time. The X-ray luminosity will likely continue to decrease while the SNe are evolving in a wind medium, but is anticipated to increase in the Sedov phase when the SNe are interacting with a constant density interstellar medium, bringing it in line with observed SNRs., Comment: Published in RNAAS.3 pages, 1 figure. Part of Focus on AAS 238 issue

Over the past two decades, I have been actively involved in teaching astronomy and astrophysics to Chicago Public School (CPS) students and their teachers, in collaboration with various groups as well as by myself. Valuable resources that we have created for schools include the Multiwavelength Astronomy Website, with modules for infrared, optical, ultraviolet, X-ray and gamma-ray astronomy. The content of each lesson is derived from interviews with scientists, archived oral histories, and/or memoirs. Lessons are evaluated by a science educator and at least one subject matter expert before being produced for the web. They are supplemented by NASA media, archival material from the University of Chicago Library and other archives, and participant contributed photographs, light curves, and spectra. Summer programs provided training to CPS teachers to use the resources in their classrooms. Currently, I lead the Chicago Area Research Mentoring (CHARM) initiative. In the past academic year I worked with a class of 17 diverse 11th grade honors students at the University of Chicago Charter School, Woodlawn. Through frequent lectures ($\sim$ every 4 weeks), these students were exposed to astrophysical topics and concepts not normally covered in a school curriculum. CHARM aims to develop the student's critical thinking, introduce them to astrophysical research methods and techniques, and prepare them for a career in science, technology, engineering and mathematics (STEM), particularly a research-oriented one. In this article, I highlight some projects, educational resources, results achieved, and lessons learned along the way., Comment: 8 pages, 4 figures. To appear in the proceedings of the International Cosmic Ray Conference 2021. To be published in the Proceedings of Science. All comments appreciated

The Supernova X-Ray Database (SNaX) was established a few years ago to make X-ray data on supernovae (SNe) publicly available via an elegant searchable web interface. The database has recently been updated to PhP7, had security updates done, and moved to a new server, ensuring its long-term stability. We urge astronomers to continue to download the data as needed for their work. Those with X-ray data on SNe are requested to upload it to the database via the easily fillable spreadsheet, making it accessible to everyone., Comment: 3 pages, 1 figure. Published in the Research Notes of the American Astronomical Society. Just a small reminder to astronomers to use the database for X-ray data on SNe, and to upload your data on X-ray SNe to the database

W49B is a supernova remnant (SNR) discovered over 60 years ago in early radio surveys. It has since been observed over the entire wavelength range, with the X-ray morphology resembling a centrally-filled SNR. The nature of its progenitor star is still debated. Applying Smoothed Particle Inference techniques to analyze the X-Ray emission from W49B, we characterize the morphology and abundance distribution over the entire remnant. We also infer the density structure and derive the mass of individual elements present in the plasma. The morphology is consistent with an interaction between the remnant and a dense medium along the eastern edge, and some obstruction towards the west. We find a total mass of 130 $(\pm 16)$ M$_{\odot}$ and an estimated ejecta mass of 1.2 $(\pm 0.2)$ M$_{\odot}$. Comparison of the inferred abundance values and individual element masses with a wide selection of SN models suggests that deflagration-to-detonation (DDT) Type Ia models are the most compatible, with Fe abundance being the major discriminating factor. The general agreement between our abundance measurements and those from previous studies suggests that disagreement between various authors is more likely due to the choice of models used for comparison, rather than the abundance values themselves. While our abundance results lean toward a Type Ia origin, ambiguities in the interpretation of various morphological and spectral characteristics of W49B do not allow us to provide a definitive classification., Comment: 14 pages, 8 figures, 5 tables. Accepted to the Astrophysical Journal

Core-collapse supernovae (SNe) expand into a medium created by winds from the pre-SN progenitor. The SN explosion and resulting shock wave(s) heat up the surrounding plasma, giving rise to thermal X-ray emission, which depends on the density of the emitting material. Tracking the variation of the X-ray luminosity over long periods of time thus allows for investigation of the kinematics of the SN shock waves, the structure of the surrounding medium, and the nature of the progenitor star. In this paper X-ray observations of five of the oldest known X-ray supernovae - SN 1970G, SN 1968D, SN 1959D, SN 1957D and SN 1941C - are analyzed, with the aim of reconstructing their light curves over several decades. For those supernovae for which we can extract multi-epoch data, the X-ray luminosity appears to decline with time, although with large error bars. No increase in the X-ray emission from SN 1970G is found at later epochs, contrary to previous reports. All five SNe show X-ray luminosities that are of comparable magnitude. We compare the late-time X-ray luminosities of these SNe to those of supernova remnants (SNRs) in the Galaxy which are a few hundred years old, and find that when the tentative decline is taken into account, the luminosity of the old SNe studied herein could fall below the luminosity of some of the younger SNRs within a few hundred years. However, the X-ray luminosity should begin to increase as the SNe expand in the Sedov phase, thus reaching that of the observed SNRs., Comment: Accepted to the Astrophysical Journal. 24 pages, 12 tables, 16 figures

