Search

We present optical and IR observations from maximum light until around 600 d of SN 2022jli, a peculiar SE SN showing two maxima, each one with a peak luminosity of about 3 x 10^{42} erg/s and separated by 50 d. The second maximum is followed by periodic undulations with a period of P ~ 12.5 days. The spectra and the photometric evolution of the first maximum are consistent with the behaviour of a standard SE SN with an ejecta mass of 1.5 +/- 0.4 Msun, and a nickel mass of 0.12 +/- 0.01 Msun. The optical spectra after 400 d correspond to a standard SN Ic event, and at late times SN 2022jli exhibits a significant drop in the optical luminosity implying that the physical phenomena that produced the secondary maximum has ceased to power the SN light curve. One possibility is that the second maximum is powered by a magnetar with an initial spin period of P=48.5 ms and a magnetic field of B = 8.5x10^{14} G, while the light curve periodic undulations could be produced by accretion of material from a companion star onto the neutron star in a binary system. The near-IR spectra shows clear 1st CO overtone emission from about 190 d after the first maximum, and it becomes undetected at 400 d. A significant near-IR excess from hot dust emission is detected at 238 d produced by either newly formed dust in the SN ejecta or due to a strong near-IR dust echo. Depending on the assumptions of the dust composition, the estimated dust mass is 2-16 x 10^{-4} Msun. The magnetar power of the second maximum can fit in a more general picture where magnetars are the power source of super-luminous SNe, could produce their frequent bumps and undulations, and where pulsars could produce the late time excess observed in some SE SNe. The detection of CO and the potential detection of dust formed in the ejecta of SN2022jli are important to understand the formation molecules and dust in the ejecta of SE SNe., Comment: Submitted to A&A (27 pages and 22 figures)

Here we present an approach to the measurement of extragalactic distances using twin SNe Ia, taken from the early down to the nebular phase.The approach is purely empirical, although we can give a theoretical background on why the method is reliable. By studying those twins in galaxies where peculiar velocities are relatively unimportant, we can tackle the H$_{0}$ tension problem. Here we apply the method to the determination of the distances to NGC 7250 and NGC 2525, who hosted respectively SN 2013dy and SN 2018gv, twins of two different SNe Ia prototypes: SN 2013aa/SN 2017cbv and SN2011fe. From the study of the SN 2013aa and SN 2017cbv twin pair, by comparing it with SN 2011fe and applying the difference between the SN 2013aa/2017cbv and the SN 2011fe class, we find as well a good estimate of the distance to NGC 5643. We have just started to measure distances with this method for the samples in Freedman et al. and Riess et al. There are differences in measured distances to the same galaxy using Cepheids or TRGBs. In this context of discrepancy, the ''twins for life '' method is very competitive because it can provide distance estimates with a modulus error of $\sigma_{\mu}$ $=$ 0.04 mag. Our findings called for a revision of the distances measured with Cepheids in Riess et al. (2022). NGC 7250 and NGC 2525 needed better measurements with Cepheids. We have noticed that the Cepheids--based distance obtained with the {\it JWST} in Riess et al. (2024a) for NGC 5643 is in a a good agreement with what we find, unlike their previous estimate in Riess et al. (2022). We address the local SNe Ia distances as part of the Hubble tension problem. We expect to apply the 'twin' SNe Ia comparison from the local sample to galaxies with z $>$0.02--0.03 well into the Hubble flow to obtain a reliable value of H$_{0.}$, Comment: Astrophysical Journal in press (accepted 2024, 21 Aug), 40 pages, 14 Figures and 8 Tables. Version as in press except details of ApJ style

Type Ia supernovae (SNe Ia) were instrumental in establishing the acceleration of the universe's expansion. By virtue of their combination of distance reach, precision, and prevalence, they continue to provide key cosmological constraints, complementing other cosmological probes. Individual SN surveys cover only over about a factor of two in redshift, so compilations of multiple SN datasets are strongly beneficial. We assemble an up-to-date "Union" compilation of 2087 cosmologically useful SNe Ia from 24 datasets ("Union3"). We take care to put all SNe on the same distance scale and update the light-curve fitting with SALT3 to use the full rest-frame optical. Over the next few years, the number of cosmologically useful SNe Ia will increase by more than a factor of ten, and keeping systematic uncertainties subdominant will be more challenging than ever. We discuss the importance of treating outliers, selection effects, light-curve shape and color populations and standardization relations, unexplained dispersion, and heterogeneous observations simultaneously. We present an updated Bayesian framework, called UNITY1.5 (Unified Nonlinear Inference for Type-Ia cosmologY), that incorporates significant improvements in our ability to model selection effects, standardization, and systematic uncertainties compared to earlier analyses. As an analysis byproduct, we also recover the posterior of the SN-only peculiar-velocity field, although we do not interpret it in this work. We compute updated cosmological constraints with Union3 and UNITY1.5, finding weak 1.7--2.6 sigma tension with LambdaCDM and possible evidence for thawing dark energy (w0 > -1, wa < 0). We release our SN distances, light-curve fits, and UNITY1.5 framework to the community., Comment: Under review at ApJ, 12 new figures, no changes to cosmological results

