The recent detection of TeV photons from two gamma-ray bursts (GRBs), GRB 190114C and GRB 180720B, has opened a new window for multi-messenger and multi-wavelength astrophysics of high-energy transients. We study the origin of very-high-energy (VHE) $γ$-rays from the short GRB 160821B, for which the MAGIC Collaboration reported a $\sim 3 σ$ statistical significance. Short GRBs are often accompanied by extended and plateau emission, which is attributed to internal dissipation resulting from activities of a long-lasting central engine, and Murase et al. (2018) recently suggested the external inverse-Compton (EIC) scenario for VHE counterparts of short GRBs and neutron star mergers. Applying this scenario to GRB 160821B, we show that the EIC flux can reach $\sim 10^{-12}\rm~erg~cm^{-2}~s^{-1}$ within a time period of $\sim 10^3 - 10^4\rm~s$, which is consistent with the MAGIC observations. EIC $γ$-rays expected during the extended and plateau emission will be detectable with greater significance by future detectors such as the Cherenkov Telescope Array (CTA). The resulting light curve has a distinguishable feature, where the VHE emission is predicted to reach the peak around the end of the seed emission.
I summarize our recent calculations on quark stars (QSs), for the purpose of explaining some short gamma-ray bursts characterized by internal plateau in their early X-ray afterglow. According to the present plateau sample, the QS central engine model is demonstrated to more preferred than the original neutron star (NS) one. New QS equation of states (PMQS1, PMQS2, PMQS3) are then proposed, respecting fully the observed burst data and the mass distribution of the Galactic NS-NS systems.
An intrinsic correlation has been identified between the luminosity and duration of plateaus in the X-ray afterglows of Gamma-Ray Bursts (GRBs; Dainotti et al. 2008), suggesting a central engine origin. The magnetar central engine model predicts an observable plateau phase, with plateau durations and luminosities being determined by the magnetic fields and spin periods of the newly formed magnetar. This paper analytically shows that the magnetar central engine model can explain, within the 1$σ$ uncertainties, the correlation between plateau luminosity and duration. The observed scatter in the …
The unknown equation of state (EoS) of neutron stars (NSs) is puzzling because of rich non-perturbative effects of strong interaction there. A method to constrain the EoS by using the detected X-ray plateaus of gamma-ray bursts (GRBs) is proposed in this paper. Observations show some GRB X-ray plateaus may be powered by strongly magnetized millisecond NSs. The properties of these NSs should then satisfy: (i) the spin-down luminosity of these NSs should be brighter than the observed luminosity of the X-ray plateaus; (ii) the total rotational energy of these NSs should be larger than the total e…
The detection of TeV gamma-ray bursts (GRBs) brought new opportunities for studying the physics of particle acceleration at relativistic shocks. The \hess telescopes recently observed very-high-energy (VHE) emission from a nearby low-luminosity GRB, GRB 190829A. Follow-up observations with, e.g., Swift-XRT, revealed unusual flare activities at $\sim 10^3\rm~s$, which can be caused by a long-lasting central engine. We show that the VHE emission during the H.E.S.S. observation time is naturally produced in the external inverse-Compton (EIC) scenario, where seed photons supplied by the flares or …
The central engine of gamma-ray bursts (GRBs) remains an open and forefront topic in the era of multimessenger astrophysics. The X-ray plateaus appear in some GRB afterglows, which are widely considered to originate from the spindown of magnetars. According to the stable magnetar scenario of GRBs, an X-ray plateau and a decay phase as $\sim t^{-2}$ should appear in X-ray afterglows. Meanwhile, the ``normal'' X-ray afterglow is produced by the external shock from GRB fireball. We analyze the Neil Gehrels \emph{Swift} GRB data, then find three gold samples, which have an X-ray plateau and a deca…
A plateau phase in the X-ray afterglow is observed in a significant fraction of gamma-ray bursts (GRBs). Previously, it has been found that there exists a correlation among three key parameters concerning the plateau phase, i.e., the end time of the plateau phase in the GRB rest frame ($T_{a}$), the corresponding X-ray luminosity at the end time ($L_{X}$) and the isotropic energy of the prompt GRB ($E_{γ,\rm{iso}}$). In this study, we systematically search through all the \emph{Swift} GRBs with a plateau phase that occurred between 2005 May and 2018 August. We collect 174 GRBs, with redshifts …
