Isotropic Peak Research Articles

A targeted search for FRB counterparts with Konus-Wind

ABSTRACT We present results of the search for hard X-ray/soft gamma-ray emission in coincidence with publicly reported (via Transient Name Server, TNS1) fast radio bursts (FRBs). The search was carried out using continuous Konus-Wind data with 2.944 s time resolution. We perform a targeted search for each individual burst from 581 FRBs, along with a stacking analysis of the bursts from eight repeating sources in our sample and a separate stacking analysis of the bursts from the non-repeating FRBs. We find no significant associations in either case. We report upper bounds on the hard X-ray (20–1500 keV) flux assuming four spectral models, which generally describe spectra of short and long gamma-ray bursts (GRBs), magnetar giant flares, and the short burst, coincident with FRB 200428 from a Galactic magnetar. Depending on the spectral model, our upper bounds are in the range of (0.1–2) × 10−6 erg cm−2. For 18 FRBs with known distances, we present upper bounds on the isotropic equivalent energy release and peak luminosity. For the nearest FRB 200120E, we derive the most stringent upper bounds of Eiso ≤ 2.0 × 1044 erg and Liso ≤ 1.2 × 1044 erg s−1. Furthermore, we report lower bounds on radio-to-gamma-ray fluence ratio Eradio/Eiso ≥ 10−11–10−9 and compare our results with previously reported searches and theoretical predictions for high-energy counterparts to FRBs.

Properties of the Extremely Energetic GRB 221009A from Konus-WIND and SRG/ART-XC Observations

We report on Konus-WIND (KW) and Mikhail Pavlinsky Astronomical Roentgen Telescope – X-ray Concentrator (ART-XC) observations and analysis of a nearby GRB 221009A, the brightest γ-ray burst (GRB) detected by KW for >28 yr of observations. The prompt, pulsed phase of the burst emission lasts for ∼600 s and is followed by a steady power-law decay lasting for more than 25 ks. From the analysis of the KW and ART-XC light curves and the KW spectral data, we derive time-averaged spectral peak energy of the burst E p ≈ 2.6 MeV, E p at the brightest emission peak ≈ 3.0 MeV, the total 20 keV–10 MeV energy fluence of ≈0.22 erg cm−2, and the peak energy flux in the same band of ≈0.031 erg cm−2 s−1. The enormous observed fluence and peak flux imply, at redshift z = 0.151, huge values of isotropic energy release E iso ≈ 1.2 × 1055 erg (or ≳6.5 solar rest mass) and isotropic peak luminosity L iso ≈ 3.4 × 1054 erg s−1 (64 ms scale), making GRB 221009A the most energetic and one of the most luminous bursts observed since the beginning of the GRB cosmological era in 1997. The isotropic energetics of the burst fit nicely both “Amati” and “Yonetoku” hardness–intensity correlations for >300 KW long GRBs, implying that GRB 221009A is most likely a very hard, super-energetic version of a “normal” long GRB.

An analytic derivation of the empirical correlations of gamma-ray bursts

Empirical correlations between various key parameters have been extensively explored ever since the discovery of gamma-ray bursts (GRBs) and have been widely used as standard candles to probe the Universe. The Amati relation and the Yonetoku relation are two good examples that enjoyed special attention. The former reflects the connection between the peak photon energy (Ep) and the isotropic γ-ray energy release (Eiso), while the latter links Ep with the isotropic peak luminosity (Lp), both in the form of a power-law function. Most GRBs are found to follow these correlations well, but a theoretical interpretation is still lacking. Some obvious outliers may be off-axis GRBs and may follow correlations that are different from those at the on-axis. Here we present a simple analytical derivation for the Amati relation and the Yonetoku relation in the framework of the standard fireball model, the correctness of which is then confirmed by numerical simulations. The off-axis Amati relation and Yonetoku relation are also derived. They differ markedly from the corresponding on-axis relation. Our results reveal the intrinsic physics behind the radiation processes of GRBs, and they highlight the importance of the viewing angle in the empirical correlations of GRBs.

