Suzaku Observation of the New Soft Gamma Repeater SGR 0501+4516 in Outburst
T. Enoto, Y. E. Nakagawa, N. Rea, P. Esposito, D. Gotz, K. Hurley, G. L. Israel, M. Kokubun, K. Makishima, S. Mereghetti, H. Murakami, K. Nakazawa, T. Sakamoto,… 展开作者
T. Enoto, Y. E. Nakagawa, N. Rea, P. Esposito, D. Gotz, K. Hurley, G. L. Israel, M. Kokubun, K. Makishima, S. Mereghetti, H. Murakami, K. Nakazawa, T. Sakamoto, L. Stella, A. Tiengo, R. Turolla, S. Yamada, K. Yamaoka, A. Yoshida, S. Zane
备注：
4 pages, 4 figures, accepted for publication in ApJL
We present the first Suzaku observation of the new Soft Gamma Repeater SGR 0501+4516, performed on 2008 August 26, four days after the onset of bursting activity of this new member of the magnetar family. The soft X-ray persistent emission was detected with the X-ray Imaging Spectrometer (XIS) at a 0.5-10 keV flux of 3.8E-11 erg/s/cm2, with a spectrum well fitted by an absorbed blackbody plus power-law model. The source pulsation was confirmed at a period of 5.762072+/-0.000002 s, and 32 X-ray bursts were detected by the XIS, four of which were also detected at higher energies by the Hard X-ray Detector (HXD). The strongest burst, which occurred at 03:16:16.9 (UTC), was so bright that it caused instrumental saturation, but its precursor phase, lasting for about 200 ms, was detected successfully over the 0.5-200 keV range, with a fluence of ~2.1E-7 erg/cm2 and a peak intensity of about 89 Crab. The entire burst fluence is estimated to be ~50 times higher. The precursor spectrum was very hard, and well modeled by a combination of two blackbodies. We discuss the bursting activity and X/gamma-ray properties of this newly discovered Soft Gamma Repeater in comparison with other members of the class.
Soft gamma repeaters (SGR) are identified as single neutron stars (NS) inside the Galaxy, or nearby galaxies, with sporadic transient gamma radiation. A total number of discovered SGR, including relative Anomalous X-ray pulsars (AXP), is few tens of objects. Many of them show periodic radiation, connected with NS rotation, with periods 2-12 s. The slow rotation is accompanied by small rate of loss of rotational energy, which is considerably smaller than the observed sporadic gamma ray luminosity, and is many orders less that the luminosity during giant bursts, observed in 4 SGR. Therefore the …
We present the first report of the detection of sudden ionospheric disturbances (SIDs) due to a Soft Gamma Ray Repeater (SGR) SGR J1550-5418 and a Gamma Ray Burst (GRB) GRB 090424. These detections were made with receiving stations of Indian Centre for Space Physics which were monitoring Very Low Frequency signals (VLFs) from the VTX transmitter located at the southern tip of Indian sub-continent. These positive detections add to the list of a handful of similar detections of other GRBs and SGRs throughout the world.
We explore the possibility that soft gamma-ray repeaters (SGRs) and anomalous X-ray pulsars (AXPs) are powered by highly magnetized white dwarfs (B-WDs). We take a sample of SGRs and AXPs and provide the possible parameter space in mass, radius, and surface magnetic field based on their observed properties (period and its derivative) and the assumption that these sources obey the mass-radius relation derived for the B-WDs. The radius and magnetic field of B-WDs are adequate to explain energies in SGRs/AXPs as the rotationally powered energy. In addition, B-WDs also adequately explain the perpl…
We show that the soft gamma-ray repeaters (SGRs) and anomalous X-ray pulsars (AXPs) can be explained as recently proposed highly magnetized white dwarfs (B-WDs). The radius and magnetic field of B-WDs are perfectly adequate to explain energies in SGRs/AXPs as the rotationally powered energy. While the highly magnetized neutron stars require an extra, observationally not well established yet, source of energy, the magnetized white dwarfs, yet following Chandrasekhar's theory (C-WDs), exhibit large ultra-violet luminosity which is observationally constrained from a strict upper limit.
