Chun Pun - Profile on Academia.edu (original) (raw)
Papers by Chun Pun
The Astrophysical Journal, Aug 20, 2005
We observed supernova 1987A (SN 1987A) with the Space Telescope Imaging Spectrograph (STIS) on th... more We observed supernova 1987A (SN 1987A) with the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope (HST) in 1999 September and again with the Advanced Camera for Surveys (ACS) on the HST in 2003 November. Our spectral observations cover ultraviolet (UV) and optical wavelengths from 1140 to 10266 8, and our imaging observations cover UV and optical wavelengths from 2900 to 9650 8. No point source is observed in the remnant. We obtain a limiting flux of F opt 1:6 ; 10 À14 ergs s À1 cm À2 in the wavelength range 2900-9650 8 for any continuum emitter at the center of the supernova remnant (SNR). This corresponds to an intrinsic luminosity of L opt 5 ; 10 33 ergs s À1. It is likely that the SNR contains opaque dust that absorbs UV and optical emission, resulting in an attenuation of $35% due to dust absorption in the SNR. Correcting for this level of dust absorption would increase our upper limit on the luminosity of a continuum source by a factor of 1.54. Taking into account dust absorption in the remnant, we find a limit of L opt 8 ; 10 33 ergs s À1. We compare this upper bound with empirical evidence from point sources in other supernova remnants and with theoretical models for possible compact sources. We show that any survivor of a possible binary system must be no more luminous than an F6 main-sequence star. Bright young pulsars such as Kes 75 or the Crab pulsar are excluded by optical and X-ray limits on SN 1987A. Other nonplerionic X-ray point sources have luminosities similar to the limits on a point source in SN 1987A; RCW 103 and Cas A are slightly brighter than the limits on SN 1987A, while Pup A is slightly fainter. Of the young pulsars known to be associated with SNRs, those with ages 5000 yr are all too bright in X-rays to be compatible with the limits on SN 1987A. Examining theoretical models for accretion onto a compact object, we find that spherical accretion onto a neutron star is firmly ruled out and that spherical accretion onto a black hole is possible only if there is a larger amount of dust absorption in the remnant than predicted. In the case of thin-disk accretion, our flux limit requires a small disk, no larger than 10 10 cm, with an accretion rate no more than 0.3 times the Eddington accretion rate. Possible ways to hide a surviving compact object include the removal of all surrounding material at early times by a photon-driven wind, a small accretion disk, or very high levels of dust absorption in the remnant. It will not be easy to improve substantially on our optical-UV limit for a point source in SN 1987A, although we can hope that a better understanding of the thermal infrared emission will provide a more complete picture of the possible energy sources at the center of SN 1987A.
The supernova 1987A in the Large Magellanic Cloud
Reports on Progress in Physics, 1989
Two years after the discovery of supernova 1987A in the Large Magellanic Cloud the huge amount of... more Two years after the discovery of supernova 1987A in the Large Magellanic Cloud the huge amount of new and exciting information is still being analysed by astronomers and astrophysicists all over the world. The authors try to summarise the present situation concerning both the observational facts and their theoretical interpretation. In particular, they focus their attention on the information contained in the light curve and the spectra, and in the detection of neutrinos. It is shown that many previously open questions have now been answered, but also that many new problems await a solution. These include the unexpected blue appearance of the progenitor star, its presupernova evolution, the explosion mechanism, apparent deviations from spherical symmetry and their origin, properties of matter at high densities and temperatures, etc. All these questions are far from being fully understood. Nevertheless, an attempt is made to give at least some hints on how solutions may be obtained.
We present HST/STIS far-UV observations of the Crab nebula and its pulsar. Broad, blueshifted abs... more We present HST/STIS far-UV observations of the Crab nebula and its pulsar. Broad, blueshifted absorption arising in the nebula is seen in C IV 1550, reaching about 2500 km/s. This can be interpreted as evidence for a fast outer shell, and we adopt a spherically symmetric model to constrain the properties of this. We find that the density appears to decrease outward in the shell. A lower limit to the mass is 0.3 solar masses with an accompanying kinetic energy of 1.5EE49 ergs. A massive 10^51 erg shell cannot be excluded, but is less likely if the density profile is much steeper than R^-4 and the velocity is <6000 km/s. The observations cover the region 1140-1720 A. With the time-tag mode of the spectrograph we obtain the pulse profile. It is similar to that in the near-UV, although the primary peak is marginally narrower. Together with the near-UV data, and new optical data from NOT, our spectrum of the pulsar covers the entire region from 1140-9250 A. Dereddening the spectrum gi...
