An improved redshift indicator for Gamma-Ray Bursts, based on the prompt emission
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We propose an improved version of the redshift indicator developed by Atteia, which gets rid of the dependence on the burst duration and provides better estimates for high‐redshift GRBs. We present first this redshift indicator, then its calibration with HETE‐GRBs with known redshifts. We also provide an estimation of the redshift for 59 bursts, and we finally discuss the redshift distribution of HETE‐bursts and the possible other applications of this redshift indicator.The Italian–Dutch X–ray mission BeppoSAX had a great impact in the field of Gamma-Ray Burst (GRB) astrophysics, in particular with the the discovery of afterglow emission, leading ultimately to the determination of GRB distance scale and energetics, the discovery of new classes of events like dark GRBs, X–ray rich GRBs and X–Ray Flashes (XRF), the first direct evidence of the GRB/SN connection. Here we review the observations and implications of the relationship between the photon energy, Ep,i, at which the intrinsic (i.e. corrected for cosmological redshift) EF(E) spectrum peaks and the isotropic equivalent radiated energy, Eiso, discovered by Amati et al.(2002) based on BeppoSAX measurements when the mission was close to the end of its operation. This relation, subsequently confirmed and extended to the X–ray richest GRBs by HETE–2 measurements, can be used to discriminate among the various scenarios for the prompt emission of GRBs, is a challenging test for jet models and the understanding of the GRB/SN connection and can be also used to build up redshift estimators.
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We investigate redshift distributions of three long burst samples, with the first sample containing 131 long bursts with observed redshifts, the second including 220 long bursts with pseudo-redshifts calculated by the variability-luminosity relation, and the third including 1194 long bursts with pseudo-redshifts calculated by the lag-luminosity relation, respectively. In the redshift range 0–1 the Kolmogorov–Smirnov probability of the observed redshift distribution and that of the variability-luminosity relation is large. In the redshift ranges 1–2, 2–3, 3–6.3 and 0–37, the Kolmogorov–Smirnov probabilities of the redshift distribution from lag-luminosity relation and the observed redshift distribution are also large. For the GRBs, which appear both in the two pseudo-redshift burst samples, the KS probability of the pseudo-redshift distribution from the lag-luminosity relation and the observed reshift distribution is 0.447, which is very large. Based on these results, some conclusions are drawn: i) the V-Liso relation might be more believable than the τ-Liso relation in low redshift ranges and the τ-Liso relation might be more real than the V-Liso relation in high redshift ranges; ii) if we do not consider the redshift ranges, the τ-Liso relation might be more physical and intrinsical than the V-L iso relation.
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The high redhsift blazars powered by supermassive black holes with masses exceeding $10^9\:M_\odot$ have the highest jet power and luminosity and are important probes to test the physics of relativistic jets at the early epochs of the Universe. We present a multi-frequency spectral and temporal study of high redshift blazar PKS 0537-286 by analyzing data from Fermi-LAT, NuSTAR Swift XRT and UVOT. Although the time averaged $\gamma$-ray spectrum of the source is relatively soft (indicating the high-energy emission peak is below the GeV range), several prominent flares were observed when the spectrum hardened and the luminosity increased above $10^{49}\:{\rm erg\:s^{-1}}$. The X-ray emission of the source varies in different observations and is characterised by a hard spectrum $\leq1.38$ with a luminosity of $>10^{47}\:{\rm erg\:s^{-1}}$. The broadband spectral energy distribution in the quiescent and flaring periods was modeled within a one-zone leptonic scenario assuming different locations of the emission region and considering both internal (synchrotron radiation) and external (from the disk, broad-line region and dusty torus) photon fields for the inverse Compton scattering. The modeling shows that the most optimistic scenario, from the energy requirement point of view, is when the jet energy dissipation occurs within the broad-line region. The comparison of the model parameters obtained for the quiescent and flaring periods suggests that the flaring activities are most likely caused by the hardening of the emitting electron spectral index and shifting of the cut-off energy to higher values.
Spectral energy distribution
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The optical afterglow of long-duration GRB 071003 is among the brightest yet to be detected from any GRB, with R ≈ 12 mag in KAIT observations starting 42 s after the GRB trigger, including filtered detections during prompt emission. However, our high-S/N afterglow spectrum displays only extremely weak absorption lines at what we argue is the host redshift of z = 1.60435, in contrast to the three other, much stronger Mg II absorption systems observed at lower redshifts. Together with Keck adaptive optics observations, which fail to reveal a host galaxy coincident with the burst position, our observations suggest a halo progenitor and offer a cautionary tale about the use of Mg II for GRB redshift determination. We present early- through late-time observations spanning the electromagnetic spectrum, constrain the connection between the prompt emission and early variations in the light curve (we observe no correlation), and discuss possible origins for an unusual, marked rebrightening that occurs a few hours after the burst: likely either a late-time refreshed shock or a wide-angle secondary jet. Analysis of the late-time afterglow is most consistent with a wind environment, suggesting a massive star progenitor. Together with GRB 070125, this may indicate that a small but significant portion of star formation in the early universe occurred far outside what we consider a normal galactic disk.
