GRB 130427A: A Nearby Ordinary Monster Maselli, A.; Melandri, A.; Nava, L. ...
Science (American Association for the Advancement of Science),
01/2014, Letnik:
343, Številka:
6166
Journal Article
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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 × 10⁵³ ...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 isotropie energies.
Here we present an original approach to generate 2D high detail riverbed based on a drone photogrammetric survey, and RTK bathymetry measurements for Mera river in the Italian Alps. The aim is to ...better represent macro-roughness and riverbed structure of the river, also extending it to an ungauged area. Specifically, we apply a step-by-step approach. I) Depth and average slope of the riverbed were calculated from bathymetry data. II) Thus, a trapezoidal channel with constant slope and variable width was defined using the drone images. III) Riffle-pool sequence was assessed as a function of river width and applied to the generated channel. IV) Finally, the semi-random Perlin Noise was added to recreate riverbed irregularities in the natural stream. HEC-RAS 2D hydraulic software was then implemented to assess spatialized water depth and velocity. The proposed methodology could be quite relevant in river hydraulics to decouple roughness coefficient from water submergence, and in Physical Habitat Simulation Model (PHABSIM), where the dependency of the output is not linear with hydraulic parameters (i.e. water depth and velocity). Indeed, we apply PHABSIM for a case study of a stretch of the river and results are compared with a previous environmental study for Mera river.
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•A new methodology to generate 2D riverbed is presented.•Point cloud bathymetry is used to model riffle-pool sequence.•Drone data are used to recreate riverbed in ungauged area.•Perlin noise is included to mimic the riverbed irregularities.•Habitat Suitability is studied basing on generated river topography.
The measurement of geometric changes in Alpine glaciers is an essential aspect to assess their reaction to climate change effects. Archive aerial images may integrate valuable information to this ...purpose at times when other types of remotely sensed data are not available. The application of photogrammetric techniques such as Structure-from-Motion (SfM) and Multi-View-Stereo matching allows the extraction of dense point clouds to model the glacier environment. The comparison of multiple datasets requires to setup a stable reference system, a task that in archive photos is generally carried out by means of ground control points (GCPs). This paper would like to propose and assess some techniques to cope with the lack of ground control. Multitemporal SfM (MSfM) is presented and tested on a dataset including six different aerial blocks collected by means of analogue (PAN/RGB) and digital airborne cameras from 1967 to 2006. These images have been downloaded from the IGNF online repository and cover the area of the Val Veny (Brenva and Miage glaciers) in the Mount Blanc massif, at the border between Italy and France. Coupled with other solutions (i.e., extraction of GCPs from maps and DTMs and ICP co-registration of point clouds), MSfM has revealed as a suitable technique for coregistration of multiple photogrammetric blocks of aerial photos with minimum ground control. Some tests carried out in the case study area demonstrated that the integration of MSfM and ICP coregistration for refinement may significantly improve the comparison between multiple point clouds, which is a fundamental pre-requisite for the analysis of glacier changes over time.
We present a carefully selected sub-sample of Swift long gamma-ray bursts (GRBs) that is complete in redshift. The sample is constructed by considering only bursts with favorable observing conditions ...for ground-based follow-up searches, which are bright in the 15-150 keV Swift/BAT band, i.e., with 1-s peak photon fluxes in excess to 2.6 photons s super(-1) cm super(-2). The sample is composed of 58 bursts, 52 of them with redshift for a completeness level of 90%, while another two have a redshift constraint, reaching a completeness level of 95%. For only three bursts we have no constraint on the redshift. The high level of redshift completeness allows us for the first time to constrain the GRB luminosity function and its evolution with cosmic times in an unbiased way. We find that strong evolution in luminosity ( delta sub()l = 2.3 + or - 0.6) or in density ( delta sub()d = 1.7 + or - 0.5) is required in order to account for the observations. The derived redshift distributions in the two scenarios are consistent with each other, in spite of their different intrinsic redshift distributions. This calls for other indicators to distinguish among different evolution models. Complete samples are at the base of any population studies. In future works we will use this unique sample of Swift bright GRBs to study the properties of the population of long GRBs.
In this paper, we compute rest-frame extinctions for the afterglows of a sample of Swift gamma-ray bursts (GRBs) complete in redshift. The selection criteria of the sample are based on observational ...high-energy parameters of the prompt emission and therefore our sample should not be biased against dusty sight-lines. It is therefore expected that our inferences hold for the general population of GRBs. Our main result is that the optical/near-infrared extinction of GRB afterglows in our sample does not follow a single distribution. 87 per cent of the events are absorbed by less than 2 mag, and 50 per cent suffer from less than 0.3-0.4 mag extinction. The remaining 13 per cent of the afterglows are highly absorbed. The true percentage of GRB afterglows showing high absorption could be even higher since a fair fraction of the events without reliable redshift measurement are probably part of this class. These events may be due to highly dusty molecular clouds/star-forming regions associated with the GRB progenitor or along the afterglow line of sight, and/or due to massive dusty host galaxies. No clear evolution in the dust extinction properties is evident within the redshift range of our sample, although the largest extinctions are at z ∼ 1.5-2, close to the expected peak of the star formation rate. Those events classified as dark are characterized, on average, by a higher extinction than typical events in the sample. A correlation between optical/near-infrared extinction and hydrogen-equivalent column density based on X-ray studies is shown, although the observed N
H appears to be well in excess compared to those observed in the Local Group. Dust extinction does not seem to correlate with GRB energetics or luminosity.