There are several phenomenological similarities between Soft Gamma Repeaters and Fast Radio Bursts, including duty factors, time scales and probable repetition. The sudden release of magnetic energy in a neutron star magnetosphere, as in popular models of SGR, can meet the energy requirements of FRB but requires both the presence of magnetospheric plasma in order that dissipation occur in a transparent region and a mechanism for releasing much of that energy quickly. FRB sources and SGR are distinguished by long-lived (up to thousands of years) current-carrying coronal arches remaining from fo…
Hard X-rays above 10 keV are detected from several anomalous X-ray pulsars (AXPs) and soft gamma-ray repeaters (SGRs), and different models have been proposed to explain the physical origin within the frame of either magnetar model or fallback disk system. Using data from $\it Suzaku$ and INTEGRAL, we study the soft and hard X-ray spectra of four AXPs/SGRs, 1RXS J170849-400910, 1E 1547.0-5408, SGR 1806-20 and SGR 0501+4516. It is found that the spectra could be well reproduced by bulk-motion Comptonization (BMC) process as was first suggested by Tr$ü$mper et al., showing that the accretion sce…
Using data with the Suzaku XIS and HXD, spectral studies of short bursts from the soft gamma repeater SGR 0501+4516 were performed. In total, 32 bursts were detected during the ~60 ks of observation conducted in the 2008 August activity. Excluding the strongest one, the remaining 31 bursts showed an average 2--40 keV fluence of 1.0(-0.5,+0.3)*10^-9 erg cm^-2. A 1--40 keV spectrum summed over them leaves significant positive residuals in the HXD-PIN band with chi^2/d.o.f. = 74/50, when fitted with a two-blackbody function. By adding a power law model, the fit became acceptable with chi^2/d.o.f.…
Starting in 2013 February, Swift has been performing short daily monitoring observations of the G2 gas cloud near Sgr A* with the X-Ray Telescope to determine whether the cloud interaction leads to an increase in the flux from the Galactic center. On 2013 April 24 Swift detected an order of magnitude rise in the X-ray flux from the region near Sgr A*. Initially thought to be a flare from Sgr A*, detection of a short hard X-ray burst from the same region by the Burst Alert Telescope suggested that the flare was from an unresolved new Soft Gamma Repeater, SGR J1745-29. Here we present the discov…
On 2010 March 19, the Swift/Burst Alert Telescope triggered on a short burst with temporal and spectral characteristics similar to those of Soft Gamma Repeater (SGR) bursts. The source location, however, did not coincide with any known SGR. Subsequent observations of the source error box with the Swift/X-ray Telescope and the Rossi X-ray Timing Explorer (RXTE) led to the discovery of a new X-ray source, with a spin period of 7.56 s, confirming SGR J1833-0832 as a new magnetar. Based on our detailed temporal and spectral analyses, we show that the new SGR is rapidly spinning down (4 x 10^{-12} …
We present a new methodology to derive the positions of the Sgr B molecular clouds (MCs) along the line of sight, as an application study of the Galactic center diffuse X-rays (GCDX). The GCDX is composed of hot plasma emission of about 7 keV and 1 keV temperatures, and non-thermal continuum emission including the 6.4 keV line from neutral irons. The former, the Galactic center plasma emission (GCPE), is uniformly distributed over 1 degree in longitude, while the latter is clumpy emission produced by Thomson scattering and fluorescence from MCs irradiated by external X-rays (the X-ray reflecti…
We present the results of a LIGO search for short-duration gravitational waves (GW) associated with soft gamma repeater (SGR) bursts. This is the first GW search sensitive to neutron star f-modes, usually considered the most efficient GW emitting modes. We find no evidence of GWs associated with any SGR burst in a sample consisting of the 2004 December 27 giant flare from SGR 1806-20 and 190 lesser events from SGR 1806-20 and SGR 1900+14 which occurred during the first year of LIGO's fifth science run. GW strain upper limits and model-dependent GW emission energy upper limits are estimated for…
