arXiv subjects

Kazimierz J. Borkowski

Publications and source records attributed to Kazimierz J. Borkowski.

At least 19 recordsLinked to original sources

arXiv2024

Brightening and Fading in the Youngest Galactic Supernova Remnant G1.9+0.3: 13 years of monitoring with the Chandra X-ray Observatory

We report results from 13 years of Chandra monitoring of nonthermal X-ray emission from the youngest Galactic supernova remnant G1.9+0.3, the only remnant known to be increasing in brightness. We confirm the spatially-integrated flux increase rate of $(1.2 \pm 0.2)$% yr$^{-1}$ between 1 and 7 keV, but find large spatial variations, from decreases of $-3$% yr$^{-1}$ to increases of 7% yr$^{-1}$, over length scales as small as $10''$ or smaller. We observe relatively little change in spectral slope, though one region shows significant hardening (photon index $ΔΓ\sim 0.4$) as it brightens by 1% yr$^{-1}$. Such rates of change can be accommodated by any of several explanations, including steady evolution of the blast wave, expansion or compression of discrete plasma blobs, strong magnetic turbulence, or variations in magnetic-field aspect angle. Our results do not constrain the mean magnetic-field strength, but a self-consistent picture of the spatially averaged rate of increase can be produced in which the maximum energies of accelerated particles are limited by the remnant age (applying both to electrons and to ions) to about 20 TeV, and the remnant-averaged magnetic field strength is about 30 $μ$G. The deceleration parameter $m$ (average shock radius varying as $t^m$) is about 0.7, consistent with estimates from overall expansion dynamics, and confirming an explosion date of about 1900 CE. Shock-efficiency factors $ε_e$ and $ε_B$ (fractions of shock energy in relativistic electrons and magnetic field) are 0.003 and 0.0002 in this picture. However, the large range of rates of brightness change indicates that such a global model is oversimplified. Temporal variations of photon index, expected to be small but measurable with longer time baselines, can discriminate among possible models.

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arXiv2024

An X-ray Synchrotron Shell and a Pulsar: The Peculiar Supernova Remnant G32.4+0.1

We present a deep Chandra observation of the shell supernova remnant G32.4+0.1, whose featureless X-ray spectrum has led to its classification as an X-ray synchrotron-dominated supernova remnant (SNR). We find a partial shell morphology whose outline is quite circular, with a radius of about 11 pc at an assumed distance of 11 kpc. Thermal and power-law spectral models for three relatively bright regions provided equally good fits, but the absence of spectral lines required ionization timescales from thermal fits that are inconsistent with mean densities derived from emission measures. We thus confirm the nonthermal, i.e., synchrotron, origin of X-rays from G32.4+0.1. Shock velocities needed to accelerate electrons to the required TeV energies are >~1000 km/s, giving remnant ages <~5,000 -- 9,000 yr. There is no obvious X-ray counterpart to the radio pulsar PSR J1850--0026, but its position adjoins a region of X-ray emission whose spectrum is somewhat harder than that of other regions of the shell, and which may be a pulsar-wind nebula (PWN), though its spectrum is steeper than almost all known X-ray PWNe. The distance of the pulsar from the center of symmetry of the shell disfavors a birth in a supernova event at that location only a few thousand years before: either the pulsar (and putative PWN) are not associated with the shell SNR, requiring a coincidence of both position and (roughly) absorbing column density, or the SNR is much older, making the origin of nonthermal emission problematic.

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arXiv2023

Rapid Expansion of the Young Type Ia Supernova Remnant 0519-69.0: More Evidence for a Circumstellar Shell

The nature of Type Ia supernovae remains controversial. The youngest remnants of Ia supernovae hold clues to the explosion and to the immediate surroundings. We present a third epoch of Chandra observations of the $\sim600$-year-old Type Ia remnant 0519-69.0 in the Large Magellanic Cloud, extending the time baseline to 21 years from the initial 2000 observations. We find rapid expansion of X-ray emitting material, with an average velocity of 4760 km s$^{-1}$. At the distance of the LMC this corresponds to an undecelerated age of 750 years, with the true age somewhat smaller. We also find that the bright ring of emission has expanded by 1.3\%, corresponding to a velocity of 1900 km s$^{-1}$ and an undecelerated age of 1600 years. The high velocity of the peripheral X-rays, contrasted with the modest expansion of the main X-ray shell, provides further evidence for a massive shell of circumstellar material.