Supernova 1987A remains the most well-observed and well-studied supernova to date. Observations p... more Supernova 1987A remains the most well-observed and well-studied supernova to date. Observations produced excellent broad-band photometric and spectroscopic coverage over a wide wavelength range at all epochs. Here, we focus on the very early spectroscopic observations. Only recently have numerical models been of sufficient detail to accurately explain the observed spectra. In SN 1987A, good agreement has been found between observed and synthetic spectra for day one, but by day four, the predicted Balmer lines become much weaker than the observed lines. We present the results of work based on a radiation-hydrodynamic model by Blinnikov and collaborators. Synthetic non-LTE spectra generated from this model by the general radiation transfer code PHOENIX strongly support the theory that significant mixing of nickel into the outer envelope is required to maintain strong Balmer lines. Preliminary results suggest a lower limit to the average nickel mass of 1.0 × 10^-5 solar masses is requi...
![Research paper thumbnail of New [ITAL]Hubble Space Telescope[/ITAL] Observations of High-Velocity L[CLC]y[/CLC]α and Hα in SNR 1987A](https://attachments.academia-assets.com/84928958/thumbnails/1.jpg)
](The Astrophysical Journal, 1998
We describe and model high velocity (≈ 15, 000 km s -1 ) Lyα and Hα emission from supernova remna... more We describe and model high velocity (≈ 15, 000 km s -1 ) Lyα and Hα emission from supernova remnant 1987A seen in September and October 1997 with the Space Telescope Imaging Spectrograph. Part of this emission comes from a reverse shock located at ≈ 75% of the radius of the inner boundary of the inner circumstellar ring and confined within ±30 • of the equatorial plane. Departure from axisymmetry in the Lyα and Hα emission correlates with that seen in nonthermal radio emission. We also see diffuse high velocity Lyα emission from supernova debris inside the reverse shock that may be due to excitation by nonthermal particles accelerated by the shock.
The Astrophysical Journal, 2006
We present new (2004 July) G750L and G140L Space Telescope Imaging Spectrograph (STIS) data of th... more We present new (2004 July) G750L and G140L Space Telescope Imaging Spectrograph (STIS) data of the Hα and Lyα emission from supernova remnant (SNR) 1987A. With the aid of earlier data, from Oct 1997 to Oct 2002, we track the local evolution of Lyα emission and both the local and global evolution of Hα emission. We find that the average Hα intensity has increased locally by a factor ∼ 3 for both blueshifted and redshifted emission, over periods of about 5 and 7 years, respectively. The average Lyα intensity has increased by a factor ∼ 9,
The Astrophysical Journal, 2011
We present the most sensitive ultraviolet observations of Supernova 1987A to date. Imaging spectr... more We present the most sensitive ultraviolet observations of Supernova 1987A to date. Imaging spectroscopy from the Hubble Space Telescope-Cosmic Origins Spectrograph shows many narrow (∆v ∼ 300 km s -1 ) emission lines from the circumstellar ring, broad (∆v ∼ 10 -20 × 10 3 km s -1 ) emission lines from the reverse shock, and ultraviolet continuum emission. The high signal-to-noise (> 40 per resolution element) broad Lyα emission is excited by soft X-ray and EUV heating of mostly neutral gas in the circumstellar ring and outer supernova debris. The ultraviolet continuum at λ > 1350 Å can be explained by H I 2-photon (2s 2 S 1/2 -1s 2 S 1/2 ) emission from the same region. We confirm our earlier, tentative detection of N V λ1240 emission from the reverse shock and present the first detections of broad He II λ1640, C IV λ1550, and N IV] λ1486 emission lines from the reverse shock. The helium abundance in the high-velocity material is He/H = 0.14 ± 0.06. The N V/Hα line ratio requires partial ion-electron equilibration (T e /T p ≈ 0.14 -0.35). We find that the N/C abundance ratio in the gas crossing the reverse shock is significantly higher than that in the circumstellar ring, a result that may be attributed to chemical stratification in the outer envelope of the supernova progenitor. The N/C abundance ratio may have been stratified prior to the ring expulsion, or this result may indicate continued CNO processing in the progenitor subsequent to the expulsion of the circumstellar ring. Subject headings: supernovae: individual (SN 1987A) -shock waves -circumstellar matter * Based on observations made with the NASA/ESA Hubble Space T elescope, obtained from the data archive at the Space Telescope Science Institute. STScI is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS 5-26555.
