On December 15, the Large-Size Telescope (LST) Collaboration announced the discovery of the source via an Astronomer’s Telegram (ATel). OP313 at very high energies with the first of his telescopes, the LST-1, which is located on the Canary Islands of La Palma.
This is the first scientific discovery of this telescope, one of the types that will feature the Cherenkov Telescope Array Observatory (CTAO), the first terrestrial gamma-ray observatory open to the scientific community with the largest and most sensitive instrument for studying the Universe at high energies.
Although OP 313 was known at lower energies, it was never detected at higher energies 100 gigaelectron volts (GeV) like right now. With these results, this source becomes the active galactic nucleus (AGNfor its acronym in English) is the most distant ever discovered by a Cherenkov telescope.
An AGN is a compact region at the center of a galaxy that emits a significant amount of energy across the electromagnetic spectrum and whose properties suggest that the luminosity is not produced by stars. This non-stellar radiation is believed to be the result of matter accretion by a supermassive black hole at the center of the parent galaxy.
OP 313 is a type of AGN known as Flat spectrum radio quasar or FSRQ (Flat spectrum radio quasar). These are very luminous objects found at the centers of some galaxies, where a supermassive black hole devours material from its surroundings, creating powerful accretion disks and jets of light and relativistic particles.
LST-1 observed this source between December 10 and 14 after receiving an alert from the Fermi-LAT satellite that showed unusually high activity in the low-energy gamma-ray region, which was also confirmed in the optical region with various instruments. With just four days of data, the LST collaboration was able to detect the source above 100 GeV, an energy level a billion times higher than the visible light that humans can detect.
“If the activity in the optical range increases, there is a high probability that the emission at very high energies will also increase,” he explains. Jorge Otero Santos, researcher at the Institute of Astrophysics of Andalusia (IAA-CSIC) and one of the lead authors of the LST-1 analysis. “This connection between optical emission and gamma emission is not yet fully understood. This fact, together with the signal received from Fermi-LAT, led us to decide to observe OP 313 with LST-1.”
In general, these types of AGN are very difficult to detect at very high energies. This is not only because the brightness of their accretion disk weakens the emission of gamma rays, but also because they are very distant objects. In this case, OP 313 is about eight billion light-years away, making it the most distant AGN and the second most distant source ever discovered at very high energies.
The further away the source, the more difficult it is to observe it at very high energies due to what is known as the Extragalactic Backlight or EBL (known by its acronym in English). The EBL is the amount of light emitted by all objects outside the Milky Way, spanning multiple wavelengths, from visible to infrared to ultraviolet light.
The EBL interacts with very high-energy gamma radiation, which weakens its flow and therefore makes it difficult to observe. The properties of LST-1, with a sensitivity optimized for the low energy range of the CTAO between 20 and 150 GeV, where gamma rays are less affected by the EBL, allowed the LST collaboration to expand the study of this source to several dozen GeV for the first time.
“There are only nine known very energetic quasars, and now OP 313 is the tenth,” he says. Daniel Morcuende, researcher at the Institute of Astrophysics of Andalusia (IAA-CSIC) and one of the lead authors of the LST-1 results. “Given its properties, it is a very interesting source because it will allow us to better understand the EBL, study the magnetic fields within this type of source or delve into fundamental intergalactic physics.”
It is important to complement this detection at very high energies with observations at the remaining wavelengths. “To achieve this, monitoring of the object in the optical range was coordinated with the Sierra Nevada Observatory (OSN) to best characterize its emission across the electromagnetic spectrum.”, explained Jorge Otero SantosCoordinator of the optical observations of OP 313.
The LST Collaboration will continue to monitor this source with LST-1 to expand the data set for more precise analysis that will allow scientists to improve their understanding of EBL.
About LST and CTAO
He Large-Size Telescope (LST) It is one of three types of telescopes being built to cover the entire CTAO energy range (20 GeV – 300 TeV). Four LSTs will be installed in the center of the Northern Hemisphere complex in La Palma, Spain, with two more planned in the Southern Hemisphere complex. These telescopes are optimized to cover low energy sensitivities between 20 and 150 GeV. Each LST is a huge telescope with a diameter of 23 meters, a mirror area of about 400 square meters and a pixel camera made up of 1,855 light sensors that can capture single photons with high efficiency. Although the LST is 45 meters tall and weighs about 100 tons, it is extremely maneuverable and can reposition itself within 20 seconds to detect short, low-energy gamma-ray signals. Both the rapid repositioning rate and low energy threshold that LSTs provide are critical for studying transient gamma-ray sources in our own galaxy, as well as for studying active galactic nuclei and high redshift gamma-ray bursts. The LST prototype LST-1 is being built at CTAO-North and is currently in service. It is expected to become CTAO’s first telescope once its commissioning is complete and officially accepted.
The LST collaboration consists of more than 400 scientists and engineers from 67 different institutions in twelve countries. The operation and maintenance of the telescope, as well as data acquisition, analysis and technical and scientific publications, are only possible thanks to the joint efforts of the entire LST collaboration.
He in turn Cherenkov Telescope Array Observatory (CTAO) It will be the first terrestrial gamma-ray observatory open to the scientific community and the world’s largest and most sensitive instrument for studying the universe at high energies. CTAO’s unprecedented precision and wide energy range (20 GeV-300 TeV) will provide new insights into the most extreme and powerful events in the cosmos, answering questions within and outside astrophysics that fall under three main themes: understanding the origin and the role of relativistic ones cosmic particles, the study of extreme environments (such as black holes and neutron stars) and the exploration of the limits of physics (such as the nature of dark matter). For this purpose, the CTAO will use three types of telescopes: Large-Sized Telescopes (LST), Medium-Sized Telescopes (MST), and Small-Sized Telescopes (SST). More than 60 telescopes will be distributed across two sets of telescopes: CTAO-North in the Northern Hemisphere at the Roque de los Muchachos Observatory of the Institute of Astrophysics of the Canary Islands (IAC) in La Palma (Spain) and CTAO-South in the Southern Hemisphere near Paranal -Observatory of the European Southern Observatory (ESO) in the Atacama Desert (Chile). The CTAO headquarters is located at the Istituto Nazionale di Astrofisica (INAF) in Bologna, Italy, and the Scientific Data Management Center (SDMC) is located at the German Electron Synchrotron (DESY) in Zeuthen, Germany. The CTAO will also be the first observatory of its kind open to scientific communities around the world as a data source for unique, high-energy astronomical observations.
The CTA-Spain consortium, made up of eleven Spanish institutions (such as the IAA) and 115 researchers and technologists, is one of the main actors in the construction of the CTAO observatory.