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arXiv2022

An X-ray Proper Motion Study of the LMC SNR 0509-67.5

We present a third epoch of Chandra observations of the Type Ia Large Magellanic Cloud Supernova remnant (SNR) 0509-67.5. With these new observations from 2020, the baseline for proper motion measurements of the expansion has grown to 20 years (from the earliest Chandra observations in 2000). We report here the results of these new expansion measurements. The lack of nearby bright point sources renders absolute image alignment difficult. However, we are able to measure the average expansion of the diameter of the remnant along several projection directions. We find that the remnant is expanding with an average velocity of 6120 (4900 -- 7360) km s$^{-1}$. This high shock velocity is consistent with previous works, and also consistent with the inference that 0509-67.5 is expanding into a very low density surrounding medium. At the distance of the LMC, this velocity corresponds to an undecelerated age of 600 yrs, with the real age somewhat smaller.

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arXiv2022

Evidence for a Dense, Inhomogeneous Circumstellar Medium in the Type Ia SNR 0519-69.0

We perform an expansion study of the Balmer dominated outer shock of the SNR 0519$-$69.0 in the LMC by using a combination of new HST WFC3 imagery obtained in 2020 and archival ACS images from 2010 and 2011. Thanks to the very long time baseline, our proper motion measurements are of unprecedented accuracy. We find a wide range of shock velocities, with the fastest shocks averaging 5280 km/s and the slowest grouping of shocks averaging just 1670 km/s. We compare the H_alpha images from HST with X-ray images from Chandra and mid-IR images from Spitzer, finding a clear anti-correlation between the brightness of the remnant in a particular location and the velocity of the blast wave at that location, supporting the idea that the bright knots of X-ray and IR emission result from an interaction with a dense inhomogeneous circumstellar medium. We find no evidence for X-ray emission, thermal or nonthermal, associated with the fastest shocks, as expected if the fastest velocities are the result of the blast wave encountering the lower density ambient medium of the LMC. We derive an age of the remnant of 670 +/- 70 yr, consistent with results derived from previous investigations.

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arXiv2022

Locating the CSM Emission within the Type Ia Supernova Remnant N103B

We present results from deep Chandra observations of the young Type Ia supernova remnant (SNR) 0509-68.7, also known as N103B, located in the Large Magellanic cloud (LMC). The remnant displays an asymmetry in brightness, with the western hemisphere appearing significantly brighter than the eastern half. Previous multi-wavelength observations have attributed the difference to a density gradient and suggested circumstellar material origins, drawing similarities to Kepler's SNR. We apply a clustering technique combined with traditional imaging analysis to spatially locate various emission components within the remnant. We find that O and Mg emission is strongest along the blast wave, and coincides with Spitzer observations of dust emission and optical emission from the non-radiative shocks. The abundances of O and Mg in these regions are enhanced relative to the average LMC abundances and appear as a distinct spatial distribution compared to the ejecta products, supporting the circumstellar medium (CSM) interpretation. We also find that the spatial distribution of Cr is identical to that of Fe in the interior of the remnant, and does not coincide at all with the O and Mg emission.

