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 (\(\Delta m_{15})_r\) = 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.
A major scientific goal of JWST is to probe the epoch of re-ionization of the Universe at z above 6, and up to 20 and beyond. At these redshifts, galaxies are just beginning to form and the ...observable objects are early black holes, supernovae, and cosmic infrared background. The JWST has the necessary sensitivity to observe these targets individually, but a public deep and wide science enabling survey in the wavelength range from 2-5 \(\mu\)m is needed to discover these black holes and supernovae and to cover the area large enough for cosmic infrared background to be reliably studied. This enabling survey will also discover a large number of other transients and enable sciences such as supernova cosmology up to z \(\sim\) 5, star formation history at high redshift through supernova explosions, faint stellar objects in the Milky Way, and galaxy evolution up to z approaching 10. The results of this survey will also serve as an invaluable target feeder for the upcoming era of ELT and SKA.
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.
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 \(\kappa=0.1\,\)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.
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.
We present Hubble Space Telescope UV spectra of the 4.6 h period double white dwarf SDSS J125733.63+542850.5. Combined with Sloan Digital Sky Survey optical data, these reveal that the massive white ...dwarf (secondary) has an effective temperature T2 = 13030 +/- 70 +/- 150 K and a surface gravity log g2 = 8.73 +/- 0.05 +/- 0.05 (statistical and systematic uncertainties respectively), leading to a mass of M2 = 1.06 Msun. The temperature of the extremely low-mass white dwarf (primary) is substantially lower at T1 = 6400 +/- 37 +/- 50 K, while its surface gravity is poorly constrained by the data. The relative flux contribution of the two white dwarfs across the spectrum provides a radius ratio of R1/R2 = 4.2, which, together with evolutionary models, allows us to calculate the cooling ages. The secondary massive white dwarf has a cooling age of about 1 Gyr, while that of the primary low-mass white dwarf is likely to be much longer, possibly larger than 5 Gyrs, depending on its mass and the strength of chemical diffusion. These results unexpectedly suggest that the low-mass white dwarf formed long before the massive white dwarf, a puzzling discovery which poses a paradox for binary evolution.
We present an analysis of the early, rising light curves of 18 Type Ia supernovae (SNe Ia) discovered by the Palomar Transient Factory (PTF) and the La Silla-QUEST variability survey (LSQ). We fit ...these early data flux using a simple power-law \((f(t) = {\alpha\times t^n})\) to determine the time of first light \(({t_0})\), and hence the rise-time \(({t_{rise}})\) from first light to peak luminosity, and the exponent of the power-law rise (\(n\)). We find a mean uncorrected rise time of \(18.98 {\pm} 0.54\) days, with individual SN rise-times ranging from \(15.98\) to \(24.7\) days. The exponent n shows significant departures from the simple 'fireball model' of \(n = 2\) (or \({f(t) \propto t^2}\)) usually assumed in the literature. With a mean value of \(n = 2.44 {\pm} 0.13\), our data also show significant diversity from event to event. This deviation has implications for the distribution of 56Ni throughout the SN ejecta, with a higher index suggesting a lesser degree of 56Ni mixing. The range of n found also confirms that the 56Ni distribution is not standard throughout the population of SNe Ia, in agreement with earlier work measuring such abundances through spectral modelling. We also show that the duration of the very early light curve, before the luminosity has reached half of its maximal value, does not correlate with the light curve shape or stretch used to standardise SNe Ia in cosmological applications. This has implications for the cosmological fitting of SN Ia light curves.
We present photometric and spectroscopic observations of SN 2013fc, a bright type II supernova (SN) in a circumnuclear star-forming ring in the luminous infrared galaxy ESO 154-G010, observed as part ...of the Public ESO Spectroscopic Survey of Transient Objects (PESSTO). SN 2013fc is both photometrically and spectroscopically similar to the well-studied type IIn SN 1998S and to the bright type II-L SN 1979C. It exhibits an initial linear decline, followed by a short plateau phase and a tail phase with a decline too fast for \(^{56}\)Co decay with full gamma-ray trapping. Initially the spectrum was blue and featureless. Later on, a strong broad (\(\sim 8000\) km s\(^{-1}\)) H \(\alpha\) emission profile became prominent. We apply a Starlight stellar population model fit to the SN location (observed when the SN had faded) to estimate a high extinction of \(A_V = 2.9 \pm 0.2\) mag and an age of \(10_{-2}^{+3}\) Myr for the underlying cluster. We compare the SN to SNe 1998S and 1979C and discuss its possible progenitor star considering the similarities to these events. With a peak brightness of \(B = -20.46 \pm 0.21\) mag, SN 2013fc is 0.9 mag brighter than SN 1998S and of comparable brightness to SN 1979C. We suggest that SN 2013fc was consistent with a massive red supergiant (RSG) progenitor. Recent mass loss probably due to a strong RSG wind created the circumstellar matter illuminated through its interaction with the SN ejecta. We also observe a near-infrared excess, possibly due to newly condensed dust.
We present the analysis of the first circumbinary planet microlensing event, OGLE-2007-BLG-349. This event has a strong planetary signal that is best fit with a mass ratio of \(q \approx ...3.4\times10^{-4}\), but there is an additional signal due to an additional lens mass, either another planet or another star. We find acceptable light curve fits with two classes of models: 2-planet models (with a single host star) and circumbinary planet models. The light curve also reveals a significant microlensing parallax effect, which constrains the mass of the lens system to be \(M_L \approx 0.7 M_\odot\). Hubble Space Telescope images resolve the lens and source stars from their neighbors and indicate excess flux due to the star(s) in the lens system. This is consistent with the predicted flux from the circumbinary models, where the lens mass is shared between two stars, but there is not enough flux to be consistent with the 2-planet, 1-star models. So, only the circumbinary models are consistent with the HST data. They indicate a planet of mass \(m_c = 80\pm 13\,M_\oplus\), orbiting a pair of M-dwarfs with masses of \(M_A = 0.41\pm 0.07 M_\odot\) and \(M_B = 0.30\pm 0.07 M_\oplus\), which makes this the lowest mass circumbinary planet system known. The ratio of the separation between the planet and the center-of-mass to the separations of the two stars is \(\sim 40\), so unlike most of the circumbinary planets found by Kepler, the planet does not orbit near the stability limit.
We report photometric and spectroscopic observations of the optical transient LSQ13zm. Historical data reveal the presence of an eruptive episode (that we label as `2013a') followed by a much ...brighter outburst (`2013b') three weeks later, that we argue to be the genuine supernova explosion. This sequence of events closely resemble those observed for SN2010mc and (in 2012) SN2009ip. The absolute magnitude reached by LSQ13zm during 2013a (\(M_R=-14.87\pm0.25\,\rm{mag}\)) is comparable with those of supernova impostors, while that of the 2013b event (\(M_R=-18.46\pm0.21\,\rm{mag}\)) is consistent with those of interacting supernovae. Our spectra reveal the presence of a dense and structured circumstellar medium, probably produced through numerous pre-supernova mass-loss events. In addition, we find evidence for high-velocity ejecta, with a fraction of gas expelled at more than 20000\kms. The spectra of LSQ13zm show remarkable similarity with those of well-studied core-collapse supernovae. From the analysis of the available photometric and spectroscopic data, we conclude that we first observed the last event of an eruptive sequence from a massive star, likely a Luminous Blue Variable, which a short time later exploded as a core-collapse supernova. The detailed analysis of archival images suggest that the host galaxy is a star-forming Blue Dwarf Compact Galaxy.
