The low kinetic energy and mass of the Crab supernova remnant challenge our understanding of core-collapse supernova explosions. A possibility is that the Crab nebula is surrounded by a shell of fast ...ejecta containing the 'missing' kinetic energy and mass. The only direct evidence for such a fast shell comes from an absorption feature in the Crab pulsar spectrum as a result of C ivλ1550. The velocities inferred from the C iv line absorption extend to at least ∼2500 km s−1, which is about twice as fast as the expansion of main shell of the remnant in our direction. We have searched for additional evidence of fast-moving ejecta in the optical spectra obtained with the FORS1 instrument at the European Southern Observatory (ESO) 8.2-m Very Large Telescope (VLT) and with the Andalucia Faint Object Spectrograph and Camera (ALFOSC) at the 2.56-m Nordic Optical Telescope (NOT), with the focus on absorption in Ca iiλλ3934,3968, and emission components in O iii λλ4959,5007. The data are compared with the C ivλ1550 absorption, and with theoretical expectations derived from shell models with ballistic gas motion, and a power-law density profile of the fast ejecta. Along the line of sight to the pulsar, we find that no gas in the nebula moves faster towards us than ≈1400 km s−1. We identify this gas as part of the known main shell of the remnant. This velocity agrees with previous results showing that the Crab nebula is moving slowly in this direction. It is slower than the velocity of 1680 km s−1 used in the models of Sollerman et al. as a minimum velocity of the presumed fast shell of supernova ejecta to account for the C iv line absorption. We find faster moving gas within 3-10 arcsec north and south of the pulsar, where the fastest gas moving towards us, as traced by O iii, has a velocity of 1650-1700 km s−1. The fastest O iii emitting gas along the line of sight to the pulsar, on the rear side of the nebula, has a velocity of ≈+1800 km s−1, which is higher than the velocity previously recorded for that direction. However, neither the O iii nor Ca ii lines display any signatures of fast shell ejecta at the velocities inferred from the C iv line absorption. To fully rule out the possibility that a chimney-like structure directed towards us could be responsible for the C iv line absorption, we need deep observations taken with 8-10-m class telescopes with good spectral resolution. We show that a spectral resolution better than ∼200 km s−1 is needed to draw any conclusions on emission lines from gas moving towards us, along the line of sight of the pulsar, faster than ≈1700 km s−1. To probe the fast shell ejecta, new observations from the Hubble Space Telescope (HST) Cosmic Origins Spectrograph (COS) should be substantially more powerful than the previous HST Space Telescope Imaging Spectrograph (STIS) data to fully explore the C ivλ1550 absorption-line profile.
We present photometric and spectroscopic datasets for SN 2020pvb, a Type IIn-P supernova (SN) that is similar to SNe 1994W, 2005cl, 2009kn, and 2011ht, with a precursor outburst detected (PS1 w band ...∼–13.8 mag) around four months before the B -band maximum light. SN 2020pvb presents a relatively bright light curve that peaked at M B = −17.95 ± 0.30 mag and a plateau that lasted at least 40 days before going into solar conjunction. After this, the object was no longer visible at phases > 150 days above –12.5 mag in the B band, suggesting that the SN 2020pvb ejecta interact with a dense, spatially confined circumstellar envelope. SN 2020pvb shows strong Balmer lines and a forest of Fe II lines with narrow P Cygni profiles in its spectra. Using archival images from the Hubble Space Telescope, we constrained the progenitor of SN 2020pvb to have a luminosity of log( L / L ⊙ )≲5.4, ruling out any single star progenitor over 50 M ⊙ . SN 2020pvb is a Type IIn-P whose progenitor star had an outburst ∼0.5 yr before the final explosion; the material lost during this outburst probably plays a role in shaping the physical properties of the SN.