At the 450 yr anniversary of its observation,the supernova named after Tycho Brahe, SN 1572, can be explained in the terms used nowadays to characterize Type Ia supernovae (SNe Ia). By assembling the records of the observations made in 1572--74 and evaluating their uncertainties, it is possible to recover the light curve and the color evolution of this supernova. It is found that, within the SNe Ia family, the event should have been a SN Ia with a normal rate of decline. Concerning the color evolution of SNe Ia, the most recently recovered records reaffirm previous findings of its being a normal SN Ia. The abundance studies from X--ray spectroscopy of the whole remnant point to a nuclear burning of the kind of a delayed detonation explosion of a Chandrasekhar--mass white dwarf. A tentative single degenerate path to explosion was suggested from the exploration of the stars in the field in SN 1572. Though, the origin in a double degenerate is being considered as well. Tycho Brahe's supernova, being the first supernova studied by astronomers, is still the subject of very intensive debates nowadays., Comment: 26 pages, 11 Figures. As published in''Supernovae since Tycho Brahe: Celebrating the 450th Anniversary of De Nova Stella'' . Research Topic in Frontiers in Astronomy and Space Sciences. Frontiers n Astronomy and Space Sciences, vol. 10, id. 1112880 (published March 2023)

We use the {\it Gaia} EDR3 to explore the Galactic supernova remnant SNR G272.2-3.2, produced by the explosion of a Type Ia supernova (SNIa), about 7,500 years ago, to search for a surviving companion. From the abundances in the SNR ejecta, G272.2-3.2 is a normal SN Ia. The {\it Gaia} parallaxes allow to select the stars located within the estimated distance range of the SNR, and the {\it Gaia} proper motions to study their kinematics. From the {\it Gaia} EDR3 photometry, we construct the HR diagram of the selected sample, which we compare with the theoretical predictions for the evolution of possible star companions of SNIa. We can discard several proposed types of companions by combining kinematics and photometry. We can also discard hypervelocity stars. We focus our study on the kinematically most peculiar star, {\it Gaia} EDR3 5323900215411075328 (hereafter MV-G272), a 8.9 $\sigma$ outlier in proper motion. It is of M1-M2 stellar type. Its trajectory on the sky locates it at the center of the SNR, 6,000--8,000 years ago, a unique characteristic among the the sample. Spectra allow a stellar parameters determination and a chemical abundance analysis. In conclusion, we have a candidate to be the surviving companion of the SN Ia that resulted in SNR G272.2-3.2. It is supported by its kinematical characteristics and its trajectory within the SNR. This opens the possibility of a single-degenerate scenario for a SN Ia with an M-type dwarf companion., Comment: 35 pages, 19 Figures, 5 Tables, published as ApJ 947, 90R

In this Letter, we report the discovery of an ultraluminous fast-evolving transient in rest-frame UV wavelengths, MUSSES2020J, soon after its occurrence by using the Hyper Suprime-Cam (HSC) mounted on the 8.2 m Subaru telescope. The rise time of about 5 days with an extremely high UV peak luminosity shares similarities to a handful of fast blue optical transients whose peak luminosities are comparable with the most luminous supernovae while their timescales are significantly shorter (hereafter "fast blue ultraluminous transient," FBUT). In addition, MUSSES2020J is located near the center of a normal low-mass galaxy at a redshift of 1.063, suggesting a possible connection between the energy source of MUSSES2020J and the central part of the host galaxy. Possible physical mechanisms powering this extreme transient such as a wind-driven tidal disruption event and an interaction between supernova and circumstellar material are qualitatively discussed based on the first multiband early-phase light curve of FBUTs, although whether the scenarios can quantitatively explain the early photometric behavior of MUSSES2020J requires systematical theoretical investigations. Thanks to the ultrahigh luminosity in UV and blue optical wavelengths of these extreme transients, a promising number of FBUTs from the local to the high-z universe can be discovered through deep wide-field optical surveys in the near future., Comment: 14 pages, 5 figures, accepted for publication in The Astrophysical Journal Letters

In order to investigate the origin of the ongoing tension between the amplitude of matter fluctuations measured by weak lensing experiments at low redshifts and the value inferred from the cosmic microwave background anisotropies, we reconstruct the evolution of this amplitude from $z\sim2$ using existing large-scale structure data. To do so, we decouple the linear growth of density inhomogeneities from the background expansion, and constrain its redshift dependence making use of a combination of 6 different data sets, including cosmic shear, galaxy clustering and CMB lensing. We analyze these data under a consistent harmonic-space angular power spectrum-based pipeline. We show that current data constrain the amplitude of fluctuations mostly in the range $0.2

The See Change survey was designed to make $z>1$ cosmological measurements by efficiently discovering high-redshift Type Ia supernovae (SNe Ia) and improving cluster mass measurements through weak lensing. This survey observed twelve galaxy clusters with the Hubble Space Telescope spanning the redshift range $z=1.13$ to $1.75$, discovering 57 likely transients and 27 likely SNe Ia at $z\sim 0.8-2.3$. As in similar previous surveys (Dawson et al. 2009), this proved to be a highly efficient use of HST for SN observations; the See Change survey additionally tested the feasibility of maintaining, or further increasing, the efficiency at yet higher redshifts, where we have less detailed information on the expected cluster masses and star-formation rates. We find that the resulting number of SNe Ia per orbit is a factor of $\sim 8$ higher than for a field search, and 45% of our orbits contained an active SN Ia within 22 rest-frame days of peak, with one of the clusters by itself yielding 6 of the SNe Ia. We present the survey design, pipeline, and SN discoveries. Novel features include fully blinded SN searches, the first random forest candidate classifier for undersampled IR data (with a 50% detection threshold within 0.05 magnitudes of human searchers), real-time forward-modeling photometry of candidates, and semi-automated photometric classifications and follow-up forecasts. We also describe the spectroscopic follow-up, instrumental in measuring host-galaxy redshifts. The cosmology analysis of our sample will be presented in a companion paper., Comment: ApJ preprint

