X-Ray Emission from SNe
SN 1987A - The Circumstellar Medium , SN Shock Interaction and Associated Emission
Dwarkadas, Vikram
American Astronomical Society, AAS Meeting #211, #105.22; Bulletin of the American Astronomical Society, Vol. 39, p.932
Abstract
We model the circumstellar medium surrounding SN 1987A in the equatorial region, using 1 and 2 dimensional numerical simulations. Data from X-ray, radio and optical observations gathered over the past 20 years is used to compute the structure of the surrounding medium as carved out by winds from the progenitor star. We then compute the evolution of the SN shock wave within this medium, and the emission resulting from the interaction of this shock with the circumstellar medium. We discuss our results in the context of the observations, and make predictions for the future evolution of the shock wave.
This research is supported by award AST-0319261 from the National Science Foundation, and by NASA through grant HST-AR-10649 awarded by STScI.
Circumstellar Interaction, X-ray And Radio Emission, And The Ambient Medium In Young Supernovae
Dwarkadas, Vikram
American Astronomical Society, AAS Meeting #213, #438.04; Bulletin of the American Astronomical Society, Vol. 41, p.311
01/2009
Abstract
Using numerical hydrodynamic simulations, we study the interaction of the supernova (SN) shock wave with the surrounding medium in young SNe. Comparison of the X-ray and radio emission resulting from this interaction with the observed data allows for a determination of the structural properties and density profile of the circumstellar medium. Using this we delineate the ambient medium in some well studied SNe such as SN 1993J and SN 1996cr.
Acknowledgements: Several collaborators have contributed to data used in this work and are appropriately listed on the poster. This work is partly supported by Chandra, NSF and STScI grants to VVD at U Chicago.
X-rays from the Explosion Site: 15 Years of Light Curves of SN 1993J
Chandra, Poonam; Dwarkadas, Vikram V.; Ray, Alak; Immler, Stefan; Pooley, David
The Astrophysical Journal, Volume 699, Issue 1, pp. 388-399 (2009).
Abstract
We present a comprehensive analysis of the X-ray light curves of supernova (SN) 1993J in a nearby galaxy M81. This is the only SN other than SN 1987A, which is so extensively followed in the X-ray bands. Here, we report on SN 1993J observations with 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, Chandra, and XMM-Newton observations from 1993 April to 2006 August. In this paper, we report the X-ray light curves of SN 1993J, extending up to 15 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 Hα line luminosity of SN 1993J with its X-ray light curve and note that the Hα line luminosity has a fairly high fraction of the X-ray emission, indicating presence of clumps in the emitting plasma.
SNR 1987A: Ten Years of Chandra Monitoring
Park, Sangwook; Burrows, David; Racusin, Judith; Zhekov, Svetozar; McCray, Richard; Dewey, Daniel; Dwarkadas, Vikram; Garmire, Gordon
Chandra's First Decade of Discovery, Proceedings of the conference held 22-25 September, 2009 in Boston, MA. Edited by Scott Wolk, Antonella Fruscione, and Douglas Swartz, abstract #22
Abstract
We have been observing the dynamical and spectral evolution of SNR 1987A with Chandra since 1999. As of 2009 July, we have performed 20 monitoring observations of SNR 1987A. We have also performed 4 deep grating spectroscopic observations. We here review the X-ray evolution of SNR 1987A over the last 10 yr, including updates from the recent observations. The current X-ray emission of SNR 1987A originates primarily from the shock interaction with complex density structures along the inner circumstellar ring, which results in a range of the shock velocities and plasma conditions. We find no evidence for the much-anticipated central point source. The latest data show that SNR 1987A continues to brighten, but probably at a lower rate than 5 yr ago. The radial expansion of the SNR has significantly slowed since ˜2004, supporting the interpretation that the blast wave is entering the main body of the inner ring. Recently we transitioned from using the ACIS to using the HETG in our monitoring program. The upcoming X-ray light curves combined with high resolution spectroscopy will help us further study the details of the shock evolution in the context of the density/chemical structures of the equatorial stellar winds and the late-stage evolution history of SN 1987A's massive progenitor.
Modeling the deep HETG observation of SN 1996cr
Dewey, Daniel; Bauer, F. E.; Dwarkadas, V. V.
Chandra's First Decade of Discovery, Proceedings of the conference held 22-25 September, 2009 in Boston, MA. Edited by Scott Wolk, Antonella Fruscione, and Douglas Swartz, abstract #85
Abstract
SN 1996cr appears to have exploded into a wind-blown bubble structure giving rise to an increasing X-ray flux as late as a decade after explosion. This behavior is rare among SNe and similar to that of SN 1987A. However, SN 1996cr's X-ray luminosity is several orders of magnitude greater than '87A's. Comparing simple 1D hydrodynamic models to the HETG spectra support a model where '96cr is exploding into a more compact and extensive circumstellar bubble-and-shell structure than '87A's.