Gamma-Ray Bursts (GRBs) are the most explosive phenomena in the Universe after the Big Bang. A large fraction of GRB lightcurves (LCs) shows X-ray plateaus. We perform the most comprehensive analysis of all GRBs (with known and unknown redshifts) with plateau emission observed by The Neil Gehrels Swift Observatory from its launch until August 2019. We fit 455 LCs showing a plateau and explore whether these LCs follow closure relations, relations between the temporal and spectral indices of the afterglow, corresponding to 2 distinct astrophysical environments and cooling regimes within the exte…
Gamma ray bursts (GRBs) have great advantages for their huge burst energies, luminosities and high redshifts in probing the Universe. A few interesting luminosity correlations of GRBs have been used to test cosmology models. Especially, for a subsample of long GRBs with known redshifts and a plateau phase in the afterglow, a correlation between the end time of the plateau phase (in the GRB rest frame) and the corresponding X-ray luminosity has been found. In this paper, we re-analyze the subsample and found that a significantly tighter correlation exists when we add a third parameter, i.e. the…
A class of long Gamma-Ray Bursts (GRBs) presenting light curves with an extended plateau phase in their X-ray afterglows obeys a correlation between the rest frame end time of the plateau, $T_a$, and its corresponding X-ray luminosity, $L_{a}$, Dainotti et al. (2008). In this work we perform an analysis of a total sample of 176 {\it Swift} GRBs with known redshifts, exhibiting afterglow plateaus. By adding a third parameter, that is the peak luminosity in the prompt emission, $L_{peak}$, we discover the existence of a new three parameter correlation. The scatter of data about this plane become…
Diverse Morphologies of GRB X-Ray Plateaus within a Common Magnetar Framework
Nanjing University（南京大学）；Guangxi University（广西大学）；Nanjing University of Information Science and Technology（南京信息工程大学）；Xinjiang Astronomical Observatory, CAS（中国科学院新疆天文台）；Purple Mountain Observatory, Chinese Academy of Sciences（中国科学院紫金山天文台）
Evidence for the central engine of gamma-ray bursts (GRBs) has been collected in the Neil Gehrels \emph{Swift} data. For instance, some GRBs show an internal X-ray plateau followed by very steep decay, which is difficult to be interpreted within the framework of a black hole (BH) central engine, but are consistent within a rapidly spinning magnetar engine picture. The very steep decay at the end of the plateau suggests a sudden cessation of the central engine, which is explained as the collapse of a supra-massive magnetar into a black hole when it spins down. Here we propose that some addition…
The Large Area Telescope (LAT) on board the \Fermi Gamma-ray Space Telescope (\Fermi) shows long-lasting high-energy emission in many gamma-ray bursts (GRBs), similar to X-ray afterglows observed by the Neil Gehrels Swift Observatory \citep[\textit{Swift};][]{gehrels2004}. Some LAT light curves (LCs) show a late-time flattening reminiscent of X-ray plateaus. We explore the presence of plateaus in LAT temporally extended emission analyzing GRBs from the second \lat GRB Catalog \citep[2FLGC;][]{Ajello2019apj} from 2008 to May 2016 with known redshifts, and check whether they follow closure relat…
Recently, very high-energy photons above 100 GeV were reported to be detected from GRB~190114C and GRB~180720B at, respectively, 100-1000 s and 10 hours after the burst. We model the available broad-band data of both GRBs with the synchrotron plus synchrotron self-Compton (SSC) emission of the afterglow shocks. We find that the sub-TeV emission of GRB~180720B can be interpreted as the SSC emission from afterglow shocks expanding in a constant density circum-burst medium. The SSC emission of GRB~190114C dominates over the synchrotron component from GeV energies at $\sim100$ s, which can explain…
Short-duration GRBs with extended emission form a subclass of short GRBs, comprising about 15% of the short-duration sample. Afterglow detections of short GRBs are also rare (about 30%) due to their smaller luminosity. We present a multi-band data set of the short burst with extended emission GRB 150424A, comprising of GROND observations, complemented with data from Swift/UVOT, Swift/XRT, HST, Keck/LRIS and data points from the literature. The GRB 150424A afterglow shows an extended plateau phase, lasting about 8hrs. The analysis of this unique GRB afterglow might shed light on the understandi…
