Abstract
We study the production of very light elements (
Z
< 20) in the dynamical and spiral-wave wind ejecta of binary neutron star mergers by combining detailed nucleosynthesis calculations with ...the outcome of numerical relativity merger simulations. All our models are targeted to GW170817 and include neutrino radiation. We explore different finite-temperature, composition-dependent nuclear equations of state, and binary mass ratios, and find that hydrogen and helium are the most abundant light elements. For both elements, the decay of free neutrons is the driving nuclear reaction. In particular, ∼0.5–2 × 10
−6
M
⊙
of hydrogen are produced in the fast expanding tail of the dynamical ejecta, while ∼1.5–11 × 10
−6
M
⊙
of helium are synthesized in the bulk of the dynamical ejecta, usually in association with heavy
r
-process elements. By computing synthetic spectra, we find that the possibility of detecting hydrogen and helium features in kilonova spectra is very unlikely for fiducial masses and luminosities, even when including nonlocal thermodynamic equilibrium effects. The latter could be crucial to observe helium lines a few days after merger for faint kilonovae or for luminous kilonovae ejecting large masses of helium. Finally, we compute the amount of strontium synthesized in the dynamical and spiral-wave wind ejecta, and find that it is consistent with (or even larger than, in the case of a long-lived remnant) the one required to explain early spectral features in the kilonova of GW170817.
We re-examine the classifications of supernovae (SNe) presented in the Lick Observatory Supernova Search (LOSS) volume-limited sample with a focus on the stripped-envelope SNe. The LOSS ...volume-limited sample, presented by Leaman et al. and Li et al., was calibrated to provide meaningful measurements of SN rates in the local universe; the results presented therein continue to be used for comparisons to theoretical and modeling efforts. Many of the objects from the LOSS sample were originally classified based upon only a small subset of the data now available, however, and recent studies have both updated some subtype distinctions and improved our ability to perform robust classifications, especially for stripped-envelope SNe. We re-examine the spectroscopic classifications of all events in the LOSS volume-limited sample (180 SNe and SN impostors) and update them if necessary. We discuss the populations of rare objects in our sample including broad-lined SNe Ic, Ca-rich SNe, SN 1987A-like events (we identify SN 2005io as SN 1987A-like here for the first time), and peculiar subtypes. The relative fractions of SNe Ia, SNe II, and stripped-envelope SNe in the local universe are not affected, but those of some subtypes are. Most significantly, after discussing the often unclear boundary between SNe Ib and Ic when only noisy spectra are available, we find a higher SN Ib fraction and a lower SN Ic fraction than calculated by Li et al.: spectroscopically normal SNe Ib occur in the local universe 1.7 0.9 times more often than do normal SNe Ic.
Common Explosion Mechanism for Type Ia Supernovae Mazzali, Paolo A; Röpke, Friedrich K; Benetti, Stefano ...
Science (American Association for the Advancement of Science),
02/2007, Letnik:
315, Številka:
5813
Journal Article
Recenzirano
Odprti dostop
Type Ia supernovae, the thermonuclear explosions of white dwarf stars composed of carbon and oxygen, were instrumental as distance indicators in establishing the acceleration of the universe's ...expansion. However, the physics of the explosion are debated. Here we report a systematic spectral analysis of a large sample of well-observed type Ia supernovae. Mapping the velocity distribution of the main products of nuclear burning, we constrain theoretical scenarios. We find that all supernovae have low-velocity cores of stable iron-group elements. Outside this core, nickel-56 dominates the supernova ejecta. The outer extent of the iron-group material depends on the amount of nickel-56 and coincides with the inner extent of silicon, the principal product of incomplete burning. The outer extent of the bulk of silicon is similar in all supernovae, having an expansion velocity of ~11,000 kilometers per second and corresponding to a mass of slightly over one solar mass. This indicates that all the supernovae considered here burned similar masses and suggests that their progenitors had the same mass. Synthetic light-curve parameters and three-dimensional explosion simulations support this interpretation. A single explosion scenario, possibly a delayed detonation, may thus explain most type Ia supernovae.
On the progenitor of the Type IIP SN 2013ej in M74 Fraser, Morgan; Maund, Justyn R; Smartt, Stephen J ...
