SN 1987A


The Presupernova H II Region around SN 1987A

Chevalier, Roger A.; Dwarkadas, Vikram V.

Astrophysical Journal Letters v.452, p.L45   10/1995



The slow expansion of the bright ring around SN 1987A and the large size estimated for the radio source at an age of ~1500 days suggest a low mass-loss rate, M dot , from the blue supergiant progenitor star; we adopt M dot = 7.5 x 10-8 Mȯ yr-1 and a wind velocity vw = 450 km s-1 as standard values. This wind density would not give substantial radio free-free absorption during the first few days when low-frequency absorption was observed, but the turnover can be attributed to synchrotron self-absorption. The X-ray and radio emission observed since 1990 require that the supernova shock be interacting with denser gas than that in the free wind. We propose that it is interacting with an H II region created by the B3 Ia progenitor star in the swept-up red supergiant wind. The H II region extends from a radius rII ~ 3 x 1017 cm to the ring radius R = 6 x 1017 cm in the equatorial plane and has a hydrogen density ~102 cm-3. The shock front will not reach the dense ring until the year 2005 +/- 3. The X-ray luminosity should slowly increase until that time. The equatorial ionization front is trapped in the swept-up gas; the dense ring and its associated bipolar nebula are the initially neutral part of the shell. In the polar direction, the ionization front broke out of the swept-up gas, and there is no dense neutral shell, consistent with the observed lack of a thin shell in that direction.

Supernova Explosions in Winds and Bubbles, with Applications to SN 1987A

Dwarkadas, V. V.

Circumstellar Media and Late Stages of Massive Stellar Evolution (Eds. G. García-Segura & E. Ramirez-Ruiz) Revista Mexicana de Astronomía y Astrofísica (Serie de Conferencias) Vol. 30, pp. 49-56 (2007)




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.

SN Shock Evolution in the Circumstellar Medium surrounding SN 1987A

Dwarkadas, Vikram V.

SUPERNOVA 1987A: 20 YEARS AFTER: Supernovae and Gamma-Ray Bursters. AIP Conference Proceedings, Volume 937, pp. 120-124 (2007).




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.

SN 1987A - The Circumstellar Medium , SN Shock Interaction and Associated Emission

Dwarkadas, Vikram

AA(Univ. of Chicago)

American Astronomical Society, AAS Meeting #211, #105.22; Bulletin of the American Astronomical Society, Vol. 39, p.932




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.

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



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.

Evolution of the High Velocity X-Ray Emission in SN 1987A

Dewey, Daniel; Haberl, F.; Dwarkadas, V. V.; Burrows, D. N.; Park, S.

American Astronomical Society, AAS Meeting #217, #256.28  01/2011



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.

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.