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Some short gamma-ray bursts (SGRBs) exhibit a short-duration and spectral hard emission (referred to as a "hard spike") followed by a slightly longer soft emission (known as a "soft tail"). We identified nine SGRBs with the known redshift in the Swift/BAT gamma-ray burst catalog by specifically searching for the soft tail. We found that the spectra of these SGRBs can be described as a cutoff power-law model for the hard spike and the soft tail, and both show a time variation keeping the E peak– L iso correlation. This suggests that the emission mechanisms of both phenomena are identical. Furthermore, we found a trend of luminosity evolution as a function of redshift. This phenomenon suggests that these bursts originate from sources that are intrinsically bright and/or energy-density-concentrated within a narrower jet at higher redshift. We demonstrate that the average jet opening angle, derived from the jet break, can be explained by considering a model based on a strongly redshift-dependent jet opening angle. [ABSTRACT FROM AUTHOR]

The detection of the short gamma-ray burst (SGRB) 050709 by the HETE-2 satellite opened the door to understanding the nature of SGRBs, offering clues about their emission mechanism and progenitors, with the crucial aid of optical follow-up observations. Here, we revisit the prompt emission of GRB 050709. Our analysis reveals an initial hard spike ∼200 ms long, followed by a subsequent soft-tail emission lasting ∼300 ms. These components could be common among other SGRBs originating from binary neutron merger events, such as GW 170817 and GRB 170817A. Detailed temporal and spectral analyses indicate that the soft-tail emission might be attributed to the cocoon formed by the relativistic jet depositing energy into the surrounding material. We find the necessary cocoon parameters at the breakout, as consistent with numerical simulation results. We compared the physical parameters of this cocoon with those of other SGRBs. The relatively higher cocoon pressure and temperature in GRB 050709 may indicate a more on-axis jet compared with GRB 170817A and GRB 150101B. [ABSTRACT FROM AUTHOR]

We analysed correlations among the rest-frame spectral peak energy Ep, the observed frame 64 ms peak isotropic luminosity Lp and the isotropic energy Eiso for 13 short gamma-ray burst (SGRB) candidates having the measured redshift z, Tobs90/(1 + z) < 2 s and well-determined spectral parameters. An SGRB candidate is regarded as a misguided SGRB if it is located in the 3σint dispersion region from the best-fitting function of the Ep-Eiso correlation for long GRBs (LGRBs), while the others are regarded as secure SGRBs possibly from compact star mergers. Using 8 secure SGRBs out of 13 SGRB candidates, we tested whether the Ep-Eiso and Ep-Lp correlations exist for SGRBs. We found that the Ep-Eiso correlation for SGRBs (Eiso = 1051.42 ± 0.15 erg s−1(Ep/774.5 keV)1.58 ± 0.28) seems to exist with the correlation coefficient r = 0.91 and chance probability p = 1.5 × 10−3. We also found that the Ep-Lp correlation for SGRBs (Lp = 1052.29 ± 0.066 erg s−1(Ep/774.5 keV)1.59 ± 0.11) is tighter than the Ep-Eiso correlation since r = 0.98 and p = 1.5 × 10−5. Both correlations for SGRBs are dimmer than those of LGRBs for the same Ep by factors ∼100 (Ep − Eiso) and ∼ 5(Ep − Lp). Applying the tighter Ep-Lp correlation for SGRBs to 71 bright Burst and Transient Source Experiment SGRBs, we found that pseudo-redshift z ranges from 0.097 to 2.258 with the mean 〈z〉 of 1.05. The redshifts of SGRBs apparently cluster at lower redshift than those of LGRBs (〈z 〉 ∼2.2), which supports the merger scenario of SGRBs. [ABSTRACT FROM AUTHOR]

We extend the Hubble diagram up to using 63 gamma-ray bursts (GRBs) via peak energy–peak luminosity relation (so-called Yonetoku relation), and obtain constraints on cosmological parameters including dynamical dark energy parametrized by . It is found that the current GRB data are consistent with the concordance model within 2σ level. Although constraints from GRBs themselves are not so strong, they can improve the conventional constraints from type Ia supernovae because GRBs have much higher redshifts. Further, we estimate the constraints on the dark energy parameters expected by future observations with Gamma-ray Large Area Space Telescope and Swift by Monte Carlo simulation. Constraints would improve substantially with another 150 GRBs. [ABSTRACT FROM AUTHOR]