Chandra High-Resolution Spectroscopy of SN 1996cr
Bauer, Franz E.; Dewey, D.; Dwarkadas, V.; Brandt, W. N.
American Astronomical Society, HEAD meeting #11, #18.11; Bulletin of the American Astronomical Society, Vol. 41, p.688
Abstract
SN1996cr is among the closest SNe to explode in the past 30 years, yet went undiscovered for many years. Due to its fortuitous location in the Circinus Galaxy at 3.7 Mpc, however, we have a wealth of serendipitous archival data available to piece together its early evolution. Like SN1987A, it appears to have exploded into a shell-like structure formed by the progenitor, sparking a unique temporal evolution. I will describe our current multi-wavelength constraints on SN1996cr, focusing on a new 485ks Chandra HETG spectrum, and discuss physical interpretations of the system with the aid of hydrodynamical simulations by our team.
Bursting SN 1996cr's bubble: hydrodynamic and X-ray modelling of its circumstellar medium
Dwarkadas, V. V.; Dewey, D.; Bauer, F.
Monthly Notices of the Royal Astronomical Society, Volume 407, Issue 2, pp. 812-829. 09/2010
Abstract
SN1996cr is one of the five closest supernovae (SNe) to explode in the past 30 yr. 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 high-energy transmission grating spectrum. In order to interpret these 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 four 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 (CSM), 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 0.03 pc 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 a luminous blue variable 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 (<104 yr) of a massive star's life (>106 yr), and provide another means to deducing the progenitor of the SN.
Evolution of the High Velocity X-Ray Emission in SN 1987A
Dewey, Daniel; Haberl, F.; Dwarkadas, V. V.; Burrows, D. N.; Park, S.
AA(MIT Kavli Institute), AB(MPE, Germany), AC(U Chicago), AD(Penn State), AE(U Texas)
American Astronomical Society, AAS Meeting #217, #256.28 01/2011
Abstract
Chandra HETG observations of SN 1987A in late 1999 showed very broad lines with observed FWHM of order 7000 km/s (Michael et al. 2002). At this time (SN day 4600) the blastwave was already interacting with the HII region around the progenitor and optical spots had recently appeared. High-resolution spectra taken from May 2003 ( day 5900) to the present by XMM-Newton and Chandra have been well fit by models with FWHM less than 2000 km/s (Zhekov et al. 2005; Dewey et al. 2008; Sturm et al 2010). The emission is increasingly dominated by these narrower components as the blastwave encounters more of the dense equatorial ring. However emission from the HII region out of the ring plane is still expected at late times and would contribute a high-velocity component to the spectra.
We analyze 6 epochs of SN 1987A grating data and include an additional very broad component in the spectral model. We find that deep HETG 2007 data are better fit when one quarter of the flux comes from a component with FWHM 8500 km/s, and that RGS 2003 data show an improved fit with a very-broad fraction that is between the 1999 and 2007 values. Later data continue a progression to lower, but still significant, very-broad fractions. The measurements are discussed in terms of the density and extent of the out-of-plane HII region, hydrodynamical simulations, and 3D models of SN 1987A's emission.
Support for this work was provided by NASA/USA through contract NAS8-03060 to the Smithsonian Astrophysical Observatory (SAO) and further SAO sub-contracts TM9-0004X to VVD (U Chicago) and SV3-73016 to MIT for support of the CXC.
Modeling The Morphology Of SN 1996cr From X-ray Lines At High Resolution
Bauer, Franz E.; Dewey, D.; Dwarkadas, V
AA(Space Science Institute), AB(MIT Kavli Institute), AC(University of Chicago)
American Astronomical Society, AAS Meeting #217, #434.26 01/2011
Abstract
SN1996cr ( 3.7 Mpc) was X-ray "dim" up to 1000 days yet brightened to 4e39 erg/s (0.5-8 keV) after 10 years (Bauer et al. 2008). A 1-D hydro model of the ejecta-CSM interaction produces good agreement with the measured X-ray light curves and spectra at multiple epochs, suggesting that SN 1996cr was most likely a massive star, M > 30 solar masses, which went from an RSG to a brief W-R phase before exploding within its r 0.04 pc wind-blown shell (Dwarkadas et al. 2010). Further analysis of a 485ks Chandra HETG observation allows velocity-profile fitting to a handful of bright emission lines in the spectrum (e.g., Si and Fe). The line shapes are well fit with axisymmetric emission models that put the higher temperature Fe XXVI emission at high latitudes. The axis orientation is well constrained to be 55 degrees from our line-of-sight. The latitude variation may be explained either by higher CSM densities near the equator, or by the ejecta having greater velocity along the poles. SN1996cr demonstrates how X-ray emission lines can provide important diagnostics of SN shock structure.
Modeling SN 1996cr's X-ray lines at high-resolution: Sleuthing the ejecta/CSM geometry
Dewey, Daniel; Bauer, Franz E.; Dwarkadas, Vikram V.
