| 1. |
- Albert, A., et al.
(författare)
-
SEARCHING FOR DARK MATTER ANNIHILATION IN RECENTLY DISCOVERED MILKY WAY SATELLITES WITH FERMI-LAT
- 2017
-
Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 834:2
-
Tidskriftsartikel (refereegranskat)abstract
- We search for excess gamma-ray emission coincident with the positions of confirmed and candidate Milky Way satellite galaxies using six years of data from the Fermi Large Area Telescope (LAT). Our sample of 45 stellar systems includes 28 kinematically confirmed dark-matter-dominated dwarf spheroidal galaxies (dSphs) and 17 recently discovered systems that have photometric characteristics consistent with the population of known dSphs. For each of these targets, the relative predicted gamma-ray flux due to dark matter annihilation is taken from kinematic analysis if available, and estimated from a distance-based scaling relation otherwise, assuming that the stellar systems are DM-dominated dSphs. LAT data coincident with four of the newly discovered targets show a slight preference (each similar to 2 sigma local) for gamma-ray emission in excess of the background. However, the ensemble of derived gamma-ray flux upper limits for individual targets is consistent with the expectation from analyzing random blank-sky regions, and a combined analysis of the population of stellar systems yields no globally significant excess (global significance < 1 sigma). Our analysis has increased sensitivity compared to the analysis of 15 confirmed dSphs by Ackermann et al. The observed constraints on the DM annihilation cross section are statistically consistent with the background expectation, improving by a factor of similar to 2 for large DM masses (m(DM, b<(b)over bar>) greater than or similar to 1 TeV and m(DM, tau+tau-) greater than or similar to 70 GeV) and weakening by a factor of similar to 1.5 at lower masses relative to previously observed limits.
|
|
| 2. |
- Dominguez-Rodrigo, Manuel, et al.
(författare)
-
Constraining time and ecology on the Zinj paleolandscape : Microwear and mesowear analyses of the archaeofaunal remains of FLK Zinj and DS (Bed I), compared to FLK North (Bed I) and BK (Bed II) at Olduvai Gorge (Tanzania)
- 2019
-
Ingår i: Quaternary International. - : Elsevier BV. - 1040-6182 .- 1873-4553. ; 526, s. 4-14
-
Tidskriftsartikel (refereegranskat)abstract
- Defining the time that any given archaeofaunal assemblage took to be accumulated is challenging. Understanding the time variable is crucial to interpret how early sites were formed and what these sites represent in terms of hominin behavior. Two complementary dental analysis techniques (microwear and mesowear) have been used to understand dietary niches of ungulates. Microwear has also specifically been used to detect the character of occupations at archaeological sites. Here, we apply these techniques to a selection of Olduvai sites. Microwear and mesowear analyses on bovid teeth from a set of anthropogenic sites (FLK Zinj, DS, BK) and a carnivore palimpsest (FLK North) yielded different results. Microwear data from the three anthropogenic sites are similar, reflecting short, seasonal occupations, in contrast with the carnivore assemblage, which suggests a more prolonged period of deposition. The similar microwear signal in the two pene-contemporaneous sites of FLK Zinj and DS is encouraging, but caution in its interpretation is applied because of limited tooth enamel preservation and the resulting small sample size. The results shown here must be considered as a baseline for future and more extensive studies. Both microwear and mesowear analyses show that the most common bovid taxa in the Bed I sites exhibit mixed feeding signals. This reinforces the caution about interpretations of dietary niches of extinct ungulates based on their modern counterparts and emphasizes that for some taxa, the adoption of a browsing or grazing diet is context (time and locus) specific.
|
|
| 3. |
- Domínguez-Rodrigo, Manuel, et al.