The recent detection of the gravitational wave event GW170817, produced by the coalescence of two neutron stars, and of its optical-infrared counterpart, powered by the radioactive decay of r-process elements, has opened a new window to gamma-ray astronomy: the direct detection of photons coming from such decays. Here we calculate the contribution of kilonovae to the diffuse gamma-ray background in the MeV range, using recent results on the spectra of the gamma-rays emitted in individual events, and we compare it with that from other sources. We find that the contribution from kilonovae is not dominant in such energy range, but within current uncertainties, its addition to other sources might help to fit the observational data., Comment: Emulated ApJ, 9 Figures (accepted for publication in ApJ)

The Hubble Space Telescope has produced astonishing science over the past thirty years. Hubble's productivity can continue to soar for years to come provided some worn out components get upgraded. While powerful new ground-based and space telescopes are expected to come online over the next decade, none of them will have the UV capabilities that make Hubble a unique observatory. Without Hubble, progress in UV and blue optical astrophysics will be halted. Observations at these wavelengths are key for a range of unresolved astrophysics questions, ranging from the characterization of solar system planets to understanding interaction of galaxies with the intergalactic medium and the formation history of the universe. Hubble will remain our only source of high-angular resolution UV imaging and high-sensitivity UV spectroscopy for the next two decades, offering the ability for continued unique science and maximizing the science return from complementary observatories. Therefore, we recommend that NASA, ESA, and the private sector study the scientific merit, technical feasibility, and risk of a new servicing mission to Hubble to boost its orbit, fix aging components, and expand its instrumentation. Doing so would: 1) keep Hubble on its path to reach its unmet full potential, 2) extend the mission's lifetime past the next decade, which will maximize the synergy of Hubble with other upcoming facilities, and 3) enable and enhance the continuation of scientific discoveries in UV and optical astrophysics., Comment: White Paper submitted to the NAS call for Astro2020 Decadal Survey APC papers

The $\alpha$-attractor inflationary models are nowadays favored by CMB Planck observations. Their similarity with canonical quintessence models motivates the exploration of a common framework that explains both inflation and dark energy. We study the expected constraints that next-generation cosmological experiments will be able to impose for the dark energy $\alpha$-attractor model. We systematically account for the constraining power of SNIa from WFIRST, BAO from DESI and WFIRST, galaxy clustering and shear from LSST and Stage-4 CMB experiments. We assume a tensor-to-scalar ratio, $10^{-3} < r < 10^{-2}$, which permits to explore the wide regime sufficiently close, but distinct, to a cosmological constant, without need of fine tunning the initial value of the field. We find that the combination S4CMB + LSST + SNIa will achieve the best results, improving the FoM by almost an order of magnitude; respect to the S4CMB + BAO + SNIa case. We find this is also true for the FoM of the $w_0 - w_a$ parameters. Therefore, future surveys will be uniquely able to probe models connecting early and late cosmic acceleration., Comment: V1: 22 pages, 10 figures, comments welcome; V2: minor changes, accepted for publication in JCAP

We review the theoretical background and the observational searches made for surviving companions of Type Ia supernovae (SNe Ia). Theory comprises the characteristics of the stellar binary companions of the exploding white dwarfs at the time of the supernova outburst and the expected effects on them of the explosion, as well as their subsequent evolution. That includes space velocities, rotation, luminosities (with discussion of possible mechanisms producing very faint companions) . We then present the searches already made in the Galactic remnants of Type Ia supernovae and we assess the results obtained up to now using ground--based telescopes and the {\it Hubble Space Telescope} ({\it HST}). The same is done for the remnants of this type in the Large Magellanic Cloud. We point to new SNRs of Type Ia that can be studied with groundbased telescopes,the {\it HST} and the {\it James Webb Space Telescope} ({\it JWST}), using various approaches such as characterization of peculiar stars through color--magnitude diagrams, determination of their stellar parameters by spectral fitting, and astrometric measurements. {\it Gaia} can provide, as well, useful astrometric information. Most of these approaches have been used in the SNe Ia remnants already explored. The future goal is to enlarge the sample to determine which stellar systems do actually produce these explosions., Comment: 80 pages, 17 Figures, 3 Tables. Accepted as invited review to New Astronomy Reviews. Final version

SN 1572 (Tycho Brahe's supernova) clearly belongs to the Ia (thermonuclear) type. It was produced by the explosion of a white dwarf in a binary system. Its remnant has been the first of this type to be explored in search of a possible surviving companion, the mass donor that brought the white dwarf to the point of explosion. A high peculiar motion with respect to the stars at the same location in the Galaxy, mainly due to the orbital velocity at the time of the explosion, is a basic criterion for the detection of such companions. Radial velocities from the spectra of the stars close to the geometrical center of Tycho's supernova remnant, plus proper motions of the same stars, obtained by astrometry with the {\it Hubble Space Telescope}, have been used so far. In addition, a detailed chemical analysis of the atmospheres of a sample of candidate stars had been made. However, the distances to the stars, remained uncertain. Now, the Second {\it Gaia} Data Release (DR2) provides unprecedent accurate distances and new proper motions for the stars can be compared with those made from the {\it HST}. We consider the Galactic orbits that the candidate stars to SN companion would have in the future. We do this to explore kinematic peculiarity. We also locate a representative sample of candidate stars in the Toomre diagram. Using the new data, we reevaluate here the status of the candidates suggested thus far, as well as the larger sample of the stars seen in the central region of the remnant., Comment: Accepted by ApJ, emulated ApJ version, 5 tables, 6 figures