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arXiv2021

Type Ia Supernova Models: Asymmetric Remnants and Supernova Remnant G1.9+0.3

The youngest Galactic supernova remnant G1.9+0.3, probably the result of a Type Ia supernova, shows surprising anomalies in the distribution of its ejecta in space and velocity. In particular, high-velocity shocked iron is seen in several locations far from the remnant center, in some cases beyond prominent silicon and sulfur emission. These asymmetries strongly suggest a highly asymmetric explosion. We present high-resolution hydrodynamic simulations in two and three dimensions of the evolution from ages of 100 seconds to hundreds of years of two asymmetric Type Ia models, expanding into a uniform medium. At the age of G1.9+0.3 (about 100 years), our 2D model shows almost no iron shocked to become visible in X-rays. Only in a much higher-density environment could significant iron be shocked, at which time the model's expansion speed is completely inconsistent with the observations of G1.9+0.3. Our 3D model, evolving the most asymmetric of a suite of Type Ia SN models from Seitenzahl et al.~(2013), shows some features resembling G1.9+0.3. We characterize its evolution with images of composition in three classes: C and O, intermediate-mass elements (IMEs), and iron-group elements (IGEs). From ages of 13 to 1800 years, we follow the evolution of the highly asymmetric initial remnant as the explosion asymmetries decrease in relative strength to be replaced by asymmetries due to evolutionary hydrodynamic instabilities. At an age of about 100 years, our 3D model has comparable shocked masses of C+O, IMEs, and IGEs, with about 0.03 $M_\odot$ each. Evolutionary changes appear to be rapid enough that continued monitoring with the Chandra X-ray Observatory may show significant variations.

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arXiv2021

Efficiencies of Magnetic-Field Amplification and Electron Acceleration in Young Supernova Remnants: Global Averages and Kepler's Supernova Remnant

Particle acceleration to suprathermal energies in strong astrophysical shock waves is a widespread phenomenon, generally explained by diffusive shock acceleration. Such shocks can also amplify upstream magnetic field considerably beyond simple compression. The complex plasma physics processes involved are often parameterized by assuming that shocks put some fraction $ε_e$ of their energy into fast particles, and another fraction $ε_B$ into magnetic field. Modelers of shocks in supernovae, supernova remnants, and gamma-ray bursters, among other locations, often assume typical values for these fractions, presumed to remain constant in time. However, it is rare that enough properties of a source are independently constrained that values of the epsilons can be inferred directly. Supernova remnants (SNRs) can provide such circumstances. Here we summarize results from global fits to spatially integrated emission in six young SNRs, finding $10^{-4} \le ε_e \le 0.05$ and $0.001 \le ε_B \le 0.1$. These large variations might be put down to the differing ages and environments of these SNRs, so we conduct a detailed analysis of a single remnant, that of Kepler's supernova. Both epsilons can be determined at seven different locations around the shock, and we find even larger ranges for both epsilons, as well as for their ratio (thus independent of the shock energy itself). We conclude that unknown factors have a large influence on the efficiency of both processes. Shock obliquity, upstream neutral fraction, or other possibilities need to be explored, while calculations assuming fixed values of the epsilons should be regarded as provisional.

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arXiv2020

Fast Blast Wave and Ejecta in the Young Core-Collapse Supernova Remnant MSH 15-52/RCW 89

One of the youngest known remnants of a core-collapse supernova (SN) in our Galaxy is G320.4$-$1.2/MSH 15-52 containing an energetic pulsar with a very short (1700 yr) spindown age and likely produced by a stripped-envelope SN Ibc. Bright X-ray and radio emission north of the pulsar overlaps with an H$α$ nebula RCW 89. The bright X-rays there have a highly unusual and quite puzzling morphology, consisting of both very compact thermally emitting knots and much more diffuse emission of nonthermal origin. We report new X-ray observations of RCW 89 in 2017 and 2018 with Chandra that allowed us to measure the motions of many knots and filaments on decade-long time baselines. We identify a fast blast wave with a velocity of $(4000 \pm 500)d_{5.2}$ km/s ($d_{5.2}$ is the distance in units of 5.2 kpc) with a purely nonthermal spectrum, and without any radio counterpart. Many compact X-ray emission knots are moving vary fast, with velocities as high as 5000 km/s, predominantly radially away from the pulsar. Their spectra show that they are Ne- and Mg-rich heavy-element SN ejecta. They have been significantly decelerated upon their recent impact with the dense ambient medium north of the pulsar. We see fast evolution in brightness and morphology of knots in just a few years. Ejecta knots in RCW 89 resemble those seen in Cas A at optical wavelengths in terms of their initial velocities and densities. They might have the same origin, still not understood but presumably related to stripped-envelope SN explosions themselves.