Some core-collapse supernovae are likely to be efficient cosmic-ray accelerators up to the PeV range, and therefore, to potentially play an important role in the overall Galactic cosmic-ray population. The TeV gamma-ray domain can be used to study particle acceleration in the multi-TeV and PeV range. This motivates the study of the detectability of such supernovae by current and future gamma-ray facilities. The gamma-ray emission of core-collapse supernovae strongly depends on the level of the two-photon annihilation process: high-energy gamma-ray photons emitted at the expanding shock wave following the supernova explosion can interact with soft photons from the supernova photosphere through the pair production channel, thereby strongly suppressing the flux of gamma rays leaving the system. In the case of SN 1993J, whose photospheric and shock-related parameters are well measured, we calculate the temporal evolution of the expected gamma-ray attenuation by accounting for the temporal and geometrical effects. We find the attenuation to be of about $10$ orders of magnitude in the first few days after the SN explosion. The probability of detection of a supernova similar to SN 1993J with the Cherenkov Telescope Array is highest if observations are performed either earlier than 1 day, or later than 10 days after the explosion, when the gamma-ray attenuation decreases to about $2$ orders of magnitude., Comment: Accepted to MNRAS, 7 pages, 7 figures

We analyze the X-Ray emission from the supernova remnant DEM L71 using the Smoothed Particle Inference (SPI) technique. The high Fe abundance found appears to confirm the Type Ia origin. Our method allows us to separate the material ejected in the supernova explosion from the material swept-up by the supernova shock wave. We are able to calculate the total mass of this swept-up material to be about 228 $\pm$ 23 M$_{\odot}$. We plot the posterior distribution for the number density parameter, and create a map of the density structure within the remnant. While the observed density shows substantial variations, we find our results are generally consistent with a two-dimensional hydrodynamical model of the remnant that we have run. Assuming the ejected material arises from a Type Ia explosion, with no hydrogen present, we use the predicted yields from Type Ia models available in the literature to characterize the emitting gas. We find that the abundance of various elements match those predicted by deflagration to detonation transition (DDT) models. Our results, compatible with the Type Ia scenario, highlight the complexity of the remnant and the nature of the surrounding medium., Comment: 6 pages, 7 Figures. Accepted for publication in Astronomische Nachrichten. To appear as part of the Proceedings of the XMM-Newton 2019 Workshop on "Astrophysics of Hot Plasma in Extended X-Ray Sources"

The interaction between the expanding supernova (SN) ejecta with the circumstellar material (CSM) that was expelled from the progenitor prior to explosion is a long-sought phenomenon, yet observational evidence is scarce. Here we confirm a new example: SN 2004dk, originally a hydrogen-poor, helium-rich Type Ib SN that reappeared as a strong H$\alpha$-emitting point-source on narrowband H$\alpha$ images. We present follow-up optical spectroscopy that reveals the presence of a broad H$\alpha$ component with full width at half maximum of ~290 km/s in addition to the narrow H$\alpha$ +[NII] emission features from the host galaxy. Such a broad component is a clear sign of an ejecta-CSM interaction. We also present observations with the XMM-Newton Observatory, the Swift satellite, and the Chandra X-ray Observatory that span 10 days to 15 years after discovery. The detection of strong radio, X-ray, and H$\alpha$ emission years after explosion allows various constraints to be put on pre-SN mass-loss processes. We present a wind-bubble model in which the CSM is "pre-prepared" by a fast wind interacting with a slow wind. Much of the outer density profile into which the SN explodes corresponds to no steady-state mass-loss process. We estimate that the shell of compressed slow wind material was ejected ~1400 yr prior to explosion, perhaps during carbon burning, and that the SN shock had swept up about 0.04 M_sun of material. The region emitting the H$\alpha$ has a density of order $10^{-20}$ g/cc., Comment: 16 pages

The progenitors of Type IIP supernovae (SNe) are known to be red supergiants, but their properties are not well determined. We employ hydrodynamical modelling to investigate the explosion characteristics of eight Type IIP supernovae, and the properties of their progenitor stars. We create evolutionary models using the {\sc MESA} stellar evolution code, explode these models, and simulate the optical lightcurves using the {\sc STELLA} code. We fit the optical lightcurves, Fe II 5169\AA\ velocity, and photospheric velocity, to the observational data. Recent research has suggested that the progenitors of Type IIP SNe have a zero age main sequence (ZAMS) mass not exceeding $\sim18$ M$_{\odot}$. Our fits give a progenitor ZAMS mass $\leq18$ M$_{\odot}$ for seven of the supernovae. Where previous progenitor mass estimates exist, from various sources such as hydrodynamical modelling, multi-wavelength observations, or semi-analytic calculations, our modelling generally tends towards the lower mass values. This result is in contrast to results from previous hydrodynamical modelling, but is consistent with those obtained using general-relativistic radiation-hydrodynamical codes. We do find that one event, SN 2015ba, has a progenitor whose mass is closer to 24 M$_{\odot}$ , although we are unable to fit it well. We also derive the amount of $^{56}$Ni required to reproduce the tail of the lightcurve, and find values generally larger than previous estimates. Overall, we find that it is difficult to characterize the explosion by a single parameter, and that a range of parameters is needed., Comment: 21 pages, 16 figures. Accepted to the Astrophysical Journal