The possibility of linking inflation and late cosmic accelerated expansion using the $\alpha$-attractor models has received increasing attention due to their physical motivation. In the early universe, $\alpha$-attractors provide an inflationary mechanism compatible with Planck satellite CMB observations and predictive for future gravitational wave CMB modes. Additionally $\alpha$-attractors can be written as quintessence models with a potential that connects a power law regime with a plateau or uplifted exponential, allowing a late cosmic accelerated expansion that can mimic behavior near a cosmological constant. In this paper we study a generalized dark energy $\alpha$-attractor model. We thoroughly investigate its phenomenology, including the role of all model parameters and the possibility of large-scale tachyonic instability clustering. We verify the relation that $1+w\sim 1/\alpha$ (while the gravitational wave power $r\sim\alpha$) so these models predict that a signature should appear in either the primordial B-modes or in late time deviation from a cosmological constant. We constrain the model parameters with current datasets, including the cosmic microwave background (Planck 2015 angular power spectrum, polarization and lensing), baryon acoustic oscillations (BOSS DR12) and supernovae (Pantheon compressed). Our results show that expansion histories close to a cosmological constant exist in large regions of the parameter space, not requiring a fine-tuning of the parameters or initial conditions., Comment: V1: 23 pages, 14 figures, comments welcome. V2: 23 pages, 14 figures, added some minor corrections and a major modification: used the Full Planck Likelihood instead of the compressed one. This version is accepted for publication in JCAP

We have surveyed Kepler's supernova remnant in search of the companion star of the explosion. We have gone as deep as 2.6 solar luminosities in the stars within 20% of the radius of the remnant. We use FLAMES at the VLT-UT2 telescope to obtain high resolution spectra of the stellar candidates selected from HST images. The resulting set of stellar parameters suggests that these stars come from a rather ordinary mixture of field stars (mostly giants). A few of the stars seem to have low [Fe/H] (< -1) and they are consistent with being metal-poor giants. The radial velocities and rotational velocities vrot sin i are very well determined. There are no fast rotating stars as vrot sin i < 20 km/s. The radial velocities from the spectra and the proper motions determined from HST images are compatible with those expected from the Besan\c{c}on model of the Galaxy. The strong limits placed on luminosity suggest that this supernova could have arisen either from the core-degenerate scenario or from the double-degenerate scenario., Comment: ApJ accepted, 7 figures and 7 tables

Type Ia supernovae (SNe Ia) arise from the thermonuclear explosion of carbon-oxygen white dwarfs. Though the uniformity of their light curves makes them powerful cosmological distance indicators, long-standing issues remain regarding their progenitors and explosion mechanisms. Recent detection of the early ultraviolet pulse of a peculiar subluminous SN Ia has been claimed as new evidence for the companion-ejecta interaction through the single-degenerate channel. Here, we report the discovery of a prominent but red optical flash at $\sim$ 0.5 days after the explosion of a SN Ia which shows hybrid features of different SN Ia sub-classes: a light curve typical of normal-brightness SNe Ia, but with strong titanium absorptions, commonly seen in the spectra of subluminous ones. We argue that the early flash of such a hybrid SN Ia is different from predictions of previously suggested scenarios such as the companion-ejecta interaction. Instead it can be naturally explained by a SN explosion triggered by a detonation of a thin helium shell either on a near-Chandrasekhar-mass white dwarf ($\gtrsim$ 1.3 M$_{\odot}$) with low-yield $^{56}$Ni or on a sub-Chandrasekhar-mass white dwarf ($\sim$ 1.0 M$_{\odot}$) merging with a less massive white dwarf. This finding provides compelling evidence that one branch of the previously proposed explosion models, the helium-ignition scenario, does exist in nature, and such a scenario may account for explosions of white dwarfs in a wider mass range in contrast to what was previously supposed., Comment: Accepted for publication in Nature on August 9, 2017 (the original version was submitted on May 3, 2017)

We present the discovery and measurements of a gravitationally lensed supernova (SN) behind the galaxy cluster MOO J1014+0038. Based on multi-band Hubble Space Telescope and Very Large Telescope (VLT) photometry of the supernova, and VLT spectroscopy of the host galaxy, we find a 97.5% probability that this SN is a SN Ia, and a 2.5% chance of a CC SN. Our typing algorithm combines the shape and color of the light curve with the expected rates of each SN type in the host galaxy. With a redshift of 2.2216, this is the highest redshift SN Ia discovered with a spectroscopic host-galaxy redshift. A further distinguishing feature is that the lensing cluster, at redshift 1.23, is the most distant to date to have an amplified SN. The SN lies in the middle of the color and light-curve shape distributions found at lower redshift, disfavoring strong evolution to z = 2.22. We estimate an amplification due to gravitational lensing of 2.8+0.6-0.5 (1.10 +- 0.23 mag)---compatible with the value estimated from the weak-lensing-derived mass and the mass-concentration relation from LambdaCDM simulations---making it the most amplified SN Ia discovered behind a galaxy cluster., Comment: Accepted for publication in ApJ

