The very-high-energy gamma-ray sky can be surveyed on a daily basis by particle-detector arrays at high (mountain) elevation. In the northern hemisphere the survey recently conducted by the HAWC gamma-ray observatory significantly enriched our knowledge about TeV gamma-ray sources. In this contribution, we will present an overview on the effort to realise a next-generation gamma-ray survey observatory in the southern hemisphere. We will discuss the unique science case for this observatory and how it will be embedded in the multi-messenger and multi-wavelength census of the non-thermal universe. In addition, we will introduce the newly founded international organisation that aims to realise this facility: The Southern Wide field-of-View Gamma-ray Observatory (SWGO) collaboration.
The Southern Wide-field Gamma-ray Observatory (SWGO) Collaboration is currently engaged in design and prototyping work towards the realisation of this future gamma-ray facility. SWGO will complement CTA and the existing ground-particle based-detectors of the Northern Hemisphere (HAWC and LHAASO) with a very wide field and high duty cycle view of the southern sky. Here I summarise the status of the project and plans for the future, including expectations for sensitivity and science targets as well as the status of the site search and technological developments.
We report the discovery of a $\sim$ $3.4\degr$-wide region of high-energy emission in data from the \emph{Fermi} LAT satellite. The centroid of the emission is located in the Southern Hemisphere sky, a few degrees away from the plane of the Galaxy at the Galactic coordinates l=350.6$\degr$, b=-4.7$\degr$. It shows a hard spectrum that is compatible with a simple power-law, $\frac{dN}{dE}\propto E^{-Γ}$, in the energy range 0.7--500 GeV, with a spectral index $Γ= 1.68 \pm 0.04_{\mbox{stat}} \pm 0.1_{\mbox{sys}}$. The integrated source photon flux above 0.7 GeV is $(4.71 \pm 0.49_{\mbox{stat}}\p…
The Fermi-LAT has detected more than 3000 sources in the GeV $γ$-ray regime. The majority are extra-galactic and these sources are dominated by blazars. However, $\sim28$ per cent of the sources in Fermi 3LAC are listed as blazar candidates of uncertain type (BCU). Increasing the number of classified Fermi-LAT sources is important for improving our understanding of extra-galactic $γ$-ray sources and can be used to search for new very high energy sources. We report on the optical spectroscopy of seven selected unclassified BCU sources during 2014 and 2015 undertaken using the SAAO 1.9-m and Sou…
Extensice Air Shower (EAS) arrays are survey instruments able to monitor continuously all the overhead sky. Their wide field of view (about 2 sr) is ideal to complement directional detectors by performing unbiased sky surveys, by monitoring variable or flaring sources, such as AGNs, and to discover transients or explosive events (GRBs). With an energy threshold in the 100 GeV range EAS arrays are transient factories. All EAS arrays presently in operation or under installation are located in the Northern hemisphere. A new survey instrument located in the Southern Hemisphere should be a high pri…
The scientific potential of a wide field-of-view, and very-high duty cycle, ground-based gamma-ray detector has been demonstrated by the current generation of instruments, such as HAWC and ARGO, and will be further extended in the Northern Hemisphere by LHAASO. Nevertheless, no such instrument exists in the Southern Hemisphere yet, where a great potential lies uncovered for the mapping of Galactic large scale emission as well as providing access to the full sky for transient and variable multi-wavelength and multi-messenger phenomena. Access to the Galactic Centre and complementarity with the …
Identification of a Large-Scale Diffuse Gamma-Ray Structure in the Southern Galactic Hemisphere
School of Astronomy and Space Science, University of Science and Technology of China（中国科学技术大学天文与空间科学学院）；Key Laboratory of Dark Matter and Space Astronomy, Purple Mountain Observatory, Chinese Academy of Sciences（中国科学院紫金山天文台暗物质与空间天文重点实验室）
The Southern Hemisphere VLBI monitoring program TANAMI provides dual-frequency (8 GHz and 22 GHz), milliarcsecond monitoring of extragalactic jets south of -30 degrees declination. The TANAMI sample consists of a combined radio and gamma-ray selected subsample of currently 80 AGN jets, with new gamma-ray bright sources being added upon detections by Fermi/LAT. Supporting programs provide simultaneous multiwavelength coverage of all sources, in order to construct broadband spectral energy distributions (SEDs) of flaring and quiescence source states, as well as a rapid follow-up of high-energy f…