There is now solid experimental evidence of at least one supernova explosion within 100 pc of Earth within the last few million years, from measurements of the short-lived isotope 60Fe in widespread deep-ocean samples, as well as in the lunar regolith and cosmic rays. This is the first established example of a specific dated astrophysical event outside the Solar System having a measurable impact on the Earth, offering new probes of stellar evolution, nuclear astrophysics, the astrophysics of the solar neighborhood, cosmic-ray sources and acceleration, multi-messenger astronomy, and astrobiology. Interdisciplinary connections reach broadly to include heliophysics, geology, and evolutionary biology. Objectives for the future include pinning down the nature and location of the established near-Earth supernova explosions, seeking evidence for others, and searching for other short-lived isotopes such as 26Al and 244Pu. The unique information provided by geological and lunar detections of radioactive 60Fe to assess nearby supernova explosions make now a compelling time for the astronomy community to advocate for supporting multi-disciplinary, cross-cutting research programs., Comment: 11 pages, 2 figures. Astro2020 Science White Paper submitted to the 2020 Decadal Survey on Astronomy and Astrophysics

A range of astronomical data indicates that ancient supernovae created the galactic environment of the Sun and sculpted the physical properties of the interstellar medium near the heliosphere. In this paper we review the characteristics of the local interstellar medium that have been affected by supernovae. The kinematics, magnetic field, elemental abundances, and configuration of the nearest interstellar material support the view that the Sun is at the edge of the Loop I superbubble, which has merged into the low density Local Bubble. The energy source for the higher temperature X-ray emitting plasma pervading the Local Bubble is uncertain. Winds from massive stars and nearby supernovae, perhaps from the Sco-Cen Association, may have contributed radioisotopes found in the geologic record and galactic cosmic ray population. Nested supernova shells in the Orion and Sco-Cen regions suggest spatially distinct sites of episodic star formation. The heliosphere properties vary with the pressure of the surrounding interstellar cloud. A nearby supernova would modify this pressure equilibrium and thereby severely disrupt the heliosphere as well as the local interstellar medium., Comment: 30 pages, 7 figures. Author version, updated and modified (several updated and new paragraphs, one new subsection), of an article that was published in the Handbook of Supernovae, A.W. Alsabti, P. Murdin (eds.), Springer, 2016

A critical constraint on solar system formation is the high $^{26}$Al/$^{27}$Al abundance ratio of 5 $\times 10^{-5}$ at the time of formation, which was about 17 times higher than the average Galactic ratio, while the $^{60}$Fe/$^{56}$Fe value was about $2 \times 10^{-8}$, lower than the Galactic value. This challenges the assumption that a nearby supernova was responsible for the injection of these short-lived radionuclides into the early solar system. We show that this conundrum can be resolved if the Solar System was formed by triggered star formation at the edge of a Wolf-Rayet (W-R) bubble. Aluminium-26 is produced during the evolution of the massive star, released in the wind during the W-R phase, and condenses into dust grains that are seen around W-R stars. The dust grains survive passage through the reverse shock and the low density shocked wind, reach the dense shell swept-up by the bubble, detach from the decelerated wind and are injected into the shell. Some portions of this shell subsequently collapses to form the dense cores that give rise to solar-type systems. The subsequent aspherical supernova does not inject appreciable amounts of $^{60}$Fe into the proto-solar-system, thus accounting for the observed low abundance of $^{60}$Fe. We discuss the details of various processes within the model and conclude that it is a viable model that can explain the initial abundances of $^{26}$Al and $^{60}$Fe. We estimate that 1-16% of all Sun-like stars could have formed in such a setting of triggered star formation in the shell of a WR bubble., Comment: 19 pages, 6 figures. Accepted version. Final published version with proof corrections can be found on the Astrophysical Journal web page for ApJ, 2017, 851, 147

X-ray emission is one of the signposts of circumstellar interaction in supernovae (SNe), but until now, it has been observed only in core-collapse SNe. The level of thermal X-ray emission is a direct measure of the density of the circumstellar medium (CSM), and the absence of X-ray emission from Type Ia SNe has been interpreted as a sign of a very low density CSM. In this paper, we report late-time (500--800 days after discovery) X-ray detections of SN 2012ca in {\it Chandra} data. The presence of hydrogen in the initial spectrum led to a classification of Type Ia-CSM, ostensibly making it the first SN~Ia detected with X-rays. Our analysis of the X-ray data favors an asymmetric medium, with a high-density component which supplies the X-ray emission. The data suggest a number density $> 10^8$ cm$^{-3}$ in the higher-density medium, which is consistent with the large observed Balmer decrement if it arises from collisional excitation. This is high compared to most core-collapse SNe, but it may be consistent with densities suggested for some Type IIn or superluminous SNe. If SN 2012ca is a thermonuclear SN, the large CSM density could imply clumps in the wind, or a dense torus or disk, consistent with the single-degenerate channel. A remote possibility for a core-degenerate channel involves a white dwarf merging with the degenerate core of an asymptotic giant branch star shortly before the explosion, leading to a common envelope around the SN., Comment: 11 pages, 4 figures. Accepted to MNRAS