We study the light curve of SN 1604 using the historical data collected at the time of observation of the outburst. Comparing the supernova with recent SNe Ia of various rates of decline after maximum light, we find that this event looks like a normal SNIa (stretch s close to 0.9: 0.9 \pm 0.13), a fact which is also favoured by the late light curve. The supernova is heavily obscured by 2.7 \pm 0.1 magnitudes in V. We obtain an estimate of the distance to the explosion with a value of d = 5 \pm 0.7 kpc. This can help to settle ongoing discussions on the distance to the supernova. It also shows that this supernova is of the same kind as those of the SNIa sets that we use for cosmology nowadays., Comment: 22 pages, 2 figures, 3 tables; submitted to the ApJ; comments welcome

We present charm (cosmic history agnostic reconstruction method), a novel inference algorithm that reconstructs the cosmic expansion history as encoded in the Hubble parameter $H(z)$ from SNe Ia data. The novelty of the approach lies in the usage of information field theory, a statistical field theory that is very well suited for the construction of optimal signal recovery algorithms. The charm algorithm infers non-parametrically $s(a)=\ln(\rho(a)/\rho_{\mathrm{crit}0})$, the density evolution which determines $H(z)$, without assuming an analytical form of $\rho(a)$ but only its smoothness with the scale factor $a=(1+z)^{-1}$. The inference problem of recovering the signal $s(a)$ from the data is formulated in a fully Bayesian way. In detail, we have rewritten the signal as the sum of a background cosmology and a perturbation. This allows us to determine the maximum a posteriory estimate of the signal by an iterative Wiener filter method. Applying charm to the Union2.1 supernova compilation, we have recovered a cosmic expansion history that is fully compatible with the standard $\Lambda$CDM cosmological expansion history with parameter values consistent with the results of the Planck mission.

We analyze a time series of optical spectra of SN~2014J from almost two weeks prior to maximum to nearly four months after maximum. We perform our analysis using the SYNOW code, which is well suited to track the distribution of the ions with velocity in the ejecta. We show that almost all of the spectral features during the entire epoch can be identified with permitted transitions of the common ions found in normal SNe Ia in agreement with previous studies. We show that 2014J is a relatively normal SN Ia. At early times the spectral features are dominated by Si II, S II, Mg II, and Ca II. These ions persist to maximum light with the appearance of Na I and Mg I. At later times iron-group elements also appear, as expected in the stratified abundance model of the formation of normal type Ia SNe. We do not find significant spectroscopic evidence for oxygen, until 100 days after maximum light. The +100 day identification of oxygen is tentative, and would imply significant mixing of unburned or only slight processed elements down to a velocity of 6,000 km/s. Our results are in relatively good agreement with other analyses in the IR. We briefly compare SN 2011fe to SN 2014J and conclude that the differences could be due to different central densities at ignition or differences in the C/O ratio of the progenitors., Comment: 13 pages, 6 figures, 4 tables, MNRAS, in press

There has been much debate about the origin of the diffuse $\gamma$--ray background in the MeV range. At lower energies, AGNs and Seyfert galaxies can explain the background, but not above $\simeq$0.3 MeV. Beyond $\sim$10 MeV blazars appear to account for the flux observed. That leaves an unexplained gap for which different candidates have been proposed, including annihilations of WIMPS. One candidate are Type Ia supernovae (SNe Ia). Early studies concluded that they were able to account for the $\gamma$--ray background in the gap, while later work attributed a significantly lower contribution to them. All those estimates were based on SN Ia explosion models which did not reflect the full 3D hydrodynamics of SNe Ia explosions. In addition, new measurements obtained since 2010 have provided new, direct estimates of high-z SNe Ia rates beyond $z\sim$2. We take into account these new advances to see the predicted contribution to the gamma--ray background. We use here a wide variety of explosion models and a plethora of new measurements of SNe Ia rates. SNe Ia still fall short of the observed background. Only for a fit, which would imply $\sim$150\% systematic error in detecting SNe Ia events, do the theoretical predictions approach the observed fluxes. This fit is, however, at odds at the highest redshifts with recent SN Ia rates estimates. Other astrophysical sources such as FSRQs do match the observed flux levels in the MeV regime, while SNe Ia make up to 30--50\% of the observed flux., Comment: 40 pages, 13 Figures, accepted to be published in ApJ

Although Type Ia supernovae (SNe Ia) are a major tool in cosmology and play a key role in the chemical evolution of galaxies, the nature of their progenitor systems (apart from the fact that they must contain at least one white dwarf, that explodes) remains largely unknown. In the last decade, considerable efforts have been made, both observationally and theoretically, to solve this problem. Observations have, however, revealed a previously unsuspected variety of events, ranging from very underluminous outbursts to clearly overluminous ones, and spanning a range well outside the peak luminosity--decline rate of the light curve relationship, used to make calibrated candles of the SNe Ia. On the theoretical side, new explosion scenarios, such as violent mergings of pairs of white dwarfs, have been explored. We review those recent developments, emphasizing the new observational findings, but also trying to tie them to the different scenarios and explosion mechanisms proposed thus far., Comment: 63 pages, 9 figures, final version to appear as an invited review in New Astronomy Reviews

