Isotropic Luminosity Research Articles

Fast Radio Bursts with Narrow Beaming Angles Can Escape from Magnetar Magnetospheres

Fast radio bursts (FRBs) are millisecond-duration transients observed in the radio band, with their origin and radiation mechanism remaining unclear to date. Growing evidence indicates that at least some FRBs originate from magnetars and are likely generated within the magnetospheres of these highly magnetized neutron stars. However, a recent study suggested that FRBs originating from magnetar magnetospheres would be scattered by magnetospheric electron–positron pair plasma, making it impossible for them to escape successfully. In this paper, we first demonstrate that the scattering effect can be greatly attenuated if the angle between the FRB propagation direction and the background magnetic field is ∼10−2 rad or smaller. When the angle is around 10−1 rad, the beaming effect of FRBs becomes significant in reducing scattering. Such FRBs have small transverse spatial sizes, which can help them instantly push the front plasma laterally out of the radiation region. This significantly mitigates the FRB-induced two-photon annihilation reaction, γ + γ → e − + e +, which was previously regarded as a key factor hindering the propagation of FRBs. A critical radiation-cone half-opening angle between 10−3 and 10−2 rad is found for an FRB with isotropic luminosity L iso ∼ 1042 erg s−1 and emitted at a radius r em ≲ 109 cm in the magnetosphere of a magnetar. Smaller beaming angles and larger emission radii can be more advantageous for the propagation of FRBs in magnetospheres. Our result supports the scenario that FRBs could originate from magnetar magnetospheres.

Disk mass after a binary neutron star merger as a constraining parameter for short gamma-ray bursts

Context. The coincident detection of GW170817 and gamma-ray burst GRB170817A marked a milestone for the connection between binary neutron star (BNS) mergers and short gamma-ray bursts (sGRBs). These mergers can lead to the formation of a black hole that is surrounded by a disk and to the generation of a powerful jet. It spends energy to break free from the merger ejecta, and then a portion of it is dissipated to produce observable emissions. Aims. Our primary goal is to enhance our comprehension of BNS mergers by constraining the disk mass for a selection of sGRBs. To do this, we used the isotropic gamma-ray luminosity and corresponding emission times as key indicators. Methods. We leveraged data from GW170817 to estimate the disk mass surrounding the BNS merger remnant, and we subsequently inferred the efficiency of the accretion onto the jet. We then statistically examined other sGRB observations to estimate whether they might have been induced by BNS mergers Results. Our findings suggest that when similar physical parameters are employed as in the only observed BNS-powered GRB event, GRB170817A, a substantial fraction of sGRBs would need an unrealistically massive disk remnant. Conclusions. This observation raises the possibility that either a different mechanism powered those events or that the post-collapse disk efficiency varies significantly in different BNS merger scenarios.

Contemporaneous X-Ray Observations of 30 Bright Radio Bursts from the Prolific Fast Radio Burst Source FRB 20220912A

We present an extensive contemporaneous X-ray and radio campaign performed on the repeating fast radio burst (FRB) source FRB 20220912A for 8 weeks immediately following the source’s detection by CHIME/FRB. This includes X-ray data from XMM-Newton, NICER, and Swift, and radio detections of FRB 20220912A from CHIME/Pulsar and Effelsberg. We detect no significant X-ray emission at the time of 30 radio bursts with upper limits on a 0.5–10.0 keV X-ray fluence of (1.5–14.5) × 10−10 erg cm−2 (99.7% credible interval, unabsorbed) on a timescale of 100 ms. Translated into a fluence ratio η x/r = F X-ray/F radio, this corresponds to η x/r < 7 × 106. For persistent emission from the location of FRB 20220912A, we derive a 99.7% 0.5–10.0 keV isotropic flux limit of 8.8 × 10−15 erg cm−2 s−1 (unabsorbed) or an isotropic luminosity limit of 1.4 × 1041 erg s−1 at a distance of 362.4 Mpc. We derive a hierarchical extension to the standard Bayesian treatment of low-count and background-contaminated X-ray data, which allows the robust combination of multiple observations. This methodology allows us to place the best (lowest) 99.7% credible interval upper limit on an FRB η x/r to date, η x/r < 2 × 106, assuming that all 30 detected radio bursts are associated with X-ray bursts with the same fluence ratio. If we instead adopt an X-ray spectrum similar to the X-ray burst observed contemporaneously with FRB-like emission from the Galactic magnetar SGR 1935+2154 detected on 2020 April 28, we derive a 99.7% credible interval upper limit on η x/r of 8 × 105, which is only 3 times the observed value of η x/r for SGR 1935+2154.