The role of hydrophobic patches of de novo designed MSI-78 and VG16KRKP antimicrobial peptides on fragmenting model bilayer membranes

Antimicrobial peptides (AMPs) with cell membrane lysing capability are considered potential candidates for the development of the next generation of antibiotics. Designing novel AMPs requires an in-depth understanding of the mechanism of action of the peptides. In this work, we used various biophysical techniques including 31P solid-state NMR to examine the interaction of model membranes with amphipathic de novo-designed peptides. Two such peptides, MSI-78 and VG16KRKP, were designed with different hydrophobicity and positive charges. The model lipid membranes were constituted by mixing lipids of varying degrees of ‘area per lipid’ (APL), which directly affected the packing properties of the membrane. The observed emergence of the isotropic peak in 31P NMR spectra as a function of time is a consequence of the fragmentation of the membrane mediated by the peptide interaction. The factors such as the charges, overall hydrophilicity of the AMPs, as well as lipid membrane packing, contributed to the kinetics of membrane fragmentation. Furthermore, we anticipate the designed AMPs follow the carpet and toroidal pore mechanisms when lysing the cell membrane. This study highlights the significance of the effect of the overall charges and the hydrophobicity of the novel AMPs designed for antimicrobial activity.

Similar properties between gamma-ray emission of 3C 454.3 and solar GeV flares

ABSTRACTBased on the survey data observed by Fermi-Large Area Telescope (LAT), we elaborate the statistical characteristics of gamma-ray flares from 3C 454.3 and solar GeV flares among flare parameters, such as isotropic energy (Eγ), peak luminosity (LP), and duration time (TDuration). We find two significant correlations as: $T_{\rm Duration} \propto E_{\gamma }^{0.31\pm 0.03}$ and $L_{\rm P} \propto E_{\gamma }^{0.61\pm 0.03}$ for 3C 454.3. The exponents are in a better agreement those of the Sun from the first Fermi-LAT solar flare catalogue, namely $T_{\rm Duration,\odot } \propto E_{\gamma ,\odot }^{0.38\pm 0.08}$ and $L_{\rm P,\odot } \propto E_{\gamma ,\odot }^{0.81\pm 0.08}$. The relationship of TDuration–Eγ and LP–Eγ could be interpreted naturally as due to magnetic dissipation through reconnection. On top of that the frequency distributions of isotropic energy, peak luminosity, and duration time of gamma-ray emission of 3C 454.3 show power-law forms, and the waiting time distribution can be described by a non-stationary Poisson process. These distribution behaviours are comparable to those of the Sun, Sagittarius A*, and M87, and follow the prediction of a self-organized criticality model. All statistical properties suggest that similar to the physical process accounting for solar GeV flares and X-ray flares in supermassive black hole systems, magnetic reconnection cloud govern the energy-release, and particle acceleration process for gamma-ray flares of 3C 454.3.

Synchrotron self-compton emission in the two-component jet model for gamma-ray bursts

Gamma-ray bursts (GRBs) are intense bursts of high-energy photons (prompt emissions) caused by relativistic jets. After the emissions, multi-wavelength afterglows, from radio to very-high-energy (VHE) gamma-ray, last for more than a few days. In the past three years, the VHE gamma-ray photons from four GRBs (GRBs 180720B, 190114C, 190829A and 201216C) were detected by ground-based Imaging Atmospheric Cherenkov Telescopes, such as the Major Atmospheric Gamma Imaging Cherenkov (MAGIC) telescopes and the High Energy Stereoscopic System (H.E.S.S.). One of them, GRB 190829A, had some peculiar features of showing achromatic peaks in X-ray and optical bands at 1.4×103 s and being classified as low-luminosity GRBs. Previously, we proposed a two-component jet model, which has ‘narrow jet’ with a small initial opening half-angle θ0=0.015 rad and large bulk Lorentz factor Γ0=350, and ‘wide jet’ with θ0=0.1 rad and Γ0=20. The narrow jet explained the early X-ray and optical emissions and apparently small isotropic gamma-ray energy and peak energy in the off-axis viewing case. Furthermore, the late X-ray and radio (1.3 and 15.5 GHz) afterglows were emitted from the wide jet. Here, we calculate the VHE gamma-ray flux by the synchrotron self-Compton (SSC) emission. The multi-wavelength afterglows of GRB 190829A including the VHE gamma-ray emission are well explained by our two-component jet model. The afterglow emissions from our two-component jet are also consistent with the observational results of GRBs 180720B, 190114C and 201216C, when the jets are viewed on-axis. Furthermore, we discuss the detectability of off-axis orphan afterglows by the Cherenkov Telescope Array (CTA).

