Astrometric detection of binary asteroids Segev, Noam; Ofek, Eran O; Polishook, David
Monthly notices of the Royal Astronomical Society,
12/2022, Letnik:
518, Številka:
3
Journal Article
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ABSTRACT
Binary asteroids probe thermal-radiation effects on the main-belt asteroids’ evolution. We discuss the possibility of detecting binary minor planet systems by the astrometric wobble of the ...centre of light around the centre of mass. This method enables the exploration of the phase-space of binary asteroids, which is difficult to explore using common detection techniques. We describe a forward model that projects the centre-of-light position with respect to the centre of mass, as it is seen by the observer. We study the performance of this method using simulated Gaia-like data. We apply the astrometric method to a subset of the Gaia DR2 Solar system catalogue and find no significant evidence of binary asteroids. This is likely because the Gaia DR2 removed astrometric outliers, which in our case may be due to astrophysical signals. Applying this method to binary asteroid (4337) Arecibo, for which Gaia DR3 reported a possible astrometric signal with a period of P = 32.85 ± 0.38 h, reveals a possible 2.2σ solution with a period of 16.26 h (about half the reported period). We find a small, marginally significant, excess of astrometric noise in the known binary asteroid population from Pravec et al. relative to the entire asteroid population in the Gaia DR2 Solar system catalogue. We also discuss some caveats like precession and asteroid rotation.
There is a growing number of Type IIn supernovae (SNe) which present an outburst prior to their presumably final explosion. These precursors may affect the SN display, and are likely related to ...poorly charted phenomena in the final stages of stellar evolution. By coadding Palomar Transient Factory (PTF) images taken prior to the explosion, here we present a search for precursors in a sample of 16 Type IIn SNe. We find five SNe IIn that likely have at least one possible precursor event (PTF 10bjb, SN 2010mc, PTF 10weh, SN 2011ht, and PTF 12cxj), three of which are reported here for the first time. For each SN we calculate the control time. We find that precursor events among SNe IIn are common: at the one-sided 99% confidence level, >50% of SNe IIn have at least one pre-explosion outburst that is brighter than 3 x 10 super(7) L sub(middot in circle) taking place up to 1/3 yr prior to the SN explosion. The average rate of such precursor events during the year prior to the SN explosion is likely gap1 yr super(-1), and fainter precursors are possibly even more common. Ignoring the two weakest precursors in our sample, the precursors rate we find is still on the order of one per year. We also find possible correlations between the integrated luminosity of the precursor and the SN total radiated energy, peak luminosity, and rise time. These correlations are expected if the precursors are mass-ejection events, and the early-time light curve of these SNe is powered by interaction of the SN shock and ejecta with optically thick circumstellar material.
The optical and near-IR emission from some classes of supernovae (SNe), including Type IIn and possibly some super-luminous SNe, is likely powered by a collision between the SN ejecta and dense ...circumstellar material (CSM). We argue that for a range of CSM masses and their radii, a collisionless shock can form, allowing for efficient cosmic ray (CR) acceleration. We show that pp collisions between these newly accelerated CRs and the CSM leads to not only gamma rays but also secondary electrons and positrons that radiate synchrotron photons in the high-frequency radio bands. Our estimates imply that various facilities including the Jansky Very Large Array (and the Atacama Large Millimeter/submillimetre Array (ALMA) may observe such SNe at Gpc distances by followup observations in months-to-years, although the detectability strongly depends on the CSM density as well as observed frequency. Detecting this signal would give us a unique probe of CR acceleration at early times, and even non-detections can put interesting limits on the possibility of CR ion acceleration. Following our previous work, we also show that GeV gamma rays can escape from the system without severe attenuation, encouraging point-source and stacking analyses with Fermi. We provide recipes for diagnosing interaction-powered SN scenario with multi-messenger (neutrino and gamma-ray) observations. PUBLICATION ABSTRACT
ABSTRACT
Lensed quasars and supernovae can be used to study galaxies’ gravitational potential and measure cosmological parameters. The typical image separation of objects lensed by galaxies is of the ...order of 0.5 arcsec. Finding the ones with small separations, and measuring their time delays using ground-based observations is challenging. We suggest a new method to identify lensed quasars and simultaneously measure their time delays, using seeing-limited synoptic observations in which the lensed quasar images and the lensing galaxy are unresolved. We show that using the light curve of the combined flux, and the astrometric measurements of the centre-of-light position of the lensed images, the lensed nature of a quasar can be identified, and its time delay can be measured. We provide the analytic formalism to do so, taking into account the measurement errors and the fact that the power spectra of quasar light curves is red. We demonstrate our method on simulated data, while its implementation to real data will be presented in future papers. Our simulations suggest that, under reasonable assumptions, the new method has the potential to detect unresolved lensed quasars and measure their time delays, even when the image separation is about 0.2 arcsec, or the flux ratio between the faintest and brightest images is as low as 0.05. python and matlab implementations are provided. In a companion paper, we present a method for measuring the time delay using the combined flux observations. This method may be useful in cases in which the astrometric information is not relevant (e.g. reverberation mapping).