(författare)
-
Early Pleistocene faunivorous hominins were not kleptoparasitic, and this impacted the evolution of human anatomy and socio-ecology
- 2021
-
Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 11:1
-
Tidskriftsartikel (refereegranskat)abstract
- Humans are unique in their diet, physiology and socio-reproductive behavior compared to other primates. They are also unique in the ubiquitous adaptation to all biomes and habitats. From an evolutionary perspective, these trends seem to have started about two million years ago, coinciding with the emergence of encephalization, the reduction of the dental apparatus, the adoption of a fully terrestrial lifestyle, resulting in the emergence of the modern anatomical bauplan, the focalization of certain activities in the landscape, the use of stone tools, and the exit from Africa. It is in this period that clear taphonomic evidence of a switch in diet with respect to Pliocene hominins occurred, with the adoption of carnivory. Until now, the degree of carnivorism in early humans remained controversial. A persistent hypothesis is that hominins acquired meat irregularly (potentially as fallback food) and opportunistically through klepto-foraging. Here, we test this hypothesis and show, in contrast, that the butchery practices of early Pleistocene hominins (unveiled through systematic study of the patterning and intensity of cut marks on their prey) could not have resulted from having frequent secondary access to carcasses. We provide evidence of hominin primary access to animal resources and emphasize the role that meat played in their diets, their ecology and their anatomical evolution, ultimately resulting in the ecologically unrestricted terrestrial adaptation of our species. This has major implications to the evolution of human physiology and potentially for the evolution of the human brain.
|
|
| 4. |
- Jose Bullejos, Francisco, et al.
(författare)
-
Nucleic Acid Content in Crustacean Zooplankton : Bridging Metabolic and Stoichiometric Predictions
- 2014
-
Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 9:1, s. e86493-
-
Tidskriftsartikel (refereegranskat)abstract
- Metabolic and stoichiometric theories of ecology have provided broad complementary principles to understand ecosystem processes across different levels of biological organization. We tested several of their cornerstone hypotheses by measuring the nucleic acid (NA) and phosphorus (P) content of crustacean zooplankton species in 22 high mountain lakes (Sierra Nevada and the Pyrenees mountains, Spain). The P-allocation hypothesis (PAH) proposes that the genome size is smaller in cladocerans than in copepods as a result of selection for fast growth towards P-allocation from DNA to RNA under P limitation. Consistent with the PAH, the RNA: DNA ratio was > 8-fold higher in cladocerans than in copepods, although 'fast-growth' cladocerans did not always exhibit higher RNA and lower DNA contents in comparison to 'slow-growth' copepods. We also showed strong associations among growth rate, RNA, and total P content supporting the growth rate hypothesis, which predicts that fast-growing organisms have high P content because of the preferential allocation to P-rich ribosomal RNA. In addition, we found that ontogenetic variability in NA content of the copepod Mixodiaptomus laciniatus (intra-and interstage variability) was comparable to the interspecific variability across other zooplankton species. Further, according to the metabolic theory of ecology, temperature should enhance growth rate and hence RNA demands. RNA content in zooplankton was correlated with temperature, but the relationships were nutrient-dependent, with a positive correlation in nutrient-rich ecosystems and a negative one in those with scarce nutrients. Overall our results illustrate the mechanistic connections among organismal NA content, growth rate, nutrients and temperature, contributing to the conceptual unification of metabolic and stoichiometric theories.
|
|
| 5. |
- Jose Bullejos, Francisco, et al.
(författare)
-
Shifts in food quality for herbivorous consumer growth : multiple golden means in the life history
- 2014
-
Ingår i: Ecology. - : Wiley. - 0012-9658 .- 1939-9170. ; 95:5, s. 1272-1284
-
Tidskriftsartikel (refereegranskat)abstract
- Consumer growth can be affected by imbalances between the nutrient content of the consumer and its food resource. Although ontogenetic-driven changes in animal composition are well documented, their potential consequences for the organism's sensitivity to food quality constraints have remained elusive. Here we show that the potential growth response of the copepod Mixodiaptomus laciniatus (as %RNA and RNA:DNA ratio) to the natural gradient of seston carbon (C):nutrient ratio is unimodal and stage specific. Solution of the equation given by the first derivative function provided the optimum C:nutrient ratio for maximum stage-specific growth, which increased during ontogeny. The peakedness of the function indicated that animal vulnerability to suboptimal food quality decreased as juveniles reached adulthood. Consistent with these results, a field experiment demonstrated that potential consumer growth responded to variations in seston C:phosphorus ratio, and that early life stages were particularly vulnerable to suboptimal food quality.
|
|
| 6. |
- Kaufman, Darrell, et al.
