HAWC Observatory makes energetic discoveries
UAEH collaboration continues

Dr. Pedro Miranda Romagnoli
Academic Area of Mathematics and Physics

Credits: HAWC Collaboration

The HAWC Gamma Ray Observatory consists of an array of water-filled tanks located at 4,100 meters above sea level on the Sierra Negra volcano in the state of Puebla, where the atmosphere is thin and offers good conditions for gamma ray observation. This is a joint effort of scientists from the USA, Mexico and Europe, mainly.

It is important to mention that the Sierra Negra volcano is the fifth highest mountain in Mexico, located just seven kilometers from Pico de Orizaba and that its summit also houses the Alfonso Serrano Large Millimeter Telescope, the largest radio telescope in the world in its frequency with an antenna of about 50 meters.

Since its inauguration in March 2015, several discoveries have taken place thanks to this Observatory. Thus, only two years after its operation was published, in 2017, the first catalog of gamma-ray sources of the order of¹⁰¹² eV or TeV (the electron-volt or simply eV is the unit of energy measurement used for particles) called 2HWC and which includes 39 sources, of which 19 are new sources, which are not associated with previously detected sources. Of the sources reported in this catalog, 10 are supernova remnants. The results can be found in the article "The 2HWC HAWC Observatory Gamma-Ray Catalog", published in The Astrophysical Journal(https://iopscience.iop.org/article/10.3847/1538-4357/aa7556

In 2018, highly energetic gamma-ray emission was discovered coming from the farthest regions of our galaxy. The source, the SS 433 microcoasar located 15 thousand light-years from Earth, composed of a black hole that devours material from a nearby star and launches jets of matter known as jets. A dozen microcoasars are known to exist in our galaxy, but only a couple of them have highly energetic emissions. For reference, see the scientific paper entitled "Very-high-energy particle acceleration powered by the jets of the microquasar SS 433" published in Nature(https://www.nature.com/articles/s41586-018-0565-5).

More recently, in 2020, nine gamma-ray sources were discovered, which have already been catalogued and are the most energetic ones detected in our galaxy. All of these sources have pulsars (highly magnetized rotating neutron stars) nearby. This finding was published in the journal Physical Review Letters under the title "Multiple Galactic Sources with Emission Above 56 TeV Detected by HAWC"(https://dx.doi.org/10.1103/PhysRevLett.124.021102).

In addition, thanks to the data stored in 1,523 days, the third HAWC catalog known as 3HWC was published that same year, in which 65 gamma-ray sources with energies above several TeV are reported. The data were published under the title "3HWC: The Third HAWC Catalog of Very-high-energy Gamma-Ray Sources" in The Astrophysical Journal(https://dx.doi.org/10.3847/1538-4357/abc2d8). This catalog not only reports new sources of highly energetic gamma rays, but will serve to corroborate the existence of sources reported by other catalogs such as the Fermi LAT (Large Area Telescope).

Figure 1. Gamma-ray map of the sky. On the left is our galaxy, as a source of high gamma-ray emission, outside it are observed the Markarian blazars 421 and 501. Geminga and the Crab Nebula are highlighted on the right. Credits: HAWC Collaboration

Contrary to cosmic rays, gamma rays suffer almost no deviations in their path from the source that originates them to the Earth, so their origin can be determined quite accurately; on the other hand, it is expected that they can help to determine the mystery of the sources that originate cosmic rays.

The HAWC Observatory is planned to be in operation until 2023, so it will be producing data for a couple of years more. Scientists participating in the International Collaboration will have to make the most of this brief period to do their research and report their results.

UAEH scientists, permanent collaborators

I, together with Dr. Roberto Noriega Papaqui, both research professors at the Academic Area of Physics and Mathematics at the Autonomous University of the State of Hidalgo (UAEH), have participated in the HAWC Collaboration since 2010, when the construction of the prototype called VAMOS began, which was used to study different possible configurations of the detector tanks.

During the construction of the main array of the HAWC Observatory, consisting of 300 tanks with a diameter of 7.3 meters and filled with water to a height of 4.5 meters, we participated in the wiring for the instrumentation of the tanks.

Currently the UAEH is responsible for the water level monitoring system of the detector tanks, since a drop in the water level can cause an error in the detection of the particle showers that affect the array.

It is worth mentioning that these 11 years of belonging to the Collaboration have allowed the definitive consolidation of the Academic Body of Mathematical Physics to Engineering, besides allowing the completion of theses and the participation of about 25 students in the different tasks assigned to the group, mainly from the Physics and Advanced Technology, Materials Science and Electronics degrees of the UAEH.

PHOTO. Dr. Roberto Noriega Papaqui and Dr. Pedro Miranda Romagnoli, both UAEH research professors, during a working session at the HAWC Observatory located at the Sierra Negra Volcano in Puebla.