arXiv subjects

T. -W. Chen

Publications and source records attributed to T. -W. Chen.

At least 109 records · Page 6Linked to original sources

arXiv2017

A long optical plateau in the afterglow of the Extended Emission short GRB 150424A: Evidence for energy injection by a magnetar?

Short-duration GRBs with extended emission form a subclass of short GRBs, comprising about 15% of the short-duration sample. Afterglow detections of short GRBs are also rare (about 30%) due to their smaller luminosity. We present a multi-band data set of the short burst with extended emission GRB 150424A, comprising of GROND observations, complemented with data from Swift/UVOT, Swift/XRT, HST, Keck/LRIS and data points from the literature. The GRB 150424A afterglow shows an extended plateau phase, lasting about 8hrs. The analysis of this unique GRB afterglow might shed light on the understanding of afterglow plateau emission, the nature of which is still under debate. We present a phenomenological analysis by applying fireball closure relations, and interpret the findings in the context of the fireball model. We discuss the plausibility of a magnetar as a central engine, being responsible for additional and prolonged energy injection into the fireball. We find convincing evidence for energy injection into the afterglow of GRB 150424A. We find that a magnetar spin down as source for a prolonged energy injection requires that at least 4% of the spin-down energy is converted to radiation.

astro-ph.HE↗

arXiv2017

Superluminous supernova progenitors have a half-solar metallicity threshold

Host galaxy properties provide strong constraints on the stellar progenitors of superluminous supernovae. By comparing a sample of 19 low-redshift (z < 0.3) superluminous supernova hosts to galaxy populations in the local Universe, we show that sub-solar metallicities seem to be a requirement. All superluminous supernovae in hosts with high measured gas-phase metallicities are found to explode at large galactocentric radii, indicating that the metallicity at the explosion site is likely lower than the integrated host value. We found that superluminous supernovae hosts do not always have star-formation rates higher than typical star-forming galaxies of the same mass. However, we confirm that high absolute specific star-formation rates are a feature of superluminous supernova host galaxies, but interpret this as simply a consequence of the anti-correlation between gas-phase metallicity and specific star-formation rate and the requirement of on-going star formation to produce young, massive stars greater than ~ 10-20 M_sol. Based on our sample, we propose an upper limit of ~ 0.5 Z_sol for forming superluminous supernova progenitors (assuming an N2 metallicity diagnostic and a solar oxygen abundance of 8.69). Finally, we show that if magnetar powering is the source of the extreme luminosity then the required initial spins appear to be correlated with metallicity of the host galaxy. This correlation needs further work, but if it holds it is a powerful link between the supernova parameters and nature of the progenitor population.

astro-ph.GA↗

arXiv2017

Complexity in the light curves and spectra of slow-evolving superluminous supernovae

A small group of the newly discovered superluminous supernovae show broad and slowly evolving light curves. Here we present extensive observational data for the slow-evolving superluminous supernova LSQ14an, which brings this group of transients to four in total in the low redshift Universe (z$<$0.2; SN 2007bi, PTF12dam, SN 2015bn). We particularly focus on the optical and near-infrared evolution during the period from 50 days up to 400 days from peak, showing that they are all fairly similar in their light curve and spectral evolution. LSQ14an shows broad, blue-shifted [O III] $λλ$4959, 5007 lines, as well as a blue-shifted [O II] $λλ$7320, 7330 and [Ca II] $λλ$7291, 7323. Furthermore, the sample of these four objects shows common features. Semi-forbidden and forbidden emission lines appear surprisingly early at 50-70 days and remain visible with almost no variation up to 400 days. The spectra remain blue out to 400 days. There are small, but discernible light curve fluctuations in all of them. The light curve of each shows a faster decline than $^{56}$Co after 150 days and it further steepens after 300 days. We also expand our analysis presenting X-ray limits for LSQ14an and SN2015bn and discuss their diagnostic power in interpreting their common features. These features are quite distinct from the faster evolving superluminous supernovae and are not easily explained in terms of only a variation in ejecta mass. While a central engine is still the most likely luminosity source, it appears that the ejecta structure is complex, with multiple emitting zones and at least some interaction between the expanding ejecta and surrounding material.

astro-ph.HE↗

arXiv2017

GRB 161219B / SN 2016jca: A low-redshift gamma-ray burst supernova powered by radioactive heating