Gamma-Ray Bursts (GRBs) are fascinating events due to their panchromatic nature. Their afterglow emission is observed from sub-TeV energies to radio wavelengths. We investigate GRBs that present an optical plateau, leveraging on the resemblance with the X-ray plateau shown in many GRB light curves (LCs). We comprehensively analyze all published GRBs with known redshifts and optical plateau observed mostly by the Neil Gehrels Swift Observatory (Swift). We fit 267 optical LCs and show the existence of the plateau in 102 cases, which is the largest compilation so far of optical plateaus. For 56 S…
The Neil Gehrels Swift observatory observe Gamma-Ray bursts (GRBs) plateaus in X-rays. We test the reliability of the closure relations through the fireball model when dealing with the GRB plateau emission. We analyze 455 X-ray lightcurves (LCs) collected by \emph{Swift} from 2005 (January) until 2019 (August) for which the redshift is both known and unknown using the phenomenological Willingale 2007 model. Using these fits, we analyze the emission mechanisms and astrophysical environments of these GRBs through the closure relations within the time interval of the plateau emission. Finally, we…
Gamma-ray bursts (GRBs), which have been observed up to redshifts z approx 9.5 can be good probes of the early universe and have the potential of testing cosmological models. The analysis by Dainotti of GRB Swift afterglow lightcurves with known redshifts and definite X-ray plateau shows an anti-correlation between the rest frame time when the plateau ends (the plateau end time) and the calculated luminosity at that time (or approximately an anti-correlation between plateau duration and luminosity). We present here an update of this correlation with a larger data sample of 101 GRBs with good l…
The X-ray afterglow plateau emission observed in many Gamma-ray Bursts (GRBs) has been interpreted as either being fueled by fallback onto a newly formed black hole, or by the spin-down luminosity of an ultra-magnetized millisecond neutron star. If the latter model is assumed, GRB X-ray afterglow light curves can be analytically reproduced. We fit a sample of GRB X-ray plateaus, interestingly yielding a distribution in the magnetic field versus spin period (B-P) diagram consistent with $B\propto P^{7/6}$. This is expected from the well-established physics of the spin-up line minimum period for…
Extended emission (EE) is a high-energy, early time rebrightening sometimes seen in the light curves of short gamma-ray bursts (GRBs). We present the first contiguous fits to the EE tail and the later X-ray plateau, unified within a single model. Our central engine is a magnetar surrounded by a fall-back accretion disc, formed by either the merger of two compact objects or the accretion-induced collapse of a white dwarf. During the EE phase, material is accelerated to super-Keplarian velocities and ejected from the system by the rapidly rotating ($P \approx 1 - 10$ ms) and very strong ($10^{15…
Under the steady state condition, the spectrum of electrons is investigated by solving the continuity equation under the complex radiation of both the synchrotron and Compton processes. The resulted GRB spectrum is a broken power law in both the fast and slow cooling phases. On the basis of this electron spectrum, the spectral indices of the Band function in four different phases are presented. In the complex radiation frame, the detail investigation on physical parameters reveals that both the reverse shock photosphere model and the forward shock with strong coupling model can answer the $α\s…
The X-ray afterglows of GRBs 060413, 060522, 060607A and 080330 are characterized by plateaus that are followed by very sharp drops. An X-ray plateau is interpretable within the framework of the external forward shock model but the sharp drop is not. In this work we interpret these peculiar X-ray afterglow data as the central engine afterglows from some magnetized central engines, plausibly magnetars. In this model, the X-ray afterglows are powered by the internal magnetic energy dissipation and the sudden drop is caused by the collapse of the magnetar. Accordingly, the X-ray plateau photons s…
The Fermi satellite has been reporting the detailed temporal properties of gamma-ray bursts (GRBs) in an extremely broad spectral range, 8 keV - 300 GeV, in particular, the unexpected delays of the GeV emission onsets behind the MeV emission of some GRBs. We focus on GRB 080916C, one of the Fermi-LAT GRBs for which the data of the delayed high-energy emission are quite extensive, and we show that the behavior of the high-energy emission of this burst can be explained by a model in which the prompt emission consists of two components: one is the MeV component due to the synchrotron-self-Compton…
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 $σ$, 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 th…
