Publication in Nature is a direct result of the PhD thesis of dr. Andrej Kopač who is also the second author of the paper. Lord Martin Rees, professor at Cambridge and British Astronomer Royal, remarked: "By homing in on this burst within a few minutes of its detection by the Swift Spacecraft, the Liverpool telescope has revealed surprising new clues to the mechanisms that power the most powerful known explosions in the universe", while prof. Enrico Costa, one of the fathers of the famous BeppoSAX GRB satellite, said: "This is one of the most important results in the past 40-year history of observations of Gamma Ray Bursts - one of the few giving a straightforward interpretation in terms of physics of the object." After the initial burst of gamma-rays that defines a γ-ray burst (GRB), expanding ejecta collide with the circumburst medium and begin to decelerate at the onset of the afterglow, during which a forward shock travels outwards and a reverse shock propagates backwards into the oncoming collimated flow, or `jet'. Light from the reverse shock should be highly polarized if the jet's magnetic field is globally ordered and advected from the central engine, with a position angle that is predicted to remain stable in magnetized baryonic jet models or vary randomly with time if the field is produced locally by plasma or magnetohydrodynamic instabilities. Degrees of linear polarization of P~10 per cent in the optical band have previously been detected in the early afterglow, but the lack of temporal measurements prevented definitive tests of competing jet models. Hours to days after the γ-ray burst, polarization levels are low (P(4 per cent), when emission from the shocked ambient medium dominates. Here we report the detection of linear polarization in the immediate afterglow of Swift γ-ray burst GRB120308A, four minutes after its discovery in the γ-ray band, which is decreasing over the subsequent ten minutes. The polarization position angle remains stable, changing by no more than 15 degrees over this time, with a possible trend suggesting gradual rotation and ruling out plasma or magnetohydrodynamic instabilities. Instead, the polarization properties show that GRBs contain magnetized baryonic jets with large-scale uniform fields that can survive long after the initial explosion.
COBISS.SI-ID: 425089
The diffuse interstellar bands (DIBs) are absorption lines observed in visual and near-infrared spectra of stars. Understanding their origin in the interstellar medium is one of the oldest problems in astronomical spectroscopy, as DIBs have been known since 1922. In a completely new approach to understanding DIBs, we combined information from nearly 500,000 stellar spectra obtained by the massive spectroscopic survey RAVE (Radial Velocity Experiment) to produce the first pseudo-three-dimensional map of the strength of the DIB at 8620 angstroms covering the nearest 3 kiloparsecs from the Sun, and show that it follows our independently constructed spatial distribution of extinction by interstellar dust along the Galactic plane. Despite having a similar distribution in the Galactic plane, the DIB 8620 carrier has a significantly larger vertical scale height than the dust. Even if one DIB may not represent the general DIB population, our observations outline the future direction of DIB research. This paper and associated 2 other papers published in the Astrophysical Journal by Kos and Zwitter, and papers led by Žerjal and Traven as leading authors led to a number of invited, keynote, and contributed talks at international conferences. The group is now responsible for all data reductions within the Hermes/GALAH project, the largest high-resolution stellar spectroscopic survey in this decade, and is leading its research of interstellar medium, active and binary stars.
COBISS.SI-ID: 473217
Meteorological part of the group is concentrating on research within the area of large/scale dynamics, data assimilation for numerical weather prediction (NWP) and predictability research, including the air quality forecast and detailed precipitation predictability. This is the only research group in the country dealing with the listed topics. The group published 20 papers in top-5 meteorological journals since 2009 and won the first project of the European Research Council (ERC) in Slovenia. The cited paper discusses deficiencies of the nesting technique for regional models and their internal variability which represent a significant source of uncertainties in regional model outputs. Presented numerical experiments on four different-size domains, two of them being midlatitude channel domains, show that the spatial structure and magnitude of uncertainties strongly depend on the domain size. The experiments are performed by using the Weather Research and Forecasting (WRF) model nested into the operational European Centre for Medium-Range Weather Forecasts (ECMWF) analyses on the same horizontal resolution 0.25° x 0.25° and by nesting WRF into a larger WRF domain with the same resolution. Uncertainties are quantified by the root-mean-square differences (rmsd) between the WRF results and their driving lateral boundary fields. The results from the midlatitude channel domain show that uncertainties in the tropospheric wind associated with the imperfect nesting method are amplified in the baroclinically active regions of the Atlantic and Pacific. The zonal wind rmsd have a dipole structure in the Atlantic in both the midlatitude channel and the half-channel simulations nested into ECMWF. The dipole is absent when WRF is nested into itself. On the contrary, the maximal rmsd for the meridional wind are always located in the domain center. When the domain centered on Europe excludes the western Atlantic and North America, the simulated uncertainties become spatially nearly homogeneous, and the magnitude of rmsd due to the imperfect nesting technique greatly reduces.
