SN 1980K Research Articles

A New, Larger Sample of Supernova Remnants in NGC 6946

Abstract The relatively nearby spiral galaxy NGC 6946 is one of the most actively star-forming galaxies in the local universe. Ten supernovae (SNe) have been observed since 1917, and hence NGC 6946 surely contains a large number of supernova remnants (SNRs). Here we report a new optical search for these SNRs using narrowband images obtained with the WIYN telescope. We identify 147 emission nebulae as likely SNRs, based on elevated [S ii]:Hα ratios compared to H ii regions. We have obtained spectra of 102 of these nebulae with Gemini North–GMOS; of these, 89 have [S ii]:Hα ratios greater than 0.4, the canonical optical criterion for identifying SNRs. There is very little overlap between our sample and the SNR candidates identified by Lacey et al. from radio data. Also, very few of our SNR candidates are known X-ray sources, unlike the situation in some other galaxies such as M33 and M83. The emission-line ratios, e.g., [N ii]:Hα, of the candidates in NGC 6946 are typical of those observed in SNR samples from other galaxies with comparable metallicity. None of the candidates observed in our low-resolution spectra show evidence of anomalous abundances or significant velocity broadening. A search for emission at the sites of all the historical SNe in NGC 6946 resulted in detections for only two: SN 1980K and SN 2004et. Spectra of both show very broad, asymmetric line profiles, consistent with the interaction between SN ejecta and the progenitor star’s circumstellar material, as seen in late spectra from other core-collapse SNe of similar age.

Dust masses for SN 1980K, SN1993J and Cassiopeia A from red–blue emission line asymmetries

We present Monte Carlo line transfer models that investigate the effects of dust on the very late time emission line spectra of the core collapse supernovae SN 1980K and SN 1993J and the young core collapse supernova remnant Cassiopeia A. Their blue-shifted emission peaks, resulting from the removal by dust of redshifted photons emitted from the far sides of the remnants, and the presence of extended red emission wings are used to constrain dust compositions and radii and to determine the masses of dust in the remnants. We estimate dust masses of between 0.08 - 0.15 M$_\odot$ for SN 1993J at year 16, 0.12 - 0.30 M$_\odot$ for SN 1980K at year 30 and $\sim$1.1 M$_\odot$ for Cas A at year $\sim$330. Our models for the strong oxygen forbidden lines of Cas A require the overall modelled profiles to be shifted to the red by between 700 - 1000 km s$^{-1}$, consistent with previous estimates for the shift of the dynamical centroid of this remnant.

LATE-TIME OPTICAL EMISSION FROM CORE-COLLAPSE SUPERNOVAE

Ground-based optical spectra and Hubble Space Telescope images of ten core-collapse supernovae (CCSNe) obtained several years to decades after outburst are analyzed with the aim of understanding the general properties of their late-time emissions. New observations of SN 1957D, 1970G, 1980K, and 1993J are included as part of the study. Blueshifted line emissions in oxygen and/or hydrogen with conspicuous line substructure are a common and long-lasting phenomenon in the late-time spectra. Followed through multiple epochs, changes in the relative strengths and velocity widths of the emission lines are consistent with expectations for emissions produced by interaction between SN ejecta and the progenitor star's circumstellar material. The most distinct trend is an increase in the strength of [O III]/([O I]+[O II]) with age, and a decline in Halpha/([O I]+[O II]) which is broadly consistent with the view that the reverse shock has passed through the H envelope of the ejecta in many of these objects. We also present a spatially integrated spectrum of the young Galactic supernova remnant Cassiopeia A (Cas A). Similarities observed between the emission line profiles of the 330 yr old Cas A remnant and decades old CCSNe suggest that observed emission line asymmetry in evolved CCSN spectra may be associated with dust in the ejecta, and that minor peak substructure typically interpreted as 'clumps' or 'blobs' of ejecta may instead be linked with large-scale rings of SN debris.

