The Compton Spectrometer and Imager (COSI) is a soft gamma-ray survey telescope (0.2-5 MeV) designed to probe the origins of Galactic positrons, uncover the sites of nucleosynthesis in the Galaxy, perform pioneering studies of gamma-ray polarization, and find counterparts to multi-messenger sources. COSI’s compact Compton telescope combines improvements in sensitivity, spectral resolution, angular resolution, and sky coverage to facilitate groundbreaking science. Learn more by reading about the Science COSI will explore and its Instrument Design.
Data Challenge
The third COSI data challenge is available here.
The COSI Data Challenges are released on a yearly basis in preparation for the launch of the COSI Small Explorer (SMEX) class mission in 2027. They are based on simulated data, which is intended to closely mimic the real flight data. There are two main goals of the Data Challenges:
- Facilitate development of the COSI data pipeline and analysis tools
- With routine feedback from scientists
- Alongside development of the expected source models by the science team
- Provide resources to the astrophysics community to become familiar with COSI data
- Excellent training for science team in preparation for first analyses after launch
- Public releases help with community building before COSI data is released
Upcoming Events
There will be a COSI Special Session on Monday, January 5th at the American Astronomical Society meeting in Phoenix, Arizona.
Session Title: Exploring the MeV Gamma-ray Sky with the Compton Spectrometer and Imager
Speakers and titles:
- John Tomsick (UC Berkeley) “Overview of the COSI mission”
- Robin Anthony-Petersen (UC Berkeley) “Germanium detectors for the COSI mission”
- Chris Karwin (Clemson University) “Probing the Galactic diffuse continuum emission with COSI”
- Hsiang-Kuang Chang (NTHU) “MeV observations of pulsars and pulsar wind nebulae”
- Nicole Rodriguez Cavero (UC Berkeley) “COSI polarimetry: science and calibration plans”
- Hannah Gulick (UC Berkeley) “The Background and Transient Observer: COSI’s student collaboration experiment”
Updates and Achievements
October 28, 2025
The COSI team is starting the flight model cryostat assembly. The photo (credit: Chris Smith and Matt Rubly) shows the first germanium detector in the detector holder assembly.
October 17-24, 2025
COSIfest 2025 was held on the campus of Washington University, St. Louis on Oct 17, 20-24, 2025. This was a meeting of the COSI Science Team and a software development workshop.
The workshop was held in the appropriately-named Compton Hall. Arthur Holly Compton was Chancellor of Washington University during 1945-1953, some time after he won the Nobel Prize for discovering the X-ray scattering effect that became know as Compton scattering, which is the basis for the operation of COSI.
The photo shows the COSI Science Team in front of Compton Hall on Oct 17 (credit: Samantha Tippett). More photos of COSIfest 2025 can be found here.
October 12-16, 2025
Many COSI team members attended and gave talks and/or posters at the High-Energy Astrophysics Division (HEAD) meeting in St. Louis, MO on Oct 12-16. There was a COSI Special Session, and many excellent (and award-winning) posters).
July 2025
The Cryostat Heat Removal Subsystem (CHRS) at GSFC has begun TVAC testing. The CHRS includes the cryocooler (for cooling the GeDs), the cryocooler control electronics, heat pipes, and radiators. The team includes (left-to-right) Hannah Goldberg, Howard Tseng, Stuart Banks, Albert Shih, and Sergey Semenov.
May 2025
COSI reached a significant milestone by assembling the engineering model cryostat and doing a successful cold vacuum test. The engineering model consists of a cryostat with a combination of 16 germanium and dummy detectors, two shield walls, and operational read out electronics.
January 22, 2025
A review of Background and Transient Observer (BTO) design took place. The BTO is a student collaboration experiment that will fly on the COSI satellite. Learn more about its goals and the design review here.
December 4-6, 2024
The Critical Design Review (CDR) occurred at Northrop Grumman (Dulles). The review was successful, and COSI is on-track to continue into the build phase.
October 15-25, 2024
COSIfest 2024! See more pictures from the event here.
July 2024
NASA has selected SpaceX to provide launch services for COSI. The launch is planned for 2027 on a Falcon 9 rocket from Cape Canaveral. The press release is here.
