arXiv subjects

S. Mattila

Publications and source records attributed to S. Mattila.

At least 145 records · Page 8Linked to original sources

arXiv2015

PESSTO : survey description and products from the first data release by the Public ESO Spectroscopic Survey of Transient Objects

The Public European Southern Observatory Spectroscopic Survey of Transient Objects (PESSTO) began as a public spectroscopic survey in April 2012. We describe the data reduction strategy and data products which are publicly available through the ESO archive as the Spectroscopic Survey Data Release 1 (SSDR1). PESSTO uses the New Technology Telescope with EFOSC2 and SOFI to provide optical and NIR spectroscopy and imaging. We target supernovae and optical transients brighter than 20.5mag for classification. Science targets are then selected for follow-up based on the PESSTO science goal of extending knowledge of the extremes of the supernova population. The EFOSC2 spectra cover 3345-9995A (at resolutions of 13-18 Angs) and SOFI spectra cover 0.935-2.53 micron (resolutions 23-33 Angs) along with JHK imaging. This data release contains spectra from the first year (April 2012 - 2013), consisting of all 814 EFOSC2 spectra and 95 SOFI spectra (covering 298 distinct objects), in standard ESO Phase 3 format. We estimate the accuracy of the absolute flux calibrations for EFOSC2 to be typically 15%, and the relative flux calibration accuracy to be about 5%. The PESSTO standard NIR reduction process does not yet produce high accuracy absolute spectrophotometry but the SOFI JHK imaging will improve this. Future data releases will focus on improving the automated flux calibration of the data products.

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arXiv2015

Selecting superluminous supernovae in faint galaxies from the first year of the Pan-STARRS1 Medium Deep Survey

The Pan-STARRS1 (PS1) survey has obtained imaging in 5 bands (grizy_P1) over 10 Medium Deep Survey (MDS) fields covering a total of 70 square degrees. This paper describes the search for apparently hostless supernovae (SNe) within the first year of PS1 MDS data with an aim of discovering new superluminous supernovae (SLSNe). A total of 249 hostless transients were discovered down to a limiting magnitude of M_AB ~ 23.5, of which 76 were classified as Type Ia SNe. There were 57 SNe with complete light curves that are likely core-collapse SNe (CCSNe) or SLSNe and 12 of these have had spectra taken. Of these 12 hostless, non-Type Ia SNe, 7 were SLSNe of Type Ic at redshifts between 0.5-1.4. This illustrates that the discovery rate of Type Ic SLSNe can be maximised by concentrating on hostless transients and removing normal SNe Ia. We present data for two new possible SLSNe; PS1-10pm (z = 1.206) and PS1-10ahf (z = 1.1), and estimate the rate of SLSNe-Ic to be between 3^{+3}_{-2} * 10^{-5} and 8^{+2}_{-1} * 10^{-5} of the CCSNe rate within 0.3 <= z <= 1.4 by applying a Monte-Carlo technique. The rate of slowly evolving, SN2007bi-like explosions is estimated as a factor of 10 lower than this range.

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arXiv2015

Core-collapse and Type Ia supernovae with the SKA

Core-collapse SNe (CCSNe): Systematic searches of radio emission from CCSNe are still lacking, and only targeted searches of radio emission from just some of the optically discovered CCSNe in the local universe have been carried out. Optical searches miss a significant fraction of CCSNe due to dust obscuration; CCSN radio searches are thus more promising for yielding the complete, unobscured star-formation rates in the local universe. The SKA yields the possibility to piggyback for free in this area of research by carrying out commensal, wide-field, blind transient survey observations. SKA1-SUR should be able to discover several hundreds of CCSNe in just one year, compared to about a dozen CCSNe that the VLASS would be able to detect in one year, at most. SKA, with an expected sensitivity ten times that of SKA1, is expected to detect CCSNe in the local Universe by the thousands. Therefore, commensal SKA observations could easily result in an essentially complete census of all CCSNe in the local universe, thus yielding an accurate determination of the volumetric CCSN rate. Type Ia SNe: We advocate for the use of the SKA to search for the putative prompt (~first few days after the explosion) radio emission of any nearby type Ia SN, via target-of-opportunity observations. The huge improvement in sensitivity of the SKA with respect to its predecessors will allow to unambiguously discern which progenitor scenario (single-degenerate vs. double-degenerate) applies to them.