Constraining Possible γ-Ray Burst Emission from GW230529 Using Swift-BAT and Fermi-GBM

GW230529 is the first compact binary coalescence detected by the LIGO–Virgo–KAGRA collaboration with at least one component mass confidently in the lower mass gap, corresponding to the range 3–5 M ⊙. If interpreted as a neutron star–black hole merger, this event has the most symmetric mass ratio detected so far and therefore has a relatively high probability of producing electromagnetic (EM) emission. However, no EM counterpart has been reported. At the merger time t 0, Swift-BAT and Fermi-GBM together covered 100% of the sky. Performing a targeted search in a time window [t 0 − 20 s, t 0 + 20 s], we report no detection by the Swift-BAT and Fermi-GBM instruments. Combining the position-dependent γ-ray flux upper limits and the gravitational-wave posterior distribution of luminosity distance, sky localization, and inclination angle of the binary, we derive constraints on the characteristic luminosity and structure of the jet possibly launched during the merger. Assuming a top-hat jet structure, we exclude at 90% credibility the presence of a jet that has at the same time an on-axis isotropic luminosity ≳1048 erg s−1 in the bolometric band 1 keV–10 MeV and a jet opening angle ≳15°. Similar constraints are derived by testing other assumptions about the jet structure profile. Excluding GRB 170817A, the luminosity upper limits derived here are below the luminosity of any GRB observed so far.

FRBs from rapid spindown neutron stars

Abstract A fast radio burst (FRB) localized to a globular cluster (GC) challenges FRB models involving ordinary young magnetars. In this paper, we examine the rapid spindown millisecond neutron star (NS) scenario, which favours the dynamic environment in GCs. Fast spindown corresponds to a larger magnetic field than regular millisecond pulsars, which empirically favours giant pulse (GP) emission. The kinetic energy in millisecond NSs can readily exceed the magnetic energy in magnetars. The high inferred isotropic luminosity of most FRBs is challenging to explain in spin-down powered pulsars. A recent observation of a GP from the Crab pulsar, on the other hand, suggests highly Doppler-beamed emission, making the required energy orders of magnitude smaller than estimated with isotropic assumptions. Considering this strong beaming effect, GPs from a recycled pulsar with a modest magnetic field could explain the energetics and burst rates for a wide range of FRBs. The short life span accounts for a paucity of bright FRBs in the Milky Way neighbourhood. We point out that tidal disruption spin-up from a main sequence star can provide sufficient accretion rate to recycle a NS with mild magnetic field. It can also explain the observed source density and the spatial offset in the GC for FRB 20200120E. Frequency variation in the scattering tail for some of the brightest FRBs is expected in this scenario.

Peak energy–isotropic luminosity correlation and jet opening angle evolution in Swift-BAT short GRBs with soft-tail emission

Abstract 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 Epeak–Liso 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.

GRB 220304A: Another Gamma-Ray Burst Dominated by Thermal Radiation

We report a recently detected long-duration gamma-ray burst (GRB) event by Fermi-GBM, GRB 220304A. The spectral analysis of the burst by the Band function shows that both the time-integrated and time-resolved spectra are very narrow, with low-energy spectral index 〈α〉 = −0.05 ± 0.30 and high-energy spectral index 〈β〉 = −3.53 ± 0.30. It is reminiscent of GRB 090902B, a special GRB with photosphere radiation characteristics. Then, we perform spectral analysis using the Planck function (blackbody, BB) and the multicolor BB model. It is found that the spectra within −1 ∼ 3 s is well fit by the BB model, indicating that the observation within the first 4 s is a pure thermal event. Apart from that most of the spectra can be well modeled as a multicolor BB. We conclude that GRB 220304A is a GRB dominated by thermal radiation. We also find that the spectral widths of the time-resolved spectrum of the burst gradually increase with time. Based on the Amati relation, we infer the redshift to be 0.23, the physical properties of the relativistic outflow, and find that the relationship between the bulk Lorentz factor and the isotropic luminosity Γ–L iso,52 still exists.