Despite mounting evidence that dark matter (DM) exists in the Universe, its fundamental nature remains unknown. We present sensitivity estimates to detect DM particles with a future very-high-energy ($\gtrsim$ TeV) wide field-of-view gamma-ray observatory in the Southern Hemisphere. This observatory would search for gamma rays from the annihilation or decay of DM particles in the Galactic halo. With a wide field of view, both the Galactic Center and a large fraction of the Galactic halo will be detectable with unprecedented sensitivity to DM in the mass range of $\sim$500 GeV to $\sim$2 PeV. T…
We present the first southern-hemisphere all-sky imager and radio-transient monitoring system implemented on two prototype stations of the low-frequency component of the Square Kilometre Array. Since its deployment the system has been used for real-time monitoring of the recorded commissioning data. Additionally, a transient searching algorithm has been executed on the resulting all-sky images. It uses a difference imaging technique, and has enabled identification of a wide variety of transient classes, ranging from human-made radio-frequency interference to genuine astrophysical events. Obser…
The Southern Wide-field Gamma-ray Observatory (SWGO) is a proposed ground-based gamma-ray detector that will be located in the Southern Hemisphere and is currently in its design phase. In this contribution, we will outline the prospects for Galactic science with this Observatory. Particular focus will be given to the detectability of extended sources, such as gamma-ray halos around pulsars; optimisation of the angular resolution to mitigate source confusion between known TeV sources; and studies of the energy resolution and sensitivity required to study the spectral features of PeVatrons at th…
The Large Array Telescope for Tracking Energetic Sources (LATTES), is a novel concept for an array of hybrid EAS array detectors, composed of a Resistive Plate Counter array coupled to a Water Cherenkov Detector, planned to cover gamma rays from less than 100 GeV up to 100 TeVs. This experiment, to be installed at high altitude in South America, could cover the existing gap in sensitivity between satellite and ground arrays. The low energy threshold, large duty cycle and wide field of view of LATTES makes it a powerful tool to detect transient phenomena and perform long term observations of va…
We report the results of our exploratory program carried out with the Southern Astrophysical Research (SOAR) telescope aimed at associating counterparts and establishing the nature of the Fermi Unidentified gamma-ray Sources (UGS). We selected the optical counterparts of 6 UGSs from the Fermi catalog on the basis of our recently discovered tight connection between infrared and gamma-ray emission found for the gamma-ray blazars detected by the Wide-Field Infrared Survey Explorer (WISE) in its the all-sky survey. We perform for the first time a spectroscopic study of the low-energy counterparts …
The High-Altitude Water Cherenkov (HAWC) observatory in central Mexico is currently the world's only synoptic survey instrument for gamma rays above 1 TeV. Because there is significant interest in covering the full TeV sky with a survey instrument, we have examined options for a Southern Hemisphere extension to HAWC. In addition to providing all-sky coverage of TeV sources, a southern site could complement existing surveys of the densest part of the Galactic Plane, provide continuous monitoring of Galactic and extragalactic transient sources in both Hemispheres, and simplify the analysis of sp…
Recent findings by the LHAASO experiment are opening a new window, that of the PeV sky, to the observation of the electromagnetic spectrum. Several astronomical objects emitting gamma-rays at energies well above 100 TeV have been observed with the LHAASO-KM2 array of scintillators and muon detectors, clearly demonstrating the feasibility of gamma-ray astronomy up to PeV energies. An all-sky gamma-ray detector in the Southern Hemisphere, operating in the GeV-PeV range, could complement LHAASO observations, monitor the Inner Galaxy and the Galactic Center looking for PeVatrons. As shown by LHAAS…
We outline the science motivation for SGSO, the Southern Gamma-Ray Survey Observatory. SGSO will be a next-generation wide field-of-view gamma-ray survey instrument, sensitive to gamma-rays in the energy range from 100 GeV to hundreds of TeV. Its science topics include unveiling galactic and extragalactic particle accelerators, monitoring the transient sky at very high energies, probing particle physics beyond the Standard Model, and the characterization of the cosmic ray flux. SGSO will consist of an air shower detector array, located in South America. Due to its location and large field of v…