We use a nearly complete sample of gamma-ray bursts (GRBs) detected by the Swift satellite to study the correlations between the spectral peak energy E
peak of the prompt emission, the isotropic ...energetics E
iso and the isotropic luminosity L
iso. This GRB sample is characterized by a high level of completeness in redshift (90 per cent). This allows us to probe in an unbiased way the issue related to the physical origin of these correlations against selection effects. We find that one burst, GRB 061021, is an outlier to the E
peak-E
iso correlation. Despite this case, we find strong E
peak-E
iso and E
peak-L
iso correlations for the bursts of the complete sample. Their slopes, normalizations and dispersions are consistent with those found with the whole sample of bursts with measured redshift and E
peak. This means that the biases present in the total sample commonly used to study these correlations do not affect their properties. Finally, we also find no evolution with redshift of the E
peak-E
iso and E
peak-L
iso correlations.
Supermassive black holes have powerful gravitational fields with strong gradients that can destroy stars that get too close, producing a bright flare in ultraviolet and X-ray spectral regions from ...stellar debris that forms an accretion disk around the black hole. The aftermath of this process may have been seen several times over the past two decades in the form of sparsely sampled, slowly fading emission from distant galaxies, but the onset of the stellar disruption event has not hitherto been observed. Here we report observations of a bright X-ray flare from the extragalactic transient Swift J164449.3+573451. This source increased in brightness in the X-ray band by a factor of at least 10,000 since 1990 and by a factor of at least 100 since early 2010. We conclude that we have captured the onset of relativistic jet activity from a supermassive black hole. A companion paper comes to similar conclusions on the basis of radio observations. This event is probably due to the tidal disruption of a star falling into a supermassive black hole, but the detailed behaviour differs from current theoretical models of such events.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Since climate change has a significant impact on glaciers, it is essential to track their morphological change by identifying variations in ice mass. In combination with modern photogrammetric ...approaches, such as Structure-from-Motion (SfM) and Multi-View-Stereo (MVS) dense matching, historical aerial photographs may offer useful information for this objective. Point clouds of the 3D surface of the glaciers may be used to track changes in thickness and height during years. By using appropriate methods for calculating the distances between pairs of point clouds, this operation may be completed. Here, an Alpine glacier massif on Mount Blanc in the Italian Alps was chosen as the case study. National Geographic and the Forestry Institute of France (IGNF) provided seven data sets of digitized analog aerial photos. These were chosen, downloaded, and utilized for photogrammetric analysis. These data sets span almost 40 years, from 1967 to 2006, in total. While the change in ice thickness of these glaciers was relatively small until the mid-1990s, this study revealed an increasing reduction rate at the beginning of 21st century. This paper describes the adopted methodological approach for photogrammetric reconstruction, quality assessment and point cloud comparison. One of the two major glaciers in the considered group (Brenva Glacier) has been focused in this paper as case study.
We report the serendipitous discovery of a bright point source flare in the Abell cluster A1795 with archival EUVE and Chandra observations. Assuming the EUVE emission is associated with the Chandra ...source, the X-ray 0.5-7 keV flux declined by a factor of ~2300 over a time span of 6 yr, following a power-law decay with index ~2.44 + or - 0.40. The Chandra data alone vary by a factor of ~20. The spectrum is well fit by a blackbody with a constant temperature of kT ~ 0.09 keV (~10 super(6) K). The flare is spatially coincident with the nuclear region of a faint, inactive galaxy with a photometric redshift consistent at the 1sigma level with the cluster (z = 0.062476). We argue that these properties are indicative of a tidal disruption of a star by a black hole (BH) with log(M sub(BH)/M sub(middot in circle)) ~ 5.5 + or - 0.5. If so, such a discovery indicates that tidal disruption flares may be used to probe BHs in the intermediate mass range, which are very difficult to study by other means.
Gamma-ray bursts (GRBs) have been separated into two classes, originally along the lines of duration and spectral properties, called 'short/hard' and 'long/soft.' The latter have been conclusively ...linked to the explosive deaths of massive stars, while the former are thought to result from the merger or collapse of compact objects. In recent years, indications have been accumulating that the short/hard versus long/soft division does not map directly onto what would be expected from the two classes of progenitors, leading to a new classification scheme called Type I and Type II which is based on multiple observational criteria. We use a large sample of GRB afterglow and prompt-emission data (adding further GRB afterglow observations in this work) to compare the optical afterglows (or the lack thereof) of Type I GRBs with those of Type II GRBs. In comparison to the afterglows of Type II GRBs, we find that those of Type I GRBs have a lower average luminosity and show an intrinsic spread of luminosities at least as wide. From late and deep upper limits on the optical transients, we establish limits on the maximum optical luminosity of any associated supernova (SN), confirming older works and adding new results. We use deep upper limits on Type I GRB optical afterglows to constrain the parameter space of possible mini-SN emission associated with a compact-object merger. Using the prompt-emission data, we search for correlations between the parameters of the prompt emission and the late optical afterglow luminosities. We find tentative correlations between the bolometric isotropic energy release and the optical afterglow luminosity at a fixed time after the trigger (positive), and between the host offset and the luminosity (negative), but no significant correlation between the isotropic energy release and the duration of the GRBs. We also discuss three anomalous GRBs, GRB 060505, GRB 060614, and GRB 060121, in light of their optical afterglow luminosities.
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