SN 1979C Research Articles

An Optical Afterglow Model for Bright Linear Type II Supernovae

We show that a gamma-ray burst (GRB) afterglow model combined with an underlying plateau Type II supernova can fit the data of at least one bright linear Type II supernova, SN 1979C. We suggest that the bright linear subclass of Type IIs could be represented by this model. We describe a scenario in which a hydrogen-rich massive star core collapses, causing a jet explosion that punctures through the star and initiates a shock that ejects the hydrogen-rich envelope. The jet is responsible for a low-density high-energy ejecta causing a GRB optical afterglow. The jet contains enough energy to create an asymmetric shock wave that ejects the He core and the overlying H envelope. We fit the observational data of SN 1979C with an analytic GRB model and a parameterized Type II light curve from the data of SN 1969L. We also show that a numerical simulation of a massive star experiencing mass loss can also fit the data with ejected mass of 12 M☉, initial radius ~300 R☉, and explosion energy of 1 × 1051 ergs coupled to a GRB afterglow. We suggest that the energy of the jet could have been dissipated by the hydrogen envelope and thus not cause the ejecta to expand with the high velocities typically seen in Type Ic supernovae associated with GRBs. The model presented here could be an example of a failed GRB and X-ray flashes.

VLBI Observations of SN 1979C and SN 1986J

SummaryWe summarize our results on multi-epoch VLBI observations of SN 1979C in the galaxy M100 in Virgo, and of SN 1986 in the galaxy NGC 891. From t = 3.7 to 22 yr after the explosion, SN 1979C expands ∝ tm, almost freely, with m = 0.95 ± 0.03. For a total kinetic energy of 3 × 1051 erg, the expansion result requires a mass-loss to wind-velocity ratio for the progenitor of only 1 × 10−5 M⊙ yr−1per 10 km s−1, an order of magnitude smaller than estimated from radio light-curve fitting. We show a first image with slightly discernible structure of the supernova. For SN 1986J we present five images from 1987 to 2002 and show our result on moderately to strongly decelerated expansion with m = 0.71 ± 0.11. We comment on our result of an inversion of the radio spectrum in terms of the emergence of a possible pulsar nebula.

High-Resolution Radio Imaging of Young Supernovae: SN 1979C, SN 1986J, and SN 2001gd

SummaryThe high resolution obtained through the use of VLBI gives an unique opportunity to directly observe the interaction of an expanding radio supernova with its surrounding medium. We present here results from our VLBI observations of the young supernovae SN 1979C, SN 1986J, and SN 2001gd.

A VLBI search for pulsar wind nebulae in supernovae

We examine recent supernovae which have been observed with very-long-baseline interferometry in order to detect or limit the emission from a possible compact remnant of the explosion. Such a remnant could be a neutron star, generating a pulsar wind nebula, or a black hole with an accretion disk and jets. Four supernovae, and also more than a dozen supernovae or their young remnants in M82, have structure sufficiently resolved to allow useful conclusions as to the strength of the emission from such young neutron stars or black holes. We recently discovered a compact component in the center of SN 1986J’s shell with a spectral luminosity at 15 GHz 200 times that of the Crab Nebula. This is most likely the compact remnant of the explosion, the first and only one found in any modern supernova. For other modern supernovae, the upper limits on the radio spectral luminosities of such young compact remnants range from 180 times that of the Crab Nebula for SN 1979C in M100 in the Virgo cluster to 0.001 times that of the Crab Nebula for SN 1987A in the Large Magellanic Cloud.

Extragalactic binaries as core-collapse supernova progenitors

Binary star systems are likely the progenitors of many core-collapse (Type II, Type Ib/c) supernovae (SNe). We present observational investigations using ground-based and Hubble Space Telescope optical imaging and radio monitoring of SNe and their environments, which either indicate or attempt to constrain the possible binary nature of the SN progenitors. For example, from radio observations with the Very Large Array of the Type II-linear SN 1979C in M100 we conclude that the progenitor was possibly in a massive, highly eccentric binary, similar to the VV Cephei systems. The Type IIb SN 1993J in M81 is presumed to have a massive progenitor in an interacting binary system, and from Hubble imaging we cannot yet constrain the nature of the presumed massive, blue companion. We will present additional results for other Type Ib/c and II SNe.