Since the first discovery of a broad-lined type Ic supernova (SN) with a long-duration gamma-ray burst (GRB) in 1998, fewer than fifty gamma-ray burst supernovae (GRB-SNe) have been discovered. The intermediate-luminosity Swift GRB 161219B and its associated supernova SN 2016jca, which occurred at a redshift of z=0.1475, represents only the seventh GRB-SN to have been discovered within 1 Gpc, and hence provides an excellent opportunity to investigate the observational and physical properties of these very elusive and rare type of SN. As such, we present optical to near-infrared photometry and optical spectroscopy of GRB 161219B and SN 2016jca, spanning the first three months since its discovery. GRB 161219B exploded in the disk of an edge-on spiral galaxy at a projected distance of 3.4 kpc from the galactic centre. GRB 161219B itself is an outlier of the Amati relation, while SN 2016jca had a rest-frame, peak absolute V-band magnitude of M_V = -19.0, which it reached after 12.5 rest-frame days. We find that the bolometric properties of SN 2016jca are inconsistent with being powered solely by a magnetar central engine, as proposed by other authors, and demonstrate that it was likely powered exclusively by energy deposited by the radioactive decay of nickel and cobalt into their daughter products, which were nucleosynthesized when its progenitor underwent core collapse. We find that 0.22 solar masses of nickel is required to reproduce the peak luminosity of SN 2016jca, and we constrain an ejecta mass of 5.8 solar masses and a kinetic energy of ~5 x 10^52 erg. Finally, we report on a chromatic, pre-maximum bump in the g-band light curve, and discuss its possible origin. [Abridged]

astro-ph.HE↗

arXiv2017

The evolution of superluminous supernova LSQ14mo and its interacting host galaxy system

We present and analyse an extensive dataset of the superluminous supernova (SLSN) LSQ14mo (z = 0.256), consisting of a multi-colour lightcurve from -30 d to +70 d in the rest-frame and a series of 6 spectra from PESSTO covering -7 d to +50 d. This is among the densest spectroscopic coverage, and best-constrained rising lightcurve, for a fast-declining hydrogen-poor SLSN. The bolometric lightcurve can be reproduced with a millisecond magnetar model with ~ 4 M_sol ejecta mass, and the temperature and velocity evolution is also suggestive of a magnetar as the power source. Spectral modelling indicates that the SN ejected ~ 6 M_sol of CO-rich material with a kinetic energy of ~ 7 x 10^51 erg, and suggests a partially thermalised additional source of luminosity between -2 d and +22 d. This may be due to interaction with a shell of material originating from pre-explosion mass loss. We further present a detailed analysis of the host galaxy system of LSQ14mo. PESSTO and GROND imaging show three spatially resolved bright regions, and we used the VLT and FORS2 to obtain a deep (five-hour exposure) spectra of the SN position and the three star-forming regions, which are at a similar redshift. The FORS spectrum at +300 days shows no trace of SN emission lines and we place limits on the strength of [O I] from comparisons with other Ic SNe. The deep spectra provides a unique chance to investigate spatial variations in the host star-formation activity and metallicity. The specific star-formation rate is similar in all three components, as is the presence of a young stellar population. However, the position of LSQ14mo exhibits a lower metallicity, with 12 + log(O/H) = 8.2 in both the R23 and N2 scales (corresponding to ~ 0.3 Z_sol). We propose that the three bright regions in the host system are interacting, which thus triggers star-formation and forms young stellar populations.

astro-ph.SR↗

arXiv2017

Long-duration superluminous supernovae at late times

Nebular-phase observations and spectral models of Type Ic superluminous supernovae are presented. LSQ14an and SN 2015bn both display late-time spectra similar to galaxy-subtracted spectra of SN 2007bi, and the class shows strong similarity with broad-lined Type Ic SNe such as SN 1998bw. Near-infrared observations of SN 2015bn show a strong Ca II triplet, O I 9263, O I 1.13 um and Mg I 1.50 um, but no distinct He, Si, or S emission. The high Ca II NIR/[Ca II] 7291,7323 ratio of ~2 indicates a high electron density of n_e >~ 10^8 cm^{-3}. Spectral models of oxygen-zone emission are investigated to put constraints on the emitting region. Models require M(O-zone) >~ 10 Msun to produce enough [O I] 6300,6364 luminosity, irrespective of the powering situation and the density. The high oxygen-zone mass, supported by high estimated magnesium masses, points to explosions of massive CO cores, requiring M_ZAMS >~ 40 Msun. Collisions of pair-instability pulsations do not provide enough mass to account for the emission. [O II] and [O III] lines emerge naturally in many models, which strengthens the identification of broad [O II] 7320,7330, [O III] 4363, and [O III] 4959,5007 in some spectra. A small filling factor f <~ 0.01 for the O/Mg zone is needed to produce enough luminosity in Mg I] 4571, Mg I 1.504 um, and O I recombination lines, which shows that the ejecta is clumped. We review the constraints from the nebular spectral modelling in the context of the various scenarios proposed for superluminous supernovae.