The short burst GRB 130912A was detected by Swift, Fermi satellites and several ground-based optical telescopes. Its X-ray light curve decayed with time normally. The optical emission, however, displayed a long term plateau, which is the longest one in current short GRB observations. In this work we examine the physical origin of the X-ray and optical emission of this peculiar event. We find that the canonical forward shock afterglow emission model can account for the X-ray and optical data self-consistently and the energy injection model that has been widely adopted to interpret the shallowly…
One favored progenitor model for short duration gamma-ray bursts (SGRBs) 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 they would collapse to black holes after losing centrifugal support due to magnetic dipole spindown. By systematically analyzing the BAT-XRT light curves of all short GRBs detected by {\em swift}, we test how well the data are consistent with this central engine model of short GRBs. We find th…
A newly formed magnetar has been proposed as the central engine of short GRBs to explain on-going energy injection giving observed plateau phases in the X-ray lightcurves. These rapidly spinning magnetars may be capable of emitting pulsed emission comparable to known pulsars and magnetars. In this paper we show that, if present, a periodic signal would be detectable during the plateau phases observed using the Swift X-Ray Telescope recording data in Window Timing mode. We conduct a targeted deceleration search for a periodic signal from a newly formed magnetar in 2 Swift short GRBs and rule ou…
Jitter radiation, the emission of relativistic electrons in a random and small-scale magnetic field, has been applied to explain the gamma-ray burst (GRB) prompt emission. The seed photons produced from jitter radiation can be scattered by thermal/nonthermal electrons to the high-energy bands. This mechanism is called jitter self-Compton (JSC) radiation. GRB 100728A, which was simultaneously observed by the Swift and Fermi, is a great example to constrain the physical processes of jitter and JSC. In our work, we utilize jitter/JSC radiation to reproduce the multiwavelength spectrum of GRB 1007…
The extended high-energy gamma-ray (>100 MeV) emission which occurs well after the prompt gamma-ray bursts (GRBs) is usually explained as the afterglow synchrotron radiation. Here we report the analysis of the Fermi Large Area Telescope observations of GRB 130907A. A 55 GeV photon compatible with the position of the burst was found at about 5 hours after the prompt phase. The probability that this photon is associated with GRB 130907A is higher than 99.96%. The energy of this photon exceeds the maximum synchrotron photon energy at this time and its occurrence thus challenges the synchrotron me…
The origin of the shallow decay segment in gamma-ray burst's (GRB) early light curves remains a mystery, especially those cases with a long-lived plateau followed by an abrupt falloff. In this paper, we propose a mechanism to understand the origin of the abrupt falloff after plateau by considering solidification of newborn quark stars with latent heat released as energy injection to GRB afterglow. We estimate the total latent heat released during the phase transition of quark stars from liquid to solid states, to be order of ~ 10^{51}ergs, which is comparable to the emission energy in the shal…
The analysis of 176 gamma ray burst (GRB) afterglow plateaus observed by Swift from GRBs with known redshifts revealed that the subsample of long GRBs associated with supernovae (LONG-SNe) - 19 events - presents a very high correlation coefficient between the luminosity at the end of the plateau phase La and the end time of the plateau T*a, hereafter Dainotti relation. Furthermore, these SNe Ib/c associated with GRBs also obey the peak-magnitude stretch relation, similar to that used to standardize the SNe Ia. We here investigate a category of GRBs with plateau and associated with SNe to compa…
The plateaus observed in about one half of the early X-ray afterglows are the most puzzling feature in gamma-ray bursts (GRBs) detected by Swift. By analyzing the temporal and spectral indices of a large X-ray plateau sample, we find that 55% can be explained by external, forward shock synchrotron emission produced by a relativistic ejecta coasting in a ρ~ r^{-2}, wind-like medium; no energy injection into the shock is needed. After the ejecta collects enough medium and transitions to the adiabatic, decelerating blastwave phase, it produces the post-plateau decay. For those bursts consistent w…