Monthly notices of the Royal Astronomical Society. Letters,
03/2014, Letnik:
439, Številka:
1
Journal Article
Recenzirano
Odprti dostop
We use natural seeing imaging of SN 2013ej in M74 to identify a progenitor candidate in archival Hubble Space Telescope (HST) + Advanced Camera for Survey images. We find a source coincident with the ...supernova (SN) in the F814W filter within the total 75 mas (∼3 pc astrometric uncertainty; however, the position of the progenitor candidate in contemporaneous F435W and F555W filters is significantly offset. We conclude that the 'progenitor candidate' is in fact two physically unrelated sources; a blue source which is likely unrelated to the SN, and a red source which we suggest exploded as SN 2013ej. Deep images with the same instrument on board HST taken when the SN has faded (in approximately two year's time) will allow us to accurately characterize the unrelated neighbouring source and hence determine the intrinsic flux of the progenitor in three filters. We suggest that the F814W flux is dominated by the progenitor of SN 2013ej, and assuming a bolometric correction appropriate to an M-type supergiant, we estimate that the mass of the progenitor of SN 2013ej was between 8 and 15.5 M.
Abstract
We present the discovery and studies of the helium-rich, fast-evolving supernova (SN) 2021agco at a distance of ∼40 Mpc. Its early-time flux is found to rise from half peak to the peak of ...−16.06 ± 0.42 mag in the
r
band within
2.4
−
1.0
+
1.5
days, and the post-peak light curves also decline at a much faster pace relative to normal stripped-envelope supernovae (SNe) of Type Ib/Ic. The early-time spectrum of SN 2021agco (
t
≈ 1.0 days after the peak) is characterized by a featureless blue continuum superimposed with a weak emission line of ionized C
iii
, and the subsequent spectra show prominent He
i
lines. Both the photometric and spectroscopic evolution show close resemblances to SN 2019dge, which is believed to have an extremely stripped progenitor. We reproduce the multicolor light curves of SN 2021agco with a model combining shock-cooling emission with
56
Ni decay. The best-fit results give an ejecta mass of ≈0.3
M
⊙
and a synthesized nickel mass of ≈2.2 × 10
−2
M
⊙
. The progenitor is estimated to have an envelope radius of
R
env
≈ 80
R
⊙
and a mass of
M
env
≈ 0.10
M
⊙
. All these suggest that SN 2021agco can be categorized as an ultra-stripped SN Ib, representing the closest object of this rare subtype. This SN is found to explode in the disk of a Sab-type galaxy with an age of ∼10.0 Gyr and low star-forming activity. Compared to normal SNe Ib/c, the host galaxies of SN 2021agco and other ultra-stripped SNe tend to have relatively lower metallicity, which complicates the properties of their progenitor populations.
It is well known that massive stars (M > 8 M☉) evolve up to the collapse of the stellar core, resulting in most cases in a supernova (SN) explosion. Their heterogeneity is related mainly to different ...configurations of the progenitor star at the moment of the explosion and to their immediate environments. We present photometry and spectroscopy of SN 2010bt, which was classified as a Type IIn SN from a spectrum obtained soon after discovery and was observed extensively for about 2 months. After the seasonal interruption owing to its proximity to the Sun, the SN was below the detection threshold, indicative of a rapid luminosity decline. We can identify the likely progenitor with a very luminous star (log L/L☉ 7) through comparison of Hubble Space Telescope images of the host galaxy prior to explosion with those of the SN obtained after maximum light. Such a luminosity is not expected for a quiescent star, but rather for a massive star in an active phase. This progenitor candidate was later confirmed via images taken in 2015 (∼5 yr post-discovery), in which no bright point source was detected at the SN position. Given these results and the SN behavior, we conclude that SN 2010bt was likely a Type IIn SN and that its progenitor was a massive star that experienced an outburst shortly before the final explosion, leading to a dense H-rich circumstellar environment around the SN progenitor.
We present observations of the Type Ic supernova (SN Ic) 2011bm spanning a period of about one year. The data establish that SN 2011bm is a spectroscopically normal SN Ic with moderately low ejecta ...velocities and with a very slow spectroscopic and photometric evolution (more than twice as slow as SN 1998bw). The Pan-STARRS1 retrospective detection shows that the rise time from explosion to peak was ~40 days in the R band. Through an analysis of the light curve and the spectral sequence, we estimate a kinetic energy of ~7-17 foe and a total ejected mass of ~7-17 M sub(middot in circle), 5-10 M sub(middot in circle) of which is oxygen and 0.6-0.7 M sub(middot in circle) is super(56)Ni. The physical parameters obtained for SN 2011bm suggest that its progenitor was a massive star of initial mass 30-50 M sub(middot in circle). The profile of the forbidden oxygen lines in the nebular spectra shows no evidence of a bi-polar geometry in the ejected material.
