aurelio-amerio/fermi-maps

Fermi-LAT maps for MapGen

HEALPix maps made from Fermi-LAT photon data, for the mapgen_jax simulator (the JAX port of MapGen.jl). The repository holds, for each dataset tag, the products the simulator reads (counts, exposure, the smoothed Galactic diffuse template, the PSF table), the raw fermitools conversions they were made from, and the NASA Fermi SSC files needed to rebuild or use them.

Layout

README.md                    this card
<tag>/data/                  the four HDF5 products (schema below)
<tag>/raw/                   `gtbin.h5`, `gtexpcube2.h5`, `gtltcube.h5`, `gtpsf.h5` and `ebins.txt`
external/                    gll_iem_v07.fits, gll_psc_v35.fit and their README.md

external/ is shared by all tags. Files under a tag are overwritten in place when a product is fixed; the repository history is the version history.

Dataset sourceveto-w9-w960-7bins

• Photons: Fermi-LAT P8R3 SOURCEVETO class, front-converting events, weekly files from week 9 to week 960, zenith angle below 90 degrees.
• Energy: 500 MeV to 1 TeV in 7 macro bins, edges 500, 1000, 2000, 5000, 10000, 50000, 200000 and 1000000 MeV, built from the 14 micro bins of the fermitools run.
• Maps: HEALPix ring order, nside 1024 (npix = 12582912), bins by increasing energy, energies in MeV. Lower nsides are made on load by downgrading.
• Size: 290.5 MB in data/ and 256 MB in raw/ for one tag (four gt*.h5 files and ebins.txt), and about 470 MB, once, for external/.
• Total counts: 45 752 368 over the 7 macro bins (table below). The four data/ files are fermi_counts.h5 12.5 MB, exposure.h5 51.6 MB, gf_v07_counts.h5 226.4 MB and psf.h5 31 kB (290.5 MB in all).
• raw/ holds gtbin.h5, gtexpcube2.h5, gtltcube.h5, gtpsf.h5 and ebins.txt. The photon event lists (gtselect, gtmktime) are not included; they can be regenerated from the public Fermi-LAT weekly photon and spacecraft files with the selection recorded in the attributes and the gtmktime filter DATA_QUAL==1&&LAT_CONFIG==1&&LAT_MODE==5&&IN_SAA!=T&&((ABS(ROCK_ANGLE)<52)).

Bin (MeV)	Counts
500 - 1000	25 310 196
1000 - 2000	12 646 836
2000 - 5000	5 861 859
5000 - 10000	1 270 936
10000 - 50000	606 061
50000 - 200000	50 786
200000 - 1000000	5 694
Total	45 752 368

The selection is recorded in every file as root attributes: event_class, event_type, irfs, zmax, tmin, tmax, weeks, fermitools_version, ontime, selection_emin, selection_emax (the gtselect energy range, MeV); the binning as nside, ordering, nbins, micro_Emin, micro_Emax; and the origin as dataset, source_run, created_by, created_at, schema_version, gll_iem_file and gll_psc_file (the external/ files used). Every file also records the build settings psf_index (the power-law index of the PSF energy weighting, 2.4) and lmax (the band limit of the beam smoothing of the foreground, 4 nside = 4096). For this tag fermitools_version is the gtbin CREATOR keyword and carries no version; the run used Fermitools 2.5.3.

Products

All maps are HEALPix ring order at nside 1024, bins ordered by increasing energy, energies in MeV.

File	Datasets	Notes
fermi_counts.h5	counts (nbins, npix) int32	Photon counts per pixel per macro bin. Integer because summing micro bins and summing child pixels keeps integers.
exposure.h5	exposure (nbins, npix) float32	cm^2 s. Mean over the micro bins inside each macro bin.
gf_v07_counts.h5	gf_counts (nbins, npix) float32	Expected counts per pixel from the smoothed gll_iem_v07 template, integrated over each macro bin with this selection's exposure.
psf.h5	theta_deg (ntheta,) float64, psf (nbins, ntheta) float64	The gtpsf table averaged inside each macro bin with E^-2.4 weights. Units as in gtpsf (sr^-1).

Every file also holds Emin (nbins,) float64 and Emax (nbins,) float64, and the same root attributes (above). Datasets are chunked one bin at a time, gzip level 4 with the shuffle filter.

Usage

from mapgen_jax import load_experiment

experiment = load_experiment("sourceveto-w9-w960-7bins", nside=128)            # downloads, downgrades
experiment = load_experiment("sourceveto-w9-w960-7bins", nside=128, bins=[1])  # one macro bin

load_experiment returns an Experiment: the maps of the selected bins downgraded to nside, the PSF and the plane mask, and the fit of the diffuse model to the counts. bins selects macro bins by index; reads are anonymous (no token). Setting MAPGEN_DATA_ROOT=<dir> reads a local directory with the same <tag>/data layout instead.

External data

external/ holds NASA public data from the Fermi Science Support Center (SSC), redistributed unmodified: the Galactic interstellar emission model gll_iem_v07.fits and the 4FGL-DR4 source catalog gll_psc_v35.fit. Their origin, attribution and citations are in external/README.md. The MIT license of this card covers the derived products under <tag>/, not those files.

Citation

If you use these maps, cite the Fermi-LAT catalog and the diffuse model (see external/README.md) and the simulator:

• MapGen-jax: https://github.com/aurelio-amerio/MapGen-jax (Aurelio Amerio)
• Ballet et al. 2023, "Fermi Large Area Telescope Fourth Source Catalog Data Release 4 (4FGL-DR4)", arXiv:2307.12546
• Abdollahi et al. 2020, ApJS 247, 33 (4FGL)