We present high spatial resolution optical imaging and polarization observations of the PSR B0540−69.3 and its highly dynamical pulsar wind nebula (PWN) performed with Hubble Space Telescope, and ...compare them with X-ray data obtained with the Chandra X-ray Observatory. In particular, we have studied the bright region south-west of the pulsar where a bright 'blob' is seen in 1999. In a recent paper by De Luca et al. it was argued that the 'blob' moves away from the pulsar at high speed. We show that it may instead be a result of local energy deposition around 1999, and that the emission from this then faded away rather than moved outward. Polarization data from 2007 show that the polarization properties show dramatic spatial variations at the 1999 blob position arguing for a local process. Several other positions along the pulsar-'blob' orientation show similar changes in polarization, indicating previous recent local energy depositions. In X-rays, the spectrum steepens away from the 'blob' position, faster orthogonal to the pulsar-'blob' direction than along this axis of orientation. This could indicate that the pulsar-'blob' orientation is an axis along where energy in the PWN is mainly injected, and that this is then mediated to the filaments in the PWN by shocks. We highlight this by constructing an S ii-to-O iii-ratio map, and comparing this to optical continuum and X-ray emission maps. We argue, through modelling, that the high S ii/O iii ratio is not due to time-dependent photoionization caused by possible rapid X-ray emission variations in the 'blob' region. We have also created a multiwavelength energy spectrum for the 'blob' position showing that one can, to within 2σ, connect the optical and X-ray emission by a single power law. The slope of that power law (defined from
) would be αν= 0.74 ± 0.03, which is marginally different from the X-ray spectral slope alone with αν= 0.65 ± 0.03. A single power law for most of the PWN is, however, not be possible. We obtain best power-law fits for the X-ray spectrum if we include 'extra' oxygen, in addition to the oxygen column density in the interstellar gas of the Large Magellanic Cloud and the Milky Way. This oxygen is most naturally explained by the oxygen-rich ejecta of the supernova remnant. The oxygen needed likely places the progenitor mass in the 20-25 M⊙ range, i.e. in the upper mass range for progenitors of Type IIP supernovae.
An accurate determination of the mass-loss rate of the progenitor stars to core-collapse supernovae is often limited by uncertainties pertaining to various model assumptions. It is shown that under ...conditions when the temperature of the circumstellar medium is set by heating due to free-free absorption, observations of the accompanying free-free optical depth allow a direct determination of the mass-loss rate from observed quantities in a rather model-independent way. The temperature is determined self-consistently, which results in a characteristic time dependence of the free-free optical depth. This can be used to distinguish free-free heating from other heating mechanisms. Since the importance of free-free heating is quite model dependent, this also makes possible several consistency checks of the deduced mass-loss rate. It is argued that the free-free absorption observed in SN 1993J is consistent with heating from free-free absorption. The deduced mass-loss rate of the progenitor star is, approximately, 10 super(-5) Mmiddot in circle yr super(-1) for a wind velocity of 10 km s super(-l).
