Iso Correlation Research Articles

Cosmography via Gaussian process with gamma ray bursts

In this paper, we firstly calibrate the Amati relation (the E p - E iso correlation) of gamma ray bursts (GRBs) at low redshifts (z < 0.8) via Gaussian process by using the type Ia supernovae samples from Pantheon+ under the philosophy that objects at the same redshift should have the same luminosity distance in any cosmology. As a result, this calibration derives the distance moduli of GRBs at high redshifts (z > 0.8). For an application of these derived distance modulus of GRBs to cosmology, via Gaussian process again, a series of cosmography parameters, which describe kinematics of our Universe, up to the fifth order and the redshift z ∼ 5, i.e. the Hubble parameter H(z), the deceleration parameter q(z), the jerk parameter j(z), the snap parameter s(z) and the lerk parameter l(z), are reconstructed from the cosmic observations. The reconstructed cosmography parameters show a transition singularity at z ∼ 6, it may resort to two possible explanations: one is that the GRBs data points at high redshift z > 5 are still reliable, it means that new physics beyond the ΛCDM model happens; another one is that the quality and quantity of GRBs data points at high redshift z > 5 are not good enough to give any viable prediction of the kinematics of our Universe. To pin down this problem, more high redshifts z > 5 cosmic observational are still needed.

Constraints on the Cosmological Parameters with Three-Parameter Correlation of Gamma-Ray Bursts

As one of the most energetic and brightest events, gamma-ray bursts (GRBs) can be treated as a promising probe of the high-redshift universe. Similar to type Ia supernovae, GRBs with the same physical origin could be treated as standard candles. We select GRB samples with the same physical origin, which are divided into two groups. The first group consists of 31 GRBs with a plateau phase feature of a constant luminosity followed by a decay index of about −2 in the X-ray afterglow light curves, and the second group has 50 GRBs with a shallow decay phase in the optical light curves. For the selected GRB samples, we confirm that there is a tight correlation between the plateau luminosity L 0, the end time of plateau t b , and the isotropic energy release E γ,iso. We also find that the L 0–t b − E γ,iso correlation is insensitive to the cosmological parameters and that no valid limitations on the cosmological parameters can be obtained using this correlation. We explore a new three-parameter correlation L 0, t b , and the spectral peak energy in the rest-frame E p,i (L 0–t b –E p,i ), and find that this correlation can be used as a standard candle to constrain the cosmological parameters. By employing the optical sample only, we find the constraints of for a flat ΛCDM model. For the non-flat ΛCDM model, the best-fitting results are , . For the combination of the X-ray and optical samples, we find for a flat ΛCDM model, and , for a non-flat ΛCDM model.

Revisiting the Spectral Energy Correlations of GRBs with Fermi Data. I. Model-wise Properties

Gamma-ray bursts (GRBs) exhibit a diversity of spectra. Several spectral models (e.g., Band, cutoff power law (CPL), and blackbody) and their hybrid versions (e.g., Band+blackbody) have been widely used to fit the observed GRB spectra. Here, we attempt to collect all the bursts detected by Fermi/GBM with known redshifts from 2008 July to 2022 May, having been motivated to (i) provide a parameter catalog independent of the official Fermi/GBM team and (ii) achieve a “clean” model-based GRB spectral energy correlation analysis. A nearly complete GRB sample is created, containing 153 such bursts (136 long GRBs and 17 short GRBs). Using the sample and by performing detailed spectral analysis and model comparisons, we investigate two GRB spectral energy correlations: the correlation of the cosmological rest-frame peak energy (E p,z ) of the ν F ν prompt emission spectrum with (i) the isotropic-bolometric-equivalent emission energy E γ,iso (the Amati relation) and (ii) the isotropic-bolometric-equivalent peak luminosity L p,iso (the Yonetoku relation). From a linear regression analysis, a tight correlation between E p,z and E γ,iso (and L γ,iso) is found for both Band-like and CPL-like bursts (except for CPL-like long burst E p,z –E γ,iso correlation). More interestingly, CPL-like bursts do not fall on the Band-like burst Amati and Yonetoku correlations, suggesting distinct radiation processes, and pointing to the fact that these spectral energy correlations are tightly reliant on the model-wise properties.