Gamma-ray bursts (GRBs), which have been observed up to redshifts $z \approx 9.5$ can be good probes of the early universe and have the potential of testing cosmological models. The analysis by Dainotti of GRB Swift afterglow lightcurves with known redshifts and definite X-ray plateau shows an anti-correlation between the \underline{rest frame} time when the plateau ends (the plateau end time) and the calculated luminosity at that time (or approximately an anti-correlation between plateau duration and luminosity). We present here an update of this correlation with a larger data sample of 101 G…
[Zhang 2014] propose to redefine the true GRB central engine activity duration, $t_{\rm burst}$, by considering the contributions from the prompt $γ$-ray emission, X-ray flare and internal plateau features. With a comprehensive study on a large sample of Swift GRBs, it is shown that the $t_{\rm burst}$ distribution in the observer frame consists of a bimodal feature, suggesting the existence of a new population of ultra-long GRBs. In this work, we make a series of further studies on $t_{\rm burst}$: we update the Swift GRB sample up to June 2016; we investigate the properties of $t_{\rm burst}…
Gamma-ray bursts (GRBs) are known to have the most relativistic jets, with initial Lorentz factors in the order of a few hundreds. Many GRBs display an early X-ray light-curve plateau, which was not theoretically expected and therefore puzzled the community for many years. Here, we show that this observed signal is naturally obtained within the classical GRB "fireball" model, provided that the initial Lorentz factor is rather a few tens, and the expansion occurs into a medium-low density "wind". The range of Lorentz factors in GRB jets is thus much wider than previously thought and bridges an …
The merger of binary neutron stars (NS-NS) as the progenitor of short Gamma-ray bursts (GRBs) has been confirmed by the discovery of the association of the gravitational wave (GW) event GW170817 with GRB 170817A. However, the merger product of binary NS remains an open question. An X-ray plateau followed by a steep decay ("internal plateau") has been found in some short GRBs, implying that a supra-massive magnetar operates as the merger remnant and then collapses into a newborn black hole (BH) at the end of the plateau. X-ray bump or second-plateau following the "internal plateau" is considere…
We present a process that accounts for the steep-decline-and-plateau phase of the Swift-XRT light curves, vexing features of GRB phenomenology. This process is an integral part of the "supercritical pile" GRB model, proposed a few years ago to provide an account for the conversion of the GRB kinetic energy into radiation with a spectral peak at $E_{\rm pk} \sim m_ec^2$. We compute the evolution of the relativistic blast wave (RBW) Lorentz factor $Γ$ to show that the radiation--reaction force due to the GRB emission can produce an abrupt, small ($\sim 25%$) decrease in $Γ$ at a radius which is …
Distinct X-ray plateau and flare phases have been observed in the afterglows of gamma-ray bursts (GRBs), and most of them should be related to central engine activities. In this paper, we collect 174 GRBs with X-ray plateau phases and 106 GRBs with X-ray flares. There are 51 GRBs that overlap in the two selected samples. We analyze the distributions of the proportions of the plateau energy $E_{\rm plateau}$ and the flare energy $E_{\rm flare}$ relative to the isotropic prompt emission energy $E_{\rm γ,iso}$. The results indicate that they well meet the Gaussian distributions and the medians of…
A nearby super-luminous burst GRB 130427A was simultaneously detected by six $γ$-ray space telescopes ({\it Swift}, Fermi-GBM/LAT, Konus-Wind, SPI-ACS/INTEGRAL, AGILE and RHESSI) and by three RAPTOR full-sky persistent monitors. The isotropic $γ-$ray energy release is of $\sim 10^{54}$ erg, rendering it the most powerful explosion among the GRBs with a redshift $z\leq 0.5$. The emission above 100 MeV lasted about one day and four photons are at energies greater than 40 GeV. We show that the count rate of 100 MeV-100 GeV emission may be mainly accounted for by the forward shock synchrotron radi…
A rapidly spinning, strongly magnetized neutron star is invoked as the central engine for some Gamma-ray bursts (GRBs), especially, the $"$internal plateau$"$ feature of X-ray afterglow. However, for these $"$internal plateau$"$ GRBs, how to produce their prompt emission remains an open question. Two different physical process have been proposed in the literature, (1) a new-born neutron star is surrounded by a hyper-accreting and neutrino cooling disk, the GRB jet can be powered by neutrino annihilation aligning the spin axis; (2) a differentially rotating millisecond pulsar was formed due to …