SN 1979C VLBI: 22 Years of Almost Free Expansion

VLBI measurements of the size of SN 1979C in M100 (NGC 4321) in the Virgo Cluster, from t = 3.7 yr after the explosion, show an expansion ∝tm, which is, with m = 0.95 ± 0.03, almost consistent with being free for 22 years. The last size measurement, at t = 22 yr, may indicate for the first time a change of the expansion of the supernova and suggests, as an alternative, free expansion ∝tm with m = 1.00 ± 0.05 up to tb ~ 17 yr followed by marginally significant deceleration with m = 0.74 ± 0.17. The possible deceleration could be weaker within the errors for tb 17 yr. With the assumption for the density profile of the circumstellar medium (CSM) of ρCSM ∝ r-s, we derive a model-dependent value of s = 1.95 up to a distance from the progenitor, r = rb, that corresponds to tb ~ 17 yr, which changes to s 1.5 for r > rb. For a kinetic energy of the shocked ejecta and CSM shells of Ekin = 1051 ergs, our results require a mass loss to wind velocity ratio for the progenitor of w/w ~ 1 × 10-5 M☉ yr-1 per w = 10 km s-1, an order of magnitude smaller than estimated from radio light-curve fitting. The swept-up mass at t = 22 yr is then Msw = 0.3 M☉ and the inferred mass of the shocked ejecta Mshock-ej = 2 M☉. Our last observations give an image of a barely resolved source with a first hint on the structure of the supernova, consistent with being circular within 9% and possibly center filled. The expanding shock front method (ESM) of combining the transverse radio expansion velocities with the radial optical velocities gives direct distance estimates to M100, with standard errors of D = 16.5 ± 2.5 to 19.8 ± 3.0 Mpc, depending on whether the supernova has a bright center or is a shell without such a center. These estimates are comparable with those from Cepheid observations (e.g., 16.1 and 15.2 Mpc).

A Search for Radio Emission from Supernovae with Ages from about 1 Week to More than 80 Years

We report Very Large Array radio observations of 29 supernovae (SNe) with ages ranging from 10 days to about 90 yr past explosion. These observations significantly contribute to the existing data pool on such objects. Included are detections of known radio SNe 1950B, 1957D, 1970G, and 1983N, the suspected radio SN 1923A, and the possible radio SN 1961V. None of the remaining 23 observations resulted in detections, providing further evidence to support the observed trend that most SNe are not detectable radio emitters. To investigate the apparent lack of radio emission from the SNe reported here, we have followed standard practice and used Chevalier's standard model to derive (upper limits to) the mass-loss rates for the supernova progenitors. These upper limits to the fluxes are consistent with a lack of circumstellar material needed to provide detectable radio emission for SNe at these ages and distances. Comparison of the radio luminosities of these supernovae as a function of age past explosion to other well-observed radio SNe indicates that the Type II SNe upper limits are more consistent with the extrapolated light curves of SN 1980K than of SN 1979C, suggesting that SN 1980K may be a more typical radio emitter than SN 1979C. For completeness, we have included an appendix where the results of analyses of the non-SN radio sources are presented. Where possible, we make (tentative) identifications of these sources using various methods.

Strongly decelerated expansion of SN 1979C

We observed SN 1979C in M100 on 4 June 1999, about twenty years after explosion, with a very sensitive four-antenna VLBI array at the wavelength of λ18 cm. The distance to M100 and the expansion velocities are such that the supernova cannot be fully resolved by our Earth-wide array. Model-dependent sizes for the source have been determined and compared with previous results. We conclude that the supernova shock was initially in free expansion for 6 ± 2 yrs and then experienced a very strong deceleration. The onset of deceleration took place a few years before the abrupt trend change in the integrated radio flux density curves. We estimate the shocked swept-up mass to be M_(sw) ~ 1.6 M_⊙, assuming a standard density profile for the CSM. Such a swept-up mass for SN 1979C suggests a mass of the hydrogen-rich envelope ejected at explosion no larger than M_(env) ~ 0.9 M_⊙. If SN 1979C originated in a binary star, the low value of M_(env) suggests that the companion of the progenitor star stripped off most of the hydrogen-rich envelope mass of the presupernova star prior to the explosion.