We present early time high-resolution (VLT/UVES) and late time low-resolution (VLT/FORS) optical spectra of the normal type Ia supernova, SN 2001el. The high-resolution spectra were obtained 9 and 2 ...days before (B-band) maximum light. This was in order to allow the detection of narrow hydrogen and/or helium emission lines from the circumstellar medium of the supernova. No such lines were detected in our data. We therefore use these spectra together with photoionisation models to derive upper limits of 9×10-6 {M}_ȯ yr-1 and 5×10-5 {M}_ȯ yr-1 for the mass loss rate from the progenitor system of SN 2001el assuming velocities of 10 km s-1 and 50 km s-1, respectively, for a wind extending to outside at least a few × 1015 cm away from the supernova explosion site. So far, these are the best Hα based upper limits obtained for a type Ia supernova, and exclude a symbiotic star in the upper mass loss rate regime (so called Mira type stars) from being the progenitor of SN 2001el. The low-resolution spectrum was obtained in the nebular phase of the supernova, 400 days after the maximum light, to search for any hydrogen rich gas originating from the supernova progenitor system. However, we see no signs of Balmer lines in our spectrum. Therefore, we model the late time spectra to derive an upper limit of 0.03 Mȯ for solar abundance material present at velocities lower than 1000 km s-1 within the supernova explosion site. According to numerical simulations of Marietta et al. (2000) this is less than the expected mass lost by a subgiant, red giant or a main-sequence secondary star at a small binary separation as a result of the SN explosion. Our data therefore exclude these scenarios as the progenitor of SN 2001el. Finally, we discuss the origin of high velocity Ca II lines previously observed in a few type Ia supernovae before the maximum light. We see both the Ca II IR triplet and the H&K lines in our earliest (-9 days) spectrum at a very high velocity of up to 34 000 km s-1. The spectrum also shows a flat-bottomed Si II "6150 Å" feature similar to the one previously observed in SN 1990N (Leibundgut et al. 1991, ApJ, 371, L23) at 14 days before maximum light. We compare these spectral features in SN 2001el to those observed in SN 1984A and SN 1990N at even higher velocities.
Using data from the Complete Nearby (redshift zhost < 0.02) sample of Type Ia Supernovae (CNIa0.02), we find a linear relation between two parameters derived from the B − V color curves of Type Ia ...supernovae: the color stretch sBV and the rising color slope s0*(B−V) after the peak, and this relation applies to the full range of sBV. The sBV parameter is known to be tightly correlated with the peak luminosity, especially for fast decliners (dim Type Ia supernovae), and the luminosity correlation with sBV is markedly better than with the classic light-curve width parameters such as Δm15(B). Thus, our new linear relation can be used to infer peak luminosity from s0*. Unlike sBV (or Δm15(B)), the measurement of s0*(B−V) does not rely on a well-determined time of light-curve peak or color maximum, making it less demanding on the light-curve coverage than past approaches.
We present seven epochs between October 1999 and November 2007 of high resolution VLT/UVES echelle spectra of the ejecta-ring collision of SN 1987A. The fluxes of most of the narrow lines from the ...unshocked gas decreased by a factor of $2{-}3$ during this period, consistent with the decay from the initial ionization by the shock break-out. However, O III in particular shows an increase up to day ~6800. This agrees with radiative shock models where the pre-shocked gas is heated by the soft X-rays from the shock. The evolution of the O III line ratio shows a decreasing temperature of the unshocked ring gas, consistent with a transition from a hot, low density component which was heated by the initial flash ionization to the lower temperature in the pre-ionized gas ahead of the shocks. The line emission from the shocked gas increases rapidly as the shock sweeps up more gas. We find that the neutral and high ionization lines follow the evolution of the Balmer lines roughly, while the intermediate ionization lines evolve less rapidly. Up to day ~6800, the optical light curves have a similar evolution to that of the soft X-rays. The break between day 6500 and day 7000 for O III and Ne III is likely due to recombination to lower ionization levels. Nevertheless, the evolution of the Fe XIV line, as well as the lines from the lowest ionization stages, continue to follow that of the soft X-rays, as expected. There is a clear difference in the line profiles between the low and intermediate ionization lines, and those from the coronal lines at the earlier epochs. This shows that these lines arise from regions with different physical conditions, with at least a fraction of the coronal lines coming from adiabatic shocks. At later epochs the line widths of the low ionization lines, however, increase and approach those of the high ionization lines of Fe X-XIV . The Hα line profile can be traced up to ~500 km s-1 at the latest epoch. This is consistent with the cooling time of shocks propagating into a density of (1-4) $\times$ 104 cm-3. This means that these shocks are among the highest velocity radiative shocks observed.
