Optical observations of the fast declining type Ib supernova iPTF13bvn

We present optical UBVRI photometry and medium resolution spectroscopy of the type Ib supernova iPTF13bvn, spanning a phase of $\sim$ $-13\,$d to $+71\,$d with respect to $B$-band maximum. The post maximum decline rates indicate a fast decline with $\Delta m_{15}(B) = 1.82$. Correcting for a galactic extinction $E(B-V){\rm_{MW}}=0.045$ and host galaxy extinction of $E(B-V){\rm_{host}}=0.17$, the absolute $V$-band magnitude peaks at M$_V=-17.23\, \pm \,0.20$. The bolometric light curve indicates that $\sim 0.09$ M$_{\odot}$ of $^{56}$Ni was synthesized in the explosion. The earliest spectrum ($-13$d) shows the presence of He~{\sc i} 5876 \AA\ feature at a velocity of $\sim$15000 km s$^{-1}$, which falls rapidly by the time the SN approaches the epoch of B-band maximum. The photospheric velocity near maximum light, as indicated by the Fe~{\sc ii} 5169~\AA\ feature, is $\sim 9000$ km s$^{-1}$. The estimate for the $^{56}$Ni mass, together with the estimates for the ejected mass ($M_{\rm{ej}}$) and kinetic energy of the explosion ($E_{\rm{k}}$) indicate that iPTF13bvn is a low luminosity type Ib supernova, with a lower than average ejected mass and kinetic energy. Our results suggest that the progenitor of iPTF13bvn is inconsistent with a single Wolf-Rayet star.Comment: Accepted for publication in MNRAS, 11 pages, 12 figure

Multiparton Cwebs at five loops

Scattering amplitudes involving multiple partons are plagued with infrared singularities. The soft singularities of the amplitude are captured by the soft function which is defined as the vacuum expectation value of Wilson line correlators. Renormalization properties of soft function allows us to write it as an exponential of the finite soft anomalous dimension. An efficient way to study the soft function is through a set of Feynman diagrams known as Cwebs (webs). We obtain the mixing matrices and exponentiated colour factors for all the Cwebs at five loops that connect six massless Wilson lines. Our results are the first key ingredient for the calculation of the soft anomalous dimension at five loops.Comment: 46 pages, 29 figures, 27 tables and 1 ancillary fil

iPTF13bvn: The First Evidence of a Binary Progenitor for a Type Ib Supernova

The recent detection in archival HST images of an object at the the location of supernova (SN) iPTF13bvn may represent the first direct evidence of the progenitor of a Type Ib SN. The object's photometry was found to be compatible with a Wolf-Rayet pre-SN star mass of ~11 Msun. However, based on hydrodynamical models we show that the progenitor had a pre-SN mass of ~3.5 Msun and that it could not be larger than ~8 Msun. We propose an interacting binary system as the SN progenitor and perform evolutionary calculations that are able to self-consistently explain the light-curve shape, the absence of hydrogen, and the pre-SN photometry. We further discuss the range of allowed binary systems and predict that the remaining companion is a luminous O-type star of significantly lower flux in the optical than the pre-SN object. A future detection of such star may be possible and would provide the first robust identification of a progenitor system for a Type Ib SN.Comment: Accepted to AJ on July 26. Slight changes from original, however delayed by slow refereeing proces

Multi-wavelength observations of multiple eruptions of the recurrent nova M31N 2008-12a

We report the optical, UV, and soft X-ray observations of the $2017-2022$ eruptions of the recurrent nova M31N 2008-12a. We infer a steady decrease in the accretion rate over the years based on the inter-eruption recurrence period. We find a ``cusp'' feature in the $r'$ and $i'$ band light curves close to the peak, which could be associated to jets. Spectral modelling indicates a mass ejection of 10$^{-7}$ to 10$^{-8}$ M$_{\odot}$ during each eruption, and an enhanced Helium abundance of He/He$_{\odot}$ $\approx$ 3. The super-soft source (SSS) phase shows significant variability, which is anti-correlated to the UV emission, indicating a common origin. The variability could be due to the reformation of the accretion disk. A comparison of the accretion rate with different models on the $\rm M_{WD}$$-\dot{M}$ plane yields the mass of a CO WD, powering the ``H-shell flashes'' every $\sim$ 1 year to be $>1.36$ M$_{\odot}$ and growing with time, making M31N 2008-12a a strong candidate for the single degenerate scenario of Type Ia supernovae progenitor.Comment: Submitted to AJ, 22 pages, 14 figures, 5 table

