A search for thermal X-ray signatures in Gamma-Ray Bursts II: The Swift sample

In several gamma-ray bursts (GRBs) excess emission, in addition to the standard synchrotron afterglow spectrum, has been discovered in the early time X-ray observations. It has been proposed that this excess comes from black body emission, which may be related to the shock break-out of a supernova in the GRBs progenitor star. This hypothesis is supported by the discovery of excess emission in several GRBs with an associated supernova. Using mock spectra we show that it is only likely to detect such a component, similar to the one proposed in GRB 101219B, at low redshift and in low absorption environments. We also perform a systematic search for black body components in all the GRBs observed with the Swift satellite and find six bursts (GRB 061021, 061110A, 081109, 090814A, 100621A and 110715A) with possible black body components. Under the assumption that their excess emission is due to a black body component we present radii, temperatures and luminosities of the emitting components. We also show that detection of black body components only is possible in a fraction of the Swift bursts.Comment: 11 pages, 8 figures, accepted for MNRA

Strong spectral evolution during the prompt emission of GRB 070616

Swift has revealed features in GRB early light curves, such as steep decays and X-ray flares, whose properties are consistent with an internal origin though they are far from understood. The steep X-ray decay is often explained using the curvature effect; however a significant number of GRBs display strong spectral evolution during this phase, and a new mechanism must be invoked to explain this. Of particular interest are the longest duration GRBs in which the early emission can be studied in most detail. Here we present data for GRB 070616, in which the prompt emission shows a complex multipeaked structure, leading to one of the longest prompt emission durations ever recorded. We take advantage of extensive coverage of such a long burst by all Swift instruments. Combining data from Swift and Suzaku we study the evolution of the prompt emission spectrum, following the temporal variability of the peak energy and spectral slope.Comment: 4 pages, 2 figures (Fig 1 in colour), contributed talk, submitted to the proceedings of Gamma Ray Bursts 2007, Santa Fe, New Mexico, November 5-9 200

The soft X-ray excess AGN RE J2248-511

We model the spectral energy distribution of the ultrasoft broad-line AGN RE J2248-511 with Comptonised accretion disc models. These are able to reproduce the steep optical and ultrasoft X-ray slopes, and the derived black hole mass is consistent with independent mass estimates. This AGN displays properties of both broad and narrow line Seyfert 1 galaxies, but we conclude that it is intrinsically a `normal' Seyfert 1 viewed at high inclination angle.Comment: 4 pages, 1 figure. MG10 Proceeding

A search for thermal X-ray signatures in Gamma-Ray Bursts I: Swift bursts with optical supernovae

The X-ray spectra of Gamma-Ray Bursts can generally be described by an absorbed power law. The landmark discovery of thermal X-ray emission in addition to the power law in the unusual GRB 060218, followed by a similar discovery in GRB 100316D, showed that during the first thousand seconds after trigger the soft X-ray spectra can be complex. Both the origin and prevalence of such spectral components still evade understanding, particularly after the discovery of thermal X-ray emission in the classical GRB 090618. Possibly most importantly, these three objects are all associated with optical supernovae, begging the question of whether the thermal X-ray components could be a result of the GRB-SN connection, possibly in the shock breakout. We therefore performed a search for blackbody components in the early Swift X-ray spectra of 11 GRBs that have or may have associated optical supernovae, accurately recovering the thermal components reported in the literature for GRBs 060218, 090618 and 100316D. We present the discovery of a cooling blackbody in GRB 101219B/SN2010ma, and in four further GRB-SNe we find an improvement in the fit with a blackbody which we deem possible blackbody candidates due to case-specific caveats. All the possible new blackbody components we report lie at the high end of the luminosity and radius distribution. GRB 101219B appears to bridge the gap between the low-luminosity and the classical GRB-SNe with thermal emission, and following the blackbody evolution we derive an expansion velocity for this source of order 0.4c. We discuss potential origins for the thermal X-ray emission in our sample, including a cocoon model which we find can accommodate the more extreme physical parameters implied by many of our model fits.Comment: 16 pages, 6 figures, accepted for MNRA

Finding LoTSS of hosts for GRBs: a search for galaxy - gamma-ray burst coincidences at low frequencies with LOFAR

The LOFAR Two-Metre Sky Survey (LoTSS) is an invaluable new tool for investigating the properties of sources at low frequencies and has helped to open up the study of galaxy populations in this regime. In this work, we perform a search for host galaxies of gamma-ray bursts (GRBs). We use the relative density of sources in Data Release 2 of LoTSS to define the probability of a chance alignment, $P_{\rm chance}$, and find 18 sources corresponding to 17 GRBs which meet a $P_{\rm chance}$<1% criterion. We examine the nature and properties of these radio sources using both LOFAR data and broadband information, including their radio spectral index, star formation rate estimates and any contributions from active galactic nucleus emission. Assuming the radio emission is dominated by star formation, we find that our sources show high star formation rates ($10^1$-$10^3$ $M_{\odot}$ yr$^{-1}$) compared with both a field galaxy sample and a sample of core-collapse supernova hosts, and the majority of putative hosts are consistent with ultraluminous infrared galaxy (ULIRG) classifications. As a result of our analyses, we define a final sample of eight likely GRB host candidates in the LoTSS DR2 survey.Comment: 15 pages, 9 figures and 6 tables. Accepted by MNRA