We present the Supernova X-ray Database (SNaX), a compilation of the X-ray data from young supernovae (SNe). The database includes the X-ray flux and luminosity of young SNe, days to years after outburst. The original goal and intent were to present a database of Type IIn SNe. After having accomplished this we are slowly expanding it to include all SNe for which published data are available. The interface allows one to search for SNe using various criteria, plot all or selected data-points, and download both the data and the plot. The plotting facility allows for significant customization. There is also a facility for the user to submit data that can be directly incorporated into the database. We include an option to fit the decay of any given SN lightcurve with a power-law. The database includes a conversion of most datapoints to a common 0.3-8 keV band so that SN lightcurves may be directly compared with each other. A mailing list has been set up to disseminate information about the database. We outline the structure and function of the database, describe its various features and outline the plans for future expansion., Comment: 9 pages, 4 figures. Accepted to the Astronomical Journal

SN 2005kd is among the most luminous supernovae (SNe) to be discovered at X-ray wavelengths. We have re-analysed all good angular resolution (better than $20"$ FWHM PSF) archival X-ray data for SN 2005kd. The data reveal an X-ray light curve that decreases as t$^{-1.62 \pm 0.06}$. Our modelling of the data suggests that the early evolution is dominated by emission from the forward shock in a high-density medium. Emission from the radiative reverse shock is absorbed by the cold dense shell formed behind the reverse shock. Our results suggest a progenitor with a mass-loss rate towards the end of its evolution of $\ge$ 4.3 $\times$ 10$^{-4} M_{\odot} \,{\rm yr}^{-1}$, for a wind velocity of 10 km s$^{-1}$, at 4.0 $\times$ 10$^{16}$ cm. This mass-loss rate is too high for most known stars, except perhaps hypergiant stars. A higher wind velocity would lead to a correspondingly higher mass-loss rate. A Luminous Blue Variable star undergoing a giant eruption could potentially fulfill this requirement, but would need a high mass-loss rate lasting for several hundred years, and need to explain the plateau observed in the optical light curve. The latter could perhaps be due to the ejecta expanding in the dense circumstellar material at relatively small radii. These observations are consistent with the fact that Type IIn SNe appear to expand into high density and high mass-loss rate environments, and also suggest rapid variability in the wind mass-loss parameters within at least the last 5000 years of stellar evolution prior to core-collapse., Comment: 11 pages, 2 tables and 4 figures. Accepted to MNRAS

Massive stars shape their surroundings with mass loss from winds during their lifetimes. Fast ejecta from supernovae, from these massive stars, shocks this circumstellar medium. Emission generated by this interaction provides a window into the final stages of stellar evolution, by probing the history of mass loss from the progenitor. Here we use Chandra and Swift x-ray observations of the type II-P/L SN 2013ej to probe the history of mass loss from its progenitor. We model the observed x-rays as emission from both heated circumstellar matter and supernova ejecta. The circumstellar density profile probed by the supernova shock reveals a history of steady mass loss during the final 400 years. The inferred mass loss rate of $3 \times 10^{-6} {\rm \; M_\odot \; yr^{-1}}$ points back to a 14 $M_\odot$ progenitor. Soon after the explosion we find significant absorption of reverse shock emission by a cooling shell. The column depth of this shell observed in absorption provides an independent and consistent measurement of the circumstellar density seen in emission. We also determine the efficiency of cosmic ray acceleration from x-rays produced by Inverse Compton scattering of optical photons by relativistic electrons. Only about 1 percent of the thermal energy is used to accelerate electrons. Our x-ray observations and modeling provides stringent tests for models of massive stellar evolution and micro-physics of shocks., Comment: 8 pages, 6 figures, 2 tables, accepted for publication in ApJ

The formation of a core collapse supernovae (SNe) results in a fast (but non- or mildly-relativistic) shock wave expanding outwards into the surrounding medium. The medium itself is likely modified due to the stellar mass-loss from the massive star progenitor, which may be Wolf-Rayet stars (for Type Ib/c SNe), red supergiant stars (for type IIP and perhaps IIb and IIL SNe), or some other stellar type. The wind mass-loss parameters determine the density structure of the surrounding medium. Combined with the velocity of the SN shock wave, this regulates the shock acceleration process. In this article we discuss the essential parameters that control the particle acceleration and gamma-ray emission in SNe, with particular reference to the Type IIb SN 1993J. The shock wave expanding into the high density medium leads to fast particle acceleration, giving rise to rapidly-growing plasma instabilities driven by the acceleration process itself. The instabilities grow over intraday timescales. This growth, combined with the interplay of non-linear processes, results in the amplification of the magnetic field at the shock front, which can adequately account for the magnetic field strengths deduced from radio monitoring of the source. The maximum particle energy can reach, and perhaps exceed, 1 PeV, depending on the dominant instability. The gamma-ray signal is found to be heavily absorbed by pair production process during the first week after the outburst. We derive the time dependent particle spectra and associated hadronic signatures of secondary particles (gamma-ray, leptons and neutrinos) arising from proton proton interactions. We find that the Cherenkov Telescope Array (CTA) should be able to detect objects like SN 1993J above 1 TeV. We predict a low neutrino flux above 10 TeV, implying a detectability horizon with current or planned neutrino telescopes of 1 Mpc., Comment: 8 pages, 1 figure. To be published in Proceedings of Science, as part of the proceedings of the 34th International Cosmic Ray Conference (ICRC), held in the Hague, Netherlands. arXiv admin note: text overlap with arXiv:1409.3670