The luminous type Ia supernova 2022ilv and its early excess emission

We present observations and analysis of the host-less and luminous type Ia supernova 2022ilv, illustrating it is part of the 2003fg-like family, often referred to as super-Chandrasekhar (Ia-SC) explosions. The ATLAS light curve shows evidence of a short-lived, pulse-like early excess, similar to that detected in another luminous type Ia supernova (SN 2020hvf). The light curve is broad and the early spectra are remarkably similar to SN 2009dc. Adopting a redshift of $z=0.026 \pm 0.005$ for SN 2022ilv based on spectral matching, our model light curve requires a large $^{56}$Ni mass in the range $0.7-1.5$ M$_{\odot}$, and a large ejecta mass in the range $1.6-2.3$ M$_{\odot}$. The early excess can be explained by fast-moving SN ejecta interacting with a thin, dense shell of circumstellar material close to the progenitor ($\sim 10^{13}$ cm), a few hours after the explosion. This may be realised in a double-degenerate scenario, wherein a white dwarf merger is preceded by ejection of a small amount ($\sim 10^{-3}-10^{-2}$ M$_{\odot}$) of hydrogen and helium-poor tidally stripped material. A deep pre-explosion Pan-STARRS1 stack indicates no host galaxy to a limiting magnitude of $r \sim 24.5$. This implies a surprisingly faint limit for any host of $M_r \gtrsim -11$, providing further evidence that these types of explosion occur predominantly in low-metallicity environments.Comment: Accepted to ApJL after minor revisio

Unprecedented early flux excess in the hybrid 02es-like type Ia supernova 2022ywc indicates interaction with circumstellar material

We present optical photometric and spectroscopic observations of the 02es-like type Ia supernova (SN) 2022ywc. The transient occurred in the outskirts of an elliptical host galaxy and showed a striking double-peaked light curve with an early excess feature detected in the ATLAS orange and cyan bands. The early excess is remarkably luminous with an absolute magnitude $\sim -19$, comparable in luminosity to the subsequent radioactively-driven second peak. The spectra resemble the hybrid 02es-like SN 2016jhr, that is considered to be a helium shell detonation candidate. We investigate different physical mechanisms that could power such a prominent early excess and rule out massive helium shell detonation, surface $^{56}$Ni distribution and ejecta-companion interaction. We conclude that SN ejecta interacting with circumstellar material (CSM) is the most viable scenario. Semi-analytical modelling with MOSFiT indicates that SN ejecta interacting with $\sim 0.05\,$M$_{\odot}$ of CSM at a distance of $\sim 10^{14}$ cm can explain the extraordinary light curve. A double-degenerate scenario may explain the origin of the CSM, either by tidally-stripped material from the secondary white dwarf, or disk-originated matter launched along polar axes following the disruption and accretion of the secondary white dwarf. A non-spherical CSM configuration could suggest that a small fraction of 02es-like events viewed along a favourable line of sight may be expected to display a very conspicuous early excess like SN 2022ywc.Comment: Accepted to ApJL after minor revisio

SN 2021zny: an early flux excess combined with late-time oxygen emission suggests a double white dwarf merger event

We present a photometric and spectroscopic analysis of the ultra-luminous and slowly evolving 03fg-like Type Ia SN 2021zny. Our observational campaign starts from $\sim5.3$ hours after explosion (making SN 2021zny one of the earliest observed members of its class), with dense multi-wavelength coverage from a variety of ground- and space-based telescopes, and is concluded with a nebular spectrum $\sim10$ months after peak brightness. SN 2021zny displayed several characteristics of its class, such as the peak brightness ($M_{B}=-19.95$ mag), the slow decline ($\Delta m_{15}(B) = 0.62$ mag), the blue early-time colours, the low ejecta velocities and the presence of significant unburned material above the photosphere. However, a flux excess for the first $\sim1.5$ days after explosion is observed in four photometric bands, making SN 2021zny the third 03fg-like event with this distinct behavior, while its $+313$ d spectrum shows prominent [O I] lines, a very unusual characteristic of thermonuclear SNe. The early flux excess can be explained as the outcome of the interaction of the ejecta with $\sim0.04\:\mathrm{M_{\odot}}$ of H/He-poor circumstellar material at a distance of $\sim10^{12}$ cm, while the low ionization state of the late-time spectrum reveals low abundances of stable iron-peak elements. All our observations are in accordance with a progenitor system of two carbon/oxygen white dwarfs that undergo a merger event, with the disrupted white dwarf ejecting carbon-rich circumstellar material prior to the primary white dwarf detonation.Comment: 19 pages, 16 figures, accepted for publication in MNRA