Calibrating Gamma-Ray Bursts by Using a Gaussian Process with Type Ia Supernovae

In this paper, we calibrate the Amati relation (the E p–E iso correlation) of gamma-ray bursts (GRBs) in a cosmology-independent way. By using a Gaussian process to reconstruct the smoothed luminosity distance from the Pantheon type Ia supernovae sample, we utilize the reconstructed results to calibrate the E p–E iso correlation with the Markov Chain Monte Carlo method and construct a Hubble diagram with the A220 GRB data, in which there are A118 GRB data with the higher qualities appropriate for cosmological purposes. With 98 GRBs at 1.4 < z ≤ 8.2 in the A118 sample and the observed Hubble data, we obtain Ωm = , h = for the flat ΛCDM model, and Ωm = , h = , w = for the flat wCDM model, which are consistent with those from fitting the coefficients of the Amati relation and the cosmological parameters simultaneously.

Magnetar giant flare originating from GRB 200415A: transient GeV emission, time-resolved Ep – L iso correlation and implications

Giant flares (GFs) are unusual bursts from soft gamma-ray repeaters (SGRs) that release an enormous amount of energy in a fraction of a second. The afterglow emission of these SGR-GFs or GF candidates is a highly beneficial means of discerning their composition, relativistic speed and emission mechanisms. GRB 200415A is a recent GF candidate observed in a direction coincident with the nearby Sculptor galaxy at 3.5 Mpc. In this work, we searched for transient gamma-ray emission in past observations by Fermi-LAT in the direction of GRB 200415A. These observations confirm that GRB 200415A is observed as a transient GeV source only once. A pure pair-plasma fireball cannot provide the required energy for the interpretation of GeV afterglow emission and a baryonic poor outflow is additionally needed to explain the afterglow emission. A baryonic rich outflow is also viable, as it can explain the variability and observed quasi-thermal spectrum of the prompt emission if dissipation is happening below the photosphere via internal shocks. Using the peak energy (Ep ) of the time-resolved prompt emission spectra and their fluxes (Fp ), we found a correlation between Ep and Fp or isotropic luminosity L iso for GRB 200415A. This supports the intrinsic nature of Ep -L iso correlation found in SGRs-GFs, hence favoring a baryonic poor outflow. Our results also indicate a different mechanism at work during the initial spike, and that the evolution of the prompt emission spectral properties in this outflow would be intrinsically due to the injection process.

GRB 180418A: A Possibly Short Gamma-Ray Burst with a Wide-angle Outflow in a Faint Host Galaxy

Abstract We present X-ray and multiband optical observations of the afterglow and host galaxy of GRB 180418A, discovered by Swift/BAT and Fermi/GBM. We present a reanalysis of the GBM and BAT data deriving durations of the prompt emission of T 90 ≈ 2.56 and 1.90 s, respectively. Modeling the Fermi/GBM catalog of 1405 bursts (2008–2014) in the hardness–T 90 plane, we obtain a probability of ≈60% that GRB 180418A is a short-hard burst. From a combination of Swift/XRT and Chandra observations, the X-ray afterglow is detected to ≈38.5 days after the burst and exhibits a single power-law decline with F X ∝ t −0.98. Late-time Gemini observations reveal a faint r ≈ 25.69 mag host galaxy at an angular offset of ≈0.″16. At the likely redshift range of z ≈ 1–2.25, we find that the X-ray afterglow luminosity of GRB 180418A is intermediate between short and long gamma-ray bursts (GRBs) at all epochs during which there are contemporaneous data and that GRB 180418A lies closer to the E γ,peak–E γ,iso correlation for short GRBs. Modeling the multiwavelength afterglow with the standard synchrotron model, we derive the burst explosion properties and find a jet opening angle of θ j ≳ 9°–14°. If GRB 180418A is a short GRB that originated from a neutron star merger, it has one of the brightest and longest-lived afterglows along with an extremely faint host galaxy. If, instead, the event is a long GRB that originated from a massive star collapse, it has among the lowest-luminosity afterglows and lies in a peculiar space in terms of the hardness–T 90 and E γ,peak–E γ,iso planes.

