Binary neutron star (NS) mergers are strong gravitational-wave (GW) sources and the leading candidates to interpret short-duration gamma-ray bursts (SGRBs). Under the assumptions that SGRBs are ...produced by double neutron star mergers and that the x-ray plateau followed by a steep decay as observed in SGRB x-ray light curves marks the collapse of a supramassive neutron star to a black hole (BH), we use the statistical observational properties of Swift SGRBs and the mass distribution of Galactic double neutron star systems to place constraints on the neutron star equation of state (EoS) and the properties of the post-merger product. Even though the initial spin energy of the merger product is similar, the final energy output of the merger product that goes into the electromagnetic channel varies in a wide range from several 1049 to several 105erg, since a good fraction of the spin energy is either released in the form of GWs or falls into the black hole as the supramassive NS collapses.
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 (T90), spectral peak energy ( ), low energy photon index ( ), 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 (R50), 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 T90, , 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.
ABSTRACT One favored progenitor model for short duration gamma-ray bursts (GRBs) is the coalescence of two neutron stars (NS-NS). One possible outcome of such a merger would be a rapidly spinning, ...strongly magnetized neutron star (known as a millisecond magnetar). These magnetars may be "supra-massive," implying that they would collapse to black holes after losing centrifugal support due to magnetic dipole spin down. By systematically analyzing the Burst Alert Telescope (BAT)-XRT light curves of all short GRBs detected by Swift, we test how consistent the data are with this central engine model of short GRBs. We find that the so-called "extended emission" feature observed with BAT in some short GRBs is fundamentally the same component as the "internal X-ray plateau" observed in many short GRBs, which is defined as a plateau in the light curve followed by a very rapid decay. Based on how likely a short GRB is to host a magnetar, we characterize the entire Swift short GRB sample into three categories: the "internal plateau" sample, the "external plateau" sample, and the "no plateau" sample. Based on the dipole spin-down model, we derive the physical parameters of the putative magnetars and check whether these parameters are consistent with expectations from the magnetar central engine model. The derived magnetar surface magnetic field and the initial spin period P0 fall into a reasonable range. No GRBs in the internal plateau sample have a total energy exceeding the maximum energy budget of a millisecond magnetar. Assuming that the beginning of the rapid fall phase at the end of the internal plateau is the collapse time of a supra-massive magnetar to a black hole, and applying the measured mass distribution of NS-NS systems in our Galaxy, we constrain the neutron star equation of state (EOS). The data suggest that the NS EOS is close to the GM1 model, which has a maximum non-rotating NS mass of .
A rapidly spinning, strongly magnetized neutron star (magnetar) has been proposed as one possible candidate of the central engine of gamma-ray bursts (GRBs). We systematically analyze the Swift/XRT ...light curves of long GRBs detected before 2013 August, and characterize them into four categories based on how likely they may harbor a magnetar central engine: Gold, Silver, Aluminum, and Non-magnetar. We also independently analyze the data of short GRBs with a putative magnetar central engine. We then perform a statistical study of various properties of the magnetar samples and the non-magnetar sample, and investigate whether the data are consistent with the hypothesis that there exist two types of central engines. By deriving the physical parameters of the putative magnetars, we find that the observations of the Gold and Silver samples are generally consistent with the predictions of the magnetar model. For a reasonable beaming factor for long GRBs, the derived magnetar surface magnetic field B sub(p) and initial spin period P sub(0) fall into the reasonable range. Magnetar winds in short GRBs, on the other hand, are consistent with being isotropic. No GRB in the magnetar sample has a beam-corrected total energy exceeding the maximum energy budget defined by the initial spin energy of the magnetar, while some non-magnetar GRBs do violate such a limit. With beaming correction, on average the non-magnetar sample is more energetic and luminous than the magnetar samples. Our analysis hints that millisecond magnetars are likely operating in a good fraction, but probably not all, GRBs.
The merger of a double neutron star (NS-NS) binary may result in a rapidly rotating massive NS with an extremely strong magnetic field (i.e., a millisecond magnetar). In this case, the magnetic ...spin-down of the NS remnant provides an additional source of sustained energy injection, which would continuously power the merger ejecta. The thermal emission from the merger ejecta would give rise to a bright optical "magnetar-powered merger-nova." In this work, we carry out a complete search for magnetar-powered merger-nova from a Swift short gamma-ray burst sample. We focus on short GRBs with extended emission or internal plateau, which may signify the presence of magnetars as the central engine. We eventually find three candidates of magnetar-powered merger-nova from the late observations of GRB 050724, GRB 070714B, and GRB 061006. With standard parameter values, the magnetar remnant scenario could well interpret the multi-band data of all three bursts, including the extended emission and their late chromatic features in the optical and X-ray data. The peak luminosities of these merger-novae reach several times , more than one order of magnitude brighter than the traditional "kilo-novae" with peak luminosity of . Intense, multi-color, late-time observations of short GRBs are encouraged to identify more merger-novae in the future.