Diagnóstico In Vivo da Sensibilidade de Nematóides a Diferentes Antihelmínticos em Ovinos do Município de Alegre, Espírito Santo

Grande variação no grau de resistência de populações de nematódeos é observada em grupos químicos, entre eles os anti-helmínticos, sendo este o principal entrave para obtenção do controle da verminose na ovinocultura. O objetivo do estudo foi avaliar a sensibilidade de nematoides de ovinos mestiços em criação semi-intensiva em três propriedades a cinco princípios ativos(levamisol, albendazol, ivermectina, monepantel e closantel) utilizados nasvermifugação. Foram analisadas amostras fecais, em três momentos (antes, 7 e 14 dias após o tratamento) utilizando a técnica de Gordon e Withlock (OPG), processadas e calculadas pelas fórmulas Eficácia=(1- [OPGtratado/OPGcontrole])x100 e Redução de OPG = 100 x [OPGt0 OPGtn/OPGt0 ]. Nos momentos sete e quatorze os grupos tratamentos diferiram significativamente (p< 0,05%) do momento zero, porém, os animais tratados com ivermectina no momento quatorze não apresentaram diferença significativa quando comparado ao grupo controle. No exame coproparasitológico os gêneros mais frequentes foram Haemonchus e Trichostrongylus. Na primeira propriedade o monepantel e o albendazol demonstraram os melhores resultados de redução de OPG, na segunda propriedade o levamisol, closantel e monepantel apresentaram resultados expressivos quando comparado aos demais fármacos e na terceira propriedade os fármacos que tiveram melhores resultados de redução de OPG foram levamisol e monepantel. Nas propriedades A, B e C, foram diagnosticadas populações de nematoides resistentes a ivermectina. Nas propriedades B e C, foram diagnosticadas populações de nematoides resistentes a albendazol

The hidden X-ray breaks in afterglow light curves

Gamma-Ray Burst (GRB) afterglow observations in the Swift era have a perceived lack of achromatic jet breaks compared to the BeppoSAX, or pre-Swift era. Specifically, relatively few breaks, consistent with jet breaks, are observed in the X-ray light curves of these bursts. If these breaks are truly missing, it has serious consequences for the interpretation of GRB jet collimation and energy requirements, and the use of GRBs as standard candles. Here we address the issue of X-ray breaks which are possibly 'hidden' and hence the light curves are misinterpreted as being single power-laws. We show how a number of precedents, including GRB 990510 & GRB 060206, exist for such hidden breaks and how, even with the well sampled light curves of the Swift era, these breaks may be left misidentified. We do so by synthesising X-ray light curves and finding general trends via Monte Carlo analysis. Furthermore, in light of these simulations, we discuss how to best identify achromatic breaks in afterglow light curves via multi-wavelength analysis.Comment: 4 pages, contributed talk, submitted to the proceedings of Gamma Ray Bursts 2007, Santa Fe, New Mexico, November 5-9 200

Gas and dust properties in the afterglow spectra of GRB 050730

We present early WHT ISIS optical spectroscopy of the afterglow of gamma-ray burst GRB 050730. The spectrum shows a DLA system with the highest measured hydrogen column to date: N(HI) = 22.1 +/- 0.1 at the third-highest GRB redshift z = 3.968. Our analysis of the Swift XRT X-ray observations of the early afterglow show X-ray flares accompanied by decreasing X-ray absorption. From both the optical and the X-ray spectra we constrain the dust and gas properties of the host galaxy. We find the host to be a low metallicity galaxy, with low dust content. Much of the X-ray absorbing gas is situated close to the GRB, whilst the HI absorption causing the DLA is most likely located further out.Comment: 5 pages, 2 figures. Accepted for A&A Letter

Extensive telomere repeat arrays in mouse are hypervariable

In this study we have analysed mouse telomeres by Pulsed Field Gel Electrophoresis (PFGE). A number of specific restriction fragments hybridising to a (TTA-GGG)4 probe in the size range 50-150kb can be detected. These fragments are devoid of sites for most restriction enzymes suggesting that they comprise simple repeats; we argue that most of these are likely to be (TTAGGG)n. Each discrete fragment corresponds to the telomere of an individual chromosome and segregates as a Mendelian character. However, new size variants are being generated in the germ line at very high rates such that inbred mice are heterozygous at all telomeres analysable. In addition we show that specific small (approximately 4-12kb) fragments can be cleaved within some terminal arrays by the restriction enzyme MnII which recognises 5'(N7)GAGG3'. Like the complete telomere-repeat arrays (TRA's) these fragments form new variants at high rates and possibly by the same process. We speculate on the mechanisms that may be involved