ABSTRACT
Eight years after the first detection of high-energy astrophysical neutrinos by IceCube, we are still almost clueless as regards to their origin, although the case for blazars being neutrino ...sources is getting stronger. After the first significant association at the $3\!-\!3.5\, \sigma$ level in time and space with IceCube neutrinos, i.e. the blazar TXS 0506+056 at z = 0.3365, some of us have in fact selected a unique sample of 47 blazars, out of which ∼16 could be associated with individual neutrino track events detected by IceCube. Building upon our recent spectroscopy work on these objects, here we characterize them to determine their real nature and check if they are different from the rest of the blazar population. For the first time we also present a systematic study of the frequency of masquerading BL Lacs, i.e. flat-spectrum radio quasars with their broad lines swamped by non-thermal jet emission, in a γ-ray- and IceCube-selected sample, finding a fraction >24 per cent and possibly as high as 80 per cent. In terms of their broad-band properties, our sources appear to be indistinguishable from the rest of the blazar population. We also discuss two theoretical scenarios for neutrino emission, one in which neutrinos are produced in interactions of protons with jet photons and one in which the target photons are from the broad-line region. Both scenarios can equally account for the neutrino–blazar correlation observed by some of us. Future observations with neutrino telescopes and X-ray satellites will test them out.
Aims. We aim to determine the redshift (or stringent lower limits) of a number of bright BL Lacs objects. Methods. We secured optical and near-infrared medium-resolution spectra of four bright BL Lac ...objects of unknown redshift using the spectrograph X-Shooter at the ESO-VLT. Results. In spite of the high quality of the spectra and the extended spectral range of the observations, we have not detected intrisic spectral features for these sources. However, we are able to provide strigent lower limits to their redshift. In particular, for the two TeV sources PG 1553+113 and H 1722+119, we infer z> 0.30 and z> 0.35 respectively. We also detect an intervening Ca II absorption doublet in the spectrum of MH 2136-428 that is ascribed to the halo of a nearby giant elliptical galaxy at a projected distance of ~100 kpc. Conclusions. Under the hypothesis that all BL Lacs are hosted by a luminous bulge-dominated galaxies, the spectroscopic observations of bright BL Lacs presently indicate that these objects are likely sources with extremely beamed nuclear emission. We present simulations to show under which circumstances it is possible to probe this hypothesis from the detection of very weak absorptions using the next generation of extremely large optical telescopes.
ABSTRACT High signal-to-noise ratio spectroscopic observations of the BL Lac object S4 0954+65 at the alleged redshift z = 0.367 are presented. This source was detected at gamma frequencies by the ...MAGIC (TeV) and FERMI (GeV) telescopes during a remarkable outburst that occurred in 2015 February, making the determination of its distance particularly relevant for our understanding of the properties of the extragalactic background light. Contrary to previous reports on the redshift, we found that the optical spectrum is featureless at an equivalent width limit of ∼0.1 . A critical analysis of the existing observations indicates that the redshift is still unknown. Based on the new data we estimate a lower limit to the redshift at z ≥ 0.45.
Abstract
Incidental memory can be challenged by increasing either the retention delay or the memory load. The dorsal hippocampus (dHP) appears to help with both consolidation from short-term (STM) to ...long-term memory (LTM), and higher memory loads, but the mechanism is not fully understood. Here we find that female mice, despite having the same STM capacity of 6 objects and higher resistance to distraction in our different object recognition task (DOT), when tested over 1 h or 24 h delays appear to transfer to LTM only 4 objects, whereas male mice have an STM capacity of 6 objects in this task. In male mice the dHP shows greater activation (as measured by c-Fos expression), whereas female mice show greater activation of the ventral midline thalamus (VMT). Optogenetic inhibition of the VMT-dHP pathway during off-line memory consolidation enables 6-object LTM retention in females, while chemogenetic VMT-activation impairs it in males. Thus, removing or enhancing sub-cortical inhibitory control over the hippocampus leads to differences in incidental memory.
ABSTRACT
We investigate the environments of galaxies around BL Lacertae (BL Lac) objects and Fanaroff–Riley class I (FR I) radio galaxies, the alleged parent populations of misaligned sources. We ...compare the environment of a sample of 50 BL Lac objects at 0.1 < z < 0.33 with that of a sample of 90 FR I galaxies at 0.1 < z < 0.15. The galaxy environment is studied by using Sloan Digital Sky Survey Data Release 14 images in the i band. We find that the galaxy excess density within 0.5 Mpc around FR I radio galaxies is a factor of ∼2 larger than that around BL Lacs. This implies a reconsideration of the parent population of BL Lac objects.