Symbiotic stars show emission across the electromagnetic spectrum from a wide array of physical processes. At cm-waves both synchrotron and thermal emission is seen, often highly variable and associated with outbursts in the optical and X-rays. Most models of the radio emission include an ionized region within the dense wind of the red giant star, that is kept ionized by activity on the white dwarf companion or its accretion disk. In some cases there is on-going shell burning on the white dwarf due to its high mass accretion rate or a prior nova eruption, in other cases nuclear fusion occurs o…
High-redshift blazars are valuable tools to study the early Universe. So far only a handful of $γ$-ray blazars have been found at redshifts above 3. $γ$-ray signals are detected in the direction of PMN J2219-2719 ($z=3.63$) and PMN J2321-0827 ($z=3.16$) by analyzing the 10-year $Fermi$-LAT Pass 8 data. PMN J2219-2719 is not distinguished from the background in the global analysis. During the 5-month epoch, the TS value is 47.8 and the flux is more than 10 times of the 10-year averaged flux. In addition, the angular distance between the $γ$-ray position and the radio position of PMN J2219-2719 …
Searching for low energy counterparts of gamma-ray sources is one of the major challenges in modern gamma-ray astronomy. In the third Fermi source catalog about 30 % of detected sources are unidentified/unassociated Gamma-ray Sources (UGSs). We recently started an optical spectroscopic follow up campaign to confirm the blazar-like nature of candidates counterparts of UGSs. Here we report the spectra of 61 targets collected with the Southern Astrophysical Research Telescope (SOAR) between 2014 and the 2017. Our sample includes 33 potential counterparts of UGSs, selected on the basis of WISE col…
Primordial Black Holes (PBHs) are remnants of objects formed in the early Universe. Their lifetime is an increasing function of their mass, so PBHs in the right mass range can end their lives in an evaporation event that is potentially detectable by our instruments now. This evaporation may result in a $γ$-ray flash that can be detected by the current generation of Very-High-Energy $γ$-ray detectors. The Southern Wide field of view Gamma-ray Observatory (SWGO) will be part of the next generation of these instruments. It will be able to establish limits on PBH evaporations for integration windo…
EAS arrays are survey instruments able to monitor continuously all the overhead sky. Their sensitivity in the sub-TeV/TeV energy domain cannot compete with that of Cherenkov telescopes, but the wide field of view (about 2 sr) is ideal to complement directional detectors by performing unbiased sky surveys, by monitoring variable or flaring sources such as Active Galactic Nuclei (AGN) and to discover transients or explosive events (GRBs). Arrays are well suited to study extended sources, such as the Galactic diffuse emission, and to measure the spectra of Galactic sources at the highest energies…
We report on a search for low-frequency radio variability in 944 bright (> 4Jy at 154 MHz) unresolved, extragalactic radio sources monitored monthly for several years with the Murchison Widefield Array. In the majority of sources we find very low levels of variability with typical modulation indices < 5%. We detect 15 candidate low frequency variables that show significant long term variability (>2.8 years) with time-averaged modulation indices M = 3.1 - 7.1%. With 7/15 of these variable sources having peaked spectral energy distributions, and only 5.7% of the overall sample having peaked spec…
The Very Long Baseline Interferometry (VLBI) monitoring program TANAMI provides bi-monthly, dualfrequency (8GHz and 22GHz) observations of extragalactic jets with milliarcsecond resolution south of -30 deg declination using the Australian Long Baseline Array (LBA) and additional radio telescopes in Antarctica, Chile, New Zealand and South Africa. Supporting programs provide multiwavelength coverage of the Fermi/LAT sources of the TANAMI sample, in order to construct simultaneous broadband spectral energy distributions (SEDs), as well as rapid follow-ups of high energy flares. The main purpose …
The Galactic center excess (GCE) remains one of the most intriguing discoveries from the Fermi Large Area Telescope (LAT) observations. We revisit the characteristics of the GCE by first producing a new set of high-resolution galactic diffuse gamma-ray emission templates, which are ultimately due to cosmic-ray interactions with the interstellar medium. Using multi-messenger observations we constrain the properties of the galactic diffuse emission. The broad properties of the GCE that we find in this work are qualitatively unchanged despite the introduction of this new set of templates, though …