COBISS.SI-ID: 310697
Extreme luminosity of gamma ray bursts makes them an excellent cosmological probe, so that we can study galactic environment at very different redshifts. Our GRB group, which co-authored 25 GRB papers in top-5 astrophysical journals since 2009, is an active participant to observing campaign which uses the X shooter spectrograph at the 8-m VLT telescope of the European Southern Observatory in Chile. GRBs allow to study their environments at different redshifts, and so to identify any systematic changes of galactic properties with age. The paper discussed here shows that the properties of a relatively nearby GRB, which has been recently discovered, are very similar to the ones of GRBs at very large reshifts, when the Universe was just a tenth of its present age. On 8th of May the group will publish yet another paper in the journal Science. This will be their 3rd Nature/Science paper within the last 6 months. Long-duration gamma-ray bursts (GRBs) are an extremely rare outcome of the collapse of massive stars and are typically found in the distant universe. Because of its intrinsic luminosity (L ~ 3 E53 ergs per second) and its relative proximity (z = 0.34), GRB 130427A reached the highest fluence observed in the γ-ray band. Here, we present a comprehensive multiwavelength view of GRB 130427A with Swift, the 2-meter Liverpool and Faulkes telescopes, and by other ground-based facilities, highlighting the evolution of the burst emission from the prompt to the afterglow phase. The properties of GRB 130427A are similar to those of the most luminous, high-redshift GRBs, suggesting that a common central engine is responsible for producing GRBs in both the contemporary and the early universe and over the full range of GRB isotropic energies.
COBISS.SI-ID: 428417
Dr. Dunja Fabjan contributed and published a number of studies on baryonic matter in clusters of galaxies and on the effect that various astrophysical processes (e.g. star formation, galactic winds, active galactic nuclei) have on the properties of gas which is observed in X-ray and radio bands and on the stellar component of the clusters. Most important are investigations on the influence of baryonic physics on the theoretical relations between mass of the galaxy clusters and gas properties. They are vital for the future cosmological use and to conduct future X-ray surveys (e.g. the ESA's mission Athena+). As an author and co-author D.F. presented (Fabjan et al. 2011, Ettori et al. 2012) results on the influence of different astrophysical processes on the theoretical relationships, connecting the mass of the cluster of galaxies, which is mostly dark matter, with the properties of gas observed in X-rays. Checking of these theoretical relationships and their evolution was done via numerical simulations using a large and statistically relevant sample of cca. 140 galaxy clusters with masses exceeding 5 x 10^13 M⊙/h. We used gas cooling and star formation scenarios together with galactic winds reaching 500 km/s. The effects of different astrophysical processes (thermal conductivity, viscosity, gas cooling, star formation, galactic wind formation, feedback of active galactic nuclei) has been studied using a smaller number of 18 groups of clusters of galaxies. All simulations have been done with the numerical TreePM-SPH code gadget (Springel et al. 2005). We showed that among the theoretical relations of M_tot-T (total mass of the cluster vs. gas temperature), M_tot-M_gas (mass of the cluster vs. mass of gas), and M_tot_X (mass of the cluster vs. the product of gas mass and gas temperature) the latter is the least sensitive to various astrophysical processes and so of likely importance for future sky surveys. Also gas mass is a good indicator of the total mass of the cluster, as the M_tot-M_gas relation shows the lowest scatter. These theoretical relations are important, as they allow us an independent check on cosmological parameters. So they are vital for future X-ray sky surveys (e.g. the future mission Athena+). In a subsequent paper (Ettori et al. 2012) we used this data to find a general scaling relation between mass of the cluster and mass of gas, X-ray luminosity and temperature, and optimized it for the lowest achievable scatter. We also presented a new relationship using a product of luminosity and temperature. The generalized relation can be used to study evolution of clusters and to determine any discrepancies between self-similarity relations and real observations. They can also serve for cosmological applications, as we can optimize the corresponding theoretical relations.
COBISS.SI-ID: 374657