Nature, 2011
When a massive star explodes as a supernova, substantial amounts of radioactive elementsprimarily... more When a massive star explodes as a supernova, substantial amounts of radioactive elementsprimarily 56 Ni, 57 Ni and 44 Ti-are produced 1 . After the initial flash of light from shock heating, the fading light emitted by the supernova is due to the decay of these elements 2 . However, after decades, the energy for a supernova remnant comes from the shock interaction between the ejecta and the surrounding medium 3 . The transition to this phase has hitherto not been
Science, 2010
Let Me See Your Supernova As the matter expelled from a supernova travels through and interacts w... more Let Me See Your Supernova As the matter expelled from a supernova travels through and interacts with the interstellar medium, it creates a radiating structure called a supernova remnant. In 1987, astronomers detected a bright supernova in our galaxy, SN 1987A, the remains of which are now expanding into and interacting with a dense ring of gas and dust that surrounds the explosion site. France et al. (p. 1624 , published online 2 September; see the Perspective by Laming ) obtained spectroscopic data of the ring surrounding SN 1987A and compared it with similar data acquired in 2004. Because SN 1987A is so close to us, the explosion was visible to the naked eye and the results provide a glimpse into the hydro dynamics and kinetics of fast astrophysical shocks in a young supernova remnant.
We describe and model high velocity (≈ 15, 000 km s −1) Lyα and Hα emission from supernova remnan... more We describe and model high velocity (≈ 15, 000 km s −1) Lyα and Hα emission from supernova remnant 1987A seen in September and October 1997 with the Space Telescope Imaging Spectrograph. Part of this emission comes from a reverse shock located at ≈ 75% of the radius of the inner boundary of the inner circumstellar ring and confined within ±30 • of the equatorial plane. Departure from axisymmetry in the Lyα and Hα emission correlates with that seen in nonthermal radio emission and reveals an asymmetry in the circumstellar gas distribution. We also see diffuse high velocity Lyα emission from supernova debris inside the reverse shock that may be due to excitation by nonthermal particles accelerated by the shock.
Two-dimensional spectra of Supernova 1987A were obtained on 1998 November 14-15 (4282 days after ... more Two-dimensional spectra of Supernova 1987A were obtained on 1998 November 14-15 (4282 days after outburst) with the Space Telescope Imaging Spectrograph (STIS) on board the Hubble Space Telescope (HST ). The slit sampled portions of the inner circumstellar ring at the east and west ansae as well as small sections of both the northern and southern outer rings. The temperature and density at these locations are estimated by nebular analysis of [N II], [O III], and [S II] emission line ratios, and with time-dependent photoionization/recombination models. The results from these two methods are mutually consistent. The electron density in the inner ring is ∼ 4000 cm for S II, with progressively lower densities for N II and O III. The electron temperatures determined from [N II] and [O III] line ratios are ∼ 11, 000 K and ∼ 22, 000 K, respectively. These results are consistent with evolutionary trends in the circumstellar gas from similar measurements at earlier epochs. We find that emiss...
Visual and ultraviolet spatially resolved ( ∼ 0. ′ ′ 1) spectra of SN 1987A obtained on days 3715... more Visual and ultraviolet spatially resolved ( ∼ 0. ′ ′ 1) spectra of SN 1987A obtained on days 3715 and 3743 with the Space Telescope Imaging Spectrograph on the Hubble Space Telescope show that the high-velocity SN debris is colliding 1 Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope
The Astrophysical Journal
Visual and ultraviolet spatially resolved (∼ 0. ′′ 1) spectra of SN 1987A obtained on days 3715 a... more Visual and ultraviolet spatially resolved (∼ 0. ′′ 1) spectra of SN 1987A obtained on days 3715 and 3743 with the Space Telescope Imaging Spectrograph on the Hubble Space Telescope show that the high-velocity SN debris is colliding 1 Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy Inc., under NASA Contract NAS5-26555.
Supernova 1987A remains the most well-observed and well-studied supernova to date. Observations p... more Supernova 1987A remains the most well-observed and well-studied supernova to date. Observations produced excellent broad-band photometric and spectroscopic coverage over a wide wavelength range at all epochs. Here, we focus on the very early spectroscopic observations. Only recently have numerical models been of sufficient detail to accurately explain the observed spectra. In SN 1987A, good agreement has been found between observed and synthetic spectra for day one, but by day four, the predicted Balmer lines become much weaker than the observed lines. We present the results of work based on a radiation-hydrodynamic model by Blinnikov and collaborators. Synthetic non-LTE spectra generated from this model by the general radiation transfer code PHOENIX strongly support the theory that significant mixing of nickel into the outer envelope is required to maintain strong Balmer lines. Preliminary results suggest a lower limit to the average nickel mass of 1.0 \times 10^{-5} solar masses is required above 5000 \kmps by day four. PHOENIX models thus have the potential to be a sensitive probe for nickel mixing in the outer layers of a supernova.
