David Polishook

Ptf 11kx: A type ia supernova with a symbiotic nova progenitor

Stellar Explosions Stars that are born with masses greater than eight times that of the Sun end their lives in luminous explosions known as supernovae. Over the past decade, access to improved sky surveys has revealed rare types of supernovae that are much more luminous than any of those that were known before. Gal-Yam (p. 927) reviews these superluminous events and groups them into three classes that share common observational and physical characteristics. Gamma-ray bursts are another type of extreme explosive events related to the death of massive stars, which occur once per day somewhere in the universe and produce short-lived bursts of gamma-ray light. Gehrels and Mészáros (p. 932) review what has been learned about these events since the launch of NASAs Swift (2004) and Fermi (2008) satellites. The current interpretation is that gamma-ray bursts are related to the formation of black holes. Type Ia supernovae are used as cosmological distance indicators. They are thought to be the result of the thermonuclear explosion of white dwarf stars in binary systems, but the nature of the stellar companion to the white dwarf is still debated. Dilday et al. (p. 942) report high-resolution spectroscopy of the supernova PTF 11kx, which was detected on 26 January 2011 by the Palomar Transient Factory survey. The data suggest a red giant star companion whose material got transferred to the white dwarf. Spectroscopic data imply that a stellar explosion arose from a binary consisting of a white dwarf and a red giant star. There is a consensus that type Ia supernovae (SNe Ia) arise from the thermonuclear explosion of white dwarf stars that accrete matter from a binary companion. However, direct observation of SN Ia progenitors is lacking, and the precise nature of the binary companion remains uncertain. A temporal series of high-resolution optical spectra of the SN Ia PTF 11kx reveals a complex circumstellar environment that provides an unprecedentedly detailed view of the progenitor system. Multiple shells of circumstellar material are detected, and the SN ejecta are seen to interact with circumstellar material starting 59 days after the explosion. These features are best described by a symbiotic nova progenitor, similar to RS Ophiuchi.

SN 2011dh: discovery of a type IIb supernova from a compact progenitor in the nearby galaxy M51

On 2011 May 31 UT a supernova (SN) exploded in the nearby galaxy M51 (the Whirlpool Galaxy). We discovered this event using small telescopes equipped with CCD cameras and also detected it with the Palomar Transient Factory survey, rapidly confirming it to be a Type II SN. Here, we present multi-color ultraviolet through infrared photometry which is used to calculate the bolometric luminosity and a series of spectra. Our early-time observations indicate that SN 2011dh resulted from the explosion of a relatively compact progenitor star. Rapid shock-breakout cooling leads to relatively low temperatures in early-time spectra, compared to explosions of red supergiant stars, as well as a rapid early light curve decline. Optical spectra of SN 2011dh are dominated by H lines out to day 10 after explosion, after which He I lines develop. This SN is likely a member of the cIIb (compact IIb) class, with progenitor radius larger than that of SN 2008ax and smaller than the eIIb (extended IIb) SN 1993J progenitor. Our data imply that the object identified in pre-explosion Hubble Space Telescope images at the SN location is possibly a companion to the progenitor or a blended source, and not the progenitor star itself, as its radius (~10^(13) cm) would be highly inconsistent with constraints from our post-explosion spectra.

The detailed optical light curve of GRB 030329

We present densely sampled BVRI light curves of the optical transient associated with the gamma-ray burst (GRB) 030329, the result of a coordinated observing campaign conducted at five observatories. Augmented with published observations of this GRB, the compiled optical data set contains 2687 photometric measurements, obtained between 78 minutes and 79 days after the burst. This data set allows us to follow the photometric evolution of the transient with unprecedented detail. We use the data to constrain the light curve of the underlying supernova (SN) 2003dh and show that it evolved faster than and was probably somewhat fainter than the Type Ic SN 1998bw, associated with GRB 980425. We find that our data can be described by a broken power-law decay perturbed by a complex variable component. The early- and late-time decay slopes are determined to be alpha(1) approximate to 1.1 and alpha(2) approximate to 2. Assuming this single-break power-law model, we constrain the break to lie between similar to3 and similar to8 days after the burst. This simple, singly broken power-law model, derived only from the analysis of our optical observations, may also account for available multiband data, provided that the break happened similar to8 days after the burst. The more complex double-jet model of Berger et al. provides a comparable fit to the optical, X-ray, millimeter, and radio observations of this event. The unique early coverage available for this event allows us to trace the color evolution of the afterglow during the first hours after the burst. We detect a significant change in optical colors during the first day. Our color analysis is consistent with a cooling-break frequency sweeping through the optical band during the first day. The light curves of GRB 030329 reveal a rich array of variations, superposed over the mean power-law decay. We find that the early variations (less than or similar to8 days after the burst) are asymmetric, with a steep rise followed by a relatively slower ( by a factor of about 2) decline. The variations maintain a similar timescale during the first 4 days and then get significantly longer. The structure of these variations is similar to those previously detected in the afterglows of several GRBs.