Abstract In the mammalian hippocampus, the dentate gyrus (DG) is characterized by sparse and powerful unidirectional projections to CA3 pyramidal cells, the so-called mossy fibers (MF). The MF form a ...distinct type of synapses, rich in zinc, that appear to duplicate, in terms of the information they convey, what CA3 cells already receive from entorhinal cortex layer II cells, which project both to the DG and to CA3. Computational models have hypothesized that the function of the MF is to enforce a new, well-separated pattern of activity onto CA3 cells, to represent a new memory, prevailing over the interference produced by the traces of older memories already stored on CA3 recurrent collateral connections. Although behavioral observations support the notion that the MF are crucial for decorrelating new memory representations from previous ones, a number of findings require that this view be reassessed and articulated more precisely in the spatial and temporal domains. First, neurophysiological recordings indicate that the very sparse dentate activity is concentrated on cells that display multiple but disorderly place fields, unlike both the single fields typical of CA3 and the multiple regular grid-aligned fields of medial entorhinal cortex. Second, neurogenesis is found to occur in the adult DG, leading to new cells that are functionally added to the existing circuitry, and may account for much of its ongoing activity. Third, a comparative analysis suggests that only mammals have evolved a DG, despite some of its features being present also in reptiles, whereas the avian hippocampus seems to have taken a different evolutionary path. Thus, we need to understand both how the mammalian dentate operates, in space and time, and whether evolution, in other vertebrate lineages, has offered alternative solutions to the same computational problems.
The use of cannabis as a therapeutic agent for various medical conditions has been well documented. However, clinical trials in patients with Parkinson disease (PD) have yielded conflicting results. ...The aim of the present open-label observational study was to assess the clinical effect of cannabis on motor and non-motor symptoms of PD.
Twenty-two patients with PD attending the motor disorder clinic of a tertiary medical center in 2011 to 2012 were evaluated at baseline and 30 minutes after smoking cannabis using the following battery: Unified Parkinson Disease Rating Scale, visual analog scale, present pain intensity scale, Short-Form McGill Pain Questionnaire, as well as Medical Cannabis Survey National Drug and Alcohol Research Center Questionnaire.
Mean (SD) total score on the motor Unified Parkinson Disease Rating Scale score improved significantly from 33.1 (13.8) at baseline to 23.2 (10.5) after cannabis consumption (t = 5.9; P < 0.001). Analysis of specific motor symptoms revealed significant improvement after treatment in tremor (P < 0.001), rigidity (P = 0.004), and bradykinesia (P < 0.001).
There was also significant improvement of sleep and pain scores. No significant adverse effects of the drug were observed. The study suggests that cannabis might have a place in the therapeutic armamentarium of PD. Larger, controlled studies are needed to verify the results.
We examine the 2008–2016 γ-ray and optical light curves of three bright BL Lac objects, 0716+714, MRK 421, BL Lac, which exhibit large structured variability. We searched for periodicities by using a ...fully Bayesian approach. For two out of three sources investigated, no significant periodic variability was found. In the case of BL Lac, we detected a periodicity of ~680 days. Although the signal related to this is modest, the coincidence of the periods in both gamma and optical bands is indicative of a physical relevance. Taking into consideration previous literature results, possibly related γ-ray and optical periodicities of about one year time scale are proposed in four bright γ-ray blazars out of the ten examined in detail. Compared with results from periodicity search of optical archives of quasars, the presence of quasi-periodicities in blazars may be more frequent by a large factor. This suggests the intriguing possibility that the basic conditions for their observability are related to the relativistic jet in the observer direction, but the overall picture remains uncertain.
On the lensed blazar B0218+357 Falomo, R; Treves, A; Scarpa, R ...
Monthly notices of the Royal Astronomical Society,
09/2017, Letnik:
470, Številka:
3
Journal Article
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Abstract
We present an optical spectrum (λλ4000–10 500) of the lensed blazar B0218+357 secured at the 10 m GTC and aimed to investigate and clarify the properties of this intriguing system. We found ...that the emission line spectrum of the blazar is characterized by only one broad emission line that interpreted as Mg ii 2800 Å yields z = 0.95. In addition, we detect narrow absorption lines of Mg ii 2800 Å and Ca ii (H,K) and Na i 5892 Å at z = 0.68437 ± 0.00005 due to intervening interstellar gas. No stellar absorption features attributable to the lens galaxy are revealed. Thus, the assumed redshift of the lens is dubious. The continuum spectrum of the object exhibits a remarkable drop towards the short wavelengths likely due to a significant extinction. This extinction cannot be produced in the lens galaxy at z = 0.684 with any value of RV
under the assumption that the intrinsic shape of the blazar is dominated by a power-law emission. However, the observed continuum is consistent with a power-law emission assuming a standard (RV
= 3.1) extinction at the source redshift (z = 0.95) as supported also by the presence of Mg ii absorptions at the same redshift. HST images of B0218+357 exhibit the double image of the source together with extended image of a face on spiral galaxy. We argue that this galaxy is possibly not the lensing galaxy but the host galaxy of the blazar. This has substantial consequences on the models of the system and on the derived values of the Hubble constant.
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