A large-scale magnetic field produced by a solar-like dynamo in binary neutron star mergers

The merger of two neutron stars launches a relativistic jet, which must be driven by a strong large-scale magnetic field. However, the magnetohydrodynamical mechanism required to build up this magnetic field remains uncertain. By performing an ab initio super-high-resolution neutrino-radiation magnetohydrodynamics merger simulation in full general relativity, we show that the αΩ dynamo mechanism, driven by the magnetorotational instability, builds up the large-scale magnetic field inside the long-lived remnant of the binary neutron star merger. As a result, the magnetic field induces a Poynting-flux-dominated relativistic outflow with an isotropic equivalent luminosity of ~1052 erg s−1 and a magnetically driven post-merger mass ejection of ~0.1 M⊙. Therefore, the magnetar hypothesis, in which an ultra-strongly magnetized neutron star drives a relativistic jet in binary neutron star mergers, is possible. Magnetars can be the engines of short, hard gamma-ray bursts, and they should be associated with very bright kilonovae, which current telescopes could observe. Therefore, this scenario is testable in future observations.

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.

Plausible association of distant late M dwarfs with low-frequency radio emission

We present the serendipitous discovery of eight distant (&gt; 50 pc) late M dwarfs with plausible associated radio emission at 144 MHz. The M-dwarf nature of our sources has been confirmed with optical spectroscopy performed using HET/LRS2 and Subaru/FOCAS, and their radio flux densities are within the range of 0.5−1.0 mJy at 144 MHz. Considering the radio-optical source separation and source densities of the parent catalogues, we suggest that it is statistically probable that the M dwarfs are associated with the radio emission. However, it remains plausible that for some of the sources the radio emission originates from an optically faint and red galaxy hiding behind the M dwarf. The isotropic radio luminosities (∼1017 − 18 erg s−1 Hz−1) of the M dwarfs suggest that if the association is real, the radio emission is likely driven by a coherent emission process produced via plasma or electron-cyclotron maser instability processes, which is potentially caused by binary interaction. Long-term monitoring in the radio and high-resolution radio follow-up observations are necessary to search for any variability and pinpoint the radio emission to determine whether our tentative conclusion that these ultracool dwarfs are radio emitting is correct. If the low-frequency radio emission is conclusively associated with the M dwarfs, this would reveal a new population of optically faint and distant (&gt; 50 pc) radio-emitting M dwarfs.

Ultraluminous X-ray sources are beamed

ABSTRACT We show that magnetar models for ultraluminous X-ray sources (ULXs) have serious internal inconsistencies. The magnetic fields required to increase the limiting luminosity for radiation pressure above the observed (assumed isotropic) luminosities are completely incompatible with the spin-up rates observed for pulsing ULXs. We note that at least one normal Be-star + neutron star system, with a standard (non-magnetar) field, is observed to become a ULX during a large outburst and return to its previous Be-star binary state afterwards. We note further that recent polarimetric observations of the well-studied binary Cyg X-3 reveal that it produces strong emission directed away from the observer, in line with theoretical predictions of its total accretion luminosity from evolutionary arguments. We conclude that the most likely explanation for ULX behaviour involves radiation beaming by accretion disc winds. A large fraction of X-ray binaries must pass through a ULX state in the course of their evolution.

Magnetar Giant Flare Origin for GRB 210410A?

In general, giant flares (GFs) produced by magnetars have a very short-hard initial spike that is followed by a weak oscillatory phase. GFs from a nearby galaxy would appear as cosmic short-hard gamma-ray bursts (GRBs), such as GRB 200415A. In this paper, we search for GF-originated bursts in the Fermi GRB category and report GRB 210410A, which is presented with a very short-hard spike followed by an extended tail emission. In the E p,z − E iso plane, GRB 210410A with a duration of T 90 ∼ 48 s differs from long GRBs, might be classified as a short GRB with a redshift of z ∼ 0.28, and could be regarded as a GF with a distance of ∼2.7 Mpc. Here, E p,z , E iso, and L iso denote the rest-frame peak photon energy, the isotropic energy, and the isotropic luminosity of the burst, respectively. The radiation spectrum of GRB 210410A, similar to that of GRB 200415A, can be well fitted with a non-dissipative photospheric emission. However, GRB 210410A in the E p,z − L iso plane is beyond the death line of cosmic GRBs for non-dissipated photospheric emission with a general initial size of the fireball. Since the E p,z − L iso relation of GFs is far beyond the death line of cosmic GRBs, GRB 210410A may have originated from the same channel that produces GFs. We also perform the analysis and discuss both the highest photon energy event (4.2 GeV) and the extended tail emission in this burst.