Type Ia supernovae are thought to occur as a white dwarf made of carbon and oxygen accretes sufficient mass to trigger a thermonuclear explosion$^{1}$. The accretion could occur slowly from an unevolved (main-sequence) or evolved (subgiant or giant) star$^{2,3}$, that being dubbed the single-degenerate channel, or rapidly as it breaks up a smaller orbiting white dwarf (the double- degenerate channel)$^{3,4}$. Obviously, a companion will survive the explosion only in the single-degenerate channel$^{5}$. Both channels might contribute to the production of type Ia supernovae$^{6,7}$ but their relative proportions still remain a fundamental puzzle in astronomy. Previous searches for remnant companions have revealed one possible case for SN 1572$^{8,9}$, though that has been criticized$^{10}$. More recently, observations have restricted surviving companions to be small, main-sequence stars$^{11,12,13}$, ruling out giant companions, though still allowing the single-degenerate channel. Here we report the result of a search for surviving companions to the progenitor of SN 1006$^{14}$. None of the stars within 4' of the apparent site of the explosion is associated with the supernova remnant, so we can firmly exclude all giant and subgiant companions to the progenitor. Combined with the previous results, less than 20 per cent of type Iae occur through the single degenerate channel., Comment: Published as a letter in Nature (2012 September 27)

New constraints on inhomogeneous Lema\^itre-Tolman-Bondi (LTB) models alternative to Dark Energy are presented, focusing on adiabatic profiles with space-independent Big Bang and baryon fraction. The Baryon Acoustic Oscillation (BAO) scale at early times is computed in terms of the asymptotic value and then projected to different redshifts by following the geodesics of the background metric. Additionally, a model-independent method to constraint the local expansion rate using a prior on supernovae luminosity is presented. Cosmologies described by an adiabatic GBH matter profile with \Omega_{out}=1 and \Omega_{out}\leq 1 are investigated using a Markov Chain Monte Carlo analysis including the latest BAO data from the WiggleZ collaboration and the local expansion rate from the Hubble Space Telescope, together with Union-II type Ia supernovae data and the position and height of the Cosmic Microwave Background acoustic peaks. The addition of BAO data at higher redshifts increases considerably their constraining power and represents a new drawback for this type of models, yielding a value of the local density parameter \Omega_{in}>0.2 which is 3\sigma apart from the value \Omega_{in}<0.15 found using supernovae. The situation does not improve if the asymptotic flatness assumption is dropped, and a Bayesian analysis shows that constrained GBH models are ruled out at high confidence. We emphasize that these are purely geometric probes, that only recently have become sufficiently constraining to independently rule out the whole class of adiabatic LTB models., Comment: 37 pages, 12 figs

We present ultraviolet (UV) spectroscopy and photometry of four Type Ia supernovae (SNe 2004dt, 2004ef, 2005M, and 2005cf) obtained with the UV prism of the Advanced Camera for Surveys on the Hubble Space Telescope. This dataset provides unique spectral time series down to 2000 Angstrom. Significant diversity is seen in the near maximum-light spectra (~ 2000--3500 Angstrom) for this small sample. The corresponding photometric data, together with archival data from Swift Ultraviolet/Optical Telescope observations, provide further evidence of increased dispersion in the UV emission with respect to the optical. The peak luminosities measured in uvw1/F250W are found to correlate with the B-band light-curve shape parameter dm15(B), but with much larger scatter relative to the correlation in the broad-band B band (e.g., ~0.4 mag versus ~0.2 mag for those with 0.8 < dm15 < 1.7 mag). SN 2004dt is found as an outlier of this correlation (at > 3 sigma), being brighter than normal SNe Ia such as SN 2005cf by ~0.9 mag and ~2.0 mag in the uvw1/F250W and uvm2/F220W filters, respectively. We show that different progenitor metallicity or line-expansion velocities alone cannot explain such a large discrepancy. Viewing-angle effects, such as due to an asymmetric explosion, may have a significant influence on the flux emitted in the UV region. Detailed modeling is needed to disentangle and quantify the above effects., Comment: 17 pages, 13 figures, accepted by ApJ

We present an analysis of the chemical abundances of the star Tycho G in the direction of the remnant of supernova (SN) 1572, based on Keck high-resolution optical spectra. The stellar parameters of this star are found to be those of a G-type subgiant with $T_{\mathrm{eff}} = 5900 \pm 100$ K, \loggl $ = 3.85 \pm 0.30$ dex, and $\mathrm{[Fe/H]} = -0.05 \pm 0.09$. This determination agrees with the stellar parameters derived for the star in a previous survey for the possible companion star of SN 1572 (Ruiz-Lapuente et al. 2004). The chemical abundances follow the Galactic trends, except for Ni, which is overabundant relative to Fe, $[{\rm Ni/Fe}] $ $=$ 0.16 $\pm$ 0.04. Co is slightly overabundant (at a low significance level). These enhancements in Fe-peak elements could have originated from pollution by the supernova ejecta. We find a surprisingly high Li abundance for a star that has evolved away from the main sequence. We discuss these findings in the context of companion stars of supernovae., Comment: Accepted for publication in the Astrophysical Journal

We investigate the equation of state w(z) in a non-parametric form using the latest compilations of distance luminosity from SNe Ia at high z. We combine the inverse problem approach with a Monte Carlo to scan the space of priors. On the light of these high redshift supernova data sets, we reconstruct w(z). A comparison between a sample including the latest results at z>1 and a sample without those results show the improvement achieved by observations of very high z supernovae. We present the prospects to measure the variation of dark energy density along z by this method., Comment: 13 pages, 6 figures