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arXiv2015

Towards Characterization of the Type IIP Supernova Progenitor Population: a Statistical Sample of Light Curves from Pan-STARRS1

In recent years, wide-field sky surveys providing deep multi-band imaging have presented a new path for indirectly characterizing the progenitor populations of core-collapse supernovae (SN): systematic light curve studies. We assemble a set of 76 grizy-band Type IIP SN light curves from Pan-STARRS1, obtained over a constant survey program of 4 years and classified using both spectroscopy and machine learning-based photometric techniques. We develop and apply a new Bayesian model for the full multi-band evolution of each light curve in the sample. We find no evidence of a sub-population of fast-declining explosions (historically referred to as "Type IIL" SNe). However, we identify a highly significant relation between the plateau phase decay rate and peak luminosity among our SNe IIP. These results argue in favor of a single parameter, likely determined by initial stellar mass, predominantly controlling the explosions of red supergiants. This relation could also be applied for supernova cosmology, offering a standardizable candle good to an intrinsic scatter of 0.2 mag. We compare each light curve to physical models from hydrodynamic simulations to estimate progenitor initial masses and other properties of the Pan-STARRS1 Type IIP SN sample. We show that correction of systematic discrepancies between modeled and observed SN IIP light curve properties and an expanded grid of progenitor properties, are needed to enable robust progenitor inferences from multi-band light curve samples of this kind. This work will serve as a pathfinder for photometric studies of core-collapse SNe to be conducted through future wide field transient searches.

astro-ph.HE↗

arXiv2014

SN 2005at - A neglected type Ic supernova at 10 Mpc

We present a photometric and spectroscopic study of a reddened type Ic supernova (SN) 2005at. We report our results based on the available data of SN 2005at, including late-time observations from the Spitzer Space Telescope and the Hubble Space Telescope. In particular, late-time mid-infrared observations are something rare for type Ib/c SNe. In our study we find SN 2005at to be very similar photometrically and spectroscopically to another nearby type Ic SN 2007gr, underlining the prototypical nature of this well-followed type Ic event. The spectroscopy of both events shows similar narrow spectral line features. The radio observations of SN 2005at are consistent with fast evolution and low luminosity at radio wavelengths. The late-time Spitzer data suggest the presence of an unresolved light echo from interstellar dust and dust formation in the ejecta, both of which are unique observations for a type Ic SN. The late-time Hubble observations reveal a faint point source coincident with SN 2005at, which is very likely either a declining light echo of the SN or a compact cluster. For completeness we study ground-based pre-explosion archival images of the explosion site of SN 2005at, however this only yielded very shallow upper limits for the SN progenitor star. We derive a host galaxy extinction of $A_{V} \approx 1.9$ mag for SN 2005at, which is relatively high for a SN in a normal spiral galaxy not viewed edge-on.

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arXiv2014

Extending the supernova Hubble diagram to z~1.5 with the Euclid space mission

We forecast dark energy constraints that could be obtained from a new large sample of Type Ia supernovae where those at high redshift are acquired with the Euclid space mission. We simulate a three-prong SN survey: a z<0.35 nearby sample (8000 SNe), a 0.2<z<0.95 intermediate sample (8800 SNe), and a 0.75<z<1.55 high-z sample (1700 SNe). The nearby and intermediate surveys are assumed to be conducted from the ground, while the high-z is a joint ground- and space-based survey. This latter survey, the "Dark Energy Supernova Infra-Red Experiment" (DESIRE), is designed to fit within 6 months of Euclid observing time, with a dedicated observing program. We simulate the SN events as they would be observed in rolling-search mode by the various instruments, and derive the quality of expected cosmological constraints. We account for known systematic uncertainties, in particular calibration uncertainties including their contribution through the training of the supernova model used to fit the supernovae light curves. Using conservative assumptions and a 1-D geometric Planck prior, we find that the ensemble of surveys would yield competitive constraints: a constant equation of state parameter can be constrained to sigma(w)=0.022, and a Dark Energy Task Force figure of merit of 203 is found for a two-parameter equation of state. Our simulations thus indicate that Euclid can bring a significant contribution to a purely geometrical cosmology constraint by extending a high-quality SN Hubble diagram to z~1.5. We also present other science topics enabled by the DESIRE Euclid observations