Formation of asteroid pairs by rotational fission

Pairs of asteroids sharing similar heliocentric orbits, but not bound together, were found recently. Backward integrations of their orbits indicated that they separated gently with low relative velocities, but did not provide additional insight into their formation mechanism. A previously hypothesized rotational fission process may explain their formation—critical predictions are that the mass ratios are less than about 0.2 and, as the mass ratio approaches this upper limit, the spin period of the larger body becomes long. Here we report photometric observations of a sample of asteroid pairs, revealing that the primaries of pairs with mass ratios much less than 0.2 rotate rapidly, near their critical fission frequency. As the mass ratio approaches 0.2, the primary period grows long. This occurs as the total energy of the system approaches zero, requiring the asteroid pair to extract an increasing fraction of energy from the primarys spin in order to escape. We do not find asteroid pairs with mass ratios larger than 0.2. Rotationally fissioned systems beyond this limit have insufficient energy to disrupt. We conclude that asteroid pairs are formed by the rotational fission of a parent asteroid into a proto-binary system, which subsequently disrupts under its own internal system dynamics soon after formation.

The Progenitor of Supernova 2011dh/PTF11eon In Messier 51

We have identified a luminous star at the position of supernova (SN) 2011dh/PTF11eon, in pre-SN archival, multi-band images of the nearby, nearly face-on galaxy Messier 51 (M51) obtained by the Hubble Space Telescope with the Advanced Camera for Surveys. This identification has been confirmed, to the highest available astrometric precision, using a Keck-II adaptive-optics image. The available early-time spectra and photometry indicate that the SN is a stripped-envelope, core-collapse Type IIb, with a more compact progenitor (radius ~ 10^(11) cm) than was the case for the well-studied SN IIb 1993J. We infer that the extinction to SN 2011dh and its progenitor arises from a low Galactic foreground contribution, and that the SN environment is of roughly solar metallicity. The detected object has absolute magnitude M^0_V ≈ –7.7 and effective temperature ~6000 K. The stars radius, ~10^(13) cm, is more extended than what has been inferred for the SN progenitor. We speculate that the detected star is either an unrelated star very near the position of the actual progenitor, or, more likely, the progenitors companion in a mass-transfer binary system. The position of the detected star in a Hertzsprung-Russell diagram is consistent with an initial mass of 17-19 M_☉. The light of this star could easily conceal, even in the ultraviolet, the presence of a stripped, compact, very hot (~10^5 K), nitrogen-rich Wolf-Rayet star progenitor.

Masses and Orbital Constraints for the OGLE-2006-BLG-109Lb,c Jupiter/Saturn Analog Planetary System

We present a new analysis of the Jupiter+Saturn analog system, OGLE-2006-BLG-109Lb,c, which was the first double planet system discovered with the gravitational microlensing method. This is the only multi-planet system discovered by any method with measured masses for the star and both planets. In addition to the signatures of two planets, this event also exhibits a microlensing parallax signature and finite source effects that provide a direct measure of the masses of the star and planets, and the expected brightness of the host star is confirmed by Keck AO imaging, yielding masses of , Mb = 231 ± 19 M ⊕, and Mc = 86 ± 7 M ⊕. The Saturn-analog planet in this system had a planetary light-curve deviation that lasted for 11 days, and as a result, the effects of the orbital motion are visible in the microlensing light curve. We find that four of the six orbital parameters are tightly constrained and that a fifth parameter, the orbital acceleration, is weakly constrained. No orbital information is available for the Jupiter-analog planet, but its presence helps to constrain the orbital motion of the Saturn-analog planet. Assuming co-planar orbits, we find an orbital eccentricity of and an orbital inclination of . The 95% confidence level lower limit on the inclination of i > 49° implies that this planetary system can be detected and studied via radial velocity measurements using a telescope of 30 m aperture.

A study of asteroid pole-latitude distribution based on an extended set of shape models derived by the lightcurve inversion method

Context. In the past decade, more than one hundred asteroid models were derived using the lightcurve inversion method. Measured by the number of derived models, lightcurve inversion has become the leading method for asteroid shape determination. Aims. Tens of thousands of sparse-in-time lightcurves from astrometric projects are publicly available. We investigate these data and use them in the lightcurve inversion method to derive new asteroid models. By having a greater number of models with known physical properties, we can gain a better insight into the nature of individual objects and into the whole asteroid population. Methods. We use sparse photometry from selected observatories from the AstDyS database (Asteroids – Dynamic Site), either alone or in combination with dense lightcurves, to determine new asteroid models by the lightcurve inversion method. We investigate various correlations between several asteroid parameters and characteristics such as the rotational state and diameter or family membership. We focus on the distribution of ecliptic latitudes of pole directions. We create a synthetic uniform distribution of latitudes, compute the method bias, and compare the results with the distribution of known models. We also construct a model for the long-term evolution of spins. Results. We present 80 new asteroid models derived from combined data sets where sparse photometry is taken from the AstDyS database and dense lightcurves are from the Uppsala Asteroid Photometric Catalogue (UAPC) and from several individual observers. For 18 asteroids, we present updated shape solutions based on new photometric data. For another 30 asteroids we present their partial models, i.e., an accurate period value and an estimate of the ecliptic latitude of the pole. The addition of new models increases the total number of models derived by the lightcurve inversion method to ∼200. We also present a simple statistical analysis of physical properties of asteroids where we look for possible correlations between various physical parameters with an emphasis on the spin vector. We present the observed and de-biased distributions of ecliptic latitudes with respect to different size ranges of asteroids as well as a simple theoretical model of the latitude distribution and then compare its predictions with the observed distributions. From this analysis we find that the latitude distribution of small asteroids (D 60 km) exhibits an evident excess of prograde rotators, probably of primordial origin.

