Identification of high energy gamma-ray sources and source populations in the era of deep all-sky coverage     

Olaf Reimer  Diego F. Torres 《Astrophysics and Space Science》2007,309(1-4):57-62

A large fraction of the anticipated source detections by the Gamma-ray Large Area Space Telescope (GLAST-LAT) will initially be unidentified. We argue that traditional approaches to identify individuals and/or populations of gamma ray sources will encounter procedural limitations. Those limitations are discussed on the background of source identifications from EGRET observations. Generally, our ability to classify (faint) source populations in the anticipated GLAST dataset with the required degree of statistical confidence will be hampered by sheer source wealth. A new paradigm for achieving the classification of gamma ray source populations is discussed.  相似文献   

Pliocene extensional tectonics in the Eastern Central Patagonian Cordillera: geochronological constraints and new field evidence     

Yves Lagabrielle  Manuel Surez  Jacques Malavieille  Diego Morata  Felipe Espinoza  Ren C. Maury  Bruno Scalabrino  Luis Barbero  Rita de la Cruz  Eduardo Rossello  Herv Bellon 《地学学报》2007,19(6):413-424

Recent field work and review of radiometric data obtained from Neogene lavas and plutonic rocks exposed in the Eastern Central Patagonian Cordillera (46–48ºS), which overlie subducted segments of the South Chile Ridge, suggest important Late Miocene to Pleistocene morphological changes in relation to base level variations and/or tectonic events. We present new field observations from a region south of Lago General Carrera‐Buenos Aires, between the main Cordillera and the Meseta del Lago Buenos Aires, demonstrating that normal faulting controlled valley incisions and occurred during lava emplacement at 5–4 Ma and after 3 Ma. We also show that the 12 Ma basaltic flows of the Meseta del Lago Buenos Aires (∼2000 m a.s.l.) have been subjected to deep incision, with younger lavas dated at 1.2 Ma partially filling the valleys. These incisions are thought to reflect progressive eastward tilting of the entire meseta. Our new observations, together with additional features from Central Patagonia, strongly suggest that tectonic events led to a regional widespread morphological change after 5 Ma. The coincidence in time and space between the subduction of segments of the South Chile Ridge at 6 and 3 Ma causing opening of a slab window, and strong base level variations in the studied area, suggests a cause‐and‐effect relationship. In Central Patagonia, compressional tectonics ended well before extensional events reported here. Causes of uplift and further extension are probably completely disconnected. The uplift is purely tectonic in origin and occurred prior to the subduction of the South Chile Ridge. Extension should be a consequence of this subduction.  相似文献   

The host galaxies of long-duration gamma-ray bursts in a cosmological hierarchical scenario     

Sebastián E. Nuza  Patricia B. Tissera  Leonardo J. Pellizza  Diego G. Lambas  Cecilia Scannapieco †  María E. De Rossi 《Monthly notices of the Royal Astronomical Society》2007,375(2):665-672

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Unveiling soft gamma-ray repeaters with INTEGRAL     

Diego Götz  Sandro Mereghetti  Kevin Hurley 《Astrophysics and Space Science》2007,308(1-4):51-59

Thanks to INTEGRAL’s long exposures of the Galactic Plane, the two brightest Soft Gamma-Ray Repeaters, SGR 1806-20 and SGR 1900+14, have been monitored and studied in detail for the first time at hard-X/soft gamma rays. This has produced a wealth of new scientific results, which we will review here. Since SGR 1806-20 was particularly active during the last two years, more than 300 short bursts have been observed with INTEGRAL and their characteristics have been studied with unprecedented sensitivity in the 15–200 keV range. A hardness-intensity anticorrelation within the bursts has been discovered and the overall Number-Intensity distribution of the bursts has been determined. In addition, a particularly active state, during which 100 bursts were emitted in 10 minutes, has been observed on October 5 2004, indicating that the source activity was rapidly increasing. This eventually led to the Giant Flare of December 27th 2004, for which a possible soft gamma-ray (>80 keV) early afterglow has been detected. The deep observations allowed us to discover the persistent emission in hard X-rays (20–150 keV) from 1806-20 and 1900+14, the latter being in a quiescent state, and to directly compare the spectral characteristics of all Magnetars (two SGRs and three Anomalous X-ray Pulsars) detected with INTEGRAL. D.G. acknowledges the French Space Agency (CNES) for financial support. Based on observations with INTEGRAL, an ESA project with instruments and the science data centre funded by ESA member states (especially the PI countries: Denmark, France, Germany, Italy, Switzerland, Spain), Czech Republic and Poland, and with the participation of Russia and the USA. ISGRI has been realized and maintained in flight by CEA-Saclay/DAPNIA with the support of CNES. K.H. is grateful for support under NASA’s INTEGRAL U.S. Guest Investigator program, Grants NAG5-13738 and NNG05GG35G.  相似文献   

A new Late Holocene sea-level record from the Mississippi Delta: evidence for a climate/sea level connection?     