astro-ph.HE↗

arXiv2016

The Superluminous Transient ASASSN-15lh as a Tidal Disruption Event from a Kerr Black Hole

When a star passes within the tidal radius of a supermassive black hole, it will be torn apart. For a star with the mass of the Sun ($M_\odot$) and a non-spinning black hole with a mass $<10^8 M_\odot$, the tidal radius lies outside the black hole event horizon and the disruption results in a luminous flare. Here we report observations over a period of 10 months of a transient, hitherto interpreted as a superluminous supernova. Our data show that the transient rebrightened substantially in the ultraviolet and that the spectrum went through three different spectroscopic phases without ever becoming nebular. Our observations are more consistent with a tidal disruption event than a superluminous supernova because of the temperature evolution, the presence of highly ionised CNO gas in the line of sight and our improved localisation of the transient in the nucleus of a passive galaxy, where the presence of massive stars is highly unlikely. While the supermassive black hole has a mass $> 10^8 M_\odot$, a star with the same mass as the Sun could be disrupted outside the event horizon if the black hole were spinning rapidly. The rapid spin and high black hole mass can explain the high luminosity of this event.

astro-ph.HE↗

arXiv2016

Slowly fading super-luminous supernovae that are not pair-instability explosions

Super-luminous supernovae that radiate more than 10^44 ergs per second at their peak luminosity have recently been discovered in faint galaxies at redshifts of 0.1-4. Some evolve slowly, resembling models of 'pair-instability' supernovae. Such models involve stars with original masses 140-260 times that of the Sun that now have carbon-oxygen cores of 65-30 solar masses. In these stars, the photons that prevent gravitational collapse are converted to electron-positron pairs, causing rapid contraction and thermonuclear explosions. Many solar masses of 56Ni are synthesized; this isotope decays to 56Fe via 56Co, powering bright light curves. Such massive progenitors are expected to have formed from metal-poor gas in the early Universe. Recently, supernova 2007bi in a galaxy at redshift 0.127 (about 12 billion years after the Big Bang) with a metallicity one-third that of the Sun was observed to look like a fading pair-instability supernova. Here we report observations of two slow-to-fade super-luminous supernovae that show relatively fast rise times and blue colours, which are incompatible with pair-instability models. Their late-time light-curve and spectral similarities to supernova 2007bi call the nature of that event into question. Our early spectra closely resemble typical fast-declining super-luminous supernovae, which are not powered by radioactivity. Modelling our observations with 10-16 solar masses of magnetar-energized ejecta demonstrates the possibility of a common explosion mechanism. The lack of unambiguous nearby pair-instability events suggests that their local rate of occurrence is less than 6x10^-6 times that of the core-collapse rate.

astro-ph.CO↗

arXiv2016

Superluminous supernova 2015bn in the nebular phase: evidence for the engine-powered explosion of a stripped massive star

We present nebular-phase imaging and spectroscopy for the hydrogen-poor superluminous supernova SN 2015bn, at redshift z=0.1136, spanning +250-400 d after maximum light. The light curve exhibits a steepening in the decline rate from 1.4 mag/(100 d) to 1.7 mag/(100 d), suggestive of a significant decrease in the opacity. This change is accompanied by a transition from a blue continuum superposed with photospheric absorption lines to a nebular spectrum dominated by emission lines of oxygen, calcium and magnesium. There are no obvious signatures of circumstellar interaction or large nickel mass. We show that the spectrum at +400 d is virtually identical to a number of energetic Type Ic supernovae such as SN 1997dq, SN 2012au, and SN 1998bw, indicating similar core conditions and strengthening the link between `hypernovae'/long gamma-ray bursts and superluminous supernovae. A single explosion mechanism may unify these events that span absolute magnitudes of -22 < M_B < -17. Both the light curve and spectrum of SN 2015bn are consistent with an engine-driven explosion ejecting 7-30 M$_\odot$ of oxygen-dominated ejecta (for reasonable choices in temperature and opacity). A strong and relatively narrow O II $λ$7774 line, seen in a number of these energetic events but not in normal supernovae, may point to an inner shell that is the signature of a central engine.