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.

183 GHz Water Megamasers in Active Galactic Nuclei: A New Accretion Disk Tracer

We present the results of an Atacama Large Millimeter/submillimeter Array survey to identify 183 GHz H2O maser emission from active galactic nuclei (AGNs) already known to host 22 GHz megamaser systems. Out of 20 sources observed, we detect significant 183 GHz maser emission from 13; this survey thus increases the number of AGN known to host (sub)millimeter megamasers by a factor of 5. We find that the 183 GHz emission is systematically fainter than the 22 GHz emission from the same targets, with typical flux densities being roughly an order of magnitude lower at 183 GHz than at 22 GHz. However, the isotropic luminosities of the detected 183 GHz sources are comparable to their 22 GHz values. For two of our sources—ESO 269-G012 and the Circinus galaxy—we detect rich 183 GHz spectral structure containing multiple line complexes. The 183 GHz spectrum of ESO 269-G012 exhibits the triple-peaked structure characteristic of an edge-on AGN disk system. The Circinus galaxy contains the strongest 183 GHz emission detected in our sample, peaking at a flux density of nearly 5 Jy. The high signal-to-noise ratios achieved by these strong lines enable a coarse mapping of the 183 GHz maser system, in which the masers appear to be distributed similarly to those seen in VLBI maps of the 22 GHz system in the same galaxy and may be tracing the circumnuclear accretion disk at larger orbital radii than the 22 GHz masers. This newly identified population of AGN disk megamasers presents a motivation for developing VLBI capabilities at 183 GHz.

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.

ALMA detection of 321 GHz water maser emission in the radio galaxy NGC 1052

Abstract The Atacama Large Millimeter/submillimeter Array (ALMA) serendipitously detected H2O $J_{K_{\rm a}, K_{\rm c}} = 10_{2,9}$–93, 6 emission at 321 GHz in NGC 1052. This is the first submillimeter maser detection in a radio galaxy and the most luminous 321 GHz H2O maser known to-date with the isotropic luminosity of $1090\, L_{\odot }$. The line profile consists of a broad velocity component with FWHM = 208 ± 12 km s−1 straddling the systemic velocity and a narrow component with FWHM = 44 ± 3 km s−1 blueshifted by 160 km s−1. The profile is significantly different from the known 22 GHz 61, 6–52, 3 maser which shows a broad profile redshifted by 193 km s−1. The submillimeter maser is spatially unresolved with a synthesized beam of ${0{^{\prime \prime}_{.}}68} \times {0{^{\prime \prime}_{.}}56}$ and coincides with the continuum core position within 12 pc. These results indicate amplification of the continuum emission through high-temperature (&amp;gt;1000 K) and dense [n(H2O) &amp;gt; 104 cm−3] molecular gas in front of the core.

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.

Large-scale outflow structure and radiation properties of super-Eddington flow: Dependence on the accretion rates