Abstract The apparent tension between the luminosity functions of red supergiant (RSG) stars and of RSG progenitors of Type II supernovae (SNe) is often referred to as the RSG problem and it ...motivated some to suggest that many RSGs end their life without an SN explosion. However, the luminosity functions of RSG SN progenitors presented so far were biased to high luminosities, because the sensitivity of the search was not considered. Here, we use limiting magnitudes to calculate a bias-corrected RSG progenitor luminosity function. We find that only (36 ± 11)% of all RSG progenitors are brighter than a bolometric magnitude of −7 mag, a significantly smaller fraction than (56 ± 5)% quoted by Davies & Beasor. The larger uncertainty is due to the relatively small progenitor sample, while uncertainties on measured quantities such as magnitudes, bolometric corrections, extinction, or SN distances, only have a minor impact, as long as they fluctuate randomly for different objects in the sample. The bias-corrected luminosity functions of RSG SN progenitors and Type M supergiants in the Large Magellanic Cloud are consistent with each other, as also found by Davies & Beasor for the uncorrected luminosity function. The RSG progenitor luminosity function, hence, does not imply the existence of failed SNe. The presented statistical method is not limited to progenitor searches, but applies to any situation in which a measurement is done for a sample of detected objects, but the probed quantity or property can only be determined for part of the sample.
ABSTRACT
Several phenomena in astrophysics generate light curves with time delays. Among these are reverberation mapping and lensed quasars. In these systems, the measurement of the time delay is ...complicated by the fact that the delayed components are unresolved and that the light curves are generated from a stochastic process. We derive the likelihood function of the observations given a model of either a combination of time-delayed light curves or a single light curve. This likelihood function is different from the auto-correlation-function-based investigated by previous studies. We demonstrate that given a single-band light curve that is a linear combination of two (or more) time-shifted copies of an original light curve, generated from a probability distribution with some roughly known power spectrum, it is possible to test if the total-flux light curve is a composition of time-delayed copies or, alternatively, is consistent with being a single copy of the original light curve. Furthermore, it is possible to measure the time delays between these components even when the flux ratio is about 1/10. In the era of synoptic sky surveys, this method is useful for identifying lensed quasars and simultaneously measuring their time delays, and also for estimating the reverberation time scales of active galactic nuclei. In a companion paper, we derive another method that uses the centre-of-light astrometric position (e.g. of a lensed quasar) along with the combined flux. We also present the proper likelihood function for fitting a power-law model to a power spectrum. We test the new method on simulations and provide python and matlab implementations.
Most telescope designs have a circular aperture. We quantify the advantages that telescopes with an elongated pupil have over circular-pupil telescopes in terms of contrast at small separations ...between a bright central star and a faint companion. We simulate images for an elongated-pupil telescope and for a circular-pupil telescope of equal aperture area and integration time, and we specifically investigate the maximal contrast when finding faint companions around bright stars as a function of angular separation. We show that this design gives better contrast at lower separation from a bright star. This is shown for diffraction-limited (for perfect and imperfect optics) and seeing-limited speckle images assuming an equal aperture area and observing time. We also show that the results are robust to errors in measurement of the point-spread function. To compensate for the wider point-spread function of the short axis, images should be taken at different rotation angles, either by rotating the telescope around the optical axis or by allowing a stationary mirror array to scan different parallactic angles with time. Images taken at different rotation angles are added using the proper image coaddition algorithms developed by Zackay & Ofek. The final image has the same contrast at all angles, rather than in specific areas of diffraction nulls. We obtained speckle observations with a small ground-based elongated-aperture telescope and show that the results are consistent with simulations.