THIRTY YEARS OF SN 1980K: EVIDENCE FOR LIGHT ECHOES

We report optical and mid-infrared photometry of SN 1980K between 2004 and 2010, which show slow monotonic fading consistent with previous spectroscopic and photometric observations made 8 to 17 years after outburst. The slow rate-of-change over two decades suggests that this evolution may result from scattered and thermal light echoes off of extended circumstellar material. We present a semi- analytic dust radiative-transfer model that uses an empirically corrected effective optical depth to provide a fast and robust alternative to full Monte-Carlo radiative transfer modeling for homogenous dust at low to intermediate optical depths. We find that unresolved echoes from a thin circumstellar shell 14-15 lt-yr from the progenitor, and containing about 0.02 Msun of carbon-rich dust, can explain the broadband spectral and temporal evolution. The size, mass and dust composition are in good agreement with the contact discontinuity observed in scattered echoes around SN 1987A. The origin of slowly-changing high-velocity [O I] and Halpha lines is also considered. We propose an origin in shocked high-velocity metal-rich clumps of ejecta, rather than arising in the impact of ejecta on slowly-moving circumstellar material, as is the case with hot spots in SN 1987A.

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.

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.

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.

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.

Radio Detection of SN 1986E in NGC 4302

Radio observations of SN 1986E show a clear detection of emission at 6 cm wavelength about 8 months after optical discovery. Combined with a number of new upper limits and a study of the possible models, these observations suggest that SN 1986E was probably a fairly normal Type IIL supernova, somewhat similar to SN 1980K, with radio emission at roughly the expected levels. This detection agrees with the general correlation between radio detection and late-time optical emission.

The peculiar type II supernova 1993J in M81: Transition to the nebular phase

We present optical spectra of the bright, peculiar Type II supernova 1993J in M81 spanning the first 14 months of its existence, revealing its transition to the nebular phase. Unlike the case in normal Type II supernovae, during the first 2-10 months the H-alpha emission line gradually becomes less prominent relative to other features such as (O I) lambda lambda 6300, 6364 and (Ca II) lambda lambda 7291, 7324, as we had predicted based on early-time (tau less than or approximately equal to 2 months) spectra. The nebular spectrum resembles those of the Type Ib/Ic supernovae 1985F and 1987M, although weak H-alpha emission is easily visible even at late times in SN 1993J. At tau = 8 months a close similarity is found with the spectrum of SN 1987K, the only other Type II supernova known to have undergone such a metamorphosis. The emission lines are considerably broader than those of normal Type II supernovae at comparable phases, consistent with the progenitor having lost a majority of its hydrogen envelope prior to exploding. Consequently, there is now little doubt that Type Ib, and probably Type Ic, supernovae result from core collapse in stripped, massive stars; models of the chemical evolution of galaxies in which these subtypes are ascribed to exploding white dwarfs must be appropriately modified. Although all of the emission lines in spectra of SN 1993J fade roughly exponentially for a considerable time, the fading of H-alpha begins to slow down at tau approximately = 8 months, and in the interval tau = 10-14 months its flux is constant, or even slightly rising in the wings of the line. This behavior, together with the box-like shape and great breadth (full width at half maximum (FWHM) approximately = 17 000 km/s) of the line profile, suggests that the H-alpha emission is being produced by the high-velocity outer layer of hydrogen ejecta interacting with circumstellar gas released by the progenitor prior to its explosion. A similar phenomenon has previously been seen at later phases in several Type II supernovae, most notably SN 1980K. Bumps (FWHM approximately = 1000 km/s, amplitude approximately = 20%) in the H-alpha profile are probably indicative of Rayleigh-Taylor instabilities in the cool gas behind the reverse shock. A very narrow component (unresolved, FWHM less than or approximately equal to 200 km/s) of H-alpha at the symmetric velocity of SN 1993J may instead be produced by a superposed H II region, or perhaps by recombination in a large circumstellar shell or ring that was ionized during the first few hours after outburst. In the near future the spectrum of SN 1993J should become increasingly dominated by broad H-alpha emission.