astro-ph.HE↗

arXiv2016

A search for an optical counterpart to the gravitational wave event GW151226

We present a search for an electromagnetic counterpart of the gravitational wave source GW151226. Using the Pan-STARRS1 telescope we mapped out 290 square degrees in the optical i_ps filter starting 11.5hr after the LIGO information release and lasting for a further 28 days. The first observations started 49.5hr after the time of the GW151226 detection. We typically reached sensitivity limits of i_ps = 20.3-20.8 and covered 26.5% of the LIGO probability skymap. We supplemented this with ATLAS survey data, reaching 31% of the probability region to shallower depths of m~19. We found 49 extragalactic transients (that are not obviously AGN), including a faint transient in a galaxy at 7Mpc (a luminous blue variable outburst) plus a rapidly decaying M-dwarf flare. Spectral classification of 20 other transient events showed them all to be supernovae. We found an unusual transient, PS15dpn, with an explosion date temporally coincident with GW151226 which evolved into a type Ibn supernova. The redshift of the transient is secure at z=0.1747 +/- 0.0001 and we find it unlikely to be linked, since the luminosity distance has a negligible probability of being consistent with that of GW151226. In the 290 square degrees surveyed we therefore do not find a likely counterpart. However we show that our survey strategy would be sensitive to NS-NS mergers producing kilonovae at D < 100 Mpc which is promising for future LIGO/Virgo searches.

astro-ph.HE↗

arXiv2016

Pan-STARRS and PESSTO search for an optical counterpart to the LIGO gravitational wave source GW150914

We searched for an optical counterpart to the first gravitational wave source discovered by LIGO (GW150914), using a combination of the Pan-STARRS1 wide-field telescope and the PESSTO spectroscopic follow-up programme. As the final LIGO sky maps changed during analysis, the total probability of the source being spatially coincident with our fields was finally only 4.2 per cent. Therefore we discuss our results primarily as a demonstration of the survey capability of Pan-STARRS and spectroscopic capability of PESSTO. We mapped out 442 square degrees of the northern sky region of the initial map. We discovered 56 astrophysical transients over a period of 41 days from the discovery of the source. Of these, 19 were spectroscopically classified and a further 13 have host galaxy redshifts. All transients appear to be fairly normal supernovae and AGN variability and none is obviously linked with GW150914. We illustrate the sensitivity of our survey by defining parameterised lightcurves with timescales of 4, 20 and 40 days and use the sensitivity of the Pan-STARRS1 images to set limits on the luminosities of possible sources. The Pan-STARRS1 images reach limiting magnitudes of i = 19.2, 20.0 and 20.8 respectively for the three timescales. For long timescale parameterised lightcurves (with FWHM=~40d) we set upper limits of M_i <= -17.2 -0.9/+1.4 if the distance to GW150914 is D = 400 +/- 200Mpc. The number of type Ia SN we find in the survey is similar to that expected from the cosmic SN rate, indicating a reasonably complete efficiency in recovering supernova like transients out to D = 400 +/- 200 Mpc.

astro-ph.HE↗

arXiv2016

SN 2015bn: a detailed multi-wavelength view of a nearby superluminous supernova

We present observations of SN 2015bn (= PS15ae = CSS141223-113342+004332 = MLS150211-113342+004333), a Type I superluminous supernova (SLSN) at redshift $z=0.1136$. As well as being one of the closest SLSNe I yet discovered, it is intrinsically brighter ($M_U\approx-23.1$) and in a fainter galaxy ($M_B\approx-16.0$) than other SLSNe at $z\sim0.1$. We used this opportunity to collect the most extensive dataset for any SLSN I to date, including densely-sampled spectroscopy and photometry, from the UV to the NIR, spanning $-$50 to +250 days from optical maximum. SN 2015bn fades slowly, but exhibits surprising undulations in the light curve on a timescale of 30-50 days, especially in the UV. The spectrum shows extraordinarily slow evolution except for a rapid transformation between +7 and +20-30 days. No narrow emission lines from slow-moving material are observed at any phase. We derive physical properties including the bolometric luminosity, and find slow velocity evolution and non-monotonic temperature and radial evolution. A deep radio limit rules out a healthy off-axis gamma-ray burst, and places constraints on the pre-explosion mass loss. The data can be consistently explained by a $\gtrsim10\,{\rm M}_\odot$ stripped progenitor exploding with $\sim 10^{51}\,$erg kinetic energy, forming a magnetar with a spin-down timescale of $\sim20$ days (thus avoiding a gamma-ray burst) that reheats the ejecta and drives ionization fronts. The most likely alternative scenario -- interaction with $\sim20\,{\rm M}_\odot$ of dense, inhomogeneous circumstellar material -- can be tested with continuing radio follow-up.

