ORCID Profile
0000-0002-2898-6532
Current Organisations
Stockholm University
,
INAF-Osservatorio Astronomico di Padova
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Publications
The Origin and Evolution of the Normal Type Ia SN 2018aoz with Infant-phase Reddening and Excess Emission
Publisher: American Astronomical Society
Date: 03-2023
Abstract: SN 2018aoz is a Type Ia SN with a B -band plateau and excess emission in infant-phase light curves ≲1 day after the first light, evidencing an over-density of surface iron-peak elements as shown in our previous study. Here, we advance the constraints on the nature and origin of SN 2018aoz based on its evolution until the nebular phase. Near-peak spectroscopic features show that the SN is intermediate between two subtypes of normal Type Ia: core normal and broad line. The excess emission may be attributable to the radioactive decay of surface iron-peak elements as well as the interaction of ejecta with either the binary companion or a small torus of circumstellar material. Nebular-phase limits on H α and He i favor a white dwarf companion, consistent with the small companion size constrained by the low early SN luminosity, while the absence of [O i ] and He i disfavors a violent merger of the progenitor. Of the two main explosion mechanisms proposed to explain the distribution of surface iron-peak elements in SN 2018aoz, the asymmetric Chandrasekhar-mass explosion is less consistent with the progenitor constraints and the observed blueshifts of nebular-phase [Fe ii ] and [Ni ii ]. The helium-shell double-detonation explosion is compatible with the observed lack of C spectral features, but current 1D models are incompatible with the infant-phase excess emission, B max – V max color, and weak strength of nebular-phase [Ca ii ]. Although the explosion processes of SN 2018aoz still need to be more precisely understood, the same processes could produce a significant fraction of Type Ia SNe that appear to be normal after ∼1 day.
SN 2018bsz: significant dust formation in a nearby superluminous supernova
Publisher: Research Square Platform LLC
Date: 15-09-2021
DOI: 10.21203/RS.3.RS-872252/V1
Abstract: We investigate the thermal emission and extinction from dust associated with the nearby superluminous supernova (SLSN) 2018bsz. Our dataset has daily cadence and simultaneous optical and near-infrared coverage up to ~ 100 days, together with late time (+1.7 yr) MIR observations. At 230 days after light curve peak the SN is not detected in the optical, but shows a surprisingly strong near-infrared excess, with r - J 3 mag and r - K s 5 mag. The time evolution of the infrared light curve enables us to investigate if the mid-infrared emission is from newly formed dust inside the SN ejecta, from a pre-existing circumstellar envelope, or interstellar material heated by the radiation from the SN. We find the latter two scenarios can be ruled out, and a scenario where new dust is forming in the SN ejecta at epochs 200 days can self-consistently reproduce the evolution of the SN flux. We can fit the spectral energy distribution well at +230d with 5x10 -4 solar mass of carbon dust, increasing over the following several hundred days to 10 -2 solar mass by +535d. SN 2018bsz is the first SLSN showing evidence for dust formation within the SN ejecta, and appears to form ten times more dust than normal core-collapse SNe at similar epochs. Together with their preference for low mass, low metallicity host galaxies, we suggest that SLSNe may be a significant contributor to dust formation in the early Universe.
