11. Flares from the centers of galaxies with Gaia and OGLE surveysNada Ihanec, 2018, magistrsko delo Opis: Modern wide-field-of-view and all-sky satellites (e.g. Gaia) and ground based surveys (e.g. OGLE) repeatedly cover a large part of the sky and are detecting new, transient astrophysical sources on daily basis.
In this thesis I analyzed the data from Gaia and OGLE transient surveys, with special focus on transients located near the centres of galaxies to detect possible Tidal Disruption Events. These occur when a star gets too close to a Super-Massive Black Hole, which lurks in the centres of most galaxies, and gets disrupted due to the black hole's gravitational tidal forces.
The goal of my research was to detect possible Tidal Disruption Events and eliminate false candidates, such as supernovae. The work involved daily inspection of new alerts, identified with Gaia and OGLE Transient Detection System. I searched for potential transients in galactic nuclei and in case there was such a transient detected, follow-up spectroscopic observations were initiated in order to help classify the object.
During the course of my work I analyzed spectra obtained with the largest telescopes in the world (SALT, VLT) and performed the spectral template matching, recognition of spectral features related to known classes of transients, determination of redshift etc. Ključne besede: Flares, transients, Gaia, OGLE, supernovae, tidal disruption events, nuclear transients Objavljeno v RUNG: 14.05.2019; Ogledov: 4145; Prenosov: 132 Celotno besedilo (8,11 MB) |
12. Prospects for Strongly Lensed Supernovae Behind Hubble FrontierFields Galaxy Clusters with the James Webb Space TelescopeTanja Petrushevska, 2018, izvirni znanstveni članek Opis: Measuring time delays from strongly lensed supernovae (SNe) is emerging as a novel andindependent tool for estimating the Hubble constant (H0). This is very important given the recent discordin the value of H0) from two methods that probe different distance ranges. The success of this techniquewill rely of our ability to discover strongly lensed SNe with measurable time delays. Here, we present themagnifications and the time delay s for the multiply-imaged galaxies behind the Hubble Frontier Fields(HFF) galaxy clusters, by using recently published lensing models. Continuing on our previous work donefor Abell 1689 (A1689) and Abell 370, we also show the prospects of observing strongly lensed SNe behindthe HFF clusters with the upcoming James Webb Space Telescope (JWST). With four 1-hour visits inone year, the summed expectations of all six HFF clusters are ∼0 .5 core-collapse (CC) SNe and 0.06Type Ia SNe (SNe Ia) in F115W band, while with F150W the expectations are higher, ∼0.9 CC SNeand ∼0.06 SNe Ia. These estimates match those expected by only surveying A1689, proving that theperformance of A1689 as gravitational telescope is superior. In the five HFF clusters presented here, wefind that F150W will be able to detect SNe Ia (SNe IIP) exploding in 93 (80) pairs multiply-imaged galaxieswith time delays of less than 5 years. Ključne besede: supernovae, JWST, Hubble constant, strong lensing Objavljeno v RUNG: 03.01.2019; Ogledov: 2914; Prenosov: 0 Gradivo ima več datotek! Več... |
13. Exploring the Universe with supernovaeTanja Petrushevska, objavljeni povzetek znanstvenega prispevka na konferenci (vabljeno predavanje) Opis: Supernovae have proven to be exquisite tools for a variety of astrophysics and cosmology topics. In this lecture, I will highlight a selection of dedicated tele- scopic surveys for detecting supernovae and I will report some of our interesting discoveries during the past few years. I will dedicate special attention to strongly lensed supernovae by galaxies and galaxy clusters. Under the right circumstances, multiple images of the lensed supernovae can be observed, and due to the variable nature of the objects, the difference between the arrival times of the images can be measured. Since the images have taken different paths through space before reaching us, the time-differences are sensitive to the expansion rate of the universe. Therefore, measuring time delays from strongly lensed supernovae is emerging as a novel and independent tool for estimating the Hubble constant (H0). This is very important given the recent discord in the value of H0 from two methods that probe different distance ranges: the ESA mission Planck value corresponds to 67.74 ± 0.46 km s−1 Mpc−1; [1], while a reanalysis of the local distance scale gives 73.24 ± 1.74 km s−1 Mpc−1; [2, 3], these measurements thus being inconsistent at the ≈ 3.5σ level. Therefore, the results of additional independent and high- precision techniques, which rely on different physics, are of key importance. In this context, I will report our discovery of the first resolved multiply-imaged gra- vitationally lensed supernova Type Ia [4]. Moving forward, I will discuss some of the prospects of upcoming facilities such as the Large Synoptic Survey Telescope and James Webb Space Telescope [5, 6]. Ključne besede: supernovae, strong lensing, neutron stars Objavljeno v RUNG: 29.11.2018; Ogledov: 3031; Prenosov: 0 Gradivo ima več datotek! Več... |
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15. Prospects for lensed supernovae behind galaxy clusters with the James Webb Space TelescopeTanja Petrushevska, 2018, objavljeni povzetek znanstvenega prispevka na konferenci Opis: Galaxies, and clusters of galaxies, can act as gravitational lenses and magnify the light of
objects behind them. The effect enables observations of very distant supernovae, that
otherwise would be too faint to be detected by existing telescopes, and allows studies of
the frequency and properties of these rare phenomena when the universe was young.