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arXiv2019

On the Expansion, Age, and Origin of the Puzzling Shell/Pulsar Wind Nebula G310.6-1.6

We present a 142-ks Chandra observation of the enigmatic combination supernova remnant G310.6-1.6 consisting of a bright pulsar-wind nebula driven by an energetic pulsar, surrounded by a highly circular, very faint shell with a featureless, probably synchrotron, spectrum. Comparison with an observation 6 years earlier shows no measurable expansion of the shell, though some features in the pulsar-wind nebula have moved. We find an expansion age of at least 2500 yr, implying a current shock velocity less than about 1000 km/s. We place severe upper limits on thermal emission from the shell; if the shell locates the blast wave, a Sedov interpretation would require the remnant to be very young, about 1000 yr, and to have resulted from a dramatically sub-energetic supernova, ejecting << 0.02 M_sun with energy E < 3 x 10^47 erg. Even a merger-induced collapse of a white dwarf to a neutron star, with a low-energy explosion, is unlikely to produce such an event. Other explanations seem equally unlikely.

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arXiv2018

Expansion and Age of the X-ray Synchrotron-Dominated Supernova Remnant G330.2+1.0

We report new Chandra observations of one of the few Galactic supernova remnants whose X-ray spectrum is dominated by nonthermal synchrotron radiation, G330.2+1.0. We find that between 2006 and 2017, some parts of the shell have expanded by about 1%, giving a free-expansion (undecelerated) age of about 1000 yr, and implying shock velocities there of 9000 km/s for a distance of 5 kpc. Somewhat slower expansion is seen elsewhere around the remnant periphery, in particular in compact knots. Because some deceleration must have taken place, we infer that G330.2+1.0 is less than about 1000 yr old. Thus, G330.2+1.0 is one of only four Galactic core-collapse remnants of the last millennium. The large size, low brightness, and young age require a very low ambient density, suggesting expansion in a stellar-wind bubble. We suggest that in the east, where some thermal emission is seen and expansion velocities are much slower, the shock has reached the edge of the cavity. The high shock velocities can easily accelerate relativistic electrons to X-ray-emitting energies. A few small regions show highly significant brightness changes by 10% to 20%, both brightening and fading, a phenomenon previously observed in only two supernova remnants, indicating strong and/or turbulent magnetic fields.

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arXiv2018

The Expansion of the Young Supernova Remnant 0509-68.7 (N103B)

We present a second epoch of {\it Chandra} observations of the Type Ia LMC SNR 0509-68.7 (N103B) obtained in 2017. When combined with the earlier observations from 1999, we have a 17.4-year baseline with which we can search for evidence of the remnant's expansion. Although the lack of strong point source detections makes absolute image alignment at the necessary accuracy impossible, we can measure the change in the diameter and the area of the remnant, and find that it has expanded by an average velocity of 4170 (2860, 5450) km s$^{-1}$. This supports the picture of this being a young remnant; this expansion velocity corresponds to an undecelerated age of 850 yr, making the real age somewhat younger, consistent with results from light echo studies. Previous infrared observations have revealed high densities in the western half of the remnant, likely from circumstellar material, so it is likely that the real expansion velocity is lower on that side of the remnant and higher on the eastern side. A similar scenario is seen in Kepler's SNR. N103B joins the rare class of Magellanic Cloud SNRs with measured proper motions.

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arXiv2018

Expansion and Brightness Changes in the Pulsar-Wind Nebula in the Composite Supernova Remnant Kes 75