Chlorine-containing guaianolide sesquiterpenoids from Achillea millefolium L. with inhibitory effects against LPS-induced NO release in BV-2 microglial cells

Chlorine-containing guaianolide sesquiterpenoids are rare natural compounds that are mainly derived from plants of the Asteraceae family. Our previous investigations on the whole plant of Achillea millefolium L. resulted in the discovery of two chlorine-containing guaianolide sesquiterpenoids. In the present study, a LC‒MS tracking strategy based on the characteristic isotropic peak of atomic chlorine was employed to isolate nine undescribed chlorine-containing guaianolide sesquiterpenoids, Millefolactons B1–B9, from A. millefolium L.. The structures of these compounds were elucidated by spectroscopic data analysis, and the corresponding absolute configurations were determined by single-crystal X-ray crystallography and ECD data analysis. Millefolactons B2–B7 displayed inhibitory activities against LPS-induced NO release in BV-2 microglial cells.

Interactions of HIV gp41's membrane-proximal external region and transmembrane domain with phospholipid membranes from 31P NMR.

HIV-1 entry into cells requires coordinated changes of the conformation and dynamics of both the fusion protein, gp41, and the lipids in the cell membrane and virus envelope. Commonly proposed features of membrane deformation during fusion include high membrane curvature, lipid disorder, and membrane surface dehydration. The virus envelope and target cell membrane contain a diverse set of phospholipids and cholesterol. To dissect how different lipids interact with gp41 to contribute to membrane fusion, here we use 31P solid-state NMR spectroscopy to investigate the curvature, dynamics, and hydration of POPE, POPC and POPS membranes, with and without cholesterol, in the presence of a peptide comprising the membrane proximal external region (MPER) and transmembrane domain (TMD) of gp41. Static 31P NMR spectra indicate that the MPER-TMD induces strong negative Gaussian curvature (NGC) to the POPE membrane but little curvature to POPC and POPC:POPS membranes. The NGC manifests as an isotropic peak in the static NMR spectra, whose intensity increases with the peptide concentration. Cholesterol inhibits the NGC formation and stabilizes the lamellar phase. Relative intensities of magic-angle spinning 31P cross-polarization and direct-polarization spectra indicate that all three phospholipids become more mobile upon peptide binding. Finally, 2D 1H-31P correlation spectra show that the MPER-TMD enhances water 1H polarization transfer to the lipids, indicating that the membrane surfaces become more hydrated. These results suggest that POPE is an essential component of the high-curvature fusion site, and lipid dynamic disorder is a general feature of membrane restructuring during fusion.

Confirmed Width–Eiso and Width–Liso Relations in Gamma-Ray Bursts: Comparison with the Amati and Yonetoku Relations

Abstract The well-known Amati and Yonetoku relations in gamma-ray bursts show strong correlations between the rest-frame νf ν spectrum peak energy, E p,i , and the isotropic energy, E iso, as well as isotropic peak luminosity, L iso. Recently, Peng et al. showed that the cosmological rest-frame spectral widths are also correlated with E iso and with L iso. In this paper, we select a sample including 141 BEST time-integrated F spectra and 145 BEST peak flux P spectra observed by Konus–Wind with known redshift to recheck the connection between the spectral width and E iso as well as L iso. We define six types of absolute spectral widths as the differences between the upper (E 2) and lower energy bounds (E 1) of the full width at 50%, 75%, 85%, 90%, 95%, and 99% of maximum of the EF E versus E spectra. It is found that all of the rest-frame absolute spectral widths are strongly positively correlated with E iso as well as L iso for the long burst for both the F and P spectra. All of the short bursts are outliers for the width–E iso relation, and most of the short bursts are consistent with the long bursts for the width–L iso relation for both F and P spectra. Moreover, all of the location energies, E 2 and E 1, corresponding to various spectral widths, are also positively correlated with E iso as well as L iso. We compare all of the relations with the Amati and Yonetoku relations and find that the width–E iso and width–L iso relations, when the widths are at about 90% maximum of the EF E spectra, almost overlap with the Amati relation and the Yonetoku relation, respectively. The correlations of E 2 − E iso, E 1 − E iso and E 2 − L iso, E 1 − L iso when the location energies are at 99% of maximum of the EF E spectra are very close to the Amati and Yonetoku relations, respectively. Therefore, we confirm the existence of tight width–E iso and width–L iso relations for long bursts. We further show that the spectral shape is indeed related to E iso and L iso. The Amati and Yonetoku relations are not necessarily the best relationships for relating the energy to the E iso and L iso. They may be special cases of the width–E iso and width–L iso relations or the energy–E iso and energy–L iso relations.