Addressing the circularity problem in the Ep−Eiso correlation of gamma-ray bursts

ABSTRACT We here propose a new model-independent technique to overcome the circularity problem affecting the use of gamma-ray bursts (GRBs) as distance indicators through the use of Ep−Eiso correlation. We calibrate the Ep−Eiso correlation and find the GRB distance moduli that can be used to constrain dark energy models. We use observational Hubble data to approximate the cosmic evolution through Bézier parametric curve obtained through the linear combination of Bernstein basis polynomials. In doing so, we build up a new data set consisting of 193 GRB distance moduli. We combine this sample with the supernova JLA data set to test the standard ΛCDM model and its wCDM extension. We place observational constraints on the cosmological parameters through Markov Chain Monte Carlo numerical technique. Moreover, we compare the theoretical scenarios by performing the Akaike and Deviance Information statistical criteria.the 2σ level, while for the wCDM model we obtain $\Omega _m=0.34^{+0.13}_{-0.15}$ and $w=-0.86^{+0.36}_{-0.38}$ at the 2σ level. Our analysis suggests that ΛCDM model is statistically favoured over the wCDM scenario. No evidence for extension of the ΛCDM model is found.

Lorentz factor — Beaming corrected energy/luminosity correlations and GRB central engine models

We work on a GRB sample whose initial Lorentz factors (Γ0) are constrained by the afterglow onset method and the jet opening angles (θj) are determined by the jet break time. We confirm the Γ0–Eγ,iso correlation by Liang et al. (2010), and the Γ0–Lγ,iso correlation by Lü et al. (2012). Furthermore, we find correlations between Γ0 and the beaming corrected γ-ray energy (Eγ) and mean γ-ray luminosity (Lγ). By also including the kinetic energy of the afterglow, we find rough correlations (with larger scatter) between Γ0 and the total (γ-ray plus kinetic) energy and the total mean luminosity, both for isotropic values and beaming corrected values: these correlations allow us to test the data with GRB central engine models. Limiting our sample to the GRBs that likely have a black hole central engine, we compare the data with theoretical predictions of two types of jet launching mechanisms from BHs, i.e. the non-magnetized νν¯-annihilation mechanism, and the strongly magnetized Blandford–Znajek (BZ) mechanism. We find that the data are more consistent with the latter mechanism, and discuss the implications of our findings for GRB jet composition.

There is a short gamma-ray burst prompt phase at the beginning of each long one

We compare the prompt intrinsic spectral properties of a sample of short Gamma--ray Burst (GRB) with the first 0.3 seconds (rest frame) of long GRBs observed by Fermi/GBM. We find that short GRBs and the first part of long GRBs lie on the same E_p--E_iso correlation, that is parallel to the relation for the time averaged spectra of long GRBs. Moreover, they are indistinguishable in the E_p--L_iso plane. This suggests that the emission mechanism is the same for short and for the beginning of long events, and both short and long GRBs are very similar phenomena, occurring on different timescales. If the central engine of a long GRB would stop after ~0.3 * (1+z) seconds the resulting event would be spectrally indistinguishable from a short GRB.

MEASURING COSMOLOGICAL PARAMETERS WITH GAMMA RAY BURSTS

In a few dozen seconds, gamma ray bursts (GRBs) emit up to ~1054 erg in terms of an equivalent isotropically radiated energy E iso , so they can be observed up to z ~ 10. Thus, these phenomena appear to be very promising tools to describe the expansion rate history of the universe. Here, we review the use of the Ep,i–E iso correlation of GRBs to measure the cosmological density parameter ΩM. We show that the present data set of GRBs, coupled with the assumption that we live in a flat universe, can provide independent evidence, from other probes, that ΩM ~ 0.3. We show that current (e.g. Swift, Fermi/GBM, Konus-WIND) and forthcoming gamma ray burst (GRB) experiments (e.g. CALET/GBM, SVOM, Lomonosov/UFFO, LOFT/WFM) will allow us to constrain ΩM with an accuracy comparable to that currently exhibited by Type Ia supernovae (SNe–Ia) and to study the properties of dark energy and their evolution with time.