The Birth of a Relativistic Jet Following the Disruption of a Star by a Cosmological Black Hole
Publisher: Springer Science and Business Media LLC
Date: 30-11-2022
The Birth of a Relativistic Jet Following the Disruption of a Star by a Cosmological Black Hole
Publisher: Research Square Platform LLC
Date: 10-06-2022
DOI: 10.21203/RS.3.RS-1700217/V1
Abstract: The tidal forces of a black hole can rip apart a star that passes too close to it, resulting in a stellar Tidal Disruption Event (TDE, (1)). In some such encounters, the black hole can launch a powerful relativistic jet (2-6). If this jet fortuitously aligns with our line of sight, the overall brightness is Doppler boosted by several orders of magnitude. Consequently, such on-axis relativistic TDEs have the potential to unveil cosmological (redshift z ) quiescent black holes and are ideal test beds to understand the radiative mechanisms operating in super-Eddington jets. Here, we present multi-wavelength (X-ray, UV, optical, and radio) observations of the optically discovered transient AT 2022cmc at z=1.193 (7). Its unusual X-ray properties, including a peak observed luminosity of 48 erg s -1 , systematic variability on timescales as short as 1000 seconds, and overall duration lasting more than 30 days in the rest-frame are traits associated with relativistic TDEs. This makes AT 2022cmc only the fourth member of this rare class and the first one identified in the optical and with well-s led optical data. The X-ray to radio spectral energy distributions spanning 5-50 days after discovery can be explained as synchrotron emission from a relativistic jet (radio), synchrotron self-Compton (X-rays), and thermal emission similar to that seen in low-redshift TDEs (UV/optical). Our modeling implies a beamed, highly relativistic jet akin to blazars (e.g., (8,9)) but requires extreme matter-domination, i.e, high ratio of electron-to-magnetic field energy densities in the jet, and challenges our theoretical understanding of jets. This work provides one of the best multi-wavelength datasets of a newborn relativistic jet to date and will be invaluable for testing more sophisticated jet models, and for identifying more such events in transient surveys.
Observations of the very young Type Ia Supernova 2019np with early-excess emission
Publisher: Oxford University Press (OUP)
Date: 02-06-2022
Abstract: Early-time radiative signals from Type Ia supernovae (SNe Ia) can provide important constraints on the explosion mechanism and the progenitor system. We present observations and analysis of SN 2019np, a nearby SN Ia discovered within 1–2 days after the explosion. Follow-up observations were conducted in optical, ultraviolet, and near-infrared bands, covering the phases from ∼−16.7 d to ∼+ 367.8 d relative to its B-band peak luminosity. The photometric and spectral evolutions of SN 2019np resemble the average behaviour of normal SNe Ia. The absolute B-band peak magnitude and the post-peak decline rate are Mmax(B) = −19.52 ± 0.47 mag and Δm15(B) = 1.04 ± 0.04 mag, respectively. No Hydrogen line has been detected in the nebular-phase spectra of SN 2019np. Assuming that the 56Ni powering the light curve is centrally located, we find that the bolometric light curve of SN 2019np shows a flux excess up to 5.0 per cent in the early phase compared to the radiative diffusion model. Such an extra radiation perhaps suggests the presence of an additional energy source beyond the radioactive decay of central nickel. Comparing the observed colour evolution with that predicted by different models, such as interactions of SN ejecta with circumstellar matter (CSM)/companion star, a double-detonation explosion from a sub-Chandrasekhar mass white dwarf (WD) and surface 56Ni mixing, we propose that the nickel mixing is more favoured for SN 2019np.
A Sensitive Search for Supernova Emission Associated with the Extremely Energetic and Nearby GRB 221009A
Publisher: American Astronomical Society
Date: 06-2023
Abstract: We report observations of the optical counterpart of the long gamma-ray burst GRB 221009A. Due to the extreme rarity of being both nearby ( z = 0.151) and highly energetic ( E γ ,iso ≥ 10 54 erg), GRB 221009A offers a unique opportunity to probe the connection between massive star core collapse and relativistic jet formation across a very broad range of γ -ray properties. Adopting a phenomenological power-law model for the afterglow and host galaxy estimates from high-resolution Hubble Space Telescope imaging, we use Bayesian model comparison techniques to determine the likelihood of an associated supernova (SN) contributing excess flux to the optical light curve. Though not conclusive, we find moderate evidence ( K Bayes = 10 1.2 ) for the presence of an additional component arising from an associated SN, SN 2022xiw, and find that it must be substantially fainter ( % as bright at the 99% confidence interval) than SN 1998bw. Given the large and uncertain line-of-sight extinction, we attempt to constrain the SN parameters ( M Ni , M ej , and E KE ) under several different assumptions with respect to the host galaxy’s extinction. We find properties that are broadly consistent with previous GRB-associated SNe: M Ni = 0.05–0.25 M ⊙ , M ej = 3.5–11.1 M ⊙ , and E KE = (1.6–5.2) × 10 52 erg. We note that these properties are weakly constrained due to the faintness of the SN with respect to the afterglow and host emission, but we do find a robust upper limit on M Ni of M Ni 0.36 M ⊙ . Given the tremendous range in isotropic gamma-ray energy release exhibited by GRBs (seven orders of magnitude), the SN emission appears to be decoupled from the central engine in these systems.