The discovery of the acceleration of the rate of expansion of the Universe fosters new explorations of the behavior of gravitation theories in the cosmological context. Either the GR framework is valid but a cosmic component with a negative equation of state is dominating the energy--matter contents or the Universe is better described at large by a theory that departs from GR. In this review we address theoretical alternatives that have been explored through supernovae., Comment: Invited Topical Review (Class. Quan. Grav) 27 pages Journal link: http://stacks.iop.org/0264-9381/24/R91

A model--independent approach to dark energy is here developed by considering the determination of its equation of state as an inverse problem. The reconstruction of w(z) as a non--parametric function using the current SNe Ia data is explored. It is investigated as well how results would improve when considering other samples of cosmic distance indicators at higher redshift. This approach reveals the lack of information in the present samples to conclude on the behavior of w(z) at z > 0.6. At low level of significance a preference is found for w_{0} < -1 and w'(z) > 0 at z ~ 0.2--0.3. The solution of w(z) along redshift never departs more than 1.95\sigma from the cosmological constant w(z)=-1, and this only occurs when using various cosmic distance indicators. The determination of w(z) as a function is readdressed considering samples of large number of SNe Ia as those to be provided by SNAP. It is found an improvement in the resolution of w(z) when using those synthetic samples, which is favored by adding data at very high z. Though the set of degenerate solutions compatible with the data can be retrieved through this method, these degeneracies in the solution will difficult the physical interpretation of the results. Through this approach, we have explored as well the gain in information in w(z) and the quality of the inversion achieved using different data sets of cosmic distance indicators., Comment: 5 figures and 3 tables, submitted to PRD

The brightness of type Ia supernovae, and their homogeneity as a class, makes them powerful tools in cosmology, yet little is known about the progenitor systems of these explosions. They are thought to arise when a white dwarf accretes matter from a companion star, is compressed and undergoes a thermonuclear explosion Unless the companion star is another white dwarf (in which case it should be destroyed by the mass-transfer process itself), it should survive and show distinguishing properties. Tycho's supernova is one of the only two type Ia supernovae observed in our Galaxy, and so provides an opportunity to address observationally the identification of the surviving companion. Here we report a survey of the central region of its remnant, around the position of the explosion, which excludes red giants as the mass donor of the exploding white dwarf. We found a type G0--G2 star, similar to our Sun in surface temperature and luminosity (but lower surface gravity), moving at more than three times the mean velocity of the stars at that distance, which appears to be the surviving companion of the supernova., Comment: accepted by Natute (subject to embargo policy), 31 pages, 4 figures

Within the Quantum Field Theory context the idea of a "cosmological constant" (CC) evolving with time looks quite natural as it just reflects the change of the vacuum energy with the typical energy of the universe. In the particular frame of Ref.[30], a "running CC" at low energies may arise from generic quantum effects near the Planck scale, M_P, provided there is a smooth decoupling of all massive particles below M_P. In this work we further develop the cosmological consequences of a "running CC" by addressing the accelerated evolution of the universe within that model. The rate of change of the CC stays slow, without fine-tuning, and is comparable to H^2 M_P^2. It can be described by a single parameter, \nu, that can be determined from already planned experiments using SNe Ia at high z. The range of allowed values for \nu follow mainly from nucleosynthesis restrictions. Present samples of SNe Ia can not yet distinguish between a "constant" CC or a "running" one. The numerical simulations presented in this work show that SNAP can probe the predicted variation of the CC either ruling out this idea or confirming the evolution hereafter expected., Comment: LaTeX, 51 pages, 13 figures, 1 table, references added, typos corrected, version accepted in JCAP

The light curve of SN 1572 is described in the terms used nowadays to characterize SNeIa. By assembling the records of the observations done in 1572--74 and evaluating their uncertainties, it is possible to recover the light curve and the color evolution of this supernova. It is found that, within the SNe Ia family, the event should have been a SNIa with a normal rate of decline, its stretch factor being {\it s} $\sim$ 0.9. Visual light curve near maximum, late--time decline and the color evolution sustain this conclusion. After correcting for extinction, the luminosity of this supernova is found to be M$_{V}$ $=$ --19.58 --5 log (D/3.5 kpc) $\pm$ 0.42., Comment: 28 pages, 3 figures, 3 tables. submitted to ApJ (Main Journal)

We construct a semiclassical FLRW cosmological model assuming a running cosmological constant (CC). It turns out that the CC becomes variable at arbitrarily low energies due to the remnant quantum effects of the heaviest particles, e.g. the Planck scale physics. These effects are universal in the sense that they lead to a low-energy structure common to a large class of high-energy theories. Remarkably, the uncertainty concerning the unknown high-energy dynamics is accumulated into a single parameter \nu, such that the model has an essential predictive power. Future Type Ia supernovae experiments (like SNAP) can verify whether this framework is correct. For the flat FLRW case and a moderate value \nu ~0.01, we predict an increase of 10-20% in the value of Omega_{Lambda} at redshifts z=1-1.5 perfectly reachable by SNAP., Comment: Added one more figure, comments and references. Version accepted in Phys. Lett. B