High-Velocity L[CLC]y[/CLC]a Emission from SNR 1987A
Astrophys J, 1998
Lawrence Berkeley National Laboratory, Mar 31, 2002
Supernova 1987A remains the most well-studied supernova to date. Observations produced excellent ... more Supernova 1987A remains the most well-studied supernova to date. Observations produced excellent broad-band photometric and spectroscopic coverage over a wide wavelength range at all epochs. We model the observed spectra from Day 1 to Day 81 using a hydrodynamical model. We show that good agreement can be obtained at times up to about 60 days, if we allow for extended nickel mixing. Later than about 60 days the observed Balmer lines become stronger than our models can reproduce. We show that this is likely due to a more complicated distribution of gamma-rays than we allow for in our spherically symmetric calculations. We present synthetic light curves in UBV RIJHK and a synthetic bolometric light curve. Using this broad baseline of detailed spectroscopic models we find a distance modulus of µ = 18.5 ± 0.2 using the SEAM method of determining distances to supernovae. We find that the explosion time agrees with that of the neutrino burst and is constrained at 68% confidence to within ±0.9 days. We argue that the weak Balmer lines of our detailed model calculations casts doubt on the accuracy of the purely photometric EPM method. We also suggest that Type IIP supernovae will be most useful as distance indicators at early times due to a variety of effects.
High-Velocity Ly(Alpha) Emission from SMR 1987A
ABSTRACT The high-velocity Ly(Alpha) emission from SN 1987A observed with the Space Telescope Ima... more ABSTRACT The high-velocity Ly(Alpha) emission from SN 1987A observed with the Space Telescope Imaging Spectrograph (STIS) evidently comes from a reverse shock formed where the outer envelope of SN 1987A strikes ionized gas inside the inner circumstellar ring. The observations can be explained by a simple kinematic model, in which the Ly(Alpha) emission comes from hydrogen atoms with radial velocity approximately 15,000 km s(exp -1) crossing a reverse shock in the shape of a slightly prolate ellipsoid with equatorial radius 4.8 x 10(exp 17) cm or approximately 80% of the distance to the inner surface of the inner ring. N v double Lambda 1239, 1243 emission, if present, has a net luminosity approximately less than 30% times that of the Ly(Alpha) emission. Future STIS observations should enable us to predict the time of impact with the inner ring and to determine unambiguously whether or not N v emission is present. These observations will offer a unique opportunity to probe the structure of SN 1987A's circumstellar environment and the hydrodynamics and kinetics of very fast shocks.
STIS Observations of Shock Interaction Around SN 1987A
Bulletin of the American Astronomical Society, Dec 1, 1997
Visual and ultraviolet spatially resolved ( ~ 0\farcs1) spectra of SN1987A obtained were with STI... more Visual and ultraviolet spatially resolved ( ~ 0\farcs1) spectra of SN1987A obtained were with STIS on days 3715 and 3743 (27 Apr. and 25 May 1997) show that high-velocity SN debris is colliding with circumstellar gas. Very broad Ly-alpha emission with velocities extending to ~ +/-20,000kms(-1) originates inside the inner circumstellar ring and appears to fill most of the surface
We report and interpret HST/STIS long-slit observations of the optical and ultraviolet (1150 - 10... more We report and interpret HST/STIS long-slit observations of the optical and ultraviolet (1150 - 10270 Angstrom) emission-line spectra of the rapidly brightening Spot 1 on the equatorial ring of SN 1987A between 1997 September and 1999 October (days 3869 -- 4606 after outburst). The emission is caused by radiative shocks created where the supernova blast wave strikes dense gas protruding inward from the equatorial ring. We measure and tabulate line identifications, fluxes and, in some cases, line widths and shifts. We compute flux correction factors to account for substantial interstellar line absorption of several emission lines. Nebular analysis shows that optical emission lines come from a region of cool (T_e ~ 10^4 K) and dense (n_e ~ 10^6 cm^-3) gas in the compressed photoionized layer behind the radiative shock. The observed line widths indicate that only shocks with shock velocities V_s < 250 km/s have become radiative, while line ratios indicate that much of the emission must have come from yet slower (V_s < 135 k/ms) shocks. We are able to fit the UV fluxes with an idealized radiative shock model consisting of two shocks (V_s = 135 and 250 km/s). The observed UV flux increase with time can be explained by the increase in shock surface areas as the blast wave overtakes more of the protrusion. The observed flux ratios of optical to highly-ionized UV lines are greater by a factor of ~ 2 -- 3 than predictions from the radiative shock models and we discuss the possible causes. We also present models for the observed H-alpha line widths and profiles, which suggests that a chaotic flow exists in the photoionized regions of these shocks. We discuss what can be learned with future observations of all the spots present on the equatorial ring.
The Three Dimensional Structure and Dynamics of the Supernova 1987A Debris
... Karin Muglach, Artep Inc.,Naval Research Laboratory, Washington DC, USA muglach@nrl.navy.mil ... more ... Karin Muglach, Artep Inc.,Naval Research Laboratory, Washington DC, USA muglach@nrl.navy.mil ... Astrophys. 392, 1119 Rouppe van der Voort, LHM, Rutten, RJ, Sütterlin, P., Sloover, PJ, Krijger, JM, 2003, Astron. Astrophys. ...