The Optical Light Curve of GRB 221009A: The Afterglow and the Emerging Supernova
Publisher: American Astronomical Society
Date: 03-2023
Abstract: We present extensive optical photometry of the afterglow of GRB 221009A. Our data cover 0.9–59.9 days from the time of Swift and Fermi gamma-ray burst (GRB) detections. Photometry in rizy -band filters was collected primarily with Pan-STARRS and supplemented by multiple 1–4 m imaging facilities. We analyzed the Swift X-ray data of the afterglow and found a single decline rate power law f ( t ) ∝ t −1.556±0.002 best describes the light curve. In addition to the high foreground Milky Way dust extinction along this line of sight, the data favor additional extinction to consistently model the optical to X-ray flux with optically thin synchrotron emission. We fit the X-ray-derived power law to the optical light curve and find good agreement with the measured data up to 5−6 days. Thereafter we find a flux excess in the riy bands that peaks in the observer frame at ∼20 days. This excess shares similar light-curve profiles to the Type Ic broad-lined supernovae SN 2016jca and SN 2017iuk once corrected for the GRB redshift of z = 0.151 and arbitrarily scaled. This may be representative of an SN emerging from the declining afterglow. We measure rest-frame absolute peak AB magnitudes of M g = −19.8 ± 0.6 and M r = − 19.4 ± 0.3 and M z = −20.1 ± 0.3. If this is an SN component, then Bayesian modeling of the excess flux would imply explosion parameters of M ej = 7.1 − 1.7 + 2.4 M ⊙ , M Ni = 1.0 − 0.4 + 0.6 M ⊙ , and v ej = 33,900 − 5700 + 5900 km s −1 , for the ejecta mass, nickel mass, and ejecta velocity respectively, inferring an explosion energy of E kin ≃ 2.6–9.0 × 10 52 erg.
Spectroscopic identification of r-process nucleosynthesis in a double neutron-star merger
Publisher: Springer Science and Business Media LLC
Date: 16-10-2017
DOI: 10.1038/NATURE24298
Abstract: The merger of two neutron stars is predicted to give rise to three major detectable phenomena: a short burst of γ-rays, a gravitational-wave signal, and a transient optical-near-infrared source powered by the synthesis of large amounts of very heavy elements via rapid neutron capture (the r-process). Such transients, named 'macronovae' or 'kilonovae', are believed to be centres of production of rare elements such as gold and platinum. The most compelling evidence so far for a kilonova was a very faint near-infrared rebrightening in the afterglow of a short γ-ray burst at redshift z = 0.356, although findings indicating bluer events have been reported. Here we report the spectral identification and describe the physical properties of a bright kilonova associated with the gravitational-wave source GW170817 and γ-ray burst GRB 170817A associated with a galaxy at a distance of 40 megaparsecs from Earth. Using a series of spectra from ground-based observatories covering the wavelength range from the ultraviolet to the near-infrared, we find that the kilonova is characterized by rapidly expanding ejecta with spectral features similar to those predicted by current models. The ejecta is optically thick early on, with a velocity of about 0.2 times light speed, and reaches a radius of about 50 astronomical units in only 1.5 days. As the ejecta expands, broad absorption-like lines appear on the spectral continuum, indicating atomic species produced by nucleosynthesis that occurs in the post-merger fast-moving dynamical ejecta and in two slower (0.05 times light speed) wind regions. Comparison with spectral models suggests that the merger ejected 0.03 to 0.05 solar masses of material, including high-opacity lanthanides.