Discovery of a Universal Correlation for Long and Short GRBs and Its Application for the Study of Luminosity Function and Formation Rate

Abstract Gamma-ray bursts (GRBs) are known to be the most violent explosions in the universe, and a variety of correlations between observable GRB properties have been proposed in the literature, but none of these correlations are valid for both long and short GRBs. In this paper we report the discovery of a universal correlation that is suitable for both long and short GRBs using three prompt emission properties of GRBs, i.e., the isotropic peak luminosity L iso, the peak energy of the time-integrated prompt emission spectrum E peak, and the “high signal” timescale T 0.45, . This universal correlation involves properties of GRB prompt emission and does not require knowledge of the afterglow phase, which can be used as a relatively unbiased redshift estimator. Here we use this correlation to estimate the pseudoredshifts for short GRBs and then use the Lynden–Bell method to obtain a nonparametric estimate of their luminosity function and formation rate. The luminosity function is for dim SGRBs and for bright SGRBs, with the break point . The local formation rate of SGRBs is about 15 events Gpc−3 yr−1 . This universal correlation may have important implications for GRB physics, implying that the long and short GRBs should share similar radiation processes.

Non-coincidence effect study of NN-Dibutyl formamide in binary liquid mixtures

Abstract The isotropic and anisotropic Raman peak frequency of C O stretching mode of N, N Dibutyl formamide (DBF) have been studied in Dimethyl Sulfoxide (DMSO) and Chlorobenzene (CLB) solvents. The shift of peak wavenumber with the increase in solute concentration has been studied. Hydrogen bonding and the difference in dielectric constant may be responsible for shifting the peak positions. The non-coincidence effect (NCE) has been studied for the CLB and DMSO solvents. The optimized geometrical structures of DBF, DBF-DMSO and DBF-CLB are determined. The peak wavenumbers of the neat solute and in binary mixtures are compared and are found consistent with the theoretical data. The relative splittings ∆ υ ∆ υ neat of the C O stretching mode of DBF for the neat liquid and in solution are determined and have been compared with three theoretical models such as Mc Hale's model, Mirone's model and Logan's model, respectively. The data obtained through theoretical models were almost consistent with the experimental data.

Bulk Lorentz factors of gamma-ray bursts

Knowledge of the bulk Lorentz factor Γ0 of gamma-ray bursts (GRBs) allows us to compute their comoving frame properties shedding light on their physics. Upon collisions with the circumburst matter, the fireball of a GRB starts to decelerate, producing a peak or a break (depending on the circumburst density profile) in the light curve of the afterglow. Considering all bursts with known redshift and with an early coverage of their emission, we find 67 GRBs (including one short event) with a peak in their optical or GeV light curves at a time tp. For another 106 GRBs we set an upper limit tpUL. The measure of tp provides the bulk Lorentz factor Γ0 of the fireball before deceleration. We show that tp is due to the dynamics of the fireball deceleration and not to the passage of a characteristic frequency of the synchrotron spectrum across the optical band. Considering the tp of 66 long GRBs and the 85 most constraining upper limits, we estimate Γ0 or a lower limit Γ0LL. Using censored data analysis methods, we reconstruct the most likely distribution of tp. All tp are larger than the time Tp,γ when the prompt γ-ray emission peaks, and are much larger than the time Tph when the fireball becomes transparent, that is, tp>Tp,γ>Tph. The reconstructed distribution of Γ0 has median value ~300 (150) for a uniform (wind) circumburst density profile. In the comoving frame, long GRBs have typical isotropic energy, luminosity, and peak energy ⟨ Eiso ⟩ = 3(8) × 1050 erg, ⟨ Liso ⟩ = 3(15) × 1047 erg s-1, and ⟨ Epeak ⟩ = 1(2) keV in the homogeneous (wind) case. We confirm that the significant correlations between Γ0 and the rest frame isotropic energy (Eiso), luminosity (Liso), and peak energy (Ep) are not due to selection effects. When combined, they lead to the observed Ep−Eiso and Ep−Liso correlations. Finally, assuming a typical opening angle of 5 degrees, we derive the distribution of the jet baryon loading which is centered around a few 10-6M⊙.