Fast access to large catalogs is required for some astronomical applications. Here we introduce the catsHTM tool, consisting of several large catalogs reformatted into HDF5-based file format, which ...can be downloaded and used locally. To allow fast access, the catalogs are partitioned into hierarchical triangular meshes and stored in HDF5 files. Several tools are provided to perform efficient cone searches at resolutions spanning from a few arc-seconds to degrees, within a few milliseconds time. The first released version includes the following catalogs (by alphabetical order): 2MASS, 2MASS extended sources, AKARI, APASS, Cosmos, DECaLS/DR5, FIRST, GAIA/DR1, GAIA/DR2, GALEX/DR6Plus7, HSC/v2, IPHAS/DR2, NED redshifts, NVSS, Pan-STARRS1/DR1, PTF photometric catalog, ROSAT faint source, SDSS sources, SDSS/DR14 spectroscopy, SkyMapper, Spitzer/SAGE, Spitzer/IRAC galactic center, UCAC4, UKIDSS/DR10, VST/ATLAS/DR3, VST/KiDS/DR3, WISE and XMM. We provide Python code that allows to perform cone searches, as well as MATLAB code for performing cone searches, catalog cross-matching, general searches, as well as load and create these catalogs.
ABSTRACT
Measuring the size distribution of small (kilometre-scale) Kuiper belt objects (KBOs) can help constrain models of Solar system formation and planetary migration. Such small, distant bodies ...are hard to detect with current or planned telescopes, but can be identified as sub-second occultations of background stars. We present the analysis of data from the Weizmann Fast Astronomical Survey Telescope, consisting of fast photometry of ∼106 star-hours at a frame rate of 10–25 Hz. Our pipeline utilizes a matched-filter approach with a large template bank, including red-noise treatment, and injection of simulated events for estimating the detection efficiency. The KBO radius at which our survey is 10 per cent (50 per cent) efficient is 1.1 (2.0) km. The data from 2020–2021 observing seasons were analysed and no occultations were identified. We discuss a sample of sub-second false-positive events, both occultation-like and flare-like, which are still not fully understood but could be instructive for future surveys looking for short-duration events. We use our null-detection result to set limits on the kilometre-scale KBO number density. Our individual radius bin limits are consistent with most previous works, with N(r > 1 km) ⪅ 106 deg−2 (95 per cent confidence limit). Our integrated (all size) limits, assuming a power law normalized to large (≈45 km) KBOs give a power-law index q < 3.93 (95 per cent confidence limit). Finally, our results are in tension with a recently reported KBO detection from the ground, at the p = 4 × 10−4 level.
Detection of templates (e.g., sources) embedded in low-number count Poisson noise is a common problem in astrophysics. Examples include source detection in X-ray images, γ-rays, UV, neutrinos, and ...search for clusters of galaxies and stellar streams. However, the solutions in the X-ray-related literature are sub-optimal in some cases by considerable factors. Using the lemma of Neyman-Pearson, we derive the optimal statistics for template detection in the presence of Poisson noise. We demonstrate that, for known template shape (e.g., point sources), this method provides higher completeness, for a fixed false-alarm probability value, compared with filtering the image with the point-spread function (PSF). In turn, we find that filtering by the PSF is better than filtering the image using the Mexican-hat wavelet (used by wavdetect). For some background levels, our method improves the sensitivity of source detection by more than a factor of two over the popular Mexican-hat wavelet filtering. This filtering technique can also be used for fast PSF photometry and flare detection; it is efficient and straightforward to implement. We provide an implementation in MATLAB. The development of a complete code that works on real data, including the complexities of background subtraction and PSF variations, is deferred for future publication.
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