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We present the observations of Lyman continuum (LyC) emission in the afterglow spectra of GRB 191004B at $z=3.5055$, together with those of the other two previously known LyC-emitting long gamma-ray bursts (LGRB) (GRB 050908 at $z=3.3467$, and GRB 060607A at $z=3.0749$), to determine their LyC escape fraction and compare their properties. From the afterglow spectrum of GRB 191004B we determine a neutral hydrogen column density at the LGRB redshift of $\log(N_{\rm HI}/cm^{-2})= 17.2 \pm 0.15$, and negligible extinction ($A_{\rm V}=0.03 \pm 0.02$ mag). The only metal absorption lines detected are CIV and SiIV. In contrast to GRB 050908 and GRB 060607A, the host galaxy of GRB 191004B displays significant Ly$α$ emission. From its Ly$α$ emission and the non-detection of Balmer emission lines we constrain its star-formation rate (SFR) to $1 \leq$ SFR $\leq 4.7$ M$_{\odot}\ yr^{-1}$. We fit the Ly$α$ emission with a shell model and find parameters values consistent with the observed ones. The absolute LyC escape fractions we find for GRB 191004B, GRB 050908 and GRB 060607A are of $0.35^{+0.10}_{-0.11}$, $0.08^{+0.05}_{-0.04}$ and $0.20^{+0.05}_{-0.05}$, respectively. We compare the LyC escape fraction of LGRBs to the values of other LyC emitters found from the literature, showing that LGRB afterglows can be powerful tools to study LyC escape for faint high-redshift star-forming galaxies. Indeed we could push LyC leakage studies to much higher absolute magnitudes. The host galaxies of the three LGRB presented here have all $M_{\rm 1600} > -19.5$ mag, with the GRB 060607A host at $M_{\rm 1600} > -16$ mag. LGRB hosts may therefore be particularly suitable for exploring the ionizing escape fraction in galaxies that are too faint or distant for conventional techniques. Furthermore the time investment is very small compared to galaxy studies. [Abridged]
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Context. X-shooter is the first second-generation instrument to become operative at the ESO Very Large Telescope (VLT). It is a broad-band medium-resolution spectrograph designed with gamma-ray burst (GRB) afterglow spectroscopy as one of its main science drivers. Aims. During the first commissioning night on sky with the instrument fully assembled, X-shooter observed the afterglow of GRB 090313 as a demonstration of the instrument's capabilities. Methods. GRB 090313 was observed almost two days after the burst onset, when the object had already faded to R~21.6. Furthermore, the 90% illuminated Moon was just 30 degrees away from the field. In spite of the adverse conditions, we obtained a spectrum that, for the first time in GRB research, covers simultaneously the range from 5700 to 23000 Angstroms. Results. The spectrum shows multiple absorption features at a redshift of 3.3736, the redshift of the GRB. These features are composed of 3 components with different ionisation levels and velocities. Some of the features have never been observed before in a GRB at such a high redshift. Furthermore, we detect two intervening systems at redshifts of 1.8005 and 1.9597. Conclusions. These results demonstrate the potential of X-shooter in the GRB field, as it was capable of observing a GRB down to a magnitude limit that would include 72% of long GRB afterglows 2 hours after the burst onset. Coupled with the rapid response mode available at VLT, allowing reaction times of just a few minutes, X-shooter constitutes an important leap forward on medium resolution spectroscopic studies of GRBs, their host galaxies and intervening systems, probing the early history of the Universe.
Very Large Telescope
Spectral resolution
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HETE‐2 has provided new evidence that gamma‐ray bursts may evolve with redshift. We investigate the consequences of this possibility for the unified jet model of XRFs and GRBs. We find that burst evolution with redshift can be naturally explained within the unified jet model, and the resulting model provides excellent agreement with existing HETE‐2 and BeppoSAX data sets. In addition, this evolution model produces reasonable fits to the BATSE peak photon number flux distribution — something that cannot be easily done without redshift evolution.
Time evolution
Unified Model
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Gamma-ray bursts (GRBs) can be divided into three subclasses: X-ray flash (XRF), X-ray rich (XRR), and classical GRB (C-GRB). An X-ray flare is the rebrightening emission shown in the early X-ray afterglow of some GRBs. In this paper, we comprehensively examine the X-ray flare properties among XRF, XRR, and C-GRB subclasses. We utilize the XRF, XRR, and C-GRB subclass samples obtained from the Swift-BAT3 catalog, and the X-ray flare observational properties are collected from Falcone et al., Chincarini et al., and Yi et al. We find that XRFs and XRRs have more bright X-ray flares than C-GRBs. The ratio of the X-ray flare fluence to the prompt emission fluence has different distributions between XRF and C-GRB subclasses. The linear correlation between the duration and the peak time of the X-ray flares is also different between XRF and C-GRB subclasses. We are inclined to identify the GRBs with the bright X-ray flares as XRFs or XRRs. We discuss some issues that are related to the XRF/XRR/C-GRB classification. We also caution the selection effects and the instrument bias in our investigation. Large samples are required in the future to further confirm our results.
Flare
X-ray reflectivity
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Several hundred gamma-ray burst (GRB) redshifts have been determined to date. One of the other important properties-besides the distance-of the GRBs is the duration of the burst. In this paper, we analyse these two important quantities of the phenomena. In this paper, we map the two-dimensional distribution and explore some suspicious areas. As it is well known that the short GRBs are closer than the others, we search for parts in the Universe where the GRB duration is different from the others. We also analyse whether there are any ranges in the duration where the redshifts differ. We find some suspicious areas, however, no other significant region was found than the short GRB region.
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