Circular RNAs (circRNAs) are a class of long, non-coding RNAs molecules that shape a covalently closed continuous loop which have no 5′–3′ polarity and contain no polyA tail. CircRNAs also possess ...relatively jarless framework and are highly tissue-specific expressed in the eukaryotic transcriptome. Emerging evidences have discovered that thousands of endogenous circRNAs are present in mammalian cells and they mediate gene expression at the transcriptional or post-transcriptional level by binding to microRNAs or other molecules and then inhibit their function. Similarly, increasing evidence indicates that circRNAs may play a role in the development of several types of diseases, including atherosclerotic vascular disease risk, neurological disorders, prion diseases, osteoarthritis and diabetes. Furthermore, circRNAs exhibit aberrant expression in multiform types of cancer, including colorectal cancer, hepatocellular carcinoma and pancreatic ductal adenocarcinoma. And based on the function of circRNAs in cancer, we believe that circRNAs may serve as diagnostic or tumor promising biomarkers. Moreover, it will provide a new therapeutic target for the treatment of cancer.
It is generally believed that long-duration gamma-ray bursts (GRBs) are associated with massive star core collapse
, whereas short-duration GRBs are associated with mergers of compact star binaries
. ...However, growing observations
have suggested that oddball GRBs do exist, and several criteria (prompt emission properties, supernova/kilonova associations and host galaxy properties) rather than burst duration only are needed to classify GRBs physically
. A previously reported long-duration burst, GRB 060614 (ref.
), could be viewed as a short GRB with extended emission if it were observed at a larger distance
and was associated with a kilonova-like feature
. As a result, it belongs to the type I (compact star merger) GRB category and is probably of binary neutron star (NS) merger origin. Here we report a peculiar long-duration burst, GRB 211211A, whose prompt emission properties in many aspects differ from all known type I GRBs, yet its multiband observations suggest a non-massive-star origin. In particular, substantial excess emission in both optical and near-infrared wavelengths has been discovered (see also ref.
), which resembles kilonova emission, as observed in some type I GRBs. These observations point towards a new progenitor type of GRBs. A scenario invoking a white dwarf (WD)-NS merger with a post-merger magnetar engine provides a self-consistent interpretation for all the observations, including prompt gamma rays, early X-ray afterglow, as well as the engine-fed
kilonova emission.
GRB 160821B is a short gamma-ray burst (SGRB) at redshift z = 0.16, with a duration less than 1 s and without any "extended emission" detected up to more than 100 s in both Swift/BAT and Fermi/GBM ...bands. An X-ray plateau with a sharp drop 180 s after the BAT trigger was observed with Swift/XRT. No supernova or kilo-nova signature was detected. Assuming the central engine of this SGRB is a recently born supra-massive magnetar, we can explain the SGRB as jet radiation and its X-ray plateau as the internal energy dissipation of the pulsar wind as it spins down. We constrain its surface magnetic field to Bp < 3.12 × 1016 G and initial spin period to P0 < 8.5 × 10−3 s. Its equation of state is consistent with the GM1 model with MTOV ∼ 2.37 M and ellipticity ϵ < 0.07. Its gravitational wave (GW) radiation may be detectable with the future Einstein Telescope, but is much weaker than the current detectability limit of Advanced LIGO. The GW radiation of such an event would be detectable by Advanced LIGO if it occurred at a distance of 100 Mpc (z = 0.023).
Traditionally, gamma-ray bursts (GRBs) are classified in the T
90–hardness ratio two-dimensional plane into long/soft and short/hard GRBs. In this paper, we suggest to add the ‘amplitude’ of GRB ...prompt emission as the third dimension as a complementary criterion to classify GRBs, especially those of short durations. We define three new parameters f, f
eff and f
eff, z
as ratios between the measured/simulated peak flux of a GRB/pseudo-GRB and the flux background, and discuss the applications of these parameters to GRB classification. We systematically derive these parameters to find that most short GRBs are likely not ‘tip-of-iceberg’ of long GRBs. However, one needs to be cautious if a short GRB has a relatively small f (e.g. f < 1.5), since the chance for an intrinsically long GRB to appear as a ‘disguised’ short GRB is higher. Based on available data, we quantify the probability of a disguised short GRB below a certain f value is as
$P (<f)\sim 0.78^{+0.71}_{-0.4} f^{-4.33\pm 1.84}$
. By progressively ‘moving’ a long GRB to higher redshifts through simulations, we also find that most long GRBs would show up as rest-frame short GRBs above a certain redshift.
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