We calibrated the peak energy–peak luminosity relation of gamma-ray bursts (GRBs; the so-called Yonetoku relation) using 33 events with redshift z < 1.62 without assuming any cosmological models. The luminosity distances to GRBs are estimated from those of large numbers of Type Ia supernovae with z < 1.755. This calibrated Yonetoku relation can be used as a new cosmic distance ladder towards higher redshifts. We determined the luminosity distances of 30 GRBs in 1.8 < z < 5.6 using the calibrated relation, and plotted the likelihood contour in the plane. We obtained for a flat universe. Because our method is free from the circularity problem, we can say that our universe in 1.8 < z < 5.6 is compatible with the so-called concordance cosmological model derived for z < 1.8. This suggests that the time variation of the dark energy is small or zero up to z∼ 6. [ABSTRACT FROM AUTHOR]

Highlights from the article: Short GRB (SGRB) afterglows with a known redshift, we investigated the ratio of the Equivalent hydrogen column density to the dust extinction, N Lent hydrogen column density is derived from the X-ray absorption, because the X-ray observation data of SGRBs were taken from the The SEDs of two SGRBs (GRB 130603B, 150424A), the.

Using 72 short gamma-ray bursts (SGRBs) with well determined spectral data observed by BATSE, we determine their redshift and luminosity by applying the Ep-Lp correlation for SGRBs found by Tsutsui et al. For 53 SGRBs with an observed flux brighter than 4 × 10–6 erg cm–2 s–1, the cumulative redshift distribution up to z = 1 agrees well with that of 22 Swift SGRBs. This suggests that the redshift determination by the Ep-Lp correlation for SGRBs works well. The minimum event rate at z = 0 is estimated as , so that the minimum beaming angle is 0.°6-7.°8 assuming a merging rate of 10–7- 4 × 10–6 events Mpc–3 yr–1 suggested from the binary pulsar data. Interestingly, this angle is consistent with that for SGRB 130603B of ∼4°-8°. On the other hand, if we assume a beaming angle of ∼6° suggested from four SGRBs with the observed beaming angle value, then the minimum event rate including off-axis SGRBs is estimated as . If SGRBs are induced by the coalescence of binary neutron stars (NSs) and/or black holes (BHs), then this event rate leads to a minimum gravitational-wave detection rate of for an NS-NS (NS-BH) binary, respectively, by a worldwide network with KAGRA, advanced-LIGO, advanced-VIRGO, and GEO. [ABSTRACT FROM AUTHOR]

A wide-field X-ray survey in the soft X-ray band is crucial for future satellite missions in the astronomical observations. HiZ-GUNDAM , currently under development, is a proposed satellite designed to observe soft X-ray transients including gamma-ray bursts. This satellite employs wide-field X-ray monitors consisting of lobster-eye optics and focal-plane pixel sensors in the soft X-ray band of 0.4–4 keV. A pnCCD is a candidate for focal-plane Si pixel detectors, featuring a back-illuminated X-ray CCD, large pixel size (70–100 µm), and a large active image area of approximately 55 × 55 mm 2 for the flight model. Here, we investigated the basic characteristics and performance of the small-size pnCCD with 128 × 256 pixels, a pixel size of 75 µm, and a detector thickness of 450 µm. High-energy cosmic rays such as protons can degrade the performance of pnCCDs by increasing dark current and charge transfer inefficiency due to ionizing and displacement damage. These factors may affect soft X-ray observations, potentially causing the degradation of lower-detectable energy thresholds and an increase in the number of hot pixels. Therefore, we conducted a radiation tolerance test at room temperature using a proton beam. After irradiating the pnCCD with 10-MeV protons equivalent to three years of nominal operation for HiZ-GUNDAM , we found that the operation temperatures of the pnCCD should be lower than -35 °C. This requirement will be incorporated into the design of the mission operation system. [ABSTRACT FROM AUTHOR]

We report the strictest observational verification of CPT invariance in the photon sector, as a result of γ-ray polarization measurement of distant gamma-ray bursts (ORBs), which are the brightest stellar-sized explosions in the Universe. We detected γ-ray polarization of three GRBs with high significance levels, and the source distances may be constrained by a well-known luminosity indicator for GRBs. For the Lorentz- and CPT-violating dispersion relation E2± = p² ± 2ξp³/MPI, where ± denotes different circular polar- ization states of the photon, the parameter ~ is constrained as ∣ξ∣ < O(l0-15). Barring precise cancellation between quantum gravity effects and dark energy effects, the stringent limit on the CPT-violating effect leads to the expectation that quantum gravity presumably respects the CPT invariance. [ABSTRACT FROM AUTHOR]