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arXiv2014

Rapidly-Evolving and Luminous Transients from Pan-STARRS1

In the past decade, several rapidly-evolving transients have been discovered whose timescales and luminosities are not easily explained by traditional supernovae (SN) models. The sample size of these objects has remained small due, at least in part, to the challenge of detecting short timescale transients with traditional survey cadences. Here we present the results from a search within the Pan-STARRS1 Medium Deep Survey (PS1-MDS) for rapidly-evolving and luminous transients. We identify 10 new transients with a time above half-maximum of less than 12 days and -16.5 > M > -20 mag. This increases the number of known events in this region of SN phase space by roughly a factor of three. The median redshift of the PS1-MDS sample is z=0.275 and they all exploded in star forming galaxies. In general, the transients possess faster rise than decline timescale and blue colors at maximum light (g - r < -0.2). Best fit blackbodies reveal photospheric temperatures/radii that expand/cool with time and explosion spectra taken near maximum light are dominated by a blue continuum, consistent with a hot, optically thick, ejecta. We find it difficult to reconcile the short timescale, high peak luminosity (L > 10^43 erg/s), and lack of UV line blanketing observed in many of these transients with an explosion powered mainly by the radioactive decay of Ni-56. Rather, we find that many are consistent with either (1) cooling envelope emission from the explosion of a star with a low-mass extended envelope which ejected very little (<0.03 M_sun) radioactive material, or (2) a shock breakout within a dense, optically thick, wind surrounding the progenitor star. After calculating the detection efficiency for objects with rapid timescales in the PS1-MDS we find a volumetric rate of 4800 - 8000 events/yr/Gpc^3 (4-7% of the core-collapse SN rate at z=0.2).

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arXiv2014

Super-luminous supernovae from PESSTO

We present optical spectra and light curves for three hydrogen-poor super-luminous supernovae followed by the Public ESO Spectroscopic Survey of Transient Objects (PESSTO). Time series spectroscopy from a few days after maximum light to 100 days later shows them to be fairly typical of this class, with spectra dominated by Ca II, Mg II, Fe II and Si II, which evolve slowly over most of the post-peak photospheric phase. We determine bolometric light curves and apply simple fitting tools, based on the diffusion of energy input by magnetar spin-down, 56Ni decay, and collision of the ejecta with an opaque circumstellar shell. We investigate how the heterogeneous light curves of our sample (combined with others from the literature) can help to constrain the possible mechanisms behind these events. We have followed these events to beyond 100-200 days after peak, to disentangle host galaxy light from fading supernova flux and to differentiate between the models, which predict diverse behaviour at this phase. Models powered by radioactivity require unrealistic parameters to reproduce the observed light curves, as found by previous studies. Both magnetar heating and circumstellar interaction still appear to be viable candidates. A large diversity is emerging in observed tail-phase luminosities, with magnetar models failing in some cases to predict the rapid drop in flux. This would suggest either that magnetars are not responsible, or that the X-ray flux from the magnetar wind is not fully trapped. The light curve of one object shows a distinct re-brightening at around 100d after maximum light. We argue that this could result either from multiple shells of circumstellar material, or from a magnetar ionisation front breaking out of the ejecta.

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arXiv2014

The nature of supernovae 2010O and 2010P in Arp 299 - I. Near-infrared and optical evolution

We present near-infrared and optical photometry, plus optical spectroscopy of two stripped-envelope supernovae (SNe) 2010O and 2010P that exploded in two different components of an interacting luminous infrared galaxy Arp 299 within only a few days of one another. SN 2010O is found to be photometrically and spectroscopically similar to many normal Type Ib SNe and our multiwavelength observations of SN 2010P suggest it to be a Type IIb SN. No signs of clear hydrogen features or interaction with the circumstellar medium are evident in the optical spectrum of SN 2010P. We derive estimates for the host galaxy line-of-sight extinctions for both SNe, based on both light-curve and spectroscopic comparison finding consistent results. These methods are also found to provide much more robust estimates of the SN host galaxy reddening than the commonly used empirical relations between extinction and equivalent width of Na I D absorption features. The SN observations also suggest that different extinction laws are present in different components of Arp 299. For completeness, we study high-resolution pre-explosion images of Arp 299 and find both SNe to be close to, but not coincident with, extended sources that are likely massive clusters. A very simple model applied to the bolometric light curve of SN 2010O implies a rough estimate for the explosion parameters of $E_{\mathrm{k}} \approx 3 \times 10^{51}$ erg, $M_{\mathrm{ej}} \approx 2.9$ M$_{\odot}$ and $M_{\mathrm{Ni}} \approx 0.16$ M$_{\odot}$.