Assuming that AXPs and SGRs accrete matter from a fallback disk, we attempt to explain both the soft and the hard X-ray emission as the result of the accretion process. We also attempt to explain their radio emission or the lack of it. We test the hypothesis that the power-law, hard X-ray spectra are produced in the accretion flow mainly by bulk-motion Comptonization of soft photons emitted at the neutron star surface. Fallback disk models invoke surface dipole magnetic fields of $10^{12} - 10^{13}$ G, which is what we assume here. Unlike normal X-ray pulsars, for which the accretion rate is h…
On 2009 June 5, the Gamma-ray Burst Monitor (GBM) onboard the Fermi Gamma-ray Space Telescope triggered on two short, and relatively dim bursts with spectral properties similar to Soft Gamma Repeater (SGR) bursts. Independent localizations of the bursts by triangulation with the Konus-RF and with the Swift satellite, confirmed their origin from the same, previously unknown, source. The subsequent discovery of X-ray pulsations with the Rossi X-ray Timing Explorer (RXTE), confirmed the magnetar nature of the new source, SGR J0418+5729. We describe here the Fermi/GBM observations, the discovery a…
Soft gamma repeaters (SGRs) have unique properties that make them intriguing targets for gravitational wave (GW) searches. They are nearby, their burst emission mechanism may involve neutron star crust fractures and excitation of quasi-normal modes, and they burst repeatedly and sometimes spectacularly. A recent LIGO search for transient GW from these sources placed upper limits on a set of almost 200 individual SGR bursts. These limits were within the theoretically predicted range of some models. We present a new search strategy which builds upon the method used there by "stacking" potential …
The knowledge of the rate of soft gamma-ray repeater (SGR) giant flares is important for understanding the giant flare mechanism and the SGR energy budget in the framework of the magnetar model. We estimate the upper limit to the rate using the results of an extensive search for extragalactic soft gamma-repeater giant flares (GFs) among 140 short gamma-ray bursts detected between 1994 and 2010 by Konus-Wind using InterPlanetary Network (IPN) localizations and temporal parameters. We show that Konus-Wind and the IPN are capable of detecting GFs with energies of 2.3x10^46 erg (which is the energ…
SGR 0526-66 was the first soft gamma-ray repeater (SGR) from which a giant flare was detected in March 1979, suggesting the existence of magnetars, i.e. neutron stars powered by the decay of their extremely strong magnetic field. Since then, very little information has been obtained on this object, mainly because it has been burst-inactive since 1983 and the study of its persistent X-ray emission has been hampered by its large distance and its location in a X-ray bright supernova remnant in the Large Magellanic Cloud. Here we report on a comprehensive analysis of all the available XMM-Newton o…
In 2008 August, the new soft gamma-ray repeater SGR 0501+4516 was discovered by Swift. The source was soon confirmed by several groups in space- and ground-based multi-wavelength observations. In this letter we report the analysis of five short bursts from the recently discovered SGR, detected with Konus-Wind gamma-ray burst spectrometer. Properties of the time histories of the observed events, as well as results of multi-channel spectral analysis, both in the 20--300 keV energy range, show, that the source exhibits itself as a typical SGR. The bursts durations are <0.75 s and their spectra ab…
Using Chandra data taken on 2008 June, we detected pulsations at 2.59439(4) s in the soft gamma-ray repeater SGR 1627-41. This is the second measurement of the source spin period and allows us to derive for the first time a long-term spin-down rate of (1.9 +/- 0.4)E-11 s/s. From this value we infer for SGR 1627-41 a characteristic age of 2.2 kyr, a spin-down luminosity of 4E+34 erg/s (one of the highest among sources of the same class), and a surface dipole magnetic field strength of 2E+14 G. These properties confirm the magnetar nature of SGR 1627-41; however, they should be considered with c…