A complete sample of brightSwiftGamma-ray bursts: X-ray afterglow luminosity and its correlation with the prompt emission

We investigate wheter there is any correlation between the X-ray afterglow luminosity and the prompt emission properties of a carefully selected sub-sample of bright Swift long Gamma-Ray Bursts (GRBs) nearly complete in redshift (~90%). Being free of selection effects (except flux limit), this sample provides the possibility to compare the rest frame physical properties of GRB prompt and afterglow emission in an unbiased way. The afterglow X-ray luminosities are computed at four different rest frame times (5 min, 1 hr, 11 hr and 24 hr after trigger) and compared with the prompt emission isotropic energy E_iso, the isotropic peak luminosity L_iso and the rest frame peak energy E_peak. We find that the rest frame afterglow X-ray luminosity do correlate with these prompt emission quantities, but the significance of each correlation decreases over time. This result is in agreement with the idea that the GRB X-ray light curve can be described as the result of a combination of different components whose relative contribution and weight change with time, with the prompt and afterglow emission dominating at early and late time, respectively. In particular, we found evidence that the plateau and the shallow decay phase often observed in GRB X-ray light curves are powered by activity from the central engine. The existence of the L_X-E_iso correlation at late times (t_rf > 11 hr) suggests a similar radiative efficiency among different bursts with on average about 6% of the total kinetic energy powering the prompt emission.

COSMOLOGY WITH THE Ep,i – Eiso CORRELATION OF GAMMA–RAY BURSTS

Gamma–Ray Bursts (GRBs) are the brightest sources in the universe, emit mostly in the hard X–ray energy band and have been detected at redshifts up to about 8.2. Thus, they are in principle very powerful probes for cosmology. I shortly review the researches aimed to use GRBs for the measurement of cosmological parameters, which are mainly based on the correlation between spectral peak photon energy and total radiated energy or luminosity. In particular, based on an enriched sample of 120 GRBs, I will provide an update of the analysis by Amati et al. (2008) aimed at extracting information on ΩM and, to a less extent, on ΩΛ, from the E p,i – E iso correlation.

Fermi/GBM and BATSE gamma-ray bursts: comparison of the spectral properties

The Gamma-ray Burst Monitor (GBM) on board Fermi allows to study the spectra of Gamma Ray Bursts (GRBs) over an unprecedented wide energy range (8 keV - 35 MeV). We compare the spectral properties of short and long GRBs detected by the GBM (up to March 2010) with those of GRBs detected by the BATSE instrument on board the CGRO. GBM and BATSE long bursts have similar distributions of fluence (F), Epeak and peak flux (P) but GBM bursts have a slightly harder low-energy spectral index \alpha with respect to BATSE GRBs. GBM and BATSE short bursts have similar distributions of fluence, \alpha and peak flux, with GBM bursts having slightly larger Epeak. We discuss these properties in light of the found correlations between Epeak and the fluence and the peak flux. GBM bursts confirm that these correlations are not determined by instrumental selection effects. Indeed, GBM bursts extend the Epeak-Fluence and Epeak-P correlations both in fluence/peak flux and in peak energy. No GBM long burst with Epeak exceeding a few MeV is found, despite the possibility of detecting it. Similarly to what found with BATSE, there are 3% of GBM long bursts (and almost all short ones) that are outliers at more than 3\sigma of the Epeak-Eiso correlation. Instead there is no outlier of the Epeak-Lp,iso correlation, for both long and short GBM bursts.

Gamma ray bursts: Short vs. long

Short and long GRBs are thought to be two distinct classes based on their different duration and spectrum. Through the spectral analysis of two similarly selected samples of BATSE short and long GRBs, we show that short GRBs are harder than long events, confirming what found from the comparison of their hardness ratio. However, this spectral diversity seems to be due to a harder low energy spectral component of short GRBs, rather than a (slightly higher) peak energy. Interestingly short GRBs have a spectrum which is similar to the spectrum of the emission of the first 1–2 s of long events. We find evidence that short GRBs are inconsistent with the E peak– E iso correlation defined by long bursts while they follow the same E peak– L iso correlation of long GRBs. These results, coupled to the similar variability timescale of short events and the first seconds of long ones, suggest that a common (or similar) dissipation mechanism could operate in both classes. The difference in the duration would then be due mainly to the central engine lifetime.