(författare)
-
A global database of Holocene paleotemperature records
- 2020
-
Ingår i: Scientific Data. - : Springer Science and Business Media LLC. - 2052-4463. ; 7:1
-
Tidskriftsartikel (refereegranskat)abstract
- A comprehensive database of paleoclimate records is needed to place recent warming into the longer-term context of natural climate variability. We present a global compilation of quality-controlled, published, temperature-sensitive proxy records extending back 12,000 years through the Holocene. Data were compiled from 679 sites where time series cover at least 4000 years, are resolved at sub-millennial scale (median spacing of 400 years or finer) and have at least one age control point every 3000 years, with cut-off values slackened in data-sparse regions. The data derive from lake sediment (51%), marine sediment (31%), peat (11%), glacier ice (3%), and other natural archives. The database contains 1319 records, including 157 from the Southern Hemisphere. The multi-proxy database comprises paleotemperature time series based on ecological assemblages, as well as biophysical and geochemical indicators that reflect mean annual or seasonal temperatures, as encoded in the database. This database can be used to reconstruct the spatiotemporal evolution of Holocene temperature at global to regional scales, and is publicly available in Linked Paleo Data (LiPD) format.
|
|
| 7. |
- Petroff, E., et al.
(författare)
-
A polarized fast radio burst at low Galactic latitude
- 2017
-
Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford Academic. - 0035-8711 .- 1365-2966. ; 469:4, s. 4465-4482
-
Tidskriftsartikel (refereegranskat)abstract
- We report on the discovery of a new fast radio burst (FRB), FRB 150215, with the Parkes radio telescope on 2015 February 15. The burst was detected in real time with a dispersion measure (DM) of 1105.6 +/- 0.8 pc cm(-3), a pulse duration of 2.8(-0.5)(+1.2) ms, and a measured peak flux density assuming that the burst was at beam centre of 0.7(-0.1)(+0.2) Jy. The FRB originated at a Galactic longitude and latitude of 24.66 degrees, 5.28 degrees and 25 degrees away from the Galactic Center. The burst was found to be 43 +/- 5 per cent linearly polarized with a rotation measure (RM) in the range -9 < RM < 12 rad m(-2) (95 per cent confidence level), consistent with zero. The burst was followed up with 11 telescopes to search for radio, optical, X-ray, gamma-ray and neutrino emission. Neither transient nor variable emission was found to be associated with the burst and no repeat pulses have been observed in 17.25 h of observing. The sightline to the burst is close to the Galactic plane and the observed physical properties of FRB 150215 demonstrate the existence of sight lines of anomalously low RM for a given electron column density. The Galactic RM foreground may approach a null value due to magnetic field reversals along the line of sight, a decreased total electron column density from the Milky Way, or some combination of these effects. A lower Galactic DM contribution might explain why this burst was detectable whereas previous searches at low latitude have had lower detection rates than those out of the plane.
|
|
| 8. |
- Abdalla, H., et al.
(författare)
-
Characterizing the γ-ray long-term variability of PKS2155 304 with HESS and Fermi-LAT
- 2017
-
Ingår i: Astronomy and Astrophysics. - : The European Southern Observatory. - 0004-6361 .- 1432-0746. ; 598
-
Tidskriftsartikel (refereegranskat)abstract
- Studying the temporal variability of BL Lac objects at the highest energies provides unique insights into the extreme physical processes occurring in relativistic jets and in the vicinity of super-massive black holes. To this end, the long-term variability of the BL Lac object PKS 2155-304 is analyzed in the high (HE, 100MeV < E < 300 GeV) and very high energy (VHE, E > 200 GeV) gamma-ray domain. Over the course of similar to 9 yr of H. E. S. S. observations the VHE light curve in the quiescent state is consistent with a log-normal behavior. The VHE variability in this state is well described by flicker noise (power-spectral-density index βVHE = 1 .10+ 0.10-0,13) on timescales larger than one day. An analysis of similar to 5.5 yr of HE Fermi-LAT data gives consistent results (βHE = 1 .20+ 0.21-0.23, on timescales larger than 10 days) compatible with the VHE findings. The HE and VHE power spectral densities show a scale invariance across the probed time ranges. A direct linear correlation between the VHE and HE fluxes could neither be excluded nor firmly established. These long-term-variability properties are discussed and compared to the red noise behavior (beta similar to 2) seen on shorter timescales during VHE-flaring states. The difference in power spectral noise behavior at VHE energies during quiescent and flaring states provides evidence that these states are influenced by different physical processes, while the compatibility of the HE and VHE long-term results is suggestive of a common physical link as it might be introduced by an underlying jet-disk connection.