Infant-phase reddening by surface Fe-peak elements in a normal type Ia supernova
Publisher: Springer Science and Business Media LLC
Date: 17-02-2022
The Early Discovery of SN 2017ahn: Signatures of Persistent Interaction in a Fast-declining Type II Supernova
Publisher: American Astronomical Society
Date: 2021
Abstract: We present high-cadence, comprehensive data on the nearby ( D ≃ 33 Mpc) Type II supernova (SN II) 2017ahn, discovered within about one day of the explosion, from the very early phases after explosion to the nebular phase. The observables of SN 2017ahn show a significant evolution over the ≃470 days of our follow-up c aign, first showing prominent, narrow Balmer lines and other high-ionization features purely in emission (i.e., flash spectroscopy features), which progressively fade and lead to a spectroscopic evolution similar to that of more canonical SNe II. Over the same period, the decline of the light curves in all bands is fast, resembling the photometric evolution of linearly declining H-rich core-collapse SNe. The modeling of the light curves and early flash spectra suggests that a complex circumstellar medium surrounds the progenitor star at the time of explosion, with a first dense shell produced during the very late stages of its evolution that is swept up by the rapidly expanding ejecta within the first ∼6 days of the SN evolution, while signatures of interaction are observed also at later phases. Hydrodynamical models support the scenario in which linearly declining SNe II are predicted to arise from massive yellow super- or hypergiants depleted of most of their hydrogen layers.
A gravitational-wave standard siren measurement of the Hubble constant
Publisher: Springer Science and Business Media LLC
Date: 16-10-2017
DOI: 10.1038/NATURE24471
Abstract: On 17 August 2017, the Advanced LIGO and Virgo detectors observed the gravitational-wave event GW170817-a strong signal from the merger of a binary neutron-star system. Less than two seconds after the merger, a γ-ray burst (GRB 170817A) was detected within a region of the sky consistent with the LIGO-Virgo-derived location of the gravitational-wave source. This sky region was subsequently observed by optical astronomy facilities, resulting in the identification of an optical transient signal within about ten arcseconds of the galaxy NGC 4993. This detection of GW170817 in both gravitational waves and electromagnetic waves represents the first 'multi-messenger' astronomical observation. Such observations enable GW170817 to be used as a 'standard siren' (meaning that the absolute distance to the source can be determined directly from the gravitational-wave measurements) to measure the Hubble constant. This quantity represents the local expansion rate of the Universe, sets the overall scale of the Universe and is of fundamental importance to cosmology. Here we report a measurement of the Hubble constant that combines the distance to the source inferred purely from the gravitational-wave signal with the recession velocity inferred from measurements of the redshift using the electromagnetic data. In contrast to previous measurements, ours does not require the use of a cosmic 'distance ladder': the gravitational-wave analysis can be used to estimate the luminosity distance out to cosmological scales directly, without the use of intermediate astronomical distance measurements. We determine the Hubble constant to be about 70 kilometres per second per megaparsec. This value is consistent with existing measurements, while being completely independent of them. Additional standard siren measurements from future gravitational-wave sources will enable the Hubble constant to be constrained to high precision.
A radio-detected type Ia supernova with helium-rich circumstellar material
Publisher: Springer Science and Business Media LLC
Date: 17-05-2023
DOI: 10.1038/S41586-023-05916-W
Abstract: Type Ia supernovae (SNe Ia) are thermonuclear explosions of degenerate white dwarf stars destabilized by mass accretion from a companion star 1 , but the nature of their progenitors remains poorly understood. A way to discriminate between progenitor systems is through radio observations a non-degenerate companion star is expected to lose material through winds 2 or binary interaction 3 before explosion, and the supernova ejecta crashing into this nearby circumstellar material should result in radio synchrotron emission. However, despite extensive efforts, no type Ia supernova (SN Ia) has ever been detected at radio wavelengths, which suggests a clean environment and a companion star that is itself a degenerate white dwarf star 4,5 . Here we report on the study of SN 2020eyj, a SN Ia showing helium-rich circumstellar material, as demonstrated by its spectral features, infrared emission and, for the first time in a SN Ia to our knowledge, a radio counterpart. On the basis of our modelling, we conclude that the circumstellar material probably originates from a single-degenerate binary system in which a white dwarf accretes material from a helium donor star, an often proposed formation channel for SNe Ia (refs. 6,7 ). We describe how comprehensive radio follow-up of SN 2020eyj-like SNe Ia can improve the constraints on their progenitor systems.
Related Organisations
Province Of The Eastern Cape Department Of Education
Location: South Africa
Related Funding Activities
No related grants have been discovered for sheng yang.