We report new Chandra X-ray observations of the shell supernova remnant (SNR) Kes 75 (G29.7-0.3) containing a pulsar and pulsar-wind nebula (PWN). Expansion of the PWN is apparent across the four epochs, 2000, 2006, 2009, and 2016. We find an expansion rate between 2000 and 2016 of the NW edge of the PWN of 0.249% +/- 0.023% yr^{-1}, for an expansion age R/(dR/dt) of 400 +/- 40 years and an expansion velocity of about 1000 km s^{-1}. We suggest that the PWN is expanding into an asymmetric nickel bubble in a conventional Type IIP supernova. Some acceleration of the PWN expansion is likely, giving a true age of 480 +/- 50 years. The pulsar's birth luminosity was larger than the current value by a factor of 3 -- 8, while the initial period was within a factor of 2 of its current value. We confirm directly that Kes 75 contains the youngest known PWN, and hence youngest known pulsar. The pulsar PSR J1846-0258 has a spindown-inferred magnetic field of 5 x 10^{13} G; in 2006 it emitted five magnetar-like short X-ray bursts, but its spindown luminosity has not changed significantly. However, the flux of the PWN has decreased by about 10% between 2009 and 2016, almost entirely in the northern half. A bright knot has declined by 30% since 2006. During this time, the photon indices of the power-law models did not change. This flux change is too rapid to be due to normal PWN evolution in one-zone models.

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arXiv2017

Expansion of Kes 73, a Shell Supernova Remnant Containing a Magnetar

Of the 30 or so Galactic magnetars, about 8 are in supernova remnants (SNRs). One of the most extreme magnetars, 1E 1841-045, is at the center of the SNR Kes 73 (G27.4+0.0), whose age is uncertain. We measure its expansion using three Chandra observations over 15 yr, obtaining a mean rate of 0.023% +/- 0.002% per yr. For a distance of 8.5 kpc, we obtain a shell velocity of 1100 km/s and infer a blast-wave speed of 1400 km/s. For Sedov expansion into a uniform medium, this gives an age of 1800 yr. Derived emission measures imply an ambient density of about 2 cm$^{-3}$ and an upper limit on the swept-up mass of about 70 solar masses, with lower limits of tens of solar masses, confirming that Kes 73 is in an advanced evolutionary stage. Our spectral analysis shows no evidence for enhanced abundances as would be expected from a massive progenitor. Our derived total energy is $1.9 \times 10^{51}$ erg, giving a very conservative lower limit to the magnetar's initial period of about 3 ms, unless its energy was lost by non-electromagnetic means. We see no evidence of a wind-blown bubble as would be produced by a massive progenitor, or any evidence that the progenitor of Kes 73/1E 1841-045 was anything but a normal red supergiant producing a Type IIP supernova, though a short-lived stripped-envelope progenitor cannot be absolutely excluded. Kes 73's magnetar thus joins SGR 1900+14 as magnetars resulting from relatively low-mass progenitors.

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arXiv2017

The Three-Dimensional Expansion of the Ejecta from Tycho's Supernova Remnant

We present the first three-dimensional measurements of the velocity of various ejecta knots in Tycho's supernova remnant, known to result from a Type Ia explosion. Chandra X-ray observations over a 12-year baseline from 2003 to 2015 allow us to measure the proper motion of nearly 60 "tufts" of Si-rich ejecta, giving us the velocity in the plane of the sky. For the line of sight velocity, we use two different methods: a non-equilibrium ionization model fit to the strong Si and S lines in the 1.2-2.8 keV regime, and a fit consisting of a series of Gaussian lines. These methods give consistent results, allowing us to determine the red or blue shift of each of the knots. Assuming a distance of 3.5 kpc, we find total velocities that range from 2400 to 6600 km s$^{-1}$, with a mean of 4430 km s$^{-1}$. We find several regions where the ejecta knots have overtaken the forward shock. These regions have proper motions in excess of 6000 km s$^{-1}$. Some Type Ia supernova explosion models predict a velocity asymmetry in the ejecta. We find no such velocity asymmetries in Tycho, and discuss our findings in light of various explosion models, favoring those delayed detonation models with relatively vigorous and symmetrical deflagrations. Finally, we compare measurements with models of the remnant's evolution that include both smooth and clumpy ejecta profiles, finding that both ejecta profiles can be accommodated by the observations.