astro-ph.SR↗

arXiv2016

450 Days of Type II SN 2013ej in Optical and Near-Infrared

We present optical and near-infrared photometric and spectroscopic observations of SN 2013ej, in galaxy M74, from 1 to 450 days after the explosion. SN 2013ej is a hydrogen-rich supernova, classified as a Type IIL due to its relatively fast decline following the initial peak. It has a relatively high peak luminosity (absolute magnitude M$_\rm{V}$ = -17.6) but a small $^{56}$Ni production of ~0.023 M$_\odot$. Its photospheric evolution is similar to other Type II SNe, with shallow absorption in the Hα profile typical for a Type IIL. During transition to the radioactive decay tail at ~100 days, we find the SN to grow bluer in B - V colour, in contrast to some other Type II supernovae. At late times, the bolometric light curve declined faster than expected from $^{56}$Co decay and we observed unusually broad and asymmetric nebular emission lines. Based on comparison of nebular emission lines most sensitive to the progenitor core mass, we find our observations are best matched to synthesized spectral models with a M$_\rm{ZAMS}$ = 12 - 15 M$_\odot$ progenitor. The derived mass range is similar to but not higher than the mass estimated for Type IIP progenitors. This is against the idea that Type IIL are from more massive stars. Observations are consistent with the SN having a progenitor with a relatively low-mass envelope.

astro-ph.SR↗

arXiv2016

The type Iax supernova, SN 2015H: a white dwarf deflagration candidate

We present results based on observations of SN 2015H which belongs to the small group of objects similar to SN 2002cx, otherwise known as type Iax supernovae. The availability of deep pre-explosion imaging allowed us to place tight constraints on the explosion epoch. Our observational campaign began approximately one day post-explosion, and extended over a period of about 150 days post maximum light, making it one of the best observed objects of this class to date. We find a peak magnitude of M$_r$ = -17.27 $\pm$ 0.07, and a ($Δm_{15})_r$ = 0.69 $\pm$ 0.04. Comparing our observations to synthetic spectra generated from simulations of deflagrations of Chandrasekhar mass carbon-oxygen white dwarfs, we find reasonable agreement with models of weak deflagrations that result in the ejection of ~0.2 M$_{\odot}$ of material containing ~0.07 M$_{\odot}$ of 56Ni. The model light curve however, evolves more rapidly than observations, suggesting that a higher ejecta mass is to be favoured. Nevertheless, empirical modelling of the pseudo-bolometric light curve suggests that $\lesssim$0.6 M_sun of material was ejected, implying that the white dwarf is not completely disrupted, and that a bound remnant is a likely outcome.

astro-ph.HE↗

arXiv2016

LSQ13fn: A type II-Plateau supernova with a possibly low metallicity progenitor that breaks the standardised candle relation

We present optical imaging and spectroscopy of supernova (SN) LSQ13fn, a type II supernova with several hitherto-unseen properties. Although it initially showed strong symmetric spectral emission features attributable to \ion{He}{ii}, \ion{N}{iii}, and \ion{C}{iii}, reminiscent of some interacting SNe, it transitioned into an object that would fall more naturally under a type II-Plateau (IIP) classification. However, its spectral evolution revealed several unusual properties: metal lines appeared later than expected, were weak, and some species were conspicuous by their absence. Furthermore, the line velocities were found to be lower than expected given the plateau brightness, breaking the SNe~IIP standardised candle method for distance estimates. We found that, in combination with a short phase of early-time ejecta-circumstellar material interaction, metal-poor ejecta, and a large progenitor radius could reasonably account for the observed behaviour. Comparisons with synthetic model spectra of SNe~IIP of a given progenitor mass would imply a progenitor star metallicity as low as 0.1\,Z$_{\odot}$. LSQ13fn highlights the diversity of SNe~II and the many competing physical effects that come into play towards the final stages of massive star evolution immediately preceding core-collapse.