Transition from fireball to Poynting-flux-dominated outflow in the three-episode GRB 160625B

The ejecta composition is an open question in gamma-ray burst (GRB) physics 1 . Some GRBs possess a quasi-thermal spectral component in the time-resolved spectral analysis 2 , suggesting a hot fireball origin. Others show a featureless non-thermal spectrum known as the Band function3–5, consistent with a synchrotron radiation origin5,6 and suggesting that the jet is Poynting-flux dominated at the central engine and probably in the emission region as well7,8. There are also bursts showing a sub-dominant thermal component and a dominant synchrotron component 9 , suggesting a probable hybrid jet composition 10 . Here, we report an extraordinarily bright GRB 160625B, simultaneously observed in gamma-ray and optical wavelengths, whose prompt emission consists of three isolated episodes separated by long quiescent intervals, with the durations of each sub-burst being approximately 0.8 s, 35 s and 212 s, respectively. Its high brightness (with isotropic peak luminosity Lp,iso ≈ 4 × 1053 erg s−1) allows us to conduct detailed time-resolved spectral analysis in each episode, from precursor to main burst and to extended emission. The spectral properties of the first two sub-bursts are distinctly different, allowing us to observe the transition from thermal to non-thermal radiation between well-separated emission episodes within a single GRB. Such a transition is a clear indication of the change of jet composition from a fireball to a Poynting-flux-dominated jet. The extremely bright GRB 160625B, consisting of three sub-bursts separated by quiescent intervals, shows a transition from thermal to non-thermal radiation that indicates a change of jet composition from a fireball to a Poynting-flux-dominated jet.

Cholesterol-binding site of the influenza M2 protein in lipid bilayers from solid-state NMR

The influenza M2 protein not only forms a proton channel but also mediates membrane scission in a cholesterol-dependent manner to cause virus budding and release. The atomic interaction of cholesterol with M2, as with most eukaryotic membrane proteins, has long been elusive. We have now determined the cholesterol-binding site of the M2 protein in phospholipid bilayers using solid-state NMR spectroscopy. Chain-fluorinated cholesterol was used to measure cholesterol proximity to M2 while sterol-deuterated cholesterol was used to measure bound-cholesterol orientation in lipid bilayers. Carbon-fluorine distance measurements show that at a cholesterol concentration of 17 mol%, two cholesterol molecules bind each M2 tetramer. Cholesterol binds the C-terminal transmembrane (TM) residues, near an amphipathic helix, without requiring a cholesterol recognition sequence motif. Deuterium NMR spectra indicate that bound cholesterol is approximately parallel to the bilayer normal, with the rough face of the sterol rings apposed to methyl-rich TM residues. The distance- and orientation-restrained cholesterol-binding site structure shows that cholesterol is stabilized by hydrophobic interactions with the TM helix and polar and aromatic interactions with neighboring amphipathic helices. At the 1:2 binding stoichiometry, lipid 31P spectra show an isotropic peak indicative of high membrane curvature. This M2-cholesterol complex structure, together with previously observed M2 localization at phase boundaries, suggests that cholesterol mediates M2 clustering to the neck of the budding virus to cause the necessary curvature for membrane scission. The solid-state NMR approach developed here is generally applicable for elucidating the structural basis of cholesterol's effects on membrane protein function.

