1. PASSERBY BECOME SUPERNOVA HUNTERS IN KUNGSTRÄDGÅRDENTanja Petrushevska, S. Papadogiannakis, Emir Karamehmetoglu, 2015, druga izvedena dela Opis: Fysik i Kungsträdgården is one of the major outreach events in Stockholm where scientists have the chance to show their research. This year the supernova group at the OKC invited the public to look for supernovae with us using the intermediate Palomar (Transient) Factory (iPTF) collaboration telescope in Palomar, California, U.S.A. Due to the time difference between Stockholm and California, we were able to look at live images as they were taken from the telescope, to search for new transient objects such as supernovae. The event was successful, bringing a lot of people from the park in central Stockholm to come and search with us.
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Ključne besede: science outreach, supernova hunting for the public
Objavljeno: 09.02.2018; Ogledov: 3115; Prenosov: 0
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5. The rise and fall of the iron-strong nuclear transient PS16dtmTanja Petrushevska, 2023, izvirni znanstveni članek Opis: Context. Thanks to the advent of large-scale optical surveys, a diverse set of flares from the nuclear regions of galaxies has recently been discovered. These include the disruption of stars by supermassive black holes at the centers of galaxies – nuclear transients known as tidal disruption events (TDEs). Active galactic nuclei (AGN) can show extreme changes in the brightness and emission line intensities, often referred to as changing-look AGN (CLAGN). Given the physical and observational similarities, the interpretation and distinction of nuclear transients as CLAGN or TDEs remains difficult. One of the obstacles of making progress in the field is the lack of well-sampled data of long-lived nuclear outbursts in AGN.
Aims. Here, we study PS16dtm, a nuclear transient in a Narrow Line Seyfert 1 (NLSy1) galaxy, which has been proposed to be a TDE candidate. Our aim is to study the spectroscopic and photometric properties of PS16dtm, in order to better understand the outbursts originating in NLSy1 galaxies.
Methods. Our extensive multiwavelength follow-up that spans around 2000 days includes photometry and spectroscopy in the UV/optical, as well as mid-infrared (MIR) and X-ray observations. Furthermore, we improved an existing semiempirical model in order to reproduce the spectra and study the evolution of the spectral lines.
Results. The UV/optical light curve shows a double peak at ∼50 and ∼100 days after the first detection, and it declines and flattens afterward, reaching preoutburst levels after 2000 days of monitoring. The MIR light curve rises almost simultaneously with the optical, but unlike the UV/optical which is approaching the preoutburst levels in the last epochs of our observations, the MIR emission is still rising at the time of writing. The optical spectra show broad Balmer features and the strongest broad Fe II emission ever detected in a nuclear transient. This broad Fe II emission was not present in the archival preoutburst spectrum and almost completely disappeared +1868 days after the outburst. We found that the majority of the flux of the broad Balmer and Fe II lines is produced by photoionization. We detect only weak X-ray emission in the 0.5−8 keV band at the location of PS16dtm, at +848, +1130, and +1429 days past the outburst. This means that the X-ray emission continues to be lower by at least an order of magnitude, compared to archival, preoutburst measurements.
Conclusions. We confirm that the observed properties of PS16dtm are difficult to reconcile with normal AGN variability. The TDE scenario continues to be a plausible explanation for the observed properties, even though PS16dtm shows differences compared to TDE in quiescent galaxies. We suggest that this event is part of a growing sample of TDEs that show broad Balmer line profiles and Fe II complexes. We argue that the extreme variability seen in the AGN host due to PS16dtm may have easily been misclassified as a CLAGN, especially if the rising part of the light curve had been missed. This implies that some changing look episodes in AGN may be triggered by TDEs. Imaging and spectroscopic data of AGN with good sampling are needed to enable testing of possible physical mechanisms behind the extreme variability in AGN.
