Design concepts for the Cherenkov Telescope Array CTA: an advanced facility for ground-based high-energy gamma-ray astronomy

Ground-based gamma-ray astronomy has had a major breakthrough with the impressive results obtained using systems of imaging atmospheric Cherenkov telescopes. Ground-based gamma-ray astronomy has a huge potential in astrophysics, particle physics and cosmology. CTA is an international initiative to build the next generation instrument, with a factor of 5-10 improvement in sensitivity in the 100 GeV-10 TeV range and the extension to energies well below 100 GeV and above 100 TeV. CTA will consist of two arrays (one in the north, one in the south) for full sky coverage and will be operated as open observatory. The design of CTA is based on currently available technology. This document reports on the status and presents the major design concepts of CTA

Southern African Large Telescope Spectroscopy of BL Lacs for the CTA project

In the last two decades, very-high-energy gamma-ray astronomy has reached maturity: over 200 sources have been detected, both Galactic and extragalactic, by ground-based experiments. At present, Active Galactic Nuclei (AGN) make up about 40% of the more than 200 sources detected at very high energies with ground-based telescopes, the majority of which are blazars, i.e. their jets are closely aligned with the line of sight to Earth and three quarters of which are classified as high-frequency peaked BL Lac objects. One challenge to studies of the cosmological evolution of BL Lacs is the difficulty of obtaining redshifts from their nearly featureless, continuum-dominated spectra. It is expected that a significant fraction of the AGN to be detected with the future Cherenkov Telescope Array (CTA) observatory will have no spectroscopic redshifts, compromising the reliability of BL Lac population studies, particularly of their cosmic evolution. We started an effort in 2019 to measure the redshifts of a large fraction of the AGN that are likely to be detected with CTA, using the Southern African Large Telescope (SALT). In this contribution, we present two results from an on-going SALT program focused on the determination of BL Lac object redshifts that will be relevant for the CTA observatory

Sensitivity of the Cherenkov Telescope Array to a dark matter signal from the Galactic centre

We provide an updated assessment of the power of the Cherenkov Telescope Array (CTA) to search for thermally produced dark matter at the TeV scale, via the associated gamma-ray signal from pair-annihilating dark matter particles in the region around the Galactic centre. We find that CTA will open a new window of discovery potential, significantly extending the range of robustly testable models given a standard cuspy profile of the dark matter density distribution. Importantly, even for a cored profile, the projected sensitivity of CTA will be sufficient to probe various well-motivated models of thermally produced dark matter at the TeV scale. This is due to CTA's unprecedented sensitivity, angular and energy resolutions, and the planned observational strategy. The survey of the inner Galaxy will cover a much larger region than corresponding previous observational campaigns with imaging atmospheric Cherenkov telescopes. CTA will map with unprecedented precision the large-scale diffuse emission in high-energy gamma rays, constituting a background for dark matter searches for which we adopt state-of-the-art models based on current data. Throughout our analysis, we use up-to-date event reconstruction Monte Carlo tools developed by the CTA consortium, and pay special attention to quantifying the level of instrumental systematic uncertainties, as well as background template systematic errors, required to probe thermally produced dark matter at these energies

"Low" concentrations of sodium fluoride inhibit neurotransmitter release from the guinea-pig superior cervical ganglion.

The role of G proteins and related second messenger system on the modulation of acetylcholine release from [3H]choline-preloaded guinea-pig superior cervical ganglion was investigated using the potent general activator NaF. The electrically evoked (1 Hz, 5 min) [3H] release was inhibited by “low” F− concentrations (1-2.5 mM), by the adenylyl cyclase blocker MDL 12330A (10 μM), alone and in combination with 1 mM NaF, and increased by 0.5 mM 8Br-cAMP, 100 μM forskolin and 0.5 mM 3-isobutyl-1-methylxantine. No effect of 1 mM F− was observed on spontaneous release. Fluoride-induced inhibition was counteracted by the G protein blocker sulmazole (1 mM), forskolin and alteration of calcium influx by increasing [Ca2+]out from 2.2 to 6 mM, raising the rate of stimulation (10 Hz, 30 s), or broadening the presynaptic action potential with 10 μM 4-aminopyridine and 50 μM tetraethylammonium chloride. Thus a NaF-sensitive G protein, linked to cAMP synthesis, is determinant for the inhibition of neurosecretion in this cholinergic synapse, involving Ca2+-dependent mechanisms

THE CONTROVERSIAL ROLE OF CAMP ON AMNIOTIC PROSTAGLANDIN RELEASE - EFFECT OF ADENYLATE-CYCLASE INHIBITION

The suggested role of cAMP in the regulation of amnionic prostaglandin release was investigated using two adenylate cyclase inhibitors, MDL 12330A and SQ 22536. These substances exhibited a dose-dependent inhibitory effect on both amnionic enzyme and cAMP levels, but they did not influence prostaglandin E (PGE) release. In addition forskolin and IBMX (3-isobutyl-1-methylxanthine), two drugs known to increase cAMP levels, did not affect PGE output, while dibutyryl cyclic cAMP showed a dose-dependent inhibitory effect. On the basis of our data, the suggested role of amnionic adenylate cyclase in triggering prostaglandin release is not confirmed, and the pathway of phospholipase A 2 activation at the onset of labor remains to be elucidated

EPIDERMAL GROWTH-FACTOR STIMULATION OF LECITHIN RELEASE BY HUMAN AMNION

Lecithin release from human amnion disks was assayed in basal conditions as well as under epidermal growth factor administration. The tissue responded to the peptide by increasing the phospholipid release. A significant effect was observed only after 30 min of treatment. A possible role of epidermal growth factor-induced amniotic lecithin release in fetal lung maturation as well as in the mechanism of delivery is discussed

Modulation of Amnionic Adenylate Cyclase and cAMP Phosphodiesterase by Prostaglandins E(1) and F2α

The action of prostaglandins E 1 and F(2α), on adenylate cyclase and cAMP phosphodiesterase was assayed in cell membrane fractions of amnion obtained before and after labor from term physiological pregnancies. Both prostaglandins stimulate the activity of adenylate cyclase in a dose-dependent manner. After spontaneous delivery both prostaglandins stimulate the activity of phosphodiesterase at lower doses and inhibit it at higher ones while the stimulatory effect of low doses is missing before labor. Such a behavior could represent a mechanism for the preservation of the cAMP-mediated processes throughout the entire event of delivery

BETAMETHASONE-INDUCED LECITHIN RELEASE INVITRO FROM THE FETAL MEMBRANES

Lecithin release from fetal membranes and placental tissue was assayed in basal conditions as well as under betamethasone administration. In the absence of the steroid, amnion and chorion released lecithin as a function of incubation time. Both tissues responded to betamethasone by increasing the lecithin release, the amnion exhibited a higher basal level and a greater responsiveness to the hormone than the chorion. Basal lecithin release from placental tissue was unaffected by any steroid concentration

Focal plane detector and front-end electronics of the stellar intensity interferometry instrument for the ASTRI Mini-Array telescopes

The ASTRI Mini-Array is an International collaboration led by the Italian National Institute for Astrophysics ( INAF), that will operate nine telescopes to perform Cherenkov and optical stellar intensity interferometry (SII) observations. At the focal plane of these telescopes we are planning to install a stellar intensity interferometry instrument. Here we present the final selected design, based on Silicon Photomultipliers (SiPMs) detectors matching the telescope point spread function together with a dedicated front end electronics