Juan L. González  Torbjörn E. Törnqvist 《Quaternary Science Reviews》2009,28(17-18):1737-1749

A detailed relative sea-level (RSL) record was constructed for the time interval 600–1600 AD, using basal peat to track sea level and containing 16 sea-level index points that capture ～60 cm of RSL rise. The study area is in the Mississippi Delta where the spring tidal range is ～0.47 m, the impact of ocean currents on sea-surface topography is limited, and crustal motions are well constrained. Age control was obtained by AMS ¹⁴C dating and most ages represent weighted means of two subsamples. Sample elevations were determined by combining differential GPS measurements with optical surveying. All index points were plotted as error boxes using 2σ confidence intervals for the ages, plus all vertical errors involved in sampling and surveying, as well as the indicative range of the samples. A striking clustering of sea-level index points between ～1000 and ～1200 AD suggests a possible acceleration in the rate of RSL rise. Removal of the long-term trend (0.60 mm yr^?1) allows for the possibility of a sea-level oscillation with a maximum amplitude of ～55 cm. However, given the size of the error boxes the possibility that oscillations did not occur cannot be entirely ruled out. Comparison of the new RSL record with various proxy climate records suggests that sea level in this area may have responded to hemispheric temperature changes, including the Medieval Warm Period and the Little Ice Age. However, given the error margins associated with this reconstruction, it is stressed that this causal mechanism is tentative and requires corroboration by high-resolution sea-level reconstructions elsewhere.  相似文献   

INTEGRAL/XMM views on the MeV source GRO J1411-64     

Diego F. Torres  Shu Zhang  Olaf Reimer  Xavier Barcons  Amalia Corral  Valentí Bosch-Ramon  Josep M. Paredes  Gustavo E. Romero  Jin Qu  Werner Collmar  Volker Schönfelder  Yousaf Butt 《Astrophysics and Space Science》2007,309(1-4):17-21

The COMPTEL unidentified source GRO J 1411-64 was observed by INTEGRAL and XMM-Newton in 2005. The Circinus Galaxy is the only source detected within the 4σ location error of GRO J1411-64, but in here excluded as the possible counterpart. At soft X-rays, 22 reliable and statistically significant sources (likelihood >10) were extracted and analyzed from XMM-Newton data. Only one of these sources, XMMU J141255.6-635932, is spectrally compatible with GRO J1411-64 although the fact the soft X-ray observations do not cover the full extent of the COMPTEL source position uncertainty make an association hard to quantify and thus risky. At the best location of the source, detections at hard X-rays show only upper limits, which, together with MeV results obtained by COMPTEL suggest the existence of a peak in power output located somewhere between 300–700 keV for the so-called low state. Such a spectrum resembles those in blazars or microquasars, and might suggest at work by the models accordingly. However, an analysis using a microquasar model consisting on a magnetized conical jet filled with relativistic electrons, shows that it is hard to comply with all observational constrains. This fact and the non-detection at hard X-rays introduce an a-posteriori question mark upon the physical reality of this source, what is discussed here.  相似文献   

Testing the suitability of frictional behaviour for pyroclastic flow simulation by comparison with a well-constrained eruption at Tungurahua volcano (Ecuador)   总被引：2，自引：2，他引：0  

Karim Kelfoun  Pablo Samaniego  Pablo Palacios  Diego Barba 《Bulletin of Volcanology》2009,71(9):1057-1075

We use a well-monitored eruption of Tungurahua volcano to test the validity of the frictional behaviour, also called Mohr–Coulomb, which is generally used in geophysical flow modelling. We show that the frictional law is not appropriate for the simulation of pyroclastic flows at Tungurahua. With this law, the longitudinal shape of the simulated flows is a thin wedge of material progressively passing, over several hundreds of metres, from an unrealistic thickness at the front (<<1 mm) to some tens of centimetres. Simulated deposits form piles which accumulate at the foot of the volcano and are more similar to sand piles than natural pyroclastic deposits. Finally, flows simulated with a frictional rheology are not channelised by the drainage system, but affect all the flanks of the volcano. In addition, their velocity can exceed 150 m s⁻¹, allowing pyroclastic flows to cross interfluves at bends in the valley, affecting areas that would not have been affected in reality and leaving clear downstream areas that would be covered in reality. Instead, a simple empirical law, a constant retarding stress (i.e. a yield strength), involving only one free parameter, appears to be much better adapted for modelling pyroclastic flows. A similar conclusion was drawn for the Socompa debris avalanche simulation (Kelfoun and Druitt, J Geophys Res 110:B12202, 2005).  相似文献   

Tropical salt marsh succession as sea-level indicator during Heinrich events     

Catalina González  Lydie M. Dupont 《Quaternary Science Reviews》2009,28(9-10):939-946

Centennial–millennial dynamics of tropical salt marsh vegetation are documented in the pollen record from marine core MD03-2622, Cariaco Basin, Venezuela, which spans the glacial period between 63 and 29 ka. Five rapid and abrupt expansions of salt marsh vegetation are linked with North Atlantic Heinrich events (HEs). Within each event, a recurrent pattern – starting with species of Chenopodiaceae, followed by grasses, and subsequently by Cyperaceae species – suggests a successional process that is determined by the close relationship between sea-level and community dynamics. The salt tolerant Chenopodiaceae, at the base of each sequence, indicate hypersaline intertidal environments, which were most likely promoted by extremely dry atmospheric conditions. Rapid sea-level rise characterizes the onset of HE stadials, causing erosion of marsh sediments, and continued recruitment of pioneer species (Chenopodiaceae), which are the only ones capable of tolerating the rapid rate of disturbance. Once, as sea-level drops or as rise decelerates, marsh plants are able to trap and stabilize sediments, favouring the establishment of more competitive species (graminoids). The increment of marsh height as a result of autochthonous sediment accumulation reduces the extent of hypersaline environments, and allows the establishment of mesohaline species. These results add to the scarce knowledge on tropical salt marsh ecosystems, and provide independent paleoclimatic evidence on sea-level changes occurring simultaneously with Antarctica climate variations.  相似文献   

Quasinormal modes and greybody factors of a four-dimensional Lifshitz black hole with z=0     

Marcela Catalán  Eduardo Cisternas  P. A. González  Yerko Vásquez 《Astrophysics and Space Science》2016,361(6):189

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Scalar perturbations of nonlinear charged Lifshitz black branes with hyperscaling violation     

P. A. González  Yerko Vásquez 《Astrophysics and Space Science》2016,361(7):224

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