|
|
| 9. |
- Abdalla, H., et al.
(författare)
-
Extended VHE gamma-ray emission towards SGR1806-20, LBV 1806-20, and stellar cluster Cl*1806-20
- 2018
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 612
-
Tidskriftsartikel (refereegranskat)abstract
- Using the High Energy Spectroscopic System (H.E.S.S.) telescopes we have discovered a steady and extended very high-energy (VHE) gamma-ray source towards the luminous blue variable candidate LBV 1806-20, massive stellar cluster Cl* 1806-20, and magnetar SGR 1806-20. The new VHE source, HESS J1808-204, was detected at a statistical significance of >6 sigma (post-trial) with a photon flux normalisation (2.9 +/- 0.4(stat) +/- 0.5(sys)) x 10(-13) ph cm(-2) s(-1) TeV-1 at 1 TeV and a power-law photon index of 2.3 +/- 0.2(stat) +/- 0.3(sys). The luminosity of this source (0.2 to 10 TeV; scaled to distance d = 8 : 7 kpc) is L-VHE similar to 1.6 x 10(34)(d = 8.7 kpc)(2) erg s(-1). The VHE gamma-ray emission is extended and is well fit by a single Gaussian with statistical standard deviation of 0.095 degrees +/- 0.015 degrees. This extension is similar to that of the synchrotron radio nebula G10.0-0.3, which is thought to be powered by LBV 1806-20. The VHE gamma-ray luminosity could be provided by the stellar wind luminosity of LBV 1806-20 by itself and/or the massive star members of Cl* 1806-20. Alternatively, magnetic dissipation (e.g. via reconnection) from SGR 1806-20 can potentially account for the VHE luminosity. The origin and hadronic and/or leptonic nature of the accelerated particles responsible for HESS J1808-204 is not yet clear. If associated with SGR 1806 20, the potentially young age of the magnetar (650 yr) can be used to infer the transport limits of these particles to match the VHE source size. This discovery provides new interest in the potential for high-energy particle acceleration from magnetars, massive stars, and/or stellar clusters.
|
|
| 10. |
- Abdalla, H., et al.
(författare)
-
First limits on the very-high energy gamma-ray afterglow emission of a fast radio burst HESS observations of FRB 150418
- 2017
-
Ingår i: Astronomy and Astrophysics. - : The European Southern Observatory (ESO). - 0004-6361 .- 1432-0746. ; 597
-
Tidskriftsartikel (refereegranskat)abstract
- Aims. Following the detection of the fast radio burst FRB150418 by the SUPERB project at the Parkes radio telescope, we aim to search for very-high energy gamma-ray afterglow emission. Methods. Follow-up observations in the very-high energy gamma-ray domain were obtained with the H.E.S.S. imaging atmospheric Cherenkov telescope system within 14.5 h of the radio burst. Results. The obtained 1.4 h of gamma-ray observations are presented and discussed. At the 99% C.L. we obtained an integral upper limit on the gamma-ray flux of Phi(gamma)(E > 350 GeV) < 1.33 x 10(-8) m(-2) s(-1). Differential flux upper limits as function of the photon energy were derived and used to constrain the intrinsic high-energy afterglow emission of FRB 150418. Conclusions. No hints for high-energy afterglow emission of FRB 150418 were found. Taking absorption on the extragalactic background light into account and assuming a distance of z = 0 : 492 based on radio and optical counterpart studies and consistent with the FRB dispersion, we constrain the gamma-ray luminosity at 1 TeV to L < 5 : 1 x 10(47) erg/s at 99% C.L.
|
|