A COMPARATIVE STUDY OF LONG AND SHORT GRBS. I. OVERLAPPING PROPERTIES

ABSTRACT Gamma-ray bursts (GRBs) are classified into long and short categories based on their durations. Broadband studies suggest that these two categories of objects roughly correspond to two different classes of progenitor systems, i.e., compact star mergers (Type I) versus massive star core collapse (Type II). However, the duration criterion sometimes leads to mis-identification of the progenitor systems. We perform a comprehensive multi-wavelength comparative study between duration-defined long GRBs and short GRBs as well as the so-called “consensus” long GRBs and short GRBs (which are believed to be more closely related to the two types of progenitor systems). The parameters we study include two parts: the prompt emission properties including duration (T 90), spectral peak energy ( ), low energy photon index (α), isotropic γ-ray energy ( ), isotropic peak luminosity ( ), and the amplitude parameters (f and ); and the host galaxy properties including stellar mass ( ), star formation rate, metallicity ([X/H]), half light radius (R 50), angular and physical ( ) offset of the afterglow from the center of the host galaxy, the normalized offset ( ), and the brightness fraction . For most parameters, we find interesting overlapping properties between the two populations in both one-dimensional (1D) and 2D distribution plots. The three best parameters for the purpose of classification are T 90, , and . However, no single parameter alone is good enough to place a particular burst into the right physical category, suggesting the need for multiple criteria for physical classification.

Distortion of the crystal structure of MnO at ambient conditions

High resolution synchrotron radiation diffraction studies of polycrystalline powder MnO show a systematic distortion from the standard NaCl-type cubic structure (space group Fm3¯m). Two models of the distortion of MnO crystallites are presented: (i) anisotropic Bragg peak broadening due to a distribution of internal microstrains, and (ii) a model with tetragonal symmetry (space group I4/mmm) with at≈ac/√2, ct≈ac. Both models show good agreement with the experimental data which is significantly better than the cubic model with isotropic Bragg peak broadening. Both models imply a distortion of the cubic symmetry of the MnO crystal structure. The size of the tetragonal distortion is x=ct/(at√2)=1±Δ, where Δ≈2×10−4 at ambient conditions. Both tetragonal structures with elongation along ct (x=1+Δ) and shrinking along ct (x=1−Δ) give the same fit quality estimators. The distortion from cubic symmetry increases with milling time for powder MnO samples milled in a planetary mill. The proposed tetragonal space group I4/mmm has a group-subgroup relation with the monoclinic space group C2/m observed in MnO below TN.

A Brief Review of the Amati Relation for GRBs

Gamma-ray bursts (GRBs) are the most powerful explosions in the universe. Alt-hough the exact mechanism behind these explosions remains elusive, GRBs hold great promise as cosmological probes for two main reasons: they have been observed up to very high redshift (z > 9), and their gamma-ray emission is unencumbered by any intervening dust. Several GRB energy and luminosity indicators have been discovered. These indicators correlate an observable quantity, like the intrinsic peak energy, Ep,i, in the spectrum of a burst to an unobservable parameter like the equivalent isotropic energy, Eiso, or the isotropic peak luminosity, Lp,iso. This paper provides a brief review of one of these energy and luminosity indicators, the Amati relation, and discusses its potential use as a cosmological probe.

The optical identification of events with poorly defined locations: the case of the Fermi GBM GRB 140801A

We report the early discovery of the optical afterglow of gamma-ray burst (GRB) 140801A in the 137 deg$^2$ 3-$\sigma$ error-box of the Fermi Gamma-ray Burst Monitor (GBM). MASTER is the only observatory that automatically react to all Fermi alerts. GRB 140801A is one of the few GRBs whose optical counterpart was discovered solely from its GBM localization. The optical afterglow of GRB 140801A was found by MASTER Global Robotic Net 53 sec after receiving the alert, making it the fastest optical detection of a GRB from a GBM error-box. Spectroscopy obtained with the 10.4-m Gran Telescopio Canarias and the 6-m BTA of SAO RAS reveals a redshift of $z=1.32$. We performed optical and near-infrared photometry of GRB 140801A using different telescopes with apertures ranging from 0.4-m to 10.4-m. GRB 140801A is a typical burst in many ways. The rest-frame bolometric isotropic energy release and peak energy of the burst is $E_\mathrm{iso} = 5.54_{-0.24}^{+0.26} \times 10^{52}$ erg and $E_\mathrm{p, rest}\simeq280$ keV, respectively, which is consistent with the Amati relation. The absence of a jet break in the optical light curve provides a lower limit on the half-opening angle of the jet $\theta=6.1$ deg. The observed $E_\mathrm{peak}$ is consistent with the limit derived from the Ghirlanda relation. The joint Fermi GBM and Konus-Wind analysis shows that GRB 140801A could belong to the class of intermediate duration. The rapid detection of the optical counterpart of GRB 140801A is especially important regarding the upcoming experiments with large coordinate error-box areas.