Abstract In order to evaluate the impacts made by super-Eddington accretors on their environments precisely, it is essential to guarantee a large enough simulation box and long computational time to avoid any artefacts from numerical settings as much as possible. In this paper, we carry out axisymmetric two-dimensional radiation hydrodynamic simulations around a 10 M⊙ black hole in large simulation boxes and study the large-scale outflow structure and radiation properties of super-Eddington accretion flow for a variety of black hole accretion rates, ${\dot{M}}_{\,\,\rm BH} = (110\!-\!380)L_{\rm Edd}/c^{\,\,2}$ (with LEdd being the Eddington luminosity and c being the speed of light). The Keplerian radius of the inflow material, at which centrifugal force balances with gravitational force, is fixed to 2430 Schwarzschild radii. We find that the mechanical luminosity grows more rapidly than the radiation luminosity with an increase of ${\dot{M}}_{\,\,\rm BH}$. When seen from a nearly face-on direction, especially, the isotropic mechanical luminosity grows in proportion to ${\dot{M}}_{\,\,\rm BH}^{\,\,2.7}$, while the total mechanical luminosity is proportional to ${\dot{M}}_{\,\,\rm BH}^{\,\,1.7}$. The reason for the former is that the higher ${\dot{M}}_{\,\,\rm BH}$ is, the more vertically inflated the disk surface becomes, which makes radiation fields more confined in the region around the rotation axis, thereby strongly accelerating outflowing gas. The outflow is classified into pure outflow and failed outflow, depending on whether the outflowing gas can reach the outer boundary of the simulation box or not. The fraction of the failed outflow decreases with a decrease of ${\dot{M}}_{\,\,\rm BH}$. We analyze physical quantities along each outflow trajectory, finding that the Bernoulli parameter (Be) is not a good indicator to discriminate between pure and failed outflows, since it is never constant because of continuous acceleration by radiation-pressure force. Pure outflow can arise, even if Be &amp;lt; 0 at the launching point.

Testing the Amati and Yonetoku correlations for short gamma-ray bursts

We use a sample of Swift and Fermi short gamma-ray bursts (SGRBs) to test the validity of the Amati and Yonetoku correlations, which were originally found for long bursts. The first relation is between \(E_{p,i}\), the intrinsic peak energy of the GRB prompt emission, and \(E_{\mathit{iso}}\), the equivalent isotropic energy. The second relationship is between \(E_{p,i}\) and \(L_{\mathit{iso}}\), the peak isotropic luminosity. The sample is composed of 36 Swift SGRBs and 15 Fermi SGRBs that have measured redshifts and whose spectral parameters, with their uncertainties, are available online. The uncertainties (error bars) on the values of the calculated energy flux P, of the energy \(E_{\mathit{iso}}\), and of the peak isotropic luminosity peak \(L_{\mathit{iso}}\) are estimated using a Monte Carlo approach.We find that SGRB energy and luminosity quantities (\(E_{p,i}\), \(L_{\mathit{iso}}\), and \(E_{\mathit{iso}}\)) can be correlated with Amati- and Yonetoku-like relations reasonably well (Pearson r-values of 0.5 and 0.6, respectively), although the data shows large scatter and hence large error bars on the slope and the intercept of the fitting line. Our results are consistent with other similar works, though we here use the largest sample of SGRBs with redshifts so far on this topic. We also find that \(E_{\mathit{iso}}\) and \(L_{\mathit{iso}}\) seem to evolve with redshift as \((1+ z)^{4.9 \pm 0.3}\) and \((1+z)^{5.5\pm 0.9}\), respectively, with a moderate goodness of fit. However, we caution that this is probably due to selection effects rather than being a genuine redshift evolution of \(E_{\mathit{iso}}\) and \(L_{\mathit{iso}}\).

Component of Energy Flow from Supercritical Accretion Disks Around Rotating Stellar Mass Black Holes

By performing two-dimensional axisymmetric general relativistic radiation magnetohydrodynamics simulations with spin parameter a* varying from −0.9 to 0.9, we investigate the dependence on the black hole spin of the energy flow from a supercritical accretion disk around a stellar mass black hole. It is found that optically and geometrically thick disks form near the equatorial plane, and a part of the disk matter is launched from the disk surface in all models. The gas ejection is mainly driven by the radiative force, but magnetic force cannot be neglected when ∣a*∣ is large. The energy outflow efficiency (total luminosity normalized by and c are the mass-accretion rate at the event horizon and the light speed) is higher for rotating black holes than for nonrotating black holes. This is 0.7% for a* = −0.7, 0.3% for a* = 0, and 5% for a* = 0.7 for (L Edd is the Eddington luminosity). Furthermore, although the energy is mainly released by radiation when a* ∼ 0, the Poynting power increases with ∣a*∣ and exceeds the radiative luminosity for models with a* ≥ 0.5 and a* ≤ −0.7. The faster the black hole rotates, the higher the power ratio of the kinetic luminosity to the isotropic luminosity tends to be. This implies that objects with a high (low) power ratio may have rapidly (slowly) rotating black holes. Among ultraluminous X-ray sources, IC342 X-1, is a candidate with a rapidly rotating black hole.