The Astrophysical Journal, Aug 20, 2005
We observed supernova 1987A (SN 1987A) with the Space Telescope Imaging Spectrograph (STIS) on th... more We observed supernova 1987A (SN 1987A) with the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope (HST) in 1999 September and again with the Advanced Camera for Surveys (ACS) on the HST in 2003 November. Our spectral observations cover ultraviolet (UV) and optical wavelengths from 1140 to 10266 8, and our imaging observations cover UV and optical wavelengths from 2900 to 9650 8. No point source is observed in the remnant. We obtain a limiting flux of F opt 1:6 ; 10 À14 ergs s À1 cm À2 in the wavelength range 2900-9650 8 for any continuum emitter at the center of the supernova remnant (SNR). This corresponds to an intrinsic luminosity of L opt 5 ; 10 33 ergs s À1. It is likely that the SNR contains opaque dust that absorbs UV and optical emission, resulting in an attenuation of $35% due to dust absorption in the SNR. Correcting for this level of dust absorption would increase our upper limit on the luminosity of a continuum source by a factor of 1.54. Taking into account dust absorption in the remnant, we find a limit of L opt 8 ; 10 33 ergs s À1. We compare this upper bound with empirical evidence from point sources in other supernova remnants and with theoretical models for possible compact sources. We show that any survivor of a possible binary system must be no more luminous than an F6 main-sequence star. Bright young pulsars such as Kes 75 or the Crab pulsar are excluded by optical and X-ray limits on SN 1987A. Other nonplerionic X-ray point sources have luminosities similar to the limits on a point source in SN 1987A; RCW 103 and Cas A are slightly brighter than the limits on SN 1987A, while Pup A is slightly fainter. Of the young pulsars known to be associated with SNRs, those with ages 5000 yr are all too bright in X-rays to be compatible with the limits on SN 1987A. Examining theoretical models for accretion onto a compact object, we find that spherical accretion onto a neutron star is firmly ruled out and that spherical accretion onto a black hole is possible only if there is a larger amount of dust absorption in the remnant than predicted. In the case of thin-disk accretion, our flux limit requires a small disk, no larger than 10 10 cm, with an accretion rate no more than 0.3 times the Eddington accretion rate. Possible ways to hide a surviving compact object include the removal of all surrounding material at early times by a photon-driven wind, a small accretion disk, or very high levels of dust absorption in the remnant. It will not be easy to improve substantially on our optical-UV limit for a point source in SN 1987A, although we can hope that a better understanding of the thermal infrared emission will provide a more complete picture of the possible energy sources at the center of SN 1987A.
The supernova 1987A in the Large Magellanic Cloud
Reports on Progress in Physics, 1989
Two years after the discovery of supernova 1987A in the Large Magellanic Cloud the huge amount of... more Two years after the discovery of supernova 1987A in the Large Magellanic Cloud the huge amount of new and exciting information is still being analysed by astronomers and astrophysicists all over the world. The authors try to summarise the present situation concerning both the observational facts and their theoretical interpretation. In particular, they focus their attention on the information contained in the light curve and the spectra, and in the detection of neutrinos. It is shown that many previously open questions have now been answered, but also that many new problems await a solution. These include the unexpected blue appearance of the progenitor star, its presupernova evolution, the explosion mechanism, apparent deviations from spherical symmetry and their origin, properties of matter at high densities and temperatures, etc. All these questions are far from being fully understood. Nevertheless, an attempt is made to give at least some hints on how solutions may be obtained.
We present HST/STIS far-UV observations of the Crab nebula and its pulsar. Broad, blueshifted abs... more We present HST/STIS far-UV observations of the Crab nebula and its pulsar. Broad, blueshifted absorption arising in the nebula is seen in C IV 1550, reaching about 2500 km/s. This can be interpreted as evidence for a fast outer shell, and we adopt a spherically symmetric model to constrain the properties of this. We find that the density appears to decrease outward in the shell. A lower limit to the mass is 0.3 solar masses with an accompanying kinetic energy of 1.5EE49 ergs. A massive 10^51 erg shell cannot be excluded, but is less likely if the density profile is much steeper than R^-4 and the velocity is <6000 km/s. The observations cover the region 1140-1720 A. With the time-tag mode of the spectrograph we obtain the pulse profile. It is similar to that in the near-UV, although the primary peak is marginally narrower. Together with the near-UV data, and new optical data from NOT, our spectrum of the pulsar covers the entire region from 1140-9250 A. Dereddening the spectrum gi...