ChandraX‐Ray Point Sources, Including Supernova 1979C, in the Spiral Galaxy M100

Six X-ray point sources, with luminosities of 4 × 1038-2 × 1039 ergs s-1 in the 0.4-7 keV band, were detected in Chandra observations of the spiral galaxy M100. One source is identified with supernova SN 1979C and appears to have roughly constant X-ray flux for the period 16-20 yr after the outburst. The X-ray spectrum is soft, as would be expected if the X-ray emission is due to the interaction of supernova ejecta with circumstellar matter. Most of the other sources are variable either within the Chandra observation or when compared to archival data. None are coincident with the peak of the radio emission at the nucleus. These sources have harder spectra than the supernova and are likely X-ray binaries. M100 has more bright X-ray sources than typical for spiral galaxies of its size. This is likely related to active star formation occurring in the galaxy.

The supernova 1998S in NGC 3877: Another supernova with Wolf-Rayet star features in pre-maximum spectrum

We present the BVR photometry and the spectra of SN 1998S taken about four months after discovery, beginning a week and 6 days before maximum brightness respectively. The light curves show a steep and linear dt:cline. which are consistent with those of SN 1979C and are typical of a SN II-L. An absolute magnitude at maximum M-B(O) less than or equal to -18.7 is derived, which is more than 2 mag brighter than the regular SNII and indicates this SN is a member of the rare class of Bright SNII. The B - V color evolution at early epoch is also typical of linear SN II with a maximum (B - V) value of +1.35, similar to the typical Ts pe II-L SN 1980K. The spectral evolution is typical for SN II-L, very similar to that of the SN 1979C. They, however, showed some differences. The spectrum before maximum showed high-ionization N III and He II emission lines superposed on a strong blue continuum. Around the maximum light the high-ionizatisn emission lines disappeared, leaving weak H I. He I emission lines, which are similar to those of SN 1983K. The extraordinary feature on the post-maximum spectra is the narrow emission P Cygni profile superposed on a much broader P Cygni structure in all five Balmer lines, Ha to HE. Such feature is reminiscent of the post-maximum spectra of SN 1984E. Rapid spectral and photometric evolution, together with the presence of obvious P Cygni profile, suggests that SN 1998S is more consistent with the nature of a type II-L, supernova than that of a IIn supernova, although narrow lines are present on the premaximum spectrum.

Radio Observations of SN 1979C: Evidence for Rapid Presupernova Evolution

We present new radio observations of the supernova SN 1979C made with the VLA at 20, 6, 3.6, and 2 cm from 1991 July to 1998 October, which extend our previously published observations (Weiler et al.1986, 1991), beginning 8 days after optical maximum in 1979 April and continuing through 1990 December. We find that the radio emission from SN 1979C has stopped declining in flux density in the manner described by Weiler et al. (1992), and has apparently entered a new stage of evolution. The observed ``flattening,'' or possible brightening, of the radio light curves for SN 1979C is interpreted as due to the SN shock wave entering a denser region of material near the progenitor star and may be indicative of complex structure in the circumstellar medium established by the stellar wind from the red supergiant (RSG) progenitor.

Hubble Space Telescope WFPC2 Imaging11Based on observations made with the NASA/ESA Hubble Space Telescope, obtained in part from the data archive of the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5‐26555. of SN 1979C and Its Environment

ABSTRACTThe locations of supernovae in the local stellar and gaseous environment in galaxies contain important clues to their progenitor stars. As part of a program to study the environments of supernovae using Hubble Space Telescope imaging data, we have examined the environment of the Type II‐L supernova SN 1979C in NGC 4321 (M100). We place rigorous constraints on the mass of the SN progenitor, based on photometry of the stellar populations in its environment. The progenitor may have had an initial mass M ≈ 17–18(±3) M⊙. Moreover, 17 years after explosion we have recovered and measured the brightness of SN 1979C in several bands, e.g., m = 23.37 in F439W [∼B; for comparison,mB(max) = 11.6].

