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Fermitools 2.5.3, released July 31, 2026, is a maintenance update that fixes user-reported bugs, updates backend libraries, and patches two significant issues from version 2.5.2. If you use Fermipy or generate radial Gaussian or radial disk source maps, this update addresses problems that could affect your analysis.

Key changes in 2.5.3

Library and dependency updates

• Xerces-C removed: The XML parsing interface Xerces-C has been removed and replaced with the header-only rapidXML interface.
• Python version bump: The toolchain moved from Python 3.11 to Python 3.12.

Bug fixes

• Radial source map generation: This release fixes a critical bug that prevented the accurate generation of radial Gaussian and radial disk source maps.
• Fermipy performance issue: A performance problem affecting analysis with Fermipy, introduced in version 2.5.2, has been patched.
• User-reported fixes: The update includes a number of bug fixes reported by users as well as by FSSC team members.

Who should upgrade

Where to find more detail

The announcement links to full release notes for a complete list of changes. The Fermi Portal also hosts related notices, including a June 5, 2026 data quality flag issue in LAT spacecraft files that may affect high time resolution analyses such as pulsar studies — if your work falls in that category, the FSSC recommends re-downloading spacecraft files and reanalyzing your data.

Start at the New Fermi Users section of the Fermi Portal (fermi.gsfc.nasa.gov), which the site describes as "a starting point for first-time Fermi users." From there, the practical path is to learn the data products, install the Fermitools analysis software, and work through the available analysis resources. If you can plan ahead, the Fermi Summer School is the most structured training opportunity mentioned on the portal.

First stop: the New Fermi Users page

The portal's homepage groups its main entry points into a few audience-based links. For someone new, the relevant one is New Fermi Users, labeled "A starting point for first-time Fermi users." Two related links are worth knowing about at the same time:

• Science Community — "Access data, tools, and resources for scientific research with Fermi."
• About Fermi — background on the mission, useful for context before you dive into analysis.

The portal also links to Fermi Research Highlights for "discoveries and latest breakthroughs," which is a reasonable way to see what kinds of science the data support before committing to a specific analysis.

Typical first steps

A workable order for a new user:

1. Understand the data products. Fermi's main instrument for most beginner analyses is the Large Area Telescope (LAT). Before downloading anything, get familiar with what the different data levels and file types represent, since analysis choices depend on them.
2. Install the Fermitools. This is the standard software package for Fermi data analysis. The portal's announcements show it is actively maintained — for example, Fermitools 2.5.3 was released on July 31, 2026, with user-reported bug fixes, a move from Python 3.11 to 3.12, and a replacement of the Xerces-C XML parsing interface with the header-only rapidXML interface. That release also fixed a critical bug affecting the accurate generation of radial gaussian and radial disk source maps, and patched a performance issue in Fermipy analyses present in version 2.5.2.
3. Run a tutorial analysis. Once the tools are installed, work through an end-to-end example rather than starting from your own science target. This is where you learn the input files, the configuration, and what a successful output looks like.
4. Check data quality before high-precision work. The portal's June 5, 2026 announcement describes a data quality flag issue in the LAT spacecraft position and history files: after the March 2026 migration to a new SLAC computing cluster, flags set during data quality monitoring were not propagated into the spacecraft files, so intervals of poor timing resolution were not correctly flagged with DATA_QUAL=2. Eight periods across March 17, 20, and 29 and April 5, 8, 16, 20, and 26 should have been flagged. The issue is resolved and correctly flagged data are available from the FSSC, but if your analysis needs high time resolution — pulsar studies, for instance — re-download the spacecraft files and reanalyze.

Tools and analysis resources for beginners

Note that the portal's announcements reference release notes for Fermitools updates — check those when you install, since backend changes (Python version, XML parsing interface) can affect existing scripts.

Training opportunities

The portal lists the Fermi Summer School as running May 26 to June 5, 2026, with a link from the Events section. For a new user, this is the most direct route to structured instruction, and it is worth planning around if the timing works for you.

A note on data availability

LAT data processing was fully restored after the Level 1 pipeline migration to the S3DF facility at SLAC, and the backlog collected during the processing pause has been cleared. According to the March 27, 2026 announcement, all LAT data and products are up to date on the public server — so a new user starting now is not working around a data gap.

