NuSTAR detection of SN2024ggi at 2 days post discovery
ATel #16587; Raffaella Margutti (UC Berkeley), Brian Grefenstette (Caltech)
on 14 Apr 2024; 00:04 UT
Credential Certification: Raffaella Margutti (rafmargutti@gmail.com)
Subjects: X-ray, Supernovae
We started observations of the very young and nearby type-II SN2024ggi (TNS Astronomical Transient Report No. 207398 and TNS Classification Report No. 16878) with NuSTAR on 2024-04-13, 07:06:09 UT, which is around 2 days post discovery (PI Margutti). Using the first 18.2 ks of NuSTAR observations we find clear evidence for hard-X-ray emission at the location of the supernova with statistical significance > 10 sigma in each of the two NuSTAR modules. A preliminary spectral analysis shows that the data can be modeled with an absorbed power-law spectrum with photon index Gamma ~1.4 +\- 0.2 and intrinsic NH<3e23 cm-2 in the energy range 3-40 keV. The inferred absorbed flux is ~3.e-12 erg/s/cm2 in the 3-80 keV energy range, corresponding to a luminosity of ~2e40 erg/s at the distance of 6.6 Mpc, which is similar to SN2023ixf at a few days post explosion (Grefenstette 2023). The hard photon index is suggestive of an intrinsic thermal bremsstrahlung spectrum. Assuming a thermal bremsstrahlung spectral model we infer T> 40 keV. Hot bremsstrahlung emission is expected to originate from the SN shock interaction with a dense medium (as was previously found for SNe 2014C and 2023ixf; Margutti et al., 2017; Brethauer et al., 2022; Grefenstette et al., 2023.).
Further analysis is ongoing and further observations are planned.
We are extremely grateful to the NuSTAR PI Fiona Harrison and to the entire NuSTAR team (in particular to Karl Foster, John McDonald and Nathan Miller) for rapidly approving and executing these observations.
