doi:10.1103/d194-7t6xengRodríguez Candón, FranciscoGanguly, SougataGiannotti, MaurizioKumar, TanmoyLella, AlessandroMescia, FedericoFresh look at the diffuse ALP background from supernovaeART-2025-145347Protoneutron stars, highly compact objects formed in the core of exploding supernovae (SNe), are powerful sources of axionlike particles (ALPs). In the SN core, ALPs are dominantly produced via nucleon-nucleon bremsstrahlung and pion conversion, resulting in an energetic ALP spectrum peaked at energies O(100)  MeV. In this work, we revisit the diffuse ALP background, produced from all past core-collapse supernovae, and update the constraints derived from -LAT observations. Assuming the maximum ALP-nucleon coupling allowed by the SN 1987A cooling, we set the upper limit gaγγ≲2×10−13  GeV−1 for ALP mass ma≲10−10  eV, which is approximately a factor of two improvement with respect to the existing bounds. On the other hand, for ma≳10−10  eV, we find that including pion conversion strengthens the bound on gaγγ, approximately by a factor of two compared to the constraint obtained from bremsstrahlung alone. Additionally, we present a sensitivity study for future experiments such as AMEGO-X, e-ASTROGAM, GRAMS-balloon, GRAMS-satellite, and MAST. We find that the expected constraint from MAST would be comparable to -LAT bound. However, SN 1987A constraint remains one order of magnitude stronger as compared to the bound derived from the current and future gamma-ray telescopes.2025http://zaguan.unizar.es/record/16277410.1103/d194-7t6xhttp://zaguan.unizar.es/record/162774oai:zaguan.unizar.es:162774info:eu-repo/grantAgreement/ES/AEI/PID2021-126078NB-C21info:eu-repo/grantAgreement/EUR/COST/CA21106-COSMIC Wispersinfo:eu-repo/grantAgreement/EC/H2020/788781/EU/Towards the detection of the axion with the International Axion Observatory/IAXOplusThis project has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No H2020 788781-IAXOplusinfo:eu-repo/grantAgreement/ES/MINECO/PID2019-108122GB-C31info:eu-repo/grantAgreement/ES/NextGenerationEU/INVESTIGO-095-28Physical Review D 112, 1 (2025), 015006 [10 pp.]byhttps://creativecommons.org/licenses/by/4.0/deed.esinfo:eu-repo/semantics/openAccess