The Fermi Portal at fermi.gsfc.nasa.gov is the official NASA-hosted web portal for the Fermi Gamma-ray Space Telescope, operated through NASA Goddard Space Flight Center. It serves the Fermi science community by publishing mission announcements, data and software releases, user resources, and events. If you are a researcher working with Fermi data, a new user looking for a starting point, an educator, or someone tracking mission status, this site is the authoritative entry point.

Who runs it and what it is for

The portal is a NASA Goddard resource, and its content is organized around the needs of the Fermi user community rather than the general public. The site's own navigation reflects this: it offers distinct entry points for the science community, new users, educators, and those seeking background about the mission.

Its main purpose is to keep the community informed and equipped: announcing software and data updates, flagging data quality issues, and pointing users to the tools and documentation needed to do Fermi analysis.

Main content areas

Announcements

The announcements section carries time-stamped operational and software news. Recent examples from the portal show the kind of information published here:

These entries are worth checking before starting or repeating an analysis, because they can change whether existing data products are still valid for your purpose.

Events

The portal lists community events, including the Fermi Summer School (scheduled for May 26 to June 5, 2026), which provides training for users of Fermi data and tools.

Audience-specific entry points

The site separates its resources by audience:

• Science Community — access data, tools, and resources for scientific research with Fermi
• New Fermi Users — a starting point for first-time users
• Educators — educational materials and teaching programs
• About Fermi — background on the mission and its discoveries

Practical takeaways

• Treat the announcements section as required reading before high time resolution analyses. The June 2026 data quality flag notice specifically recommends re-downloading spacecraft files and reanalyzing data if your work depends on high time resolution, such as pulsar studies.
• Software versions matter. The Fermitools 2.5.3 release notes describe both bug fixes and dependency changes (including a move from Python 3.11 to 3.12), so confirm your environment matches the version you intend to use.
• If you are new to Fermi, start from the "New Fermi Users" entry point rather than the science community pages, which assume familiarity with the data and tools.

The portal does not present itself as a commercial or subscription service; it is a NASA mission resource. For specifics on data access, tool installation, or event registration, follow the links from the relevant section of the site itself, since those details are maintained there rather than on this overview.

If your Fermi LAT analysis depends on high time resolution — pulsar timing studies in particular — re-download the LAT spacecraft position and history files and rerun your analysis. Data quality flags were not being propagated into those files after the March 2026 migration to the new SLAC computing cluster, so intervals of poor timing resolution were not correctly marked with DATA_QUAL=2. The problem has been resolved and correctly flagged data are now available from the FSSC, but files you downloaded during the affected window may still carry the old, unflagged values.

What went wrong

When LAT data quality monitoring runs, it sets flags in the spacecraft files that downstream analysis uses to filter out bad intervals. Following the migration to the new SLAC computing cluster in March 2026, those flags stopped being written into the spacecraft files. The practical consequence: intervals with degraded timing resolution were left unflagged instead of being marked DATA_QUAL=2.

This matters most when you are working at fine time scales. A pulsar study that assumes every retained interval has good timing resolution can be biased by intervals that should have been excluded. Lower-cadence analyses are generally less exposed, but the flag is there for a reason and the corrected files are the authoritative version.

Affected dates

Eight periods were affected, most spanning multiple orbits:

If your time window overlaps any of these, treat your current spacecraft files as suspect.

What to do

1. Check whether you are exposed. If your analysis uses high time resolution — pulsar studies are the example given — and your data window covers any of the dates above, assume you are affected.
2. Re-download the spacecraft position and history files from the FSSC. The corrected, properly flagged data are now available there.
3. Rerun the analysis with the new files so the DATA_QUAL=2 filtering is applied correctly.
4. If your analysis does not need high time resolution, the impact is limited, but re-downloading is still the safe choice if you want your files to match the current FSSC release.

Related context worth knowing

The flag issue is separate from the processing pause that followed the Level 1 pipeline migration to the S3DF facility at SLAC. That backlog was cleared and normal LAT data processing and deliveries were fully restored as of the March 27, 2026 announcement, with all LAT data and products up to date on the public server. In other words, the data themselves are current — the problem was specifically the quality flags inside the spacecraft files, not missing or delayed observations.

If you are also running Fermitools, note that version 2.5.3 (released July 31, 2026) fixed a critical bug affecting the accurate generation of radial gaussian and radial disk source maps and patched a Fermipy performance issue from 2.5.2. That is a separate matter from the data quality flag, but if you are reanalyzing data anyway, it is a reasonable moment to confirm your tool version.