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Ključne besede: nuclear transients, supermassive black holes, tidal disruption events, active galactic nuclei
Objavljeno: 24.01.2023; Ogledov: 272; Prenosov: 12
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6. Strongly lensed supernovae at high-redshiftsTanja Petrushevska, predavanje na tuji univerzi Opis: The searches and observations of supernovae (SNe) have been motivated by the fact that they are exceptionally useful for various astrophysical and cosmological applications. Most prominently, Type Ia SNe (SNe Ia) have been used as distance indicators showing that the expansion rate of the Universe is accelerating. The strong gravitational lensing effect provides another powerful tool and occurs when a foreground mass distribution is located along the line of sight to a background source. It can happen so that galaxies and galaxy clusters can act as “gravitational telescopes”, boosting the faint signals from distant SNe and galaxies. Thanks to the magnification boost provided by the gravitational telescope, we are able to probe galaxies and SNe that otherwise would be undetectable. Therefore, the combination of the two tools, SNe and strong lensing, in the single phenomenon of strongly lensed SNe, provides a powerful simultaneous probe of several cosmological and astrophysical phenomena. In this talk, I will present some of the past results that have been possible due to the observations of strongly lensed supernovae and anticipate what we can expect in the future from the upcoming telescope surveys.
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Ključne besede: supernovae, strong lensing
Objavljeno: 16.03.2023; Ogledov: 231; Prenosov: 0
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8. THE RISE OF SN 2014J IN THE NEARBY GALAXY M82Ariel Goobar, Joel Johansson, Rahman Amanullah, Yi Cao, Mansi Kasliwal, Raphael Ferretti, Peter Nugent, Daniel Perley, Avishay Gal-Yam, Eran Ofek, S. P. Tendulkar, M. Dennefeld, Stefano Valenti, Iair Arcavi, D.P.K. Banerjee, V. Venkataraman, Brad Cenko, Tanja Petrushevska, T.J. Dupuy, M.C. Liu, 2014, izvirni znanstveni članek Opis: We report on the discovery of SN 2014J in the nearby galaxy M82. Given its proximity, it offers the best opportunity
to date to study a thermonuclear supernova (SN) over a wide range of the electromagnetic spectrum. Optical, nearIR,
and mid-IR observations on the rising light curve, orchestrated by the intermediate Palomar Transient Factory,
show that SN 2014J is a spectroscopically normal Type Ia supernova (SN Ia), albeit exhibiting high-velocity features
in its spectrum and heavily reddened by dust in the host galaxy. Our earliest detections start just hours after the
fitted time of explosion. We use high-resolution optical spectroscopy to analyze the dense intervening material and
do not detect any evolution in the resolved absorption features during the light curve rise. Similar to other highly
reddened SNe Ia, a low value of total-to-selective extinction, RV 2, provides the best match to our observations.
We also study pre-explosion optical and near-IR images from Hubble Space Telescope with special emphasis on
the sources nearest to the SN location.
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Ključne besede: dust, extinction – galaxies: individual (Messier 82) – supernovae: individual (SN 2014J)
Objavljeno: 22.01.2018; Ogledov: 3215; Prenosov: 0
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10. THE PECULIAR EXTINCTION LAW OF SN 2014J MEASURED WITH THE HUBBLE SPACE TELESCOPERahman Amanullah, Ariel Goobar, Joel Johansson, D.P.K. Banerjee, V. Venkataraman, V. Joshi, N.M. Ashok, Yi Cao, Mansi Kasliwal, S.R. Kulkarni, P.E. Nugent, Tanja Petrushevska, V. Stanishev, 2014, izvirni znanstveni članek Opis: The wavelength dependence of the extinction of Type Ia SN 2014J in the nearby galaxy M82 has been measured
using UV to near-IR photometry obtained with the Hubble Space Telescope, the Nordic Optical Telescope, and
the Mount Abu Infrared Telescope. This is the first time that the reddening of an SN Ia is characterized over the
full wavelength range of 0.2–2μm. A total-to-selective extinction, RV 3.1, is ruled out with high significance.
The best fit at maximum using a Galactic type extinction law yields RV = 1.4 ± 0.1. The observed reddening of
SN 2014J is also compatible with a power-law extinction, Aλ/AV = (λ/λV )
p as expected from multiple scattering
of light, with p = −2.1 ± 0.1. After correcting for differences in reddening, SN 2014J appears to be very similar
to SN 2011fe over the 14 broadband filter light curves used in our study.
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Ključne besede: dust, extinction – galaxies: individual (Messier 82) – supernovae: individual SN2014J
Objavljeno: 22.01.2018; Ogledov: 2787; Prenosov: 0
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