Using a code that employs a self-consistent method for computing the effects of photoionization on circumstellar gas dynamics, we model the formation of wind-driven nebulae around massive Wolf-Rayet (W-R) stars. Our algorithm incorporates a simplified model of the photo-ionization source, computes the fractional ionization of hydrogen due to the photoionizing flux and recombination, and determines self-consistently the energy balance due to ionization, photo-heating and radiative cooling. We take into account changes in stellar properties and mass-loss over the star's evolution. Our multi-dimensional simulations clearly reveal the presence of strong ionization front instabilities. Using various X-ray emission models, and abundances consistent with those derived for W-R nebulae, we compute the X-ray flux and spectra from our wind bubble models. We show the evolution of the X-ray spectral features with time over the evolution of the star, taking the absorption of the X-rays by the ionized bubble into account. Our simulated X-ray spectra compare reasonably well with observed spectra of Wolf-Rayet bubbles. They suggest that X-ray nebulae around massive stars may not be easily detectable, consistent with observations., Comment: 3 pages, 4 figures. To be published in the Proceedings of the International Workshop on Wolf-Rayet Stars, Potsdam, 1-5 June 2015. Editors W.-R. Hamann, A. Sander, and H. Todt

Type IIP Supernovae (SNe) are expected to arise from Red Supergiant stars (RSGs). These stars have observed mass-loss rates that span more than two orders of magnitude, from $< 10^{-6}$ solar masses yr$^{-1}$ to almost $ 10^{-4} $ solar masses yr$^{-1}$. Thermal bremsstrahlung X-ray emission from at least some IIP's should reflect the larger end of the high mass-loss rates. Strangely, no IIP SNe are seen where the X-ray luminosity is large enough to suggest mass-loss rates greater than about $ 10^{-5} $ solar masses yr$^{-1}$. We investigate if this could be due to absorption of the X-ray emission. After carefully studying all the various aspects, we conclude that absorption would not be large enough to prevent us from having detected X-ray emission from high mass-loss rate IIP's. This leads us to the conclusion that there may be an upper limit of $\sim 10^{-5} $ solar masses yr$^{-1}$ to the mass-loss rate of Type IIP progenitors, and therefore to the luminosity of RSGs that explode to form Type IIPs. This is turn suggests an upper limit of $\leq 19 $ solar masses for the progenitor mass of a Type IIP SN. This limit is close to that obtained by direct detection of IIP progenitors, as well as that suggested by recent stellar evolution calculations. Although the statistics need to be improved, many current indicators support the notion that RSGs above $\sim 19 $ solar masses do not explode to form Type IIP SNe., Comment: 9 pages, 1 figure, 1 table. Accepted to MNRAS

Using a simplified model for the hadronic emission from young supernova remnants (SNRs), we derive an expression to calculate the hadronic luminosity with time, depending on the SN ejecta density profile and the density structure of the surrounding medium. Our analysis shows that the hadronic emission will decrease with time for core-collapse SNe expanding in the winds of their progenitor stars, but increase with time for SNe expanding into a constant density medium, typical of Type Ia SNe. Using our expressions, we can compute the time-dependent hadronic flux from some well-known young SNe and SNRs with time, and where applicable reproduce previous results in the appropriate parameter regime. Using our calculations, we also emphasize the exciting possibility that SN 1987A may become a visible gamma-ray source in the next decade., Comment: Accepted to MNRAS. 11 pages, 0 figures

Massive stars, possibly red supergiants, which retain extended hydrogen envelopes until core collapse, produce Type II Plateau (IIP) supernovae. The ejecta from these explosions shock the circumstellar matter originating from the mass loss of the progenitor during the final phases of its life. This interaction accelerates particles to relativistic energies which then lose energy via synchrotron radiation in the shock-amplified magnetic fields and inverse Compton scattering against optical photons from the supernova. These processes produce different signatures in the radio and X-ray part of the electromagnetic spectrum. Observed together, they allow us to break the degeneracy between shock acceleration and magnetic field amplification. In this work we use X-rays observations from the Chandra and radio observations from the ATCA to study the relative importance of processes which accelerate particles and those which amplify magnetic fields in producing the non-thermal radiation from SN 2011ja. We use radio observations to constrain the explosion date. Multiple Chandra observations allow us to probe the history of variable mass loss from the progenitor. The ejecta expands into a low density bubble followed by interaction with a higher density wind from a red supergiant consistent with ZAMS mass greater than 16 solar masses. Our results suggest that a fraction of type IIP supernovae may interact with circumstellar media set up by non-steady winds., Comment: 9 pages, 5 figures, updated

