We investigate whether the new horizon first law proposed recently still work in f( R) theory. We identify the entropy and the energy of black hole as quantities proportional to the corresponding...

We present the analysis of the brightest flare that was recorded in the Insight-HMXT data set in a broad energy range (2–200 keV) from the microquasar GRS 1915+105 during an unusual low-luminosity state. This flare was detected by Insight-HXMT among a series of flares during 2019 June 2 UTC 16:37:06–20:11:36 with a 2–200 keV luminosity of 3.4–7.27 × 10³⁸ erg s⁻¹. Basing on the broadband spectral analysis, we find that the flare spectrum shows different behaviors during bright and faint epochs. The spectrum of the flare can be fitted with a model dominated by a power-law component. Additional components show up in the bright epoch with a hard tail and in the faint epoch with an absorption line of ∼6.78 keV. The reflection component of the latter is consistent with an inner disk radius ∼five times larger than that of the former. These results on the giant flare during the “unusual” low-luminosity state of GRS 1915+105 may suggest that the source experiences a possible fast transition from a jet-dominated state to a wind-dominated state. We speculate that the evolving accretion disk and the large-scale magnetic field may play important roles in this peculiar huge flare.

We consider the new horizon first law in $f\left(R\right)$ theory. We derive the general formulas to computed the entropy and energy for static spherically symmetric black hole. For applications, some nontrivial solutions in some popular $f\left(R\right)$ theories are investigated, the entropies and the energies of static spherically symmetric black holes in these models are first calculated.

Detection of short gamma-ray bursts (SGRBs) is critically important for the research of compact object mergers and multimessenger astrophysics, but a significant part of SGRBs fall below the trigger threshold of GRB detectors, and thus are often missed. Here we present a systematic search for and verification of missed SGRBs using Fermi/Gamma-ray Burst Monitor (GBM) subthreshold triggers, jointly analyzing data from GBM, Gravitational Wave High-energy Electromagnetic Counterpart All-sky Monitor (GECAM)-B, and GECAM-C. Among 466 Fermi/GBM subthreshold events (with reliability ≥5) from 2021 to 2024, 181 are within GECAM’s field of view. We find that 49 out of 181 are confirmed astrophysical transients, and 41 can be classified as SGRBs. Thus, the SGRB detection rate of Fermi/GBM is increased to about 50 per year. Additionally, a complete multi-instrument monitoring and systematic verification of GBM subthreshold events is expected to further increase the SGRB rate to about 80 per year, which is ∼100% improvement relative to the GBM-triggered SGRBs. These results may have important implications on the local formation rate of SGRBs and the binary neutron star merger rate. We also searched for potential temporal coincidences between these SGRBs and gravitational waves from the LIGO–Virgo–KAGRA O4 run resulting in no detection.

In this paper, we propose that since Hawking radiation may be a kind of superradiation, the action of superradiation with preset bounds satisfies some higher-dimensional action structure, e.g., bosons in the preset springs of Kerr black hole. The superradiation meets the algebraic system of bosons on Kerr-Schild black holes. We think that the superradiation of bounded fermions to Kerr structure black holes benefits the mapping structure of wormholes. By analogy, we find the entropy algebraic expression of the wormhole in the charged black hole under f(R) gravity and then conduct thermodynamic geometric analysis to find out the stability condition of the wormhole.