A TIGHTLiso–Ep,z–Γ0CORRELATION OF GAMMA-RAY BURSTS

We select a sample of 34 gamma-ray bursts (GRBs) whose $\Gamma_0$ values are derived with the onset peaks observed in the afterglow lightcurves (except for GRB 060218 whose $\Gamma_0$ is estimated with its radio data), and investigate the correlations among $\Gamma_0$, the isotropic peak luminosity ($L_{\rm iso}$), and the peak energy ($E_{\rm p,z}$) of the $\nu f_\nu$ spectrum in the cosmological rest frame. An analysis of pair correlations among these observables well confirms the results reported by the previous papers. More interestingly, a tight correlation among $L_{\rm iso}$, $E_{\rm p,z}$, and $\Gamma_0$ is found from a multiple regression analysis, which takes the form of $L_{\rm iso} \propto E_{\rm p,z}^{1.34\pm 0.14} \Gamma_0^{1.32\pm 0.19}$ or $E_{\rm p,z} \propto L_{\rm iso}^{0.55\pm 0.06}\Gamma_0^{-0.50\pm 0.17}$. Nine other GRBs whose $\Gamma_0$ are derived via the pair production opacity constraint also follow such a correlation. Excluding GRB 060218, the $L_{\rm iso}-E_{\rm p,z}-\Gamma_0$ correlation is valid, and it even holds in the jet co-moving frame. However, GRB 060218 deviates the $L^{'}_{\rm iso}-E^{'}_{\rm p}$ relation of typical GRBs in the jet co-moving frame with $3\sigma$. We argue that the $L_{\rm iso} - E_{\rm p, z} - \Gamma_0$ correlation may be more physical than the $L_{\rm iso} - E_{\rm p,z}$ correlation, since physically the relationship between the observed $L_{\rm iso}$ and $E_{\rm p,z}$ not only depends on radiation physics, but also depends on the bulk motion of the jet. We explore the possible origins of this correlation and discuss its physical implications for understanding GRB jet composition and radiation mechanism.

Luminosity–time and luminosity–luminosity correlations for GRB prompt and afterglow plateau emissions

We present an analysis of 123 Gamma-ray bursts (GRBs) with known redshifts possessing an afterglow plateau phase. We reveal that $L_a-T^{*}_a$ correlation between the X-ray luminosity $L_a$ at the end of the plateau phase and the plateau duration, $T^*_a$, in the GRB rest frame has a power law slope different, within more than 2 $\sigma$, from the slope of the prompt $L_{f}-T^{*}_{f}$ correlation between the isotropic pulse peak luminosity, $L_{f}$, and the pulse duration, $T^{*}_{f}$, from the time since the GRB ejection. Analogously, we show differences between the prompt and plateau phases in the energy-duration distributions with the afterglow emitted energy being on average $10\%$ of the prompt emission. Moreover, the distribution of prompt pulse versus afterglow spectral indexes do not show any correlation. In the further analysis we demonstrate that the $L_{peak}-L_a$ distribution, where $L_{peak}$ is the peak luminosity from the start of the burst, is characterized with a considerably higher Spearman correlation coefficient, $\rho=0.79$, than the one involving the averaged prompt luminosity, $L_{prompt}-L_a$, for the same GRB sample, yielding $\rho=0.60$. Since some of this correlation could result from the redshift dependences of the luminosities, namely from their cosmological evolution we use the Efron-Petrosian method to reveal the intrinsic nature of this correlation. We find that a substantial part of the correlation is intrinsic. We apply a partial correlation coefficient to the new de-evolved luminosities showing that the intrinsic correlation exists.