The recent discovery of gravitational waves from GW170817, associated with a short Gamma-Ray Burst (GRB) at a distance of $40$Mpc, has demonstrated that short GRBs can occur locally and at a reasonable rate. Furthermore, gravitational waves enable us to detect close by GRBs, even when we are observing at latitudes far from the jet's axis. We consider here Compton echoes, the scattered light from the prompt and afterglow emission. Compton echoes, an as yet undetected counterpart of GRBs, peak in X-rays and maintain a roughly constant flux for hundreds to thousands of years after the burst. Thou…
Synchrotron radiation from a decelerating blastwave is a widely accepted model of radio to X-ray afterglow emission from gamma-ray bursts (GRBs). GeV gamma-ray emission detected by the Fermi Large Area Telescope (LAT) and the duration of which extends beyond the prompt gamma-ray emission phase, is also compatible with broad features of afterglow emission. We revisit the synchrotron self-Compton (SSC) emission model from a decelerating blastwave to fit multiwavelength data from three bright GRBs, namely GRB~190114C, GRB~130427A and GRB~090510. We constrain the afterglow model parameters using t…
Context: The origin of GRBs' prompt emission is highly debated. Proposed scenarios involve dissipation processes above or below the photosphere of an ultra-relativistic outflow. Aims: We search for observational features that would favour one scenario over the others by constraining the dissipation radius, the outflow magnetization or by indicating the presence of shocks. Bursts showing peculiarities can emphasize the role of a specific physical ingredient, which becomes more apparent under certain circumstances. Methods: We study GRB 070110, which exhibited several remarkable features during …
We study the observed correlations between the duration and luminosity of the early afterglow plateau and the isotropic gamma-ray energy release during the prompt phase. We discuss these correlations in the context of two scenarios for the origin of the plateaus. In the first one the afterglow is made by the forward shock and the plateau results from variations of the microphysics parameters while in the second one the early afterglow is made by a long-lived reverse shock propagating in a low Lorentz factor tail of the ejecta.
Using multiple observational arguments, recent work has shown that cosmological GRBs are typically viewed at angles within, or close to the cores of their relativistic jets. One of those arguments relied on the lack of tens-of-days-long periods of very shallow evolution that would be seen in the afterglow light-curves of GRBs viewed at large angles. Motivated by these results, we consider that GRBs efficiently produce $γ$-rays only within a narrow region around the core. We show that, on these near-core lines-of-sight, structured jets naturally produce shallow phases in the X-ray afterglow of …
GRB 120326A is an unusual gamma-ray burst (GRB) which has a quite long plateau and a very late rebrightening both in X-ray and optical bands. The similar behavior of the optical and X-ray light curves suggests that they maybe have a common origin. The long plateau starts from several hundred seconds and ends at tens of thousands seconds. The peak time of the late rebrightening is about 30000 s. We analyze the energy injection model by means of numerical and analytical solutions, considering both the wind environment and ISM environment for GRB afterglows. We especially study the influence of t…
The follow-up of $γ$-ray bursts (GRBs) by the X-ray telescope (XRT, 0.3-10 keV) on board the Neil Gehrels Swift Observatory led to the discovery of a shallow decay phase (the so-called plateau) of the X-ray emission in a good fraction of GRBs. This unexpected temporal behaviour does not fit the standard GRB afterglow expectation. Thus, in the last years, many models emerged, that invoke energy injection into the external shock, requiring long-lasting activity of the central engine of GRBs. We discuss a new alternative, comprehensive model: the plateau phase originates from the high latitude em…
A long duration gamma-ray burst, GRB 160530A, was detected by the Compton Spectrometer and Imager (COSI) during the 2016 COSI Super Pressure Balloon campaign. As a Compton telescope, COSI is inherently sensitive to the polarization of gamma-ray sources in the energy range 0.2-5.0 MeV. We measured the polarization of GRB 160530A using 1) a standard method (SM) based on fitting the distribution of azimuthal scattering angles with a modulation curve, and 2) an unbinned, maximum likelihood method (MLM). In both cases, the measured polarization level was below the $99\%$ confidence minimum detectab…
