fermi: migrate from LATDataQuery.cgi scraping to the new REST API

CHANGES.rst

@@ -72,6 +72,32 @@ vizier
 
 - Methods ``get_catalog``, ``get_catalog_async`` and ``query_*`` now always return UCD1+ instead of UCD1. [#3458]
 
+fermi
+^^^^^
+
+- The module now uses the new Fermi LAT Data Query REST API
+  (``https://fermi.gsfc.nasa.gov/ssc/data/access/lat/query/api/v1``), which is replacing the
+  ``LATDataQuery.cgi`` endpoint whose HTML responses were previously scraped
+  with regular expressions. The user-facing ``FermiLAT.query_object()``
+  signature is unchanged. [#3647]
+- ``FermiLAT.query_object_async()`` now returns the server-assigned
+  ``query_id`` instead of the URL of an HTML results page. [#3647]
+- New methods ``FermiLAT.get_status()``, ``FermiLAT.list_results()``,
+  ``FermiLAT.wait_for_completion()`` and ``FermiLAT.get_file_urls()`` expose
+  the individual steps of the asynchronous query workflow. [#3647]
+- New keyword arguments: ``zenithangle`` (maximum zenith angle in degrees) and
+  ``coordsystem`` (``'J2000'``, ``'B1950'`` or ``'Galactic'``). All-sky
+  queries (radius > 60 deg, observation window <= 24 h) are now supported. [#3647]
+- ``GetFermilatDatafile`` and ``get_fermilat_datafile`` are deprecated; they
+  now delegate to ``FermiLAT.get_file_urls()`` and take a ``query_id`` rather
+  than a results-page URL. [#3647]
+- The module no longer emits an "Experimental" warning on import. [#3647]
+- Failed queries now surface the server's error message: an HTTP error
+  response with a JSON body such as ``{"error": "..."}`` is raised as a
+  ``RemoteServiceError`` carrying that message, rather than a bare status
+  code. [#3647]
+
+
 mast
 ^^^^
 - ``utils.mast_relative_path`` is now deprecated in favor of ``utils.get_cloud_paths``. [#3488]

astroquery/fermi/__init__.py

@@ -4,6 +4,10 @@
 
 https://fermi.gsfc.nasa.gov
 https://fermi.gsfc.nasa.gov/ssc/data/
+
+As of 2026, the Fermi LAT Data Server exposes a JSON REST API.  This module
+targets that API; the legacy ``LATDataQuery.cgi`` HTML-scraping path has been
+removed.
 """
 from astropy import config as _config
 
@@ -14,25 +18,28 @@ class Conf(_config.ConfigNamespace):
     """
 
     url = _config.ConfigItem(
-        'https://fermi.gsfc.nasa.gov/cgi-bin/ssc/LAT/LATDataQuery.cgi',
-        'Fermi query URL.')
+        'https://fermi.gsfc.nasa.gov/ssc/data/access/lat/query/api/v1',
+        'Base URL of the Fermi LAT Data Query REST API. Endpoints '
+        '(/query, /query/{id}/status, /query/{id}/results) are appended to it.')
+    file_base_url = _config.ConfigItem(
+        # NOTE: the results endpoint returns bare filenames; download URLs are
+        # reconstructed against this staging area. Currently a /test/ path -
+        # revisit if the staging location changes at production cutover.
+        'https://fermi.gsfc.nasa.gov/FTP/fermi/data/lat/test/queries/',
+        'Base URL under which query result files are staged.')
     timeout = _config.ConfigItem(
         60,
-        'Time limit for connecting to Fermi server.')
+        'Time limit for connecting to the Fermi server.')
     retrieval_timeout = _config.ConfigItem(
         120,
         'Time limit for retrieving a data file once it has been located.')
 
 
 conf = Conf()
 
-from .core import FermiLAT, FermiLATClass, GetFermilatDatafile, get_fermilat_datafile
+from .core import FermiLAT, FermiLATClass, GetFermilatDatafile, get_fermilat_datafile  # noqa: E402
 
 __all__ = ['FermiLAT', 'FermiLATClass',
            'GetFermilatDatafile', 'get_fermilat_datafile',
            'Conf', 'conf',
            ]
-
-import warnings
-warnings.warn("Experimental: Fermi-LAT has not yet been refactored to have "
-              "its API match the rest of astroquery.")