GENERALIZED TESTS FOR SELECTION EFFECTS IN GAMMA-RAY BURST HIGH-ENERGY CORRELATIONS

Several correlations among parameters derived from modeling the high-energy properties of gamma-ray bursts (GRBs) have been reported. We show that well known examples of these have common features indicative of strong contamination by selection effects. We focus here on the impact of detector threshold truncation on the spectral peak versus isotropic equivalent energy release (E pk-E iso) relation, extended to a large sample of 218 Swift and 56 HETE-2 GRBs with and without measured redshift. The existence of faint Swift events missing from pre-Swift surveys calls into question inferences based on pre-Swift surveys which must be subject to complicated incompleteness effects. We demonstrate a generalized method for treating data truncation in correlation analyses and apply this method to Swift and pre-Swift data. Also, we show that the E pk-E γ (Ghirlanda) correlation is effectively independent of the GRB redshifts, which suggests that its existence has little to do with intrinsic physics. We suggest that a physically based correlation, manifest observationally, must show significantly reduced scatter in the rest frame relative to the observer frame and must not persist if the assumed redshifts are scattered. As with the E pk-E γ correlation, we find that the pre-Swift, bright GRB E pk-E iso correlation of Amati does not rigorously satisfy these conditions.

Peak energy of the prompt emission of long gamma-ray bursts versus their fluence and peak flux

The spectral-energy (and luminosity) correlations in long gamma-ray bursts are being hotly debated to establish, first of all, their reality against possible selection effects. These are best studied in the observer planes, namely the peak energy E obs peak versus the fluence F or the peak flux P. In a recent paper, we have started to investigate this problem considering all bursts with known redshift and spectral properties. Here, we consider instead all bursts with known E obs peak , irrespective of redshift, adding to those a sample of 100 faint BATSE bursts representative of a larger population of 1000 objects. This allows us to construct a complete, fluence-limited, sample, tailored to study the selection/instrumental effects we consider. We found that the fainter BATSE bursts have smaller E obs peak than those of bright events. As a consequence, the E obs peak of these bursts is correlated with the fluence, though with a slope flatter than that defined by bursts with z. Selection effects, which are present, are shown not to be responsible for the existence of such a correlation. About six per cent of these bursts are surely outliers of the E peak -E iso correlation (updated in this paper to include 83 bursts), since they are inconsistent with it for any redshift. E obs peak also correlates with the peak flux, with a slope similar to the Ep eak -L iso correlation. In this case, there is only one sure outlier. The scatter of the E obs peak -P correlation defined by the BATSE bursts of our sample is significantly smaller than the E obs peak -F correlation of the same bursts, while for the bursts with known redshift the E peak -E iso correlation is tighter than the E peak -L iso one. Once a very large number of bursts with E obs peak and redshift will be available, we thus expect that the E peak -L iso correlation will be similar to that currently found, whereas it is very likely that the E peak -E iso correlation will become flatter and with a larger scatter.

Testing theEp,iLp,isoT0.45correlation on aBeppoSAXandSwiftsample of gamma-ray bursts

