We present predictions of centimeter and millimeter radio emission from reverse shocks (RSs) in the early afterglows of gamma-ray bursts (GRBs) with the goal of determining their detectability with current and future radio facilities. We simulate radio light curves in a framework generalized for any circumburst medium structure and including a parameterization of the shell thickness regime that is more realistic than the simple assumption of thick- or thin-shell approximations. We show that the brightest and most distinct RS radio signatures are detectable up to 1 day after the burst, emphasizing the need for rapid radio follow-up. Detection is easier for bursts with later optical peaks, high isotropic energies, lower circumburst medium densities, and at observing frequencies that are less prone to synchrotron self-absorption effects -- typically above a few GHz. Given recent detections of polarized prompt gamma-ray and optical RS emission, we suggest that detection of polarized radio/millimeter emission will unambiguously confirm the presence of low-frequency RSs at early time.
COBISS.SI-ID: 547457
Gamma-ray burst GRB 140430A was detected by the Swift satellite and observed promptly with the imaging polarimeter RINGO3 mounted on the Liverpool Telescope, with observations beginning 124 seconds after the GRB trigger, while the prompt gamma-ray emission was still ongoing. In this paper, we present densely sampled (10-second temporal resolution) early optical light curves in 3 optical bands and limits to the degree of optical polarization. We compare optical, X-ray and gamma-ray properties and present an analysis of the optical emission during a period of high-energy flaring. The complex optical light curve cannot be explained merely with a combination of forward and reverse shock emission from a standard external shock, implying additional contribution of emission from internal shock dissipation. We estimate an upper limit for optical polarization during the prompt phase to be as low as P ( 12% (1sigma). This low value is in contrast to previous detections of highly polarized prompt gamma-ray flares at P ) 30% from INTEGRAL and IKAROS satellites, and could be reconciled if individual components in GRB 140430A are highly polarized but have significantly different or variable position angles which would produce an apparent net low polarization degree when combined.
COBISS.SI-ID: 567937
We use gamma-ray burst (GRB) afterglow spectra observed with the VLT/X-Shooter spectrograph to measure rest-frame extinction in GRB lines-of-sight by modelling the broadband near-infrared (NIR) to X-ray afterglow spectral energy distributions (SEDs). Our sample consists of nine Swift GRBs, of which eight belong to the long-duration and one to the short-duration class. Dust is modelled using the average extinction curves of the Milky Way and the two Magellanic Clouds. We derive the rest-frame extinction of the entire sample, which fall in the range 0 ≲ AV ≲ 1.2. Moreover, the SMC extinction curve is the preferred extinction curve template for the majority of our sample, a result that is in agreement with those commonly observed in GRB lines of sights. In one analysed case (GRB 120119A), the common extinction curve templates fail to reproduce the observed extinction. To illustrate the advantage of using the high-quality, X-Shooter afterglow SEDs over the photometric SEDs, we repeat the modelling using the broadband SEDs with the NIR-to-UV photometric measurements instead of the spectra. The main result is that the spectroscopic data, thanks to a combination of excellent resolution and coverage of the blue part of the SED, are more successful in constraining extinction curves and therefore dust properties in GRB hosts with respect to photometric measurements. In all cases but one the extinction curve of one template is preferred over the others. We show that the modelled values of the extinction AV and the spectral slope, obtained through spectroscopic and photometric SED analysis, can differ significantly for individual events, though no apparent trend in the differences is observed. Finally we stress that, regardless of the resolution of the optical-to-NIR data, the SED modelling gives reliable results only when the fit is performed on a SED covering a broader spectral region (in our case extending to X-rays).
COBISS.SI-ID: 547201
The article presents a new method for the three-dimensional multivariate decomposition of the Madden-Julian Oscillation (MJO) into balanced and inertio-gravity (IG) components. The method analyzes global fields with no filtering involved, and it provides a quantitative comparison between the contribution of the Rossby, Kelvin, and other balanced and IG modes to the MJO circulation and its teleconnections. Results show that the Rossby mode with the lowest meridional index is the largest contributor to the MJO circulation over the Pacific. A smaller role of the Kelvin mode is diagnosed over the Indian Ocean and the maritime continent. The presented method shows new ways of evaluating the MJO structure and its global impacts in weather and climate models.
COBISS.SI-ID: 337321
The second phase of the Air Quality Model Evaluation International Initiative (AQMEII) brought together sixteen modeling groups from Europe and North America, running eight operational online-coupled air quality models over Europe and North America on common emissions and boundary conditions. The main aim of this study is to compare the response of coupled air quality models to simulate levels of O3 over the two continental regions. The simulated annual, seasonal, continental and sub-regional ozone surface concentrations and vertical profiles for the year 2010 have been evaluated against a large observational database from different measurement networks operating in Europe and North America. Results show that the simulated levels highly depend on the meteorological and chemical configurations used in the models, even within the same modeling system. Among others, models have a tendency to severely under-predict high O3 values that are of concern for air quality forecast and control policy applications.
COBISS.SI-ID: 327337