astro-ph.SR↗

arXiv2014

The nature of supernovae 2010O and 2010P in Arp 299 - II. Radio emission

We report radio observations of two stripped-envelope supernovae (SNe), 2010O and 2010P, which exploded within a few days of each other in the luminous infrared galaxy Arp 299. Whilst SN 2010O remains undetected at radio frequencies, SN 2010P was detected (with an astrometric accuracy better than 1 milli arcsec in position) in its optically thin phase in epochs ranging from ~1 to ~3yr after its explosion date, indicating a very slow radio evolution and a strong interaction of the SN ejecta with the circumstellar medium. Our late-time radio observations toward SN 2010P probe the dense circumstellar envelope of this SN, and imply a mass-loss rate (Msun/yr) to wind velocity (in units of 10 km/s) ratio of (3.0-5.1)E-05, with a 5 GHz peak luminosity of ~1.2E+27 erg/s/Hz on day ~464 after explosion. This is consistent with a Type IIb classification for SN 2010P, making it the most distant and most slowly evolving Type IIb radio SN detected to date.

astro-ph.GA↗

arXiv2014

Super Star Clusters in Luminous Infrared Galaxies: the SUNBIRD Survey

We present recent results from an adaptive optics imaging survey of 40 Luminous IR Galaxies (LIRGs) searching for obscured core collapse supernovae and studying the galaxies themselves. Here, in particular, we discuss the Super Star Clusters (SSC) populations in the LIRGs. We have constructed the first statistically significant samples of Luminosity Functions (LF) of SSCs in the near-IR, and find evidence that the LF slopes in LIRGs are shallower than in more quiescent spiral galaxies. Distance and blending effects were investigated in detail paving the way for SSC studies further out than done previously. We have also correlated the luminosities of the brightest clusters with the star formation rates (SFR) of the hosts. The relation is similar, though somewhat steeper than that found in the optical and at lower SFR levels, suggesting systematic extinction and/or age effects. We find that the characteristics of the relation suggest an underlying physical driver rather than solely a size-of-sample effect. In particular, a truncated luminosity/mass function would naturally explain the small scatter we find. Finally, we are modelling the ages and masses of our near-IR detected clusters in conjunction with HST optical data and present early results of using SSC properties to trace the histories of the target LIRG systems.

astro-ph.GA↗

arXiv2014

Underluminous Type II Plateau Supernovae: II. Pointing towards moderate mass precursors

We present new data for five under-luminous type II-plateau supernovae (SNe IIP), namely SN 1999gn, SN 2002gd, SN 2003Z, SN 2004eg and SN 2006ov. This new sample of low-luminosity SNe IIP (LL SNe IIP) is analyzed together with similar objects studied in the past. All of them show a flat light curve plateau lasting about 100 days, an under luminous late-time exponential tail, intrinsic colours that are unusually red, and spectra showing prominent and narrow P-Cygni lines. A velocity of the ejected material below 10^3 km/s is inferred from measurements at the end of the plateau. The 56Ni masses ejected in the explosion are very small (less than 10^-2 solar masses). We investigate the correlations among 56Ni mass, expansion velocity of the ejecta and absolute magnitude in the middle of the plateau, confirming the main findings of Hamuy (2003), according to which events showing brighter plateau and larger expansion velocities are expected to produce more 56Ni. We propose that these faint objects represent the low luminosity tail of a continuous distribution in parameters space of SNe IIP. The physical properties of the progenitors at the explosion are estimated through the hydrodynamical modeling of the observables for two representative events of this class, namely SN 2005cs and SN 2008in. We find that the majority of LL SNe IIP, and quite possibly all, originate in the core-collapse of intermediate mass stars, in the mass range 10-15 solar masses.