Supernova 1987A remains the most well-observed and well-studied supernova to date. Observations p... more Supernova 1987A remains the most well-observed and well-studied supernova to date. Observations produced excellent broad-band photometric and spectroscopic coverage over a wide wavelength range at all epochs. Here, we focus on the very early spectroscopic observations. Only recently have numerical models been of sufficient detail to accurately explain the observed spectra. In SN 1987A, good agreement has been found between observed and synthetic spectra for day one, but by day four, the predicted Balmer lines become much weaker than the observed lines. We present the results of work based on a radiation-hydrodynamic model by Blinnikov and collaborators. Synthetic non-LTE spectra generated from this model by the general radiation transfer code PHOENIX strongly support the theory that significant mixing of nickel into the outer envelope is required to maintain strong Balmer lines. Preliminary results suggest a lower limit to the average nickel mass of 1.0 × 10^-5 solar masses is requi...
The Astrophysical Journal, 1998
We describe and model high velocity (≈ 15, 000 km s -1 ) Lyα and Hα emission from supernova remna... more We describe and model high velocity (≈ 15, 000 km s -1 ) Lyα and Hα emission from supernova remnant 1987A seen in September and October 1997 with the Space Telescope Imaging Spectrograph. Part of this emission comes from a reverse shock located at ≈ 75% of the radius of the inner boundary of the inner circumstellar ring and confined within ±30 • of the equatorial plane. Departure from axisymmetry in the Lyα and Hα emission correlates with that seen in nonthermal radio emission. We also see diffuse high velocity Lyα emission from supernova debris inside the reverse shock that may be due to excitation by nonthermal particles accelerated by the shock.
The Astrophysical Journal, 2006
We present new (2004 July) G750L and G140L Space Telescope Imaging Spectrograph (STIS) data of th... more We present new (2004 July) G750L and G140L Space Telescope Imaging Spectrograph (STIS) data of the Hα and Lyα emission from supernova remnant (SNR) 1987A. With the aid of earlier data, from Oct 1997 to Oct 2002, we track the local evolution of Lyα emission and both the local and global evolution of Hα emission. We find that the average Hα intensity has increased locally by a factor ∼ 3 for both blueshifted and redshifted emission, over periods of about 5 and 7 years, respectively. The average Lyα intensity has increased by a factor ∼ 9,
The Astrophysical Journal, 2011
We present the most sensitive ultraviolet observations of Supernova 1987A to date. Imaging spectr... more We present the most sensitive ultraviolet observations of Supernova 1987A to date. Imaging spectroscopy from the Hubble Space Telescope-Cosmic Origins Spectrograph shows many narrow (∆v ∼ 300 km s -1 ) emission lines from the circumstellar ring, broad (∆v ∼ 10 -20 × 10 3 km s -1 ) emission lines from the reverse shock, and ultraviolet continuum emission. The high signal-to-noise (> 40 per resolution element) broad Lyα emission is excited by soft X-ray and EUV heating of mostly neutral gas in the circumstellar ring and outer supernova debris. The ultraviolet continuum at λ > 1350 Å can be explained by H I 2-photon (2s 2 S 1/2 -1s 2 S 1/2 ) emission from the same region. We confirm our earlier, tentative detection of N V λ1240 emission from the reverse shock and present the first detections of broad He II λ1640, C IV λ1550, and N IV] λ1486 emission lines from the reverse shock. The helium abundance in the high-velocity material is He/H = 0.14 ± 0.06. The N V/Hα line ratio requires partial ion-electron equilibration (T e /T p ≈ 0.14 -0.35). We find that the N/C abundance ratio in the gas crossing the reverse shock is significantly higher than that in the circumstellar ring, a result that may be attributed to chemical stratification in the outer envelope of the supernova progenitor. The N/C abundance ratio may have been stratified prior to the ring expulsion, or this result may indicate continued CNO processing in the progenitor subsequent to the expulsion of the circumstellar ring. Subject headings: supernovae: individual (SN 1987A) -shock waves -circumstellar matter * Based on observations made with the NASA/ESA Hubble Space T elescope, obtained from the data archive at the Space Telescope Science Institute. STScI is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS 5-26555.
Nature, 2011
When a massive star explodes as a supernova, substantial amounts of radioactive elementsprimarily... more When a massive star explodes as a supernova, substantial amounts of radioactive elementsprimarily 56 Ni, 57 Ni and 44 Ti-are produced 1 . After the initial flash of light from shock heating, the fading light emitted by the supernova is due to the decay of these elements 2 . However, after decades, the energy for a supernova remnant comes from the shock interaction between the ejecta and the surrounding medium 3 . The transition to this phase has hitherto not been
Science, 2010
Let Me See Your Supernova As the matter expelled from a supernova travels through and interacts w... more Let Me See Your Supernova As the matter expelled from a supernova travels through and interacts with the interstellar medium, it creates a radiating structure called a supernova remnant. In 1987, astronomers detected a bright supernova in our galaxy, SN 1987A, the remains of which are now expanding into and interacting with a dense ring of gas and dust that surrounds the explosion site. France et al. (p. 1624 , published online 2 September; see the Perspective by Laming ) obtained spectroscopic data of the ring surrounding SN 1987A and compared it with similar data acquired in 2004. Because SN 1987A is so close to us, the explosion was visible to the naked eye and the results provide a glimpse into the hydro dynamics and kinetics of fast astrophysical shocks in a young supernova remnant.