Late-Time Optical and Ultraviolet Spectra of SN 1979C and SN 1980K

A low-dispersion Keck I spectrum of SN 1980K taken in 1995 August (t = 14.8 yr after explosion) and a spectrum taken in 1997 November (t = 17.0 yr) at the MDM Observatory show broad 5500 km s-1 emission lines of Hα, [O I] 6300, 6364 Å, and [O II] 7319, 7330 Å. Weaker but similarly broad lines detected include [Fe II] 7155 Å, [S II] 4068, 4072 Å, and a blend of [Fe II] lines at 5050–5400 Å. The presence of strong [S II] 4068, 4072 Å emission but a lack of [S II] 6716, 6731 Å emission suggests electron densities of 105–106 cm-3. From the 1997 spectrum, we estimate an Hα flux of (1.3 ± 0.2) × 10-15 ergs cm-2 s-1, indicating a 25% decline from the 1987–1992 levels during the period 1994 to 1997, possibly related to a reported decrease in its nonthermal radio emission. A 1993 May, Multiple Mirror Telescope spectrum of SN 1979C (t = 14.0 yr) shows a somewhat different spectrum from that of SN 1980K. Broad, 6000 km s-1 emission lines are also seen but with weaker Hα, stronger [O III] 4959, 5007 Å, more highly clumped [O I] and [O II] line profiles, no detectable [Fe II] 7155 Å emission, and a faint but very broad emission feature near 5750 Å. A 1997 Hubble Space Telescope Faint Object Spectrograph, near-UV spectrum (2200–4500 Å) shows strong lines of C II] 2324, 2325 Å, [O II] 2470 Å, and Mg II 2796, 2803 Å, along with weak [Ne III] 3969 Å, [S II] 4068, 4072 Å, and [O III] 4363 Å emissions. The UV emission lines show a double-peak profile with the blueward peak substantially stronger than the red, suggesting dust extinction within the expanding ejecta [E(B-V) = 0.11–0.16 mag]. The lack of detectable [O II] 3726, 3729 Å emission, together with [O III] λλ(4959 + 5007)/λ4363 ≃ 4, implies electron densities 106–107 cm-3. These Type II linear supernovae (SNe II-L) spectra show general agreement with the lines expected in a circumstellar interaction model, but the specific models that are available show several differences with the observations. High electron densities (105–107 cm-3) result in stronger collisional de-excitation than assumed in the models, thereby explaining the absence of several moderate to strong predicted lines such as [O II] 3726, 3729 Å, [N II] 6548, 6583 Å, and [S II] 6716, 6731 Å. Interaction models are needed that are specifically suited to these supernovae. We review the overall observed range of late-time SNe II-L properties and briefly discuss their properties relative to young, ejecta-dominated Galactic supernova remnants.

Radio Observations of SN 1980K: Evidence for Rapid Presupernova Evolution

We present new radio observations of the supernova SN 1979C made with the Very Large Array (VLA) at 20, 6, 3.6, and 2 cm from 1991 July to 1998 October, which extend our previously published observations (Weiler et al.), which began 8 days after optical maximum in 1979 April and continued through 1990 December. We find that the radio emission from SN 1979C has stopped declining in flux density in the manner described by Weiler et al. and has apparently entered a new stage of evolution. The observed flattening, or possible brightening, of the radio light curves for SN 1979C is interpreted as due to the supernova shock wave entering a denser region of material near the progenitor star and may be indicative of complex structure in the circumstellar medium established by the stellar wind from the red supergiant (RSG) progenitor.

Synchrotron Self‐Absorption in Radio Supernovae

The radio emission from supernovae has been modeled as synchrotron emission from the interaction between the supernova and a presupernova stellar wind. The emission shows a late power-law decline and early rise due to a low-frequency absorption process, which, in some cases (SN 1979C and SN 1980K), is well modeled as free-free absorption by the external wind. However, the flux rises in many radio supernovae (e.g., SN 1987A and Type Ib and Type Ic supernovae) have not been sufficiently well observed to define the absorption mechanism. The assumption of synchrotron self-absorption yields an approximate radius of the emission region at the time of peak flux. If another mechanism is dominant, the radius must be even larger. The large radii implied for SN 1987A and the observed Type Ib and Type Ic supernovae make external free-free absorption unlikely, given what else is known about these systems, so that synchrotron self-absorption is the probable absorption mechanism. Synchrotron self-absorption may play a role in the radio emission from SN 1981K (type unknown) and SN 1978K (Type IIn). Model supernova light curves with synchrotron self-absorption are presented. A combination of synchrotron self-absorption and external free-free absorption may be relevant to SN 1993J. The radii implied for the Type II supernovae SN 1979C and SN 1980K in the synchrotron self-absorption model are smaller than the radii expected for circumstellar interaction and are thus consistent with the free-free absorption mechanism.