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arXiv2013

Optical and near-infrared observations of SN 2011dh - The first 100 days

We present optical and near-infrared (NIR) photometry and spectroscopy of the Type IIb supernova (SN) 2011dh for the first 100 days. We complement our extensive dataset with SWIFT ultra-violet (UV) and Spitzer mid-infrared (MIR) data to build a UV to MIR bolometric lightcurve using both photometric and spectroscopic data. Hydrodynamical modelling of the SN based on this bolometric lightcurve have been presented in Bersten (2012). We find that the absorption minimum for the hydrogen lines is never seen below ~11000 km/s but approaches this value as the lines get weaker. This suggests that the interface between the helium core and hydrogen rich envelope is located near this velocity in agreement with the Bersten et al. (2012) He4R270 ejecta model. Spectral modelling of the hydrogen lines using this ejecta model supports the conclusion and we find a hydrogen mass of 0.01-0.04 solar masses to be consistent with the observed spectral evolution. We estimate that the photosphere reaches the helium core at 5-7 days whereas the helium lines appear between ~10 and ~15 days, close to the photosphere and then move outward in velocity until ~40 days. This suggests that increasing non-thermal excitation due to decreasing optical depth for the gamma-rays is driving the early evolution of these lines. We also provide and discuss pre- and post-explosion observations of the SN site which shows a reduction by 75 percent in flux at the position of the yellow supergiant coincident with SN 2011dh. The B, V and r band decline rates of 0.0073, 0.0090 and 0.0053 mag/day respectively are consistent with the remaining flux being emitted by the SN. Hence we find that the star was indeed the progenitor of SN 2011dh as previously suggested by Maund et al. (2011) and which is also consistent with the results from the hydrodynamical modelling.

astro-ph.SR↗

arXiv2013

A new precise mass for the progenitor of the Type IIP SN 2008bk

The progenitor of the Type IIP SN 2008bk was discovered in pre-explosion g'r'i'IYJHKs images, acquired with European Southern Observatory Very Large Telescope FORS, HAWK-I and ISAAC instruments and the Gemini GMOS-S instrument. The wealth of pre-explosion observations makes the progenitor of this SN one of the best studied, since the detection of the progenitor of SN1987A. Previous analyses of the properties of the progenitor were hampered by the limited quality of the photometric calibration of the pre-explosion images and the crowded nature of the field containing the SN. We present new late-time observations of the site of SN2008bk acquired with identical instrument and filter configurations as the pre-explosion observations, and confirm that the previously identified red supergiant star was the progenitor of this SN and has now disappeared. Image subtraction techniques were used to conduct precise photometry of the now missing progenitor, independently of blending from any nearby stars. The nature of the surrounding stellar population and their contribution to the flux attributed to the progenitor in the pre-explosion images are probed using HST WFC3 UVIS/IR observations. In comparison with MARCS synthetic spectra, we find the progenitor was a highly reddened RSG with luminosity log (L/Lsun)=4.84+/-0.11, corresponding to an initial mass of Minit=12.9+/-1.7Msun. The temperature of the progenitor was hotter than previously expected for RSGs (T ~ 4330K), but consistent with new temperatures derived for RSGs using SED fitting techniques. We show that there is evidence for significant extinction of the progenitor, possibly arising in the CSM; but that this dust yields a similar reddening law to dust found in the ISM (E(B-V)=0.77 with Rv=3.1). [Abridged]

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arXiv2013

A Late-Time View of the Progenitors of Five Type IIP Supernovae

The acquisition of late-time imaging is an important step in the analysis of pre-explosion observations of the progenitors of supernovae. We present late-time HST ACS WFC observations of the sites of five Type IIP SNe: 1999ev, 2003gd, 2004A, 2005cs and 2006my. Observations were conducted using the F435W, F555W and F814W filters. We confirm the progenitor identifications for SNe 2003gd, 2004A and 2005cs, through their disappearance. We find that a source previously excluded as being the progenitor of SN 2006my has now disappeared. The late-time observations of the site of SN 1999ev cast significant doubt over the nature of the source previously identified as the progenitor in pre-explosion WFPC2 images. The use of image subtraction techniques yields improved precision over photometry conducted on just the pre-explosion images alone. In particular, we note the increased depth of detection limits derived on pre-explosion frames in conjunction with late-time images. We use SED fitting techniques to explore the effect of different reddening components towards the progenitors. For SNe 2003gd and 2005cs, the pre-explosion observations are sufficiently constraining that only limited amounts of dust (either interstellar or circumstellar) are permitted. Assuming only a Galactic reddening law, we determine the initial masses for the progenitors of SNe 2003gd, 2004A, 2005cs and 2006my of 8.4+/-2.0, 12.0+/-2.1, 9.5(+3.4,-2.2) and 9.8+/-1.7Msun, respectively.

