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Register a new userSearching for differences in Swifts intermediate GRBs
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Antonio de Ugarte Postigo
Publication date
2010
fields
Physics
and research's language is
English
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Gamma-ray bursts are usually classified through their high-energy emission into short-duration and long-duration bursts, which presumably reflect two different types of progenitors. However, it has been shown on statistical grounds that a third, intermediate population is needed in this classification scheme, although an extensive study of the properties of this class has so far not been done. The large amount of follow-up studies generated during the Swift era allows us to have a suficient sample to attempt a study of this third population through the properties of their prompt emission and their afterglows. Our study is focused on a sample of GRBs observed by Swift during its first four years of operation. The sample contains those bursts with measured redshift since this allows us to derive intrinsic properties. Intermediate bursts are less energetic and have dimmer afterglows than long GRBs, especially when considering the X-ray light curves, which are on average one order of magnitude fainter than long bursts. There is a less significant trend in the redshift distribution that places intermediate bursts closer than long bursts. Except for this, intermediate bursts show similar properties to long bursts. In particular, they follow the Epeak vs. Eiso correlation and have, on average, positive spectral lags with a distribution similar to that of long bursts. Like long GRBs, they normally have an associated supernova, although some intermediate bursts have shown no supernova component. This study shows that intermediate bursts are different from short bursts and, in spite of sharing many properties with long bursts, there are some differences between them as well. We suggest that the physical difference between intermediate and long bursts could be that for the first the ejecta are thin shells while for the latter they are thick shells.
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As soon as their extragalactic origins were established, the hope to make Gamma - Ray Bursts (GRBs) standardizeable candles to probe the very high - z universe has opened the search for scaling relations between redshift independent observable quantities and distance dependent ones. Although some remarkable success has been achieved, the empirical correlations thus found are still affected by a significant intrinsic scatter which downgrades the precision in the inferred GRBs Hubble diagram. We investigate here whether this scatter may come from fitting together objects belonging to intrinsically different classes. To this end, we rely on a cladistics analysis to partition GRBs in homogenous families according to their rest frame properties. Although the poor statistics prevent us from drawing a definitive answer, we find that both the intrinsic scatter and the coefficients of the $E_{peak}$,-,$E_{iso}$ and $E_{peak}$,-,$L$ correlations significantly change depending on which subsample is fitted. It turns out that the fit to the full sample leads to a scaling relation which approximately follows the diagonal of the region delimited by the fits to each homogenous class. We therefore argue that a preliminary identification of the class a GRB belongs to is necessary in order to select the right scaling relation to be used in order to not bias the distance determination and hence the Hubble diagram.
A range of Bayesian tools has become widely used in cosmological data treatment and parameter inference (see Kunz, Bassett & Hlozek (2007), Trotta (2008), Amendola, Marra & Quartin (2013)). With increasingly big datasets and higher precision, tools that enable us to further enhance the accuracy of our measurements gain importance. Here we present an approach based on internal robustness, introduced in Amendola, Marra & Quartin (2013) and adopted in Heneka, Marra & Amendola (2014), to identify biased subsets of data and hidden correlation in a model independent way.
Intermediate-mass black holes are theoretically predicted but observationally elusive, and evidence for them is often indirect. The nearby face-on spiral galaxy NGC3310 has hosted many supernovae in recent history, and recent Chandra observations have shown a group of strong off-nuclear X-ray sources that are coincident with radio emission seen in archival VLA and MERLIN observations. Their luminosity, spectrum and off-nuclear location make these sources excellent IMBH candidates. To investigate this possibility, we used combined EVN/e-MERLIN observations at both 1.4 and 5 GHz to look for compact radio emission and evidence of jet activity. We detect a compact radio source within one arcsecond of a Chandra source with an estimated mass ${rm M}_{rm BH}sim3times10^4 {rm M}_{odot}$.
Gamma-Ray Bursts can provide information about star formation at high redshifts. Even in the absence of a optical/near-infrared/radio afterglow, the high detection rate of X-ray afterglows by swift/XRT and its localization precision of 2-3 arcsec facilitates the identification and study of GRB host galaxies. We focus on the search for the host galaxies of a sample of 17 bursts with XRT error circles but no detected long-wavelength afterglow. Three of these events can also be classified as truly dark bursts: the observed upper limit on the optical flux of the afterglow was less than expected based on the X-ray flux. Our study is based on deep R and K-band observations performed with ESO/VLT instruments, supported by GROND and NEWFIRM. To be conservative, we searched for host galaxies in an area with a radius twice the 90% swift/XRT error circle. For 15 of the 17 bursts we find at least one galaxy inside the doubled XRT error circle. In seven cases we discover extremely red objects in the error circles. The most remarkable case is the host of GRB 080207 which as a colour of R-K~4.7 mag (AB), one of the reddest galaxies ever associated with a GRB. As a by-product of our study we identify the optical afterglow of GRB 070517A. Optically dim afterglows result from cosmological Lyman drop out and dust extinction, but the former process is only equired for a minority of cases (<1/3). Extinction by dust in the host galaxies might explain all other events. Thereby, a seemingly non-negligible fraction of these hosts are globally dust-enshrouded, extremely red galaxies. This suggests that bursts with optically dim afterglows trace a subpopulation of massive starburst galaxies, which are markedly different from the main body of the GRB host galaxy population, namely the blue, subluminous, compact galaxies.
Since their serendipitous discovery, Fast Radio Bursts (FRBs) have garnered a great deal of attention from both observers and theorists. A new class of radio telescopes with wide fields of view have enabled a rapid accumulation of FRB observations, confirming that FRBs originate from cosmological distances. The high occurrence rate of FRBs and the development of new instruments to observe them create opportunities for FRBs to be utilized for a host of astrophysical and cosmological studies. We focus on the rare, and as yet undetected, subset of FRBs that undergo repeated bursts and are strongly gravitationally lensed by intervening structure. An extremely precise timing of burst arrival times is possible for strongly lensed repeating FRBs, and we show how this timing precision enables the search for long wavelength gravitational waves, including those sourced by supermassive black hole binary systems. The timing of burst arrival for strongly lensed repeating FRBs is sensitive to gravitational wave sources near the FRB host galaxy, which may lie at cosmological distances and would therefore be extremely challenging to detect by other means. Timing of strongly lensed FRBs can also be combined with pulsar timing array data to search for correlated time delays characteristic of gravitational waves passing through the Earth.
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