GAMMA RAY BURSTS 2010. AIP Conference Proceedings, 1358, pp. 289-292 (2011)
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 Lx~4×1039 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 Msolar, which went from an RSG to a brief W-R phase before exploding within its r~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.
The Evolution And Hydrodynamics Of SN 1987A Seen With HETG & RGS Spectra
Dewey, Daniel; Dwarkadas, V. V.; Haberl, F.; Canizares, C. R.
American Astronomical Society, HEAD meeting #12, #34.22
The interaction of SN 1987A with its environment gives rise to X-ray emission from multiple components of the system: the H_II region, the dense protrusions of the equatorial ring (ER) including clumpy ER material, and, at late times, the reverse-shocked SN ejecta itself.
Deep Chandra and XMM gratings observations span the period from late 1999 to the present. The HETG observation in 1999 showed very broad lines with FWHM of order 7000 km/s (Michael et al. 2002); at this time the blast wave was primarily interacting with the H_II region around the progenitor. Since then, the X-ray emission has been increasingly dominated by narrower components as the blast wave encounters the dense ER. Even so, the grating data suggest that flux from the H_II region is still present, indicated by a very-broad component in the grating spectra. We find that deep HETG 2007 and 2011 data are better fit when of order 0.2 of the flux comes from a component with FWHM around 9000 km/s.
Based on this, the observed light curves in the 0.5-2 and 3-10 keV bands are modeled as the weighted sum of the non-equilibrium-ionization (NEI) X-ray emission from two simple 1D hydrodynamic simulations: one for the very-broad H_II interaction and one for the dense ER collision. Using these simple models we can better understand and interpret the X-ray emission components and their properties (e.g., abundances), predict future light curve changes under different model assumptions, and set initial parameters for a multi-D model of SN 1987A's interaction.
Support for this work was provided by NASA contract NAS8-03060 to the Smithsonian Astrophysical Observatory (SAO) and SAO sub-contracts TM9-0004X to VVD (U Chicago) and SV3-73016 to MIT for support of the CXC.
What are published X-ray light curves telling us about young supernova expansion?
Dwarkadas, V. V.; Gruszko, J.
Monthly Notices of the Royal Astronomical Society, 419, pp. 1515-1524
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 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 light curves of all known supernovae (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 SNe, which are the brightest X-ray luminosity class, do not appear to be expanding into steady winds. Some Type IIn SNe appear to have very steep X-ray luminosity declines, indicating density declines much steeper than r-2. However, other Type IIn SNe 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.
Evolution and Hydrodynamics of the Very Broad X-Ray Line Emission in SN 1987A
Dewey, D.; Dwarkadas, V. V.; Haberl, F.; Sturm, R.; Canizares, C. R.
The Astrophysical Journal, Volume 752, 22 pp. (2012)
Observations of SN 1987A by the Chandra High Energy Transmission Grating (HETG) in 1999 and the XMM-Newton Reflection Grating Spectrometer (RGS) in 2003 show very broad (v-b) lines with a full width at half-maximum (FWHM) of order 104 km s-1 at these times the blast wave (BW) was primarily interacting with the H II region around the progenitor. Since then, the X-ray emission has been increasingly dominated by narrower components as the BW encounters dense equatorial ring (ER) material. Even so, continuing v-b emission is seen in the grating spectra suggesting that the interaction with H II region material is ongoing. Based on the deep HETG 2007 and 2011 data sets, and confirmed by RGS and other HETG observations, the v-b component has a width of 9300 ± 2000 km s-1 FWHM and contributes of order 20% of the current 0.5-2 keV flux. Guided by this result, SN 1987A's X-ray spectra are modeled as the weighted sum of the non-equilibrium-ionization emission from two simple one-dimensional hydrodynamic simulations; this "2 × 1D" model reproduces the observed radii, light curves, and spectra with a minimum of free parameters. The interaction with the H II region (ρinit ≈ 130 amu cm-3, ± 15° opening angle) produces the very broad emission lines and most of the 3-10 keV flux. Our ER hydrodynamics, admittedly a crude approximation to the multi-D reality, gives ER densities of ~104 amu cm-3, requires dense clumps (×5.5 density enhancement in ~30% of the volume), and predicts that the 0.5-2 keV flux will drop at a rate of ~17% per year once no new dense ER material is being shocked.
The Progenitor of SN 2011ja: Clues from Circumstellar Interaction
Chakraborti, Sayan; Ray, Alak; Smith, Randall; Ryder, Stuart; Yadav, Naveen; Sutaria, Firoza; Dwarkadas, Vikram V.; Chandra, Poonam; Pooley, David; Roy, Rupak
The Astrophysical Journal, Volume 774, 8 pp. (2013)
Massive stars, possibly red supergiants, which retain extended hydrogen envelopes until core collapse, produce Type II plateau (IIP) supernovae. The ejecta from these explosions shocks 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 parts 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 Australia Telescope Compact Array 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 M ZAMS >~ 12 M ⊙. Our results suggest that a fraction of Type IIP supernovae may interact with circumstellar media set up by non-steady winds.