Massive Stars (> 8 solar masses) lose mass in the form of strong winds. These winds accumulate around the star, forming wind-blown bubbles. When the star explodes as a supernova (SN), the resulting shock wave expands within this wind-blown bubble, rather than the interstellar medium. The properties of the resulting remnant, its dynamics and kinematics, the morphology, and the resulting evolution, are shaped by the structure and properties of the wind-blown bubble. In this article we focus on Kes 27, a supernova remnant (SNR) that has been proposed by Chen et al (2008) to be evolving in a wind-blown bubble, explore its properties, and investigate whether the properties could be ascribed to evolution of a SNR in a wind-blown bubble. Our initial model does not support this conclusion, due to the fact that the reflected shock is expanding into much lower densities., Comment: 5 pages, 3 figures. Revised version submitted to High Energy Density Physics. To be published in a special issue of the proceedings of the 2012 HEDLA conference

Using an ionization gasdynamics code, we simulate a model of the wind-blown bubble around a 40 solar mass star. We use this to compute the X-ray spectra from the bubble, which can be directly compared to observations. We outline our methods and techniques for these computations, and contrast them with previous calculations. Our simulated X-ray spectra compare reasonably well with observed spectra of Wolf-Rayet bubbles. They suggest that X-ray nebulae around massive stars may not be easily detectable, consistent with observations., Comment: 7 pages, 2 figures. Revised and shortened version following referee comments. Accepted to High Energy Density Physics

Massive stars lose mass in the form of stellar winds and outbursts. This material accumulates around the star. When the star explodes as a supernova (SN) the resulting shock wave expands within this circumstellar medium. The X-ray emission resulting from the interaction depends, among other parameters, on the density of this medium, and therefore the variation in the X-ray luminosity can be used to study the variation in the density structure of the medium. In this paper we explore the X-ray emission and lightcurves of all known SNe, in order to study the nature of the medium into which they are expanding. In particular we wish to investigate whether young SNe are expanding into a steady wind medium, as is most often assumed in the literature. We find that in the context of the theoretical arguments that have been generally used in the literature, many young SNe, and especially those of Type IIn, which are the brightest X-ray luminosity class, do not appear to be expanding into steady winds. Some IIns appear to have very steep X-ray luminosity declines, indicating density declines much steeper than r$^{-2}$. However, other IIns show a constant or even increasing X-ray luminosity over periods of months to years. Many other SNe do not appear to have declines consistent with expansion in a steady wind. SNe with lower X-ray luminosities appear to be more consistent with steady wind expansion, although the numbers are not large enough to make firm statistical comments. The numbers do indicate that the expansion and density structure of the circumstellar medium must be investigated before assumptions can be made of steady wind expansion. Unless a steady wind can be shown, mass-loss rates deduced using this assumption may need to be revised., Comment: 12 pages, 3 color Figures. Accepted to MNRAS

We describe the propagation of supernova shocks within the surrounding medium, which may be due to mass-loss from the progenitor star. The structure and density profile of the ejected material and surrounding medium are considered. Shock wave interaction with clouds and wind-bubbles, and issues relevant to cosmic rays are briefly discussed., Comment: 6 pages, 3 figures. Final version, minor changes. Invited review presented at the conference on Cosmic Rays and the Interstellar Medium (CRISM-2011), Montpellier, France, June 26-July 1. Published in a special issue of MEMORIE della Societa Astronomica Italiana

SN 1996cr, located in the Circinus Galaxy (3.7 Mpc, z ~ 0.001) was non-detected in X-rays at ~ 1000 days yet brightened to ~ 4 x 10^{39} erg/s (0.5-8 keV) after 10 years (Bauer et al. 2008). A 1-D hydrodynamic model of the ejecta-CSM interaction produces good agreement with the measured X-ray light curves and spectra at multiple epochs. We conclude that the progenitor of SN 1996cr could have been a massive star, M > 30 M_solar, which went from an RSG to a brief W-R phase before exploding within its ~ 0.04 pc wind-blown shell (Dwarkadas et al. 2010). Further analysis of the deep Chandra HETG observations allows line-shape fitting of a handful of bright Si and Fe lines in the spectrum. The line shapes are well fit by axisymmetric emission models with an axis orientation ~ 55 degrees to our line-of-sight. In the deep 2009 epoch the higher ionization Fe XXVI emission is constrained to high lattitudes: the Occam-est way to get the Fe H-like emission coming from high latitude/polar regions is to have more CSM at/around the poles than at mid and lower lattitudes, along with a symmetric ejecta explosion/distribution. Similar CSM/ejecta characterization may be possible for other SNe and, with higher-throughput X-ray observations, for gamma-ray burst remnants as well., Comment: 4 pages, 5 figures. To appear in the Proceedings of the Gamma Ray Bursts 2010 Conference, Annapolis, USA. Editors: McEnery, Racusin, Gehrels