Under the right circumstances, multiple images of the lensed supernovae can be
observed, and due to the variable nature of the objects, the difference between the arrival
times of the images can be measured. Since the images have taken different paths
through space before reaching us, the time-differences are sensitive to the expansion rate
of the universe. One class of supernovae, Type Ia, are of particular interest to detect. Their
well known brightness can be used to determine the magnification, which can be used to
understand the lensing systems. I will also report our discovery of the first resolved
multiply-imaged gravitationally lensed supernova Type Ia. I will also show the expectations
of search campaigns that can be conducted with future facilities, such as the James Webb
Space Telescope (JWST) or the Wide-Field Infrared Survey Telescope (WFIRST). Ključne besede: Strong lensing, Hubble constant, measuring expansion history with time delays, lensed supernovae Objavljeno v RUNG: 09.07.2018; Ogledov: 3579; Prenosov: 139 Celotno besedilo (4,14 MB) |
16. Searching for supernovae in the multiply-imaged galaxies behind the gravitational telescope A370Tanja Petrushevska, Ariel Goobar, D. J. Lagattuta, R. Amanullah, Laura Hangard, S. Fabbro, C. Lindman, K. Paech, J. Richard, J.P. Kneib, 2017, izvirni znanstveni članek Opis: Aims. Strong lensing by massive galaxy clusters can provide magnification of the flux and even multiple images of the galaxies that lie behind them. This phenomenon facilitates observations of high-redshift supernovae (SNe) that would otherwise remain undetected. Type Ia supernovae (SNe Ia) detections are of particular interest because of their standard brightness, since they can be used to improve either cluster lensing models or cosmological parameter measurements.
Methods. We present a ground-based, near-infrared search for lensed SNe behind the galaxy cluster Abell 370. Our survey was based on 15 epochs of J-band observations with the HAWK-I instrument on the Very Large Telescope (VLT). We use Hubble Space Telescope (HST) photometry to infer the global properties of the multiply-imaged galaxies. Using a recently published lensing model of Abell 370, we also present the predicted magnifications and time delays between the images.