Using a sample of 14 BeppoSAX and 74 Swift GRBs with measured redshift we tested the correlation between the intrinsic peak energy of the time-integrated spectrum, E p,i , the isotropic-equivalent peak luminosity, L p,iso , and the duration of the most intense parts of the GRB computed as T 0.45 ('Firmani correlation'). For 41 out of 88 GRBs we could estimate all of the three required properties. Apart from 980425, which appears to be a definite outlier and notoriously peculiar in many respects, we used 40 GRBs to fit the correlation with the maximum likelihood method discussed by D'Agostini, suitable to account for the extrinsic scatter in addition to the intrinsic uncertainties affecting every single GRB. We confirm the correlation. However, unlike the results by Firmani et al., we found that the correlation does have a logarithmic scatter comparable with that of the E p,i -E iso ('Amati') correlation. We also find that the slope of the product L p,iso T 0.45 is equal to ∼0.5, which is consistent with the hypothesis that the E p,i -L p,iso -T 0.45 correlation is equivalent to the E p,i -E iso correlation (slope ∼0.5). We conclude that, based on presently available data, there is no clear evidence that the E p,i -L p,iso -T 0.45 correlation is different (both in terms of slope and dispersion) from the E p,i -E iso correlation.

On the consistency of peculiar GRBs 060218 and 060614 with the $E_\mathsf{p,i}$ – $E_\mathsf{iso}$ correlation

We analyze and discuss the position of GRB 060218 and GRB 060614 in the E p,i - E iso plane. GRB 060218 is important because of its similarity with GRB 980425, the prototypical event of the GRB-SN connection. While GRB 980425 is an outlier of the E p,i - E iso correlation, we find that GRB 060218 is fully consistent with it. This evidence, combined with the chromatic behavior of the afterglow light curves, is at odds with the hypothesis that GRB 060218 was a standard GRB seen off-axis and supports the existence ol a class of truly sub-energetic GRBs. GRB 060614 is a peculiar event not accompanied by a bright supernova. Based on published spectral information, we find that also this event is consistent with the E p,i - E iso correlation. We discuss the implications of our results for the rate of sub-energetic GRBS, the GRB/SN connection and the properties of the newly discovered sub-class of long GRBs not associated with bright supernovae. We have included in our analysis other recent GRBs with clear evidence (or clear evidence of lack) of associated SNe.

Investigating the dispersion of the E p,i -E iso correlation

The E p,i -E iso correlation, although it is very significant (chance probability ∼ 10 -14 ), shows an intrinsic log E p,i dispersion of ∼ 0.2, which decreases to ∼ 0.14 by accounting for the sample variance. We present the results of a preliminary work aimed to quantify the extra-Poissonian dispersion of the correlation by investigating and accounting for the main possible sources of systematics on the estimate of E p,i and E iso .

The Ep,i-Eiso correlation in gamma-ray bursts: updated observational status, re-analysis and main implications

The correlation between the cosmological rest-frame vF v spectrum peak energy, E p,i , and the isotropic-equivalent radiated energy, E iso , discovered by Amati et al. in 2002 and confirmed/extended by subsequent osbervations, is one of the most intriguing and debated observational evidences in gamma-ray burst (GRB) astrophysics. In this paper, I provide an update and a re-analysis of the E p,i -E iso correlation basing on an updated sample consisting of 41 long GRBs/X-ray flashes (XRFs) with firm estimates of z and observed peak energy, E p,obs , 12 GRB s with uncertain values of z and/or E p,obs , two short GRBs with firm estimates of z and E p,obs and the peculiar subenergetic events GRB 980425/SN1998bw and GRB 031203/SN20031w. In addition to standard correlation analysis and power-law fitting, the data analysis here reported includes modelling that accounts for sample variance. All 53 classical long GRBs and XRFs, including 11 Swift events with published spectral parameters and fluences, have E p,i and E iso values, or upper/lower limits, consistent with the correlation, which shows a chance probability as low as ∼7 x 10 -15 , a slope of ∼0.57 (∼0.5 when fitting by accounting for sample variance) and an extra-Poissonian logarithmic dispersion of ∼0.15, it extends over ∼5 orders of magnitude in E iso and ∼3 orders of magnitude in E p,i and holds from the closer to the higher z GRBs. Subenergetic GRBs (980425 and possibly 031203) and short GRBs are found to be inconsistent with the E p,i -E iso correlation, showing that it can be a powerful tool for discriminating different classes of GRBs and understanding their nature and differences. I also discuss the main implications of the updated E p,i -E iso correlation for the models of the physics and geometry of GRB emission, its use as a pseudo-redshift estimator and the tests of possible selection effects with GRBs of unknown redshift.