Luminous blue variable (LBV) stars are very massive, luminous, unstable stars that suffer frequent eruptions. In the last few years, these stars have been proposed as the direct progenitors of some core-collapse supernovae (SNe), particularly Type IIn SNe, in conflict with stellar evolution theory. In this paper we investigate various scenarios wherein LBV stars have been suggested as the immediate progenitors of SNe. Many of these suggestions stem from the fact that the SNe appear to be expanding in a high density medium, which has been interpreted as resulting from a wind with a high mass-loss rate. Others arise due to perceived similarities between the SN characteristics and those of LBVs. Only in the case of SN 2005gl do we find a valid possibility for an LBV-like progenitor. Other scenarios encounter various levels of difficulty. The evidence that points to LBVs as direct core-collapse SNe progenitors is far from convincing. High mass-loss rates are often deduced by making assumptions regarding the wind parameters, which are contradicted by the results themselves. A high density need not necessarily imply a high wind mass-loss rate: wind shocks sweeping up the surrounding medium may give a high density shell with a low associated wind mass-loss rate. High densities may also arise due to wind clumps, or due to a previous LBV phase before the SN explodes as a Wolf-Rayet star. Some Type IIn SNe appear to signify more a phase in the life of a SN than a class of SNe, and may arise from more than one type of progenitor. A Wolf-Rayet phase that lasts for a few thousand years or less could be one of the more probable progenitors of Type IIns, and channels for creating short-lived W-R phases are briefly discussed., Comment: Accepted to MNRAS. 13 pages, 1 figure

SN1996cr is one of the five closest SNe to explode in the past 30 years. Due to its fortuitous location in the Circinus Galaxy at ~ 3.7 Mpc, there is a wealth of recently acquired and serendipitous archival data available to piece together its evolution over the past decade, including a recent 485 ks Chandra HETG spectrum. In order to interpret this data, we have explored hydrodynamic simulations, followed by computations of simulated spectra and light curves under non-equilibrium ionization conditions, and directly compared them to the observations. Our simulated spectra manage to fit both the X-ray continuum and lines at 4 epochs satisfactorily, while our computed light curves are in good agreement with additional flux-monitoring data sets. These calculations allow us to infer the nature and structure of the circumstellar medium, the evolution of the SN shock wave, and the abundances of the ejecta and surrounding medium. The data imply that SN 1996cr exploded in a low-density medium before interacting with a dense shell of material about 0.03pc away from the progenitor star. We speculate that the shell could be due to the interaction of a blue supergiant or Wolf-Rayet wind with a previously existing red supergiant (RSG) wind. The shock wave has now exited the shell and is expanding in the medium exterior to it, possibly the undisturbed continuation of the dense RSG wind. The narrow lines that earned SN 1996cr its IIn designation possibly arise from dense, shocked clumps in the CSM. Although the possibility for an LBV progenitor for this Type IIn SN cannot be completely excluded, it is inconsistent with much of the data. These calculations allow us to probe the stellar mass loss in the very last phases ($ < 10^4$ years) of a massive star's life ($> 10^6$ years), and provide another means to deducing the progenitor of the SN., Comment: Accepted to MNRAS. 21 pages, 8 Figures, 6 in color. For a version with higher resolution colour figures see http://astro.uchicago.edu/~vikram/1996cr/

We present a comprehensive analysis of the X-ray light curves of SN 1993J in a nearby galaxy M81. This is the only supernova other than SN 1987A, which is so extensively followed in the X-ray bands. Here we report on SN 1993J observations with the {\it Chandra} in the year 2005 and 2008, and Swift observations in 2005, 2006 and 2008. We combined these observations with all available archival data of SN 1993J, which includes ROSAT, ASCA, {\it Chandra}, and XMM-{\it Newton} observations from 1993 April to 2006 August. In this paper we report the X-ray light curves of SN 1993J, extending up to fifteen years, in the soft (0.3--2.4 keV), hard (2--8 keV) and combined (0.3--8 keV) bands. The hard and soft-band fluxes decline at different rates initially, but after about 5 years they both undergo a $t^{-1}$ decline. The soft X-rays, which are initially low, start dominating after a few hundred days. We interpret that most of the emission below 8 keV is coming from the reverse shock which is radiative initially for around first 1000-2000 days and then turn into adiabatic shock. Our hydrodynamic simulation also confirms the reverse shock origin of the observed light curves. We also compare the H$\alpha$ line luminosity of SN 1993J with its X-ray light curve and note that the H$\alpha$ line luminosity has a fairly high fraction of the X-ray emission, indicating presence of clumps in the emitting plasma., Comment: 33 pages, 8 figures, Accepted for publication in Astrophysical Journal

Winds from massive stars (> 8 solar masses) result in the formation of wind-blown "bubbles" around these stars. In this paper we study, via two-dimensional numerical hydrodynamic simulations, the onset and growth of turbulence during the formation and evolution of these wind-blown "bubbles". Our simulations reveal the formation of vortex rolls during the Main-Sequence stage of the evolution, and Rayleigh-Taylor instabilities in the subsequent stages due to accelerating and/or decelerating wind-blown shells. The bubble shows a very turbulent interior just prior to the death of the star, with a significant percentage of the internal energy expended in non-radial motions. This would affect the subsequent evolution of the resultant supernova shock wave. We discuss the implications of these results, show how the ratio of kinetic energy in radial versus non-radial motions varies throughout the evolution, and discuss how these results would carry over to three dimensions., Comment: 12 pages, 5 Figs, in proceedings of "Turbulent Mixing and Beyond". This is an author-created, un-copyedited version accepted for publication to Physica Scripta T. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The definitive publisher authenticated version will be available online