The optical recovery of SN 1970G in M101 (NGC 5457)

view Abstract Citations (28) References (36) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Optical Recovery of SN 1970G in M101 (NGC 5457) Fesen, Robert A. Abstract Optical emission from SN 1970G nearly 22 yr after maximum light is presented and discussed. Images show SN 1970G to have occurred 3.8" +/- 0.2" N and 1.9" +/- 0.2" W off the optical peak of M101's bright H II region NGC 5455. A low-dispersion spectrum shows broad 5400 to 6500 km s^-1^ emissions of Hα and [O I] λλ6300, 6364 with luminosities comparable to those seen in SN 1980K. We compare the SN 1970G spectrum to those of other optically detected, radio-bright evolved SNe and suggest SN-circumstellar matter interaction as the dominant late-time energy source for the observed optical emission. The detection of this 20 + yr old, rather ordinary Type II-L SN raises the possibility of detecting even older Type II SNe, especially if located in relatively uncrowded regions of the parent galaxy. Publication: The Astrophysical Journal Pub Date: August 1993 DOI: 10.1086/186971 Bibcode: 1993ApJ...413L.109F Keywords: Emission Spectra; H Alpha Line; Light Emission; Supernova Remnants; Charge Coupled Devices; Interstellar Matter; Astrophysics full text sources ADS | data products NED (12) SIMBAD (7)

The optical recovery of SN 1979C in NGC 4321 (M100)

view Abstract Citations (40) References (44) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Optical Recovery of SN 1979C in NGC 4321 (M100) Fesen, Robert A. ; Matonick, David M. Abstract Optical images and spectra of the Type II-L SN 1979C taken in 1990 and 1991 are presented. SN 1979C occurred in a faint H II region located just south of a prominent spiral arm in NGC 4321. Low-dispersion spectra show faint, broad Hα emission (V_exp_ = 6300 km s^-1^) with an asymmetric profile brighter toward the blue. Somewhat stronger emissions of [O I] λ6300, [O II] λ7325, and [O III] λ5007 show broad line profiles with two emission maxima at V_r_ = - 5700 km s^-1^ and ~0 km s^-1^, possibly corresponding to ejecta in the front portion of the facing expanding hemisphere and in the plane of the sky, respectively. No redshifted oxygen line emission was detected. The blueshifts of SN 1979C's line emission are more extreme than seen in other old, radio bright SNs and suggest clumped O-rich ejecta with substantial dust formation. Despite the absence of redshifted emission, SN 1979C's [O I] luminosity is more than 5 times larger than seen in the comparable object SN 1980K, possibly suggesting strong shock interactions with the progenitor's circumstellar material. Publication: The Astrophysical Journal Pub Date: April 1993 DOI: 10.1086/172496 Bibcode: 1993ApJ...407..110F Keywords: Astronomical Photometry; Astronomical Spectroscopy; Light Emission; Supernovae; H Ii Regions; Line Spectra; Supernova Remnants; Astrophysics full text sources ADS | data products SIMBAD (5) NED (2)

Full evolution of the 6 and 20 centimeter radio emission from SN 1980K

First detected at 6 cm in 1980 November, only 1 month after optical maximum, and several months later at 20 cm in 1981 March, SN 1980K has now dropped below reasonable monitoring limits of the VLA at these two frequencies. It thus represents the first Type II radio supernova to have been well-studied at centimeter wavelengths from «turn-on» to «turn-off.» It also represents one of the few radio supernovae to have such an extensive, decade-long, multiple-frequency data set. New observations of SN 1980K made with the VLA at 20 and 6 cm from 1984 November through 1990 December ar presented

Spectra of two very old supernovae - SN 1986J and SN 1980K

Spectra are presented for SN 1986J in NGC 891, observed 4 and 7 years after the explosion, and SN 1980K, observed 9 years after maximum light. A narrow-line and a broad-line component are noted in SN 1986J; these are respectively attributed to a circumstellar shell and the actual stellar interior (without hydrogen). SN 1980K continues to emit in very broad lines. Comparison with earlier observations suggests that this SN halted its exponential flux decline in the early 1980s, and is currently emitting at a constant rate. In both SNs studies, the identity of the energy source which sustains emission remains uncertain.