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arXiv2017

A Massive Shell of Supernova-formed Dust in SNR G54.1+0.3

While theoretical dust condensation models predict that most refractory elements produced in core-collapse supernovae (SNe) efficiently condense into dust, a large quantity of dust has so far only been observed in SN 1987A. We present the analysis of Spitzer Space Telescope, Herschel Space Observatory, Stratospheric Observatory for Infrared Astronomy (SOFIA), and AKARI observations of the infrared (IR) shell surrounding the pulsar wind nebula in the supernova remnant G54.1+0.3. We attribute a distinctive spectral feature at 21 $μ$m to a magnesium silicate grain species that has been invoked in modeling the ejecta-condensed dust in Cas A, which exhibits the same spectral signature. If this species is responsible for producing the observed spectral feature and accounts for a significant fraction of the observed IR continuum, we find that it would be the dominant constituent of the dust in G54.1+0.3, with possible secondary contributions from other compositions, such as carbon, silicate, or alumina grains. The smallest mass of SN-formed dust required by our models is 1.1 $\pm$ 0.8 $\rm M_{\odot}$. We discuss how these results may be affected by varying dust grain properties and self-consistent grain heating models. The spatial distribution of the dust mass and temperature in G54.1+0.3 confirms the scenario in which the SN-formed dust has not yet been processed by the SN reverse shock and is being heated by stars belonging to a cluster in which the SN progenitor exploded. The dust mass and composition suggest a progenitor mass of 16$-$27 $\rm M_{\odot}$ and imply a high dust condensation efficiency, similar to that found for Cas A and SN 1987A. The study provides another example of significant dust formation in a Type IIP SN and sheds light on the properties of pristine SN-condensed dust.

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arXiv2016

An X-ray and Radio Study of the Varying Expansion Velocities in Tycho's Supernova Remnant

We present newly obtained X-ray and radio observations of Tycho's supernova remnant using {\it Chandra} and the Karl G. Jansky Very Large Array in 2015 and 2013/14, respectively. When combined with earlier epoch observations by these instruments, we now have time baselines for expansion measurements of the remnant of 12-15 year in the X-rays and 30 year in the radio. The remnant's large angular size allows for proper motion measurements at many locations around the periphery of the blast wave. We find, consistent with earlier measurements, a clear gradient in the expansion velocity of the remnant, despite its round shape. The proper motions on the western and southwestern sides of the remnant are about a factor of two higher than those in the east and northeast. We showed in an earlier work that this is related to an offset of the explosion site from the geometric center of the remnant due to a density gradient in the ISM, and using our refined measurements reported here, we find that this offset is $\sim 23"$ towards the northeast. An explosion center offset in such a circular remnant has implications for searches for progenitor companions in other remnants.

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arXiv2016

G11.2-0.3: The Young Remnant of a Stripped-Envelope Supernova

We present results of a 400-ks Chandra observation of the young shell supernova remnant (SNR) G11.2-0.3, containing a pulsar and pulsar-wind nebula (PWN). We measure a mean expansion rate for the shell since 2000 of 0.0277+/-0.0018% per yr, implying an age between 1400 and 2400 yr, and making G11.2-0.3 one of the youngest core-collapse SNRs in the Galaxy. However, we find very high absorption ($A_V \sim 16^m \pm 2^m$), confirming near-IR determinations and ruling out a claimed association with the possible historical SN of 386 CE. The PWN shows strong jets and a faint torus within a larger, more diffuse region of radio emission and nonthermal X-rays. Central soft thermal X-ray emission is anticorrelated with the PWN; that, and more detailed morphological evidence, indicates that the reverse shock has already reheated all ejecta and compressed the PWN. The pulsar characteristic energy-loss timescale is well in excess of the remnant age, and we suggest that the bright jets have been produced since the recompression. The relatively pronounced shell and diffuse hard X-ray emission in the interior, enhanced at the inner edge of the shell, indicate that the immediate circumstellar medium into which G11.2-0.3 is expanding was quite anisotropic. We propose a possible origin for G11.2-0.3 in a stripped-envelope progenitor that had lost almost all its envelope mass, in an anisotropic wind or due to binary interaction, leaving a compact core whose fast winds swept previously lost mass into a dense irregular shell, and which exploded as a Type cIIb or Ibc supernova.

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