(Abridged) Mass-loss from massive stars leads to the formation of circumstellar wind-blown bubbles surrounding the star, bordered by a dense shell. When the star ends its life in a supernova (SN) explosion, the resulting shock wave will interact with this modified medium. In a previous paper we discussed the basic parameters of this interaction. In this paper we go a step further and study the evolution of SNe in the wind blown bubble formed by a 35 $\msun$ star that starts off as an O star, goes through a red supergiant phase, and ends its life as a Wolf-Rayet star. We model the evolution of the CSM and then the expansion of the SN shock wave within this medium. Our simulations clearly reveal fluctuations in density and pressure within the surrounding medium. The SN shock interacting with these fluctuations, and then with the dense shell surrounding the wind-blown cavity, gives rise to a variety of transmitted and reflected shocks in the wind bubble. The interactions between these various shocks and discontinuities is examined, and its effects on the X-ray emission is noted. Our simulations reveal the presence of several hydrodynamic instabilities. They show that the turbulent interior, coupled with the large fluctuations in density and pressure, gives rise to an extremely corrugated SN shock wave. The shock shows considerable wrinkles as it impacts the dense shell, and the impact occurs in a piecemeal fashion, with some parts of the shock wave interacting with the shell before the others. Therefore different parts of the shell will `light-up' at different times. The non-spherical nature of the interaction means that it will occur over a prolonged period of time, and the spherical symmetry of the initial shock wave is destroyed., Comment: 50 pages, 19 figures. Accepted to the Astrophysical Journal. For a version with the original high-resolution color figures please download from http://astro.uchicago.edu/~vikram/sncsm.html

We study the structure of the circumstellar medium surrounding SN 1987A in the equatorial plane. Furthermore, we study the evolution of the SN shock within this medium during the first 25 years, and the resulting hard X-ray and radio emission from the remnant., Comment: 5 pages, 3 Figures. To be published in the proceedings of the conference on "Supernova 1987A: 20 Years After: Supernovae and Gamma-Ray Bursters" AIP, New York, eds. S. Immler, K.W. Weiler, and R. McCray

Massive stars can significantly modify the surrounding medium during their lifetime. When the stars explode as supernovae, the resulting shock wave expands within this modified medium and not within the interstellar medium. We explore the evolution of the medium around massive stars, and the expansion of the shock wave within this medium. We then apply these results to understanding the expansion of the shock wave in the ambient medium surrounding SN 1987A, and the evolution of the radio and X-ray emission in this case., Comment: 8 pages, 5 figues. To appear in RMxAA, as part of the proceedings of the conference "Circumstellar Media and Late Stages of Massive Stellar Evolution" held in Ensenada, Mexico, Sept 2006. A version with higher resolution figures is available at http://astro.uchicago.edu/~vikram/bubbles_87a.pdf

We review the effects of winds from massive O and B stars on the surrounding medium over the various stages of stellar evolution. Furthermore we discuss some of the implications for SNe and GRB evolution within this wind-blown medium., Comment: 6 pages, 1 figure. To be published by AIP press, in proceedings of the conference, "The Multicoloured Landscape of Compact Objects and their Explosive Origins", held in Cefalu, Sicily (Italy), June 11 - 24, 2006

We present narrow-band images of the Red Rectangle (RR) nebula which reveal the distinct morphologies of this intriguing nebula in different optical emission bands. The morphology of the RR nebula in blue luminescence (BL) and extended red emission (ERE) are almost mutually exclusive. We also present the optical detection of the circum-binary disk of the RR in the light of the BL. The total intensities from the two optical band emissions (BL and ERE) when summed over the nebula are of comparable magnitude. Their spatial distributions with respect to the embedded illumination sources lead us to suggest that they may be attributed to different ionization stages of the same family of carriers., Comment: Accepted to ApJ

Core-Collapse supernovae arise from stars greater than 8 $\msun$. These stars lose a considerable amount of mass during their lifetime, which accumulates around the star forming wind-blown bubbles. Upon the death of the star in a spectacular explosion, the resulting SN shock wave will interact with this modified medium. We study the evolution of the shock wave, and investigate the properties of this interaction. We concentrate on the evolution of the SN shock wave in the medium around a 35 solar mass star. We discuss the hydrodynamics of the resulting interaction, the formation and growth of instabilities, and deviations from sphericity., Comment: 11 pages, 4 figures. Accepted to Astrophysics and Space Science. To be published by Springer in special volume of the High Energy Density Lab Astrophysics Conference #6. For a version with higher resolution figures see http://astro.uchicago.edu/~vikram/sncirc/vikram_2.pdf