Radio Detection of SN 1985L in NGC 5033

Observations of SN 1985L in NGC 5033 with the Very Large Array radio telescope have resulted in two detections of radio emission at 6 cm wavelength about 8 and 16 months after optical discovery. Combined with a number of upper limits and a study of possible models, these indicate that SN 1985L was probably a fairly normal Type II-L radio supernova, somewhat intermediate in radio properties between the well-studied radio supernovae SN 1979C and SN 1980K. A possible late-time optical detection, discussed in an accompanying paper by Fesen (1998), continues the observed correlation between radio and late-time optical emission.

Radio Supernovae as Direct Evidence of Stellar Evolution in Real Time

The radio emission from supernovae provides a direct probe of a supernova’s circumstellar environment, which presumably was established by mass-loss episodes in the late stages of the progenitor’s presupernova evolution. The observed synchrotron emission is generated by the SN shock interacting with the relatively high-density circumstellar medium which has been fully ionized and heated by the initial UV/X-ray flash. The study of radio supernovae therefore provides many clues to and constraints on stellar evolution. We will present the recent results on several cases, including SN 1980K, whose recent abrupt decline provides us with a stringent constraint on the progenitor’s initial mass; SN 1993J, for which the profile of the wind matter supports the picture of the progenitor’s evolution in an interacting binary system; and SN 1979C, where a clear change in presupernova mass-loss rate occurred about 104 years before explosion. Other examples, such as SNe 19941 and 1996cb, will also be discussed.

X‐ray supernovae in nearby galaxies: detection of SN 1979C in NGC 4321 (M 100)

X‐ray supernovae in nearby galaxies: detection of SN 1979C in NGC 4321 (M 100)

A self-colliding stellar wind model for SN 1979C

SN 1979C shows significant deviations from the well-established Chevalier minishell model for the general, long-term radio light-curve behaviour. The implication is that the deviations are primarily due to fluctuations in the radio emission. In Chevalier's mini-shell model the radio emission is directly related to the density in the circumstellar shell which is established by mass-loss from the red supergiant progenitor star, suggesting that the deviations are the result of density variations in the shell. A possible mechanism which could account for such variations is the dynamical modulation of the red supergiant wind by a binary companion. In order to explore the feasibility of such a mechanism in relation to SN 1979C, we determine the associated circumstellar shells using numerical hydrodynamics and calculate radio light curves from the resulting shells using a modified mini-shell model. We compare these light curves with the observations and find that it is possible to account for the deviations from the standard mini-shell model, thus confirming the feasibility of the binary scenario.

Compact radio sources in the starburst galaxy M82 and the Sigma-D relation for supernova remnants

We have obtained an 8.4 GHz Very Large Array (VLA) A-array map of the starburst galaxy M82 with a resolution Full Width at Half Maximum (FWHM) approximately 0.182 sec. About 50 compact radio sources in the central region of M82 were detected with a peak surface brightness approximately greater than 10(exp -17) W/Hz/sq m/sr. Comparison with previous observations shows that most sources are declining in flux. Three previously visible sources have faded into the background of our map (approximately less than 0.2 mJy/beam), while a few sources, including the second and third brightest radio sources in M82, may have increased slightly in flux over the last decade. No new radio supernova was found. The birth rate of the compact radio sources is estimated to be 0.11 + or - 0.05/yr. We attribute the population of such bright, small supernova remnants (SNRs) in M82 to the high pressure in the central region that can truncate the mass loss during a red supergiant phase or allow dense ionized clouds to be present. The compact radio sources obey a Sigma(radio surface brightness) - D(diameter) relation which is remarkably similar to that followed by supernova remnants in the Galaxy and the Magellanic Clouds and by two of the strongest known extragalactic radio supernovae: SN 1986J and SN 1979C. A least-squares fit to the SNR data gives: Sigma(sub 8.4 GHz) (W/Hz/sq m/sr) = 4.4 x 10(exp -16) D(sub pc)(exp -3.5 +/- 0.1) covering seven orders of magnitude in Sigma. Possible selection effects are discussed and a theoretical discussion of the correlation is presented.