astro-ph.HE↗

arXiv2016

On type IIn/Ia-CSM supernovae as exemplified by SN 2012ca

We present the complete set of ultra-violet, optical and near-infrared photometry and spectroscopy for SN 2012ca, covering the period from 6~days prior to maximum light, until 531 days after maximum. The spectroscopic time series for SN 2012ca is essentially unchanged over 1.5 years, and appear to be dominated at all epochs by signatures of interaction with a dense circumstellar medium rather than the underlying supernova (SN). At late phases, we see a near infrared excess in flux which is possibly associated with dust formation, although without any signs of accompanying line shifts. SN 2012ca is a member of the set of type of the ambiguous IIn/Ia-CSM SNe, the nature of which have been debated extensively in the literature. The two leading scenarios are either a type Ia SN exploding within a dense CSM from a non-degenerate, evolved companion, or a core-collapse SN from a massive star. While some members of the population have been unequivocally associated with type Ia SNe, in other cases the association is less certain. While it is possible that SN 2012ca does arise from a thermonuclear SN, this would require a relatively high (between 20 and 70 per cent) efficiency in converting kinetic energy to optical luminosity, and a massive (~2.3-2.6 Msun) circumstellar medium. On the basis of energetics, and the results of simple modelling, we suggest that SN 2012ca is more likely associated with a core-collapse SN. This would imply that the observed set of similar SNe to SN 2012ca is in fact originated by two populations, and while these are drawn from physically distinct channels, they can have observationally similar properties.

astro-ph.SR↗

arXiv2016

On the diversity of super-luminous supernovae: ejected mass as the dominant factor

We assemble a sample of 24 hydrogen-poor super-luminous supernovae (SLSNe). Parameterizing the light curve shape through rise and decline timescales shows that the two are highly correlated. Magnetar-powered models can reproduce the correlation, with the diversity in rise and decline rates driven by the diffusion timescale. Circumstellar interaction models can exhibit a similar rise-decline relation, but only for a narrow range of densities, which may be problematic for these models. We find that SLSNe are approximately 3.5 magnitudes brighter and have light curves 3 times broader than SNe Ibc, but that the intrinsic shapes are similar. There are a number of SLSNe with particularly broad light curves, possibly indicating two progenitor channels, but statistical tests do not cleanly separate two populations. The general spectral evolution is also presented. Velocities measured from Fe II are similar for SLSNe and SNe Ibc, suggesting that diffusion time differences are dominated by mass or opacity. Flat velocity evolution in most SLSNe suggests a dense shell of ejecta. If opacities in SLSNe are similar to other SNe Ibc, the average ejected mass is higher by a factor 2-3. Assuming $κ=0.1\,$cm$^2\,$g$^{-1}$, we estimate a mean (median) SLSN ejecta mass of 10$\,$M$_\odot$ (6$\,$M$_\odot$), with a range of 3-30$\,$M$_\odot$. Doubling the assumed opacity brings the masses closer to normal SNe Ibc, but with a high-mass tail. The most probable mechanism for generating SLSNe seems to be the core-collapse of a very massive hydrogen-poor star, forming a millisecond magnetar.

astro-ph.SR↗

arXiv2015

The host galaxy and late-time evolution of the Super-Luminous Supernova PTF12dam

Super-luminous supernovae of type Ic have a tendency to occur in faint host galaxies which are likely to have low mass and low metallicity. PTF12dam is one of the closest and best studied super-luminous explosions that has a broad and slowly fading lightcurve similar to SN 2007bi. Here we present new photometry and spectroscopy for PTF12dam from 200-500 days (rest-frame) after peak and a detailed analysis of the host galaxy (SDSS J142446.21+461348.6 at z = 0.107). Using deep templates and image subtraction we show that the full lightcurve can be fit with a magnetar model if escape of high-energy gamma rays is taken into account. The full bolometric lightcurve from -53 to +399 days (with respect to peak) cannot be fit satisfactorily with the pair-instability models. An alternative model of interaction with a dense CSM produces a good fit to the data although this requires a very large mass (~ 13 M_sun) of hydrogen free CSM. The host galaxy is a compact dwarf (physical size ~ 1.9 kpc) and with M_g = -19.33 +/- 0.10, it is the brightest nearby SLSN Ic host discovered so far. The host is a low mass system (2.8 x 10^8 M_sun) with a star-formation rate (5.0 M_sun/year), which implies a very high specific star-formation rate (17.9 Gyr^-1). The remarkably strong nebular lines provide detections of the [O III] λ4363 and [O II] λλ7320,7330 auroral lines and an accurate oxygen abundance of 12 + log(O/H) = 8.05 +/- 0.09. We show here that they are at the extreme end of the metallicity distribution of dwarf galaxies and propose that low metallicity is a requirement to produce these rare and peculiar supernovae.

astro-ph.GA↗