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arXiv2013

Supernovae and radio transients in M 82

We present optical and near-infrared (IR) photometry and near-IR spectroscopy of SN 2004am, the only optically detected supernova (SN) in M 82. These demonstrate that SN 2004am was a highly reddened type II-P SN similar to the low luminosity type II-P events such as SNe 1997D and 2005cs. We show that SN 2004am was located coincident with the obscured super star cluster M 82-L, and from the cluster age infer a progenitor mass of 12 +7/-3 Msun. In addition to this, we present a high spatial resolution Gemini-N K-band adaptive optics image of the site of SN 2008iz and a second transient of uncertain nature, both detected so far only at radio wavelengths. Using image subtraction techniques together with archival data from the Hubble Space Telescope, we are able to recover a near-IR transient source co-incident with both objects. We find the likely extinction towards SN 2008iz to be not more than Av ~ 10. The nature of the second transient remains elusive and we regard an extremely bright microquasar in M 82 as the most plausible scenario.

astro-ph.CO↗

arXiv2013

Interacting Supernovae and Supernova Impostors. SN 2009ip, is this the end?

We report the results of a 3 year-long dedicated monitoring campaign of a restless Luminous Blue Variable (LBV) in NGC 7259. The object, named SN 2009ip, was observed photometrically and spectroscopically in the optical and near-infrared domains. We monitored a number of erupting episodes in the past few years, and increased the density of our observations during eruptive episodes. In this paper we present the full historical data set from 2009-2012 with multi-wavelength dense coverage of the two high luminosity events between August - September 2012. We construct bolometric light curves and measure the total luminosities of these eruptive or explosive events. We label them the 2012a event (lasting ~50 days) with a peak of 3x10^41 erg/s, and the 2012b event (14 day rise time, still ongoing) with a peak of 8x10^42 erg/s. The latter event reached an absolute R-band magnitude of about -18, comparable to that of a core-collapse supernova (SN). Our historical monitoring has detected high-velocity spectral features (~13000 km/s) in September 2011, one year before the current SN-like event. This implies that the detection of such high velocity outflows cannot, conclusively, point to a core-collapse SN origin. We suggest that the initial peak in the 2012a event was unlikely to be due to a faint core-collapse SN. We propose that the high intrinsic luminosity of the latest peak, the variability history of SN 2009ip, and the detection of broad spectral lines indicative of high-velocity ejecta are consistent with a pulsational pair-instability event, and that the star may have survived the last outburst. The question of the survival of the LBV progenitor star and its future fate remain open issues, only to be answered with future monitoring of this historically unique explosion.

astro-ph.SR↗

arXiv2012

Core-collapse supernovae missed by optical surveys

We estimate the fraction of core-collapse supernovae (CCSNe) that remain undetected by optical SN searches due to obscuration by large amounts of dust in their host galaxies. This effect is especially important in luminous and ultraluminous infrared galaxies, which are locally rare but dominate the star formation at redshifts of z~1-2. We perform a detailed investigation of the SN activity in the nearby luminous infrared galaxy Arp 299 and estimate that up to 83% of the SNe in Arp 299 and in similar galaxies in the local Universe are missed by observations at optical wavelengths. For rest-frame optical surveys we find the fraction of SNe missed due to high dust extinction to increase from the average local value of ~19% to ~38% at z~1.2 and then stay roughly constant up to z~2. It is therefore crucial to take into account the effects of obscuration by dust when determining SN rates at high redshift and when predicting the number of CCSNe detectable by future high-z surveys such as LSST, JWST, and Euclid. For a sample of nearby CCSNe (distances 6-15 Mpc) detected during the last 12 yr, we find a lower limit for the local CCSN rate of 1.5 +0.4/-0.3 x 10^-4 yr^-1 Mpc^-3, consistent with that expected from the star formation rate. Even closer, at distances less than ~6 Mpc, we find a significant increase in the CCSN rate, indicating a local overdensity of star formation caused by a small number of galaxies that have each hosted multiple SNe.

astro-ph.CO↗