We present early time high-resolution (VLT/UVES) and late time low-resolution (VLT/FORS) optical spectra of the normal type Ia supernova, SN 2001el. The high-resolution spectra were obtained 9 and 2 ...days before (B-band) maximum light. This was in order to allow the detection of narrow hydrogen and/or helium emission lines from the circumstellar medium of the supernova. No such lines were detected in our data. We therefore use these spectra together with photoionisation models to derive upper limits of 9 x 10-6 M QQQ ? yr-1 and 5 x 10-5 M QQQ ? yr-1 for the mass loss rate from the progenitor system of SN 2001el assuming velocities of 10 km s-1 and 50 km s-1, respectively, for a wind extending to outside at least a few x1015 cm away from the supernova explosion site. So far, these are the best Ha based upper limits obtained for a type Ia supernova, and exclude a symbiotic star in the upper mass loss rate regime (so called Mira type stars) from being the progenitor of SN 2001el. The low-resolution spectrum was obtained in the nebular phase of the supernova, 6400 days after the maximum light, to search for any hydrogen rich gas originating from the supernova progenitor system. However, we see no signs of Balmer lines in our spectrum. Therefore, we model the late time spectra to derive an upper limit of 60.03 M QQQ ? for solar abundance material present at velocities lower than 1000 km s-1 within the supernova explosion site. According to numerical simulations of Marietta et al. (2000) this is less than the expected mass lost by a subgiant, red giant or a main-sequence secondary star at a small binary separation as a result of the SN explosion. Our data therefore exclude these scenarios as the progenitor of SN 2001el. Finally, we discuss the origin of high velocity Ca II lines previously observed in a few type Ia supernovae before the maximum light. We see both the Ca II IR triplet and the H&K lines in our earliest (-9 days) spectrum at a very high velocity of up to 634 000 km s-1. The spectrum also shows a flat-bottomed Si II "6150 AA" feature similar to the one previously observed in SN 1990N (Leibundgut et al. 1991, ApJ, 371, L23) at 14 days before maximum light. We compare these spectral features in SN 2001el to those observed in SN 1984A and SN 1990N at even higher velocities.
ABSTRACT
We present late-time near-infrared (NIR) and optical observations of the Type IIn SN 1998S. The NIR photometry spans 333-1242 d after explosion, while the NIR and optical spectra cover ...333-1191 and 305-1093 d, respectively. The NIR photometry extends to the M′ band (4.7 μm), making SN 1998S only the second ever supernova for which such a long IR wavelength has been detected. The shape and evolution of the Hα and He i 1.083-μm line profiles indicate a powerful interaction with a progenitor wind, as well as providing evidence of dust condensation within the ejecta. The latest optical spectrum suggests that the wind had been flowing for at least 430 yr. The intensity and rise of the HK continuum towards longer wavelengths together with the relatively bright L′ and M′ magnitudes show that the NIR emission was due to hot dust newly formed in the ejecta and/or pre-existing dust in the progenitor circumstellar medium (CSM). The NIR spectral energy distribution (SED) at about 1 yr is well described by a single-temperature blackbody spectrum at about 1200 K. The temperature declines over subsequent epochs. After ∼2 yr, the blackbody matches are less successful, probably indicating an increasing range of temperatures in the emission regions. Fits to the SEDs achieved with blackbodies weighted with λ−1 or λ−2 emissivity are almost always less successful. Possible origins for the NIR emission are considered. Significant radioactive heating of ejecta dust is ruled out, as is shock/X-ray-precursor heating of CSM dust. More plausible sources are (a) an IR echo from CSM dust driven by the ultraviolet/optical peak luminosity, and (b) emission from newly-condensed dust which formed within a cool, dense shell produced by the ejecta shock/CSM interaction. We argue that the evidence favours the condensing dust hypothesis, although an IR echo is not ruled out. Within the condensing-dust scenario, the IR luminosity indicates the presence of at least 10−3 M⊙ of dust in the ejecta, and probably considerably more. Finally, we show that the late-time (K-L′)0 evolution of Type II supernovae may provide a useful tool for determining the presence or absence of a massive CSM around their progenitor stars.
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