We present U,B,V,R_C,and I_C photometry of the optical afterglow of the gamma-ray burst GRB 021004 taken at the Nordic Optical Telescope between approximately eight hours and 30 days after the burst. This data is combined with an analysis of the 87 ksec Chandra X-ray observations of GRB 021004 taken at a mean epoch of 33 hours after the burst to investigate the nature of this GRB. We find an intrinsic spectral slope at optical wavelengths of beta_UH = 0.39 +/- 0.12 and an X-ray slope of beta_X = 0.94 +/- 0.03. There is no evidence for colour evolution between 8.5 hours and 5.5 days after the burst. The optical decay becomes steeper approximately five days after the burst. This appears to be a gradual break due to the onset of sideways expansion in a collimated outflow. Our data suggest that the extra-galactic extinction along the line of sight to the burst is between A_V = 0.3 and A_V = 0.5 and has an extinction law similar to that of the Small Magellanic Cloud. The optical and X-ray data are consistent with a relativistic fireball with the shocked electrons being in the slow cooling regime and having an electron index of p = 1.9 +/- 0.1. The burst occurred in an ambient medium that is homogeneous on scales larger than approximately 10e18 cm but inhomogeneous on smaller scales. The mean particle density is similar to what is seen for other bursts (0.1 < n < 100 cm^{-3}). Our results support the idea that the brightening seen approximately 0.1 days was due to interaction with a clumpy ambient medium within 10^{17} and 10^{18} cm of the progenitor. The agreement between the predicted optical decay and that observed approximately ten minutes after the burst suggests that the physical mechanism controlling the observed flux approximately ten minutes is the same as the one operating at t > 0.5 days., Comment: 21 pages with five figures. Uses AASTEX 5.02. To appear in AJ. Minor typographical and grammatical corrections

We have applied two different automatic classifier algorithms to the BATSE Current GRB Catalog data and we obtain three different classes of GRBs. Our results confirm the existence of a third, intermediate class of GRBs, with mean duration \sim 25-50 s, as deduced from a cluster analysis and from a neural network algorithm. Our analyses imply longer durations than those found by Mukherjee et al. (1998) and Horvath (1998), whose intermediate class had durations \sim 2-10 s. From the neural network analysis no difference in hardness between the two longest classes is found, and from both methods we find that the intermediate-duration class constitutes the most homogeneous sample of GRBs in its space distribution while the longest-duration class constitutes the most inhomogeneous one with \sim 0.1, being thus the deepest population of GRBs with z_max \sim 10. The trend previously found in long bursts, of spatial inhomogeneity increasing with hardness, only holds for this new longest-duration class., Comment: 8 pages, 11 figures, to appear in MNRAS

The subject of late-time emission of Type Ia supernovae and its implications for the understanding of the explosions of C+O WDs is reviewed., Comment: 24 pages, including 7 figures. uuencoded, gzipped ps file. Lecture given at the NATO ASI on Thermonuclear Supernovae (Aiguablava, Spain: June 20-30 1995). To appear in "Thermonuclear Supernovae", ed. R. Canal & P. Ruiz-Lapuente (Dordrecht: Kluwer)

Type Ia supernovae (SNe Ia), produced by the thermonuclear explosion of white dwarf (WD) stars, are used here to derive extragalactic distances and an estimate of the Hubble constant from their emission signatures at late phases ({\it Nebular SNe Ia Method}, NSM). The method, first developed in Ruiz--Lapuente \& Lucy (1992), makes use here of an improved modeling of the forbidden line emission at late phases. Hydrodynamic models of the explosion of WDs of different masses, both sub--Chandrasekhar and Chandrasekhar, provide the basis for comparison with the observations. It is shown that it is possible to probe the overall density structure of the ejecta and the mass of the exploding WD by the effect that the electron density profile has in shaping the forbidden line emission of the iron ions, and that a robust diagnostic of the mass of the exploding WD can be obtained. Cosmic distance scale can thus be related to basic diagnostics of excitation of iron lines. Once the most adequate model is selected, comparison of the predicted line emission at these phases with the observed spectra gives an internal estimate of both the reddening and the distance to the SNe Ia. The results presented here favor denser models than those corresponding to sub--Chandrasekhar explosions. From a sample of seven SNe Ia in Leo, Virgo, Fornax and beyond, a value of the Hubble constant $H_{0} = 68 \ \pm 6\ (stat) \pm 7\ (syst)\ km\ s^{-1}\ Mpc^{-1}$ is derived. The depth of the Virgo cluster is found to be large, ranging from 13 to 23 Mpc at least. If NGC 4526 traces well the core of the Virgo Cluster, then the latter is located at $16\pm 2 \ Mpc$. The galaxy NGC 3267 in Leo appears to be located at 9.8 $\pm$ 1.5 Mpc., Comment: 17 pages, including 2 figures. uuencoded, gzipped ps file. Submitted to the ApJ (Letters)

We have obtained photometry and spectra of SN~1991T which extend more than 1000 days past maximum light, by far the longest a SN~Ia has been followed. Although SN~1991T exhibited nearly normal photometric behavior in the first 400 days following maximum, by 600 days its decline had slowed, and by 950~days the supernova brightness was consistent with a constant apparent magnitude of $m_B=21.30$. Spectra near maximum showed minor variations on the SN~Ia theme which grew less conspicuous during the exponential decline. At 270 days the nebular spectrum was composed of Fe and Co lines common to SNe~Ia. However, by 750 days past maximum light, these lines had shifted in wavelength, and were superimposed on a strong blue continuum. The luminosity of SN~1991T at 950 days is more than $9.0\times10^{38}(D/13~{\rm Mpc})^2$~ergs~s$^{-1}$ with a rate of decline of less than $0.04$ mags/100~days. We show that this emission is likely to be light that was emitted by SN~1991T near maximum light which has reflected from foreground dust, much like the light echos observed around SN~1987A., Comment: 15 pages (includes figures and tables) uuencoded compressed postscript, CfA Preprint - To Appear in ApJL