Khagol No.133

The photons are the main clues to unlock the mysteries of the Universe. The higher the energy of photons, the more violent the circumstances they originate. The most energetic are γ -ray photons with wavelengths smaller than an atomic nucleus's diameter. On Earth, γ rays are produced by nuclear fusion/fission, lightning, and radioactive decay. In the Universe, γ -ray photons carry the signatures of the violent phenomena happening on various astronomical scales. This includes supernova remnants, pulsars, and pulsar wind nebulae in the Galactic environment and extragalactic relativistic jets associated with active galactic nuclei (AGN). The identification of γ -ray-emitting astrophysical objects is one of the crucial research problems in high-energy astrophysics. Furthermore, with the advent of multimessenger astronomy, the γ -ray source population has emerged as a promising candidate for the cosmic neutrinos detected with the IceCube observatory. Active Galactic Nuclei hosting closely aligned relativistic jets, also known as blazars, are the most abundant γ -ray emitters. The star-forming galaxies and pulsars have also been detected in the γ - ray band. However, thanks to the sensitive, high-resolution multiwavelength data provided by the latest wide-field sky surveys, the discovery potential to identify a γ -ray emitting, non-jetted source population remains high. The right panel of Figure 1 shows “Kathryn's Wheel” as observed by the SuperCOSMOS H α survey. The image is a continuum subtracted to highlight the zones of star formation. The spectacular star-forming ring, triggered by galaxy collision, surrounding the central galaxy, ESO 179-13, is evident. The central galaxy shows little star formation, possibly stripped of gas due to interaction with the “bullet” galaxy, which itself is undergoing rapid star formation. Research Highlights A Mysterious Gamma-ray Emitting Galaxy System in Our Galactic Neighbourhood | 02 | KHAG L | No. 133 - JULY 2024 The Scientific Advisory Committee (SAC) meeting of IUCAA was held from April 22- 26, 2024. The Committee consists of Professor Phil Charles (University of Sou t hamp t on ; Cha i r ) , P r o f es so r Priyamvada Natarajan (Yale University; Member ), Professor T. R. Seshadri (Delhi University; Member), Professor Ravi Sheth (University of Pennsylvania: Membe r ) , Pr o f esso r Luc S ima rd (University of Victoria; Member), Professor P. Sreekumar (Manipal Centre for Natural Sciences; Member), Professor Alan Weinstein (California Institute of Technology; Member) and Professor R. Srianand (Director, IUCAA; Member Secretary). Professor Priyamvada Natarajan could not attend themeeting. The Committee received reports and presentations by faculty on all aspects of the activities of the Centre. The SAC m e m b e r s w e r e g i v e n s c i e n c e presentations by a wide range of speakers from IUCAA and Associates. The SAC also had informal interactions with IUCAA's scientific staff, graduate students, postdoctoral fellows, visitors and personnel from the administration. The SAC members, in their report, were very impressed with the accomplishments made by IUCAA in terms of fulfilling their mandate of bringing astronomical research and education opportunities to a wider geographical spread of Indian universities. They also provided various suggestions and recommendations to sustain and improve various activities of the Centre. IUCAA is in the process of developing a road map to implement these recommendations well ahead of the next SAC meeting scheduled two years from now. Fig. 1: (Left) The optical image of the gamma-ray emitting collisional ring galaxy system “Kathryn'sWheel”. (Right): Glowing hydrogen gas characteristic of star-forming regions is seen in the H-alpha band image of the same region, highlighting the ring of star formation. The dotted ellipse is added to guide the eye.