DISCOVERY OF A COSMOLOGICAL, RELATIVISTIC OUTBURST VIA ITS RAPIDLY FADING OPTICAL EMISSION

We report the discovery by the Palomar Transient Factory (PTF) of the transient source PTF11agg, which is distinguished by three primary characteristics: (1) bright (Rpeak = 18.3mag), rapidly fading (ΔR = 4mag in Δt = 2 days) optical transient emission; (2) a faint (R = 26.2 ± 0.2mag), blue (g � − R = 0.17 ± 0.29mag) quiescent optical counterpart; and (3) an associated year-long, scintillating radio transient. We argue that these observed properties are inconsistent with any known class of Galactic transients (flare stars, X-ray binaries, dwarf novae), and instead suggest a cosmological origin. The detection of incoherent radio emission at such distances implies a large emitting region, from which we infer the presence of relativistic ejecta. The observed properties are allconsistentwiththepopulationoflong-durationgamma-raybursts(GRBs),markingthefirsttimesuchanoutburst has been discovered in the distant universe independent of a high-energy trigger. We searched for possible highenergy counterparts to PTF11agg, but found no evidence for associated prompt emission. We therefore consider three possible scenarios to account for a GRB-like afterglow without a high-energy counterpart: an “untriggered” GRB (lack of satellite coverage), an “orphan” afterglow (viewing-angle effects), and a “dirty fireball” (suppressed high-energy emission). The observed optical and radio light curves appear inconsistent with even the most basic predictions for off-axis afterglow models. The simplest explanation, then, is that PTF11agg is a normal, on-axis long-durationGRBforwhichtheassociatedhigh-energyemissionwassimplymissed.However,wehavecalculated the likelihood of such a serendipitous discovery by PTF and find that it is quite small (≈2.6%). While not definitive, we nonetheless speculate that PTF11agg may represent a new, more common (>4 times the on-axis GRB rate at 90% confidence) class of relativistic outbursts lacking associated high-energy emission. If so, such sources will be uncovered in large numbers by future wide-field optical and radio transient surveys.

EXTREME MAGNIFICATION MICROLENSING EVENT OGLE-2008-BLG-279: STRONG LIMITS ON PLANETARY COMPANIONS TO THE LENS STAR

We analyze the extreme high-magnification microlensing event OGLE-2008-BLG-279, which peaked at a maximum magnification of A ~ 1600 on 2008 May 30. The peak of this event exhibits both finite-source effects and terrestrial parallax, from which we determine the mass of the lens, Ml = 0.64 ? 0.10 M ?, and its distance, Dl = 4.0 ? 0.6 kpc. We rule out Jupiter-mass planetary companions to the lens star for projected separations in the range 0.5-20 AU. More generally, we find that this event was sensitive to planets with masses as small as with projected separations near the Einstein ring (~3 AU).

An early and comprehensive millimetre and centimetre wave and X-ray study of SN 2011dh: a non-equipartition blast wave expanding into a massive stellar wind

Only a handful of supernovae (SNe) have been studied in multiwavelengths from the radio to X-rays, starting a few days after the explosion. The early detection and classification of the nearby Type IIb SN 2011dh/PTF 11eon in M51 provides a unique opportunity to conduct such observations. We present detailed data obtained at one of the youngest phase ever of a core-collapse SN (days 3–12 after the explosion) in the radio, millimetre and X-rays; when combined with optical data, this allows us to explore the early evolution of the SN blast wave and its surroundings. Our analysis shows that the expanding SN shock wave does not exhibit equipartition (ϵ_e/ϵ_B ∼ 1000), and is expanding into circumstellar material that is consistent with a density profile falling like R^(−2). Within modelling uncertainties we find an average velocity of the fast parts of the ejecta of 15 000 ± 1800 km s^(−1), contrary to previous analysis. This velocity places SN 2011dh in an intermediate blast wave regime between the previously defined compact and extended SN Type IIb subtypes. Our results highlight the importance of early (∼1 d) high-frequency observations of future events. Moreover, we show the importance of combined radio/X-ray observations for determining the microphysics ratio ϵ_e/ϵ_B.