We show that the X-ray outburst light curves of four transient anomalous X-ray pulsars (AXPs) and soft gamma-ray repeaters (SGRs), namely XTE J1810-197, SGR 0501+4516, SGR 1627-41 and CXOU J164710.2-455216, can be produced by the fallback disk model that was also applied to the outburst light curves of persistent AXPs and SGRs in our earlier work. The model solves the diffusion equation for the relaxation of a disk which has been pushed back by a soft gamma-ray burst. The sets of main disk parameters used for these transient sources are very similar to each other and to those employed in our e…
A new cellular automaton (CA) model is presented for the self-organized criticality (SOC) in recurrent bursts of soft gamma repeaters (SGRs), which are interpreted as avalanches of reconnection in the magnetosphere of neutron stars. The nodes of a regular dodecahedron and a truncated icosahedron are adopted as spherically closed grids enclosing a neutron star. It is found that the system enters the SOC state if there are sites where the expectation value of the added perturbation is nonzero. The energy distributions of SOC avalanches in CA simulations are described by a power law with a cutoff…
We have investigated the long-term evolution of individual anomalous X-ray pulsars (AXPs) and soft gamma repeaters (SGRs) with relatively well constrained X-ray luminosity and rotational properties. In the frame of the fallback disc model, we have obtained the ranges of disc mass and dipole field strength that can produce the observed source properties. We have compared our results with those obtained earlier for dim isolated neutron stars (XDINs). Our results show that (1) the X-ray luminosity, period and period derivative of the individual AXP/SGR sources can be produced self-consistently in…
Magnetars have been suggested as the most promising site for the origin of observed soft gamma-ray repeaters (SGRs) and anomalous X-ray pulsars (AXPs). In this work we investigate the possibility that SGRs and AXPs might be observational evidence for a magnetic phase separation in magnetars. We study magnetic domain formation as a new mechanism for SGRs and AXPs in which magnetar-matter separates into two phases containing different flux densities. We identify the parameter space in matter density and magnetic field strength at which there is an instability for magnetic domain formation. We co…
The Broad-band Noise Characteristics of Selected Anomalous X-Ray Pulsars and Soft Gamma-ray Repeaters
本文给出了2-60 keV能区反常X射线脉冲星（AXP）和软γ重复源（SGR）的宽带噪声结构。我们已经分析了罗西X射线定时探测器正比计数器阵列档案光曲线的四个AXP和一个SGR。我们检测到，这些源的持续发射显示在0.005-0.05 Hz的范围内的低频带限噪声变化从2.5%到70%的综合均方根时间的长时间的静止和以下爆发。我们在1 E 2259+586中发现了仅在2002年大爆发后$\sim$ 2年的限带红噪声。除此之外，系统没有显示出宽带噪声。虽然1 E 2259+586中的噪声上升发生在包括旋转毛刺的爆发之后，但其他毛刺AXP显示宽带噪声没有明显变化，因此该噪声似乎与毛刺无关。唯一显示出宽带噪声显著变化的源是1 E 1048.1-5937，其中噪声以每年$\sim$ 3.6%的速率逐渐上升1.95年。对于这个源的宽带噪声的增加是不相关的持续性和脉冲流量的大幅增加，或其两个短SGR样的爆发。这种噪声的上升确实是在一个长脉冲群之后开始的，但是考虑到该事件的稀疏性，以及类似脉冲群未被注意到的可能性，1 E 1048.1-5937中的噪声上升触发因素不像1 E 2259+586那样明确。其他三个源表明，相比之下，持续的低电平带限噪声。
Emission of two short hard X-ray bursts on 2009 June 5 disclosed the existence of a new soft gamma-ray repeater, now catalogued as SGR 0418+5729. After a few days, X-ray pulsations at a period of 9.1 s were discovered in its persistent emission. SGR 0418+5729 was monitored almost since its discovery with the Rossi X-ray Timing Explorer (2-10 keV energy range) and observed many times with Swift (0.2-10 keV). The source persistent X-ray emission faded by a factor 10 in about 160 days, with a steepening in the decay about 19 days after the activation. The X-ray spectrum is well described by a sim…