We describe and model high velocity (≈ 15, 000 km s −1) Lyα and Hα emission from supernova remnan... more We describe and model high velocity (≈ 15, 000 km s −1) Lyα and Hα emission from supernova remnant 1987A seen in September and October 1997 with the Space Telescope Imaging Spectrograph. Part of this emission comes from a reverse shock located at ≈ 75% of the radius of the inner boundary of the inner circumstellar ring and confined within ±30 • of the equatorial plane. Departure from axisymmetry in the Lyα and Hα emission correlates with that seen in nonthermal radio emission and reveals an asymmetry in the circumstellar gas distribution. We also see diffuse high velocity Lyα emission from supernova debris inside the reverse shock that may be due to excitation by nonthermal particles accelerated by the shock.
Two-dimensional spectra of Supernova 1987A were obtained on 1998 November 14-15 (4282 days after ... more Two-dimensional spectra of Supernova 1987A were obtained on 1998 November 14-15 (4282 days after outburst) with the Space Telescope Imaging Spectrograph (STIS) on board the Hubble Space Telescope (HST ). The slit sampled portions of the inner circumstellar ring at the east and west ansae as well as small sections of both the northern and southern outer rings. The temperature and density at these locations are estimated by nebular analysis of [N II], [O III], and [S II] emission line ratios, and with time-dependent photoionization/recombination models. The results from these two methods are mutually consistent. The electron density in the inner ring is ∼ 4000 cm for S II, with progressively lower densities for N II and O III. The electron temperatures determined from [N II] and [O III] line ratios are ∼ 11, 000 K and ∼ 22, 000 K, respectively. These results are consistent with evolutionary trends in the circumstellar gas from similar measurements at earlier epochs. We find that emiss...
Visual and ultraviolet spatially resolved ( ∼ 0. ′ ′ 1) spectra of SN 1987A obtained on days 3715... more Visual and ultraviolet spatially resolved ( ∼ 0. ′ ′ 1) spectra of SN 1987A obtained on days 3715 and 3743 with the Space Telescope Imaging Spectrograph on the Hubble Space Telescope show that the high-velocity SN debris is colliding 1 Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope
The Astrophysical Journal
Visual and ultraviolet spatially resolved (∼ 0. ′′ 1) spectra of SN 1987A obtained on days 3715 a... more Visual and ultraviolet spatially resolved (∼ 0. ′′ 1) spectra of SN 1987A obtained on days 3715 and 3743 with the Space Telescope Imaging Spectrograph on the Hubble Space Telescope show that the high-velocity SN debris is colliding 1 Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy Inc., under NASA Contract NAS5-26555.
Supernova 1987A remains the most well-observed and well-studied supernova to date. Observations p... more Supernova 1987A remains the most well-observed and well-studied supernova to date. Observations produced excellent broad-band photometric and spectroscopic coverage over a wide wavelength range at all epochs. Here, we focus on the very early spectroscopic observations. Only recently have numerical models been of sufficient detail to accurately explain the observed spectra. In SN 1987A, good agreement has been found between observed and synthetic spectra for day one, but by day four, the predicted Balmer lines become much weaker than the observed lines. We present the results of work based on a radiation-hydrodynamic model by Blinnikov and collaborators. Synthetic non-LTE spectra generated from this model by the general radiation transfer code PHOENIX strongly support the theory that significant mixing of nickel into the outer envelope is required to maintain strong Balmer lines. Preliminary results suggest a lower limit to the average nickel mass of 1.0 \times 10^{-5} solar masses is required above 5000 \kmps by day four. PHOENIX models thus have the potential to be a sensitive probe for nickel mixing in the outer layers of a supernova.