Late-time spectroscopy of two supernovas - The type II 1980K and the type V 1986J

Late-time spectra of the type II SN 1980K and the type V SN 1986J are presented. The SN 1980K spectrum is similar to one obtained nearly a year earlier by Fesen and Becker (1990) except that the Fe II multiplet 42 lines have changed relative strengths. Supernova 1986J shows a spectrum qualitatively similar to, but much fainter than, that observed earlier by Rupen et al. (1987). Its H-alpha flux declines exponentially, but not at the rate of any radioactive element expected to be formed in a supernova. Both of these objects are much brighter than expected if radioactive decay of Co-56 provided the energy source for their late-time luminosity. The optical and radio data available for SN 1986J indicates that it was probably not a true supernova but instead the outburst of a luminous blue variable similar to Eta Car. 30 refs.

Optical detection of the remnant of SN 1980K in NGC 6946

This paper discusses imaging and spectroscopic data collected with the Cassegrain CCD detector on the 3-m Shane telescope at the Lick Observatory on SN 1980K in NGC 6946 between seven and eight years after maximum. The spectrum of SN 1980K taken in 1987 revealed the presence of faint unresolved H-alpha emission coincident with the supernova's reported position, which remained constant to + or - 0.2 mag between 1987.5 and 1988.6. Guided by the H-alpha interference filter images, a 3-hr-long low-dispersion spectrum was obtained in August 1988, showing several broad emission lines on top of the faint continuum. The detection of optical emission from SN 1980K nearly eight years after the outburst indicates the formation of a young bright supernova remnant and suggests that similarly detectable levels of optical emission may exist from other young historical extragalactic supernovae, particularly those with detectable radio emission. 42 refs.

The type Ib supernova 1984L in NGC 991

view Abstract Citations (71) References (59) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Type Ib Supernova 1984L in NGC 991 Schlegel, Eric M. ; Kirshner, Robert P. Abstract We present photometry from ~380 to ~520 days past maximum and spectroscopy at ~400 days past maximum for the type Ib supernova 1984L. The late-time light curve shows an exponential decline with an e-folding time of ~116 days, within the errors, the same as for ^56^Co decay, which powers SN 1987A. If the observed flux arises from the radioactive decay of ^56^Co, the luminosity implies an initial ^56^Ni mass of ~0.1 M_sun_. The late-time spectrum is dominated by [O I] 6300-6363 emission. The required mass of oxygen (~1 M_sun_), the ratios of magnesium to oxygen and magnesium to carbon all seem consistent with the origin of this SN Ib in a star of roughly 20 M_sun_. In addition, we compare SN 1984L to the Type II SN 1980K and SN 1987A, to the type Ib SN 1985F and SN 1987K, and to models. While the SN 1984L data do not exclude the possible origin of SN Ib in C-0 white dwarfs, they demonstrate that direct analysis of supernova photometry and spectra can provide significant clues to the progenitors. Publication: The Astronomical Journal Pub Date: August 1989 DOI: 10.1086/115158 Bibcode: 1989AJ.....98..577S Keywords: Astronomical Photometry; Astronomical Spectroscopy; Supernovae; Cobalt Isotopes; Light Curve; Luminosity; Nickel Isotopes; Radioactive Decay; Supernova 1987a; Visible Spectrum; White Dwarf Stars; Astronomy; STARS: SUPERNOVAE full text sources ADS | data products SIMBAD (8) NED (8)

The Circumstellar Structure Around Supernovae

AbstractThe time dependent ionization and temperature structure of the circumstellar medium around supernovae has been calculated, in order to interpret recent supernova radio observations. For a stellar wind origin of the circumstellar medium, we relate the time of radio turn-on to the progenitor mass loss rate. We also show that large column densities for the UV resonance lines are expected. The results are applied to SN 1979c, SN 1980k and SN 1987A.