Abstract
When discovered, SN 2017egm was the closest (redshift
z
= 0.03) hydrogen-poor superluminous supernova (SLSN-I) and a rare case that exploded in a massive and metal-rich galaxy. Thus, it has ...since been extensively observed and studied. We report spectroscopic data showing strong emission at around He
i
λ
10830 and four He
i
absorption lines in the optical. Consequently, we classify SN 2017egm as a member of an emerging population of helium-rich SLSNe-I (i.e., SLSNe-Ib). We also present our late-time photometric observations. By combining them with archival data, we analyze high-cadence ultraviolet, optical, and near-infrared light curves spanning from early pre-peak (∼−20 days) to late phases (∼+300 days). We obtain its most complete bolometric light curve, in which multiple bumps are identified. None of the previously proposed models can satisfactorily explain all main light-curve features, while multiple interactions between the ejecta and circumstellar material (CSM) may explain the undulating features. The prominent infrared excess with a blackbody luminosity of 10
7
–10
8
L
⊙
detected in SN 2017egm could originate from the emission of either an echo of a pre-existing dust shell or newly formed dust, offering an additional piece of evidence supporting the ejecta–CSM interaction model. Moreover, our analysis of deep Chandra observations yields the tightest-ever constraint on the X-ray emission of an SLSN-I, amounting to an X-ray-to-optical luminosity ratio ≲10
−3
at late phases (∼100–200 days), which could help explore its close environment and central engine.
We present optical photometric and low-resolution spectroscopic observations of the Type II plateau supernova (SN) 2008in, which occurred in the outskirts of the nearly face-on spiral galaxy M61. ...Photometric data in the X-ray, ultraviolet, and near-infrared bands have been used to characterize this event. The SN field was imaged with the ROTSE-IIIb optical telescope about seven days before the explosion. This allowed us to constrain the epoch of the shock breakout to JD = 2454825.6. The duration of the plateau phase, as derived from the photometric monitoring, was ~98 days. The spectra of SN 2008in show a striking resemblance to those of the archetypal low-luminosity IIP SNe 1997D and 1999br. A comparison of ejecta kinematics of SN 2008in with the hydrodynamical simulations of Type IIP SNe by Dessart et al. indicates that it is a less energetic event (~5 X 1050 erg). However, the light curve indicates that the production of radioactive 56Ni is significantly higher than that in the low-luminosity SNe. Adopting an interstellar absorption along the SN direction of AV ~ 0.3 mag and a distance of 13.2 Mpc, we estimated a synthesized 56Ni mass of ~0.015 M . Employing semi-analytical formulae derived by Litvinova and Nadezhin, we derived a pre-SN radius of ~126 R , an explosion energy of ~5.4 X 1050 erg, and a total ejected mass of ~16.7 M . The latter indicates that the zero-age main-sequence mass of the progenitor did not exceed 20 M . Considering the above properties of SN 2008in and its occurrence in a region of sub-solar metallicity (O/H ~ 8.44 dex), it is unlikely that fall-back of the ejecta onto a newly formed black hole occurred in SN 2008in. We therefore favor a low-energy explosion scenario of a relatively compact, moderate-mass progenitor star that generates a neutron star.
We report distinctly double-peaked H and Hβ emission lines in the late-time, nebular-phase spectra ( 200 days) of the otherwise normal at early phases ( 100 days) type IIP supernova ASASSN-16at (SN ...2016X). Such distinctly double-peaked nebular Balmer lines have never been observed for a type II SN. The nebular-phase Balmer emission is driven by the radioactive 56Co decay, so the observed line profile bifurcation suggests a strong bipolarity in the 56Ni distribution or in the line-forming region of the inner ejecta. The strongly bifurcated blueshifted and redshifted peaks are separated by ∼3 × 103 km s−1 and are roughly symmetrically positioned with respect to the host-galaxy rest frame, implying that the inner ejecta are composed of two almost-detached blobs. The red peak progressively weakens relative to the blue peak, and disappears in the 740 days spectrum. One possible reason for the line-ratio evolution is increasing differential extinction from continuous formation of dust within the envelope, which is also supported by the near-infrared flux excess that develops after ∼100 days.
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