High-Velocity L[CLC]y[/CLC]a Emission from SNR 1987A
Astrophys J, 1998
Lawrence Berkeley National Laboratory, Mar 31, 2002
Supernova 1987A remains the most well-studied supernova to date. Observations produced excellent ... more Supernova 1987A remains the most well-studied supernova to date. Observations produced excellent broad-band photometric and spectroscopic coverage over a wide wavelength range at all epochs. We model the observed spectra from Day 1 to Day 81 using a hydrodynamical model. We show that good agreement can be obtained at times up to about 60 days, if we allow for extended nickel mixing. Later than about 60 days the observed Balmer lines become stronger than our models can reproduce. We show that this is likely due to a more complicated distribution of gamma-rays than we allow for in our spherically symmetric calculations. We present synthetic light curves in UBV RIJHK and a synthetic bolometric light curve. Using this broad baseline of detailed spectroscopic models we find a distance modulus of µ = 18.5 ± 0.2 using the SEAM method of determining distances to supernovae. We find that the explosion time agrees with that of the neutrino burst and is constrained at 68% confidence to within ±0.9 days. We argue that the weak Balmer lines of our detailed model calculations casts doubt on the accuracy of the purely photometric EPM method. We also suggest that Type IIP supernovae will be most useful as distance indicators at early times due to a variety of effects.
High-Velocity Ly(Alpha) Emission from SMR 1987A
ABSTRACT The high-velocity Ly(Alpha) emission from SN 1987A observed with the Space Telescope Ima... more ABSTRACT The high-velocity Ly(Alpha) emission from SN 1987A observed with the Space Telescope Imaging Spectrograph (STIS) evidently comes from a reverse shock formed where the outer envelope of SN 1987A strikes ionized gas inside the inner circumstellar ring. The observations can be explained by a simple kinematic model, in which the Ly(Alpha) emission comes from hydrogen atoms with radial velocity approximately 15,000 km s(exp -1) crossing a reverse shock in the shape of a slightly prolate ellipsoid with equatorial radius 4.8 x 10(exp 17) cm or approximately 80% of the distance to the inner surface of the inner ring. N v double Lambda 1239, 1243 emission, if present, has a net luminosity approximately less than 30% times that of the Ly(Alpha) emission. Future STIS observations should enable us to predict the time of impact with the inner ring and to determine unambiguously whether or not N v emission is present. These observations will offer a unique opportunity to probe the structure of SN 1987A's circumstellar environment and the hydrodynamics and kinetics of very fast shocks.
STIS Observations of Shock Interaction Around SN 1987A
Bulletin of the American Astronomical Society, Dec 1, 1997
Visual and ultraviolet spatially resolved ( ~ 0\farcs1) spectra of SN1987A obtained were with STI... more Visual and ultraviolet spatially resolved ( ~ 0\farcs1) spectra of SN1987A obtained were with STIS on days 3715 and 3743 (27 Apr. and 25 May 1997) show that high-velocity SN debris is colliding with circumstellar gas. Very broad Ly-alpha emission with velocities extending to ~ +/-20,000kms(-1) originates inside the inner circumstellar ring and appears to fill most of the surface
We report and interpret HST/STIS long-slit observations of the optical and ultraviolet (1150 - 10... more We report and interpret HST/STIS long-slit observations of the optical and ultraviolet (1150 - 10270 Angstrom) emission-line spectra of the rapidly brightening Spot 1 on the equatorial ring of SN 1987A between 1997 September and 1999 October (days 3869 -- 4606 after outburst). The emission is caused by radiative shocks created where the supernova blast wave strikes dense gas protruding inward from the equatorial ring. We measure and tabulate line identifications, fluxes and, in some cases, line widths and shifts. We compute flux correction factors to account for substantial interstellar line absorption of several emission lines. Nebular analysis shows that optical emission lines come from a region of cool (T_e ~ 10^4 K) and dense (n_e ~ 10^6 cm^-3) gas in the compressed photoionized layer behind the radiative shock. The observed line widths indicate that only shocks with shock velocities V_s < 250 km/s have become radiative, while line ratios indicate that much of the emission must have come from yet slower (V_s < 135 k/ms) shocks. We are able to fit the UV fluxes with an idealized radiative shock model consisting of two shocks (V_s = 135 and 250 km/s). The observed UV flux increase with time can be explained by the increase in shock surface areas as the blast wave overtakes more of the protrusion. The observed flux ratios of optical to highly-ionized UV lines are greater by a factor of ~ 2 -- 3 than predictions from the radiative shock models and we discuss the possible causes. We also present models for the observed H-alpha line widths and profiles, which suggests that a chaotic flow exists in the photoionized regions of these shocks. We discuss what can be learned with future observations of all the spots present on the equatorial ring.
The Three Dimensional Structure and Dynamics of the Supernova 1987A Debris
... Karin Muglach, Artep Inc.,Naval Research Laboratory, Washington DC, USA muglach@nrl.navy.mil ... more ... Karin Muglach, Artep Inc.,Naval Research Laboratory, Washington DC, USA muglach@nrl.navy.mil ... Astrophys. 392, 1119 Rouppe van der Voort, LHM, Rutten, RJ, Sütterlin, P., Sloover, PJ, Krijger, JM, 2003, Astron. Astrophys. ...