Results. In our survey, we did not discover any live SNe from the 13 lensed galaxies with 47 multiple images behind Abell 370. This is consistent with the expectation of 0.09 ± 0.02 SNe calculated based on the measured star formation rate. We compare the expectations of discovering strongly lensed SNe in our survey and that performed with HST during the Hubble Frontier Fields (HFF) programme. We also show the expectations of search campaigns that can be conducted with future facilities, such as the James Webb Space Telescope (JWST) or the Wide-Field Infrared Survey Telescope (WFIRST). We show that the NIRCam instrument aboard the JWST will be sensitive to most SN multiple images in the strongly lensed galaxies and thus will be able to measure their time delays if observations are scheduled accordingly. Ključne besede: gravitational lensing: strong / supernovae: general / galaxies: clusters: individual: A 370 Objavljeno v RUNG: 28.06.2018; Ogledov: 3590; Prenosov: 139 Celotno besedilo (4,14 MB) |
17. Supernovae seen through gravitational telescopesTanja Petrushevska, 2018, objavljeni povzetek znanstvenega prispevka na konferenci (vabljeno predavanje) Opis: Galaxies, and clusters of galaxies, can act as gravitational lenses and magnify the light of objects behind them. The effect enables observations of very distant supernovae, that otherwise would be too faint to be detected by existing telescopes, and allows studies of the frequency and properties of these rare phenomena when the universe was young. Under the right circumstances, multiple images of the lensed supernovae can be observed, and due to the variable nature of the objects, the difference between the arrival times of the images can be measured. Since the images have taken different paths through space before reaching us, the time-differences are sensitive to the expansion rate of the universe. One class of supernovae, Type Ia, are of particular interest to detect. Their well known brightness can be used to determine the magnification, which can be used to understand the lensing systems. I will also report our discovery of the first resolved multiply-imaged gravitationally lensed supernova Type Ia. Ključne besede: lensed supernovae, strong lensing Objavljeno v RUNG: 03.05.2018; Ogledov: 3278; Prenosov: 0 Gradivo ima več datotek! Več... |
18. Supernovae seen through gravitational telescopesTanja Petrushevska, 2017, druga izvedena dela Opis: Galaxies, and clusters of galaxies, can act as gravitational lenses and magnify the light of objects behind them. The effect enables observations of very distant supernovae, that otherwise would be too faint to be detected by existing telescopes, and allows studies of the frequency and properties of these rare phenomena when the universe was young. Under the right circumstances, multiple images of the lensed supernovae can be observed, and due to the variable nature of the objects, the difference between the arrival times of the images can be measured. Since the images have taken different paths through space before reaching us, the time-differences are sensitive to the expansion rate of the universe. One class of supernovae, Type Ia, are of particular interest to detect. Their well known brightness can be used to determine the magnification, which can be used to understand the lensing systems. I will also report our discovery of the first resolved multiply-imaged gravitationally lensed supernova Type Ia. Ključne besede: lensed supernovae Objavljeno v RUNG: 06.02.2018; Ogledov: 2945; Prenosov: 0 Gradivo ima več datotek! Več... |
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20. Searching for lensed supernovae behind galaxy clusters with upcoming telescopesTanja Petrushevska, objavljeni povzetek znanstvenega prispevka na konferenci Opis: Aims. Strong lensing by massive galaxy clusters can provide magnification of the flux and even multiple images of the galaxies that lie behind them. This phenomenon allows one to observe high-redshift supernovae (SNe), that otherwise would remain undetected. Type Ia supernovae (SNe Ia) detections are of particular interest because of their standard brightness, since they can be used to improve either cluster lensing models or cosmological parameter measurements.
Methods. We present a ground-based, near-infrared search for lensed SNe behind the galaxy cluster Abell 370. Our survey was based on 15 epochs of J-band observations with the HAWK-I instrument on the Very Large Telescope (VLT). We use Hubble Space Telescope (HST) photometry to infer the global properties of the multiply-imaged galaxies. Using a recently published lensing model of Abell 370, we also present the predicted magnifications and the time-delays between the images.
Results. In our survey, we did not discover any live SNe from the 13 lensed galaxies with 47 multiple images behind Abell 370. This is consistent with the expectation of 0.09 ± 0.02 SNe calculated based on the measured star formation rate. We compare the expectations of discovering strongly lensed SNe in our survey and that performed with HST during the Hubble Frontier Fields (HFF) program. We also show the expectations of search campaigns that can be conducted with future facilities, such as the James Webb Space Telescope (JWST) or the Wide-Field Infrared Survey Telescope (WFIRST). We show that NIRCam instrument aboard the JWST will be sensitive to most SN multiple images in the strongly-lensed galaxies and thus able to measure their time-delays if observations are scheduled accordingly. Ključne besede: JWST, WFIRST, lensed supernovae, transient search Objavljeno v RUNG: 29.01.2018; Ogledov: 3083; Prenosov: 0 Gradivo ima več datotek! Več... |