X-ray timing properties of the magnetar SGR 1900+14 were studied, using the data taken with Suzaku in 2009 and NuSTAR in 2016, for a time lapse of 114 ks and 242 ks, respectively. On both occasions, the object exhibited the characteristic two-component spectrum. The soft component, dominant in energies below $\sim 5$ keV, showed a regular pulsation, with a period of $P=5.21006$ s as determined with the Suzaku XIS, and $P=5.22669$ with NuSTAR. However, in $\gtrsim 6$ keV where the hard component dominates, the pulsation became detectable with the Suzaku HXD and NuSTAR, only after the data were …
The recent discovery of a Galactic fast radio burst (FRB) associated with a hard X-ray burst from the soft gamma-ray repeater (SGR) J1935+2154 has established the magnetar origin of at least some FRBs. In this work, we study the statistical properties of soft gamma-/hard X-ray bursts from SGRs 1806--20 and J1935+2154 and of radio bursts from the repeating FRB 121102. For SGRs, we show that the probability density functions for the differences of fluences, fluxes, and durations at different times have fat tails with a $q$-Gaussian form. The $q$ values in the $q$-Gaussian distributions are appro…
We exploited the high sensitivity of the INTEGRAL IBIS/ISGRI instrument to study the persistent hard X-ray emission of the soft gamma-ray repeater SGR 1900+14, based on ~11.6 Ms of archival data. The 22-150 keV INTEGRAL spectrum can be well fit by a power law with photon index 1.9 +/- 0.3 and flux F_x = (1.11 +/- 0.17)E-11 erg/cm^2/s (20-100 keV). A comparison with the 20-100 keV flux measured in 1997 with BeppoSAX, and possibly associated with SGR 1900+14, shows a luminosity decrease by a factor of ~5. The slope of the power law above 20 keV is consistent within the uncertainties with that of…
Studies were made of the 1-70 keV persistent spectra of fifteen magnetars as a complete sample observed with Suzaku from 2006 to 2013. Combined with early NuSTAR observations of four hard X-ray emitters, nine objects showed a hard power-law emission dominating at $\gtrsim$10 keV with the 15--60 keV flux of $\sim$1-$11\times 10^{-11}$ ergs s$^{-1}$ cm$^{-2}$. The hard X-ray luminosity $L_{\rm h}$, relative to that of a soft-thermal surface radiation $L_{\rm s}$, tends to become higher toward younger and strongly magnetized objects. Updated from the previous study, their hardness ratio, defined …
We examine an external trigger mechanism that gives rise to the intense soft gamma-ray repeater (SGR) giant flares. Out of the three giant flares, two showcased the existence of a precursor, which we show to have had initiated the main flare. We develop a reconnection model based on the hypothesis that shearing motion of the footpoints causes the materialization of a Sweet-Parker current layer in the magnetosphere. The thinning of this macroscopic layer due to the development of an embedded super-hot turbulent current layer switches on the impulsive Hall reconnection, which powers the giant fl…
We present the results from the analysis of the broad-band X-ray spectra of 5 Anomalous X-ray Pulsars (AXPs) and Soft $γ$-ray Repeaters (SGRs). We fit their Suzaku and INTEGRAL spectra with models appropriate for the X-ray emission from the accretion flow onto a pulsar. We find that their X-ray spectra can be well described with this model. In particular we find that: (a) the radius of the accretion column is $\sim150-350$ m resulting in a transverse optical depth of $\sim 1$; (b) the vertical Thompson optical depth is $\approx 50-400$, and (c) their luminosity translates in accretion rates $\…
We show that the period clustering of anomalous X-ray pulsars (AXPs) and soft gamma-ray repeaters (SGRs), their X-ray luminosities, ages and statistics can be explained with fallback disks with large initial specific angular momentum. The disk evolution models are developed by comparison to self-similar analytical models. The initial disk mass and angular momentum set the viscous timescale. An efficient torque, with (1 - w^2) dependence on the fastness parameter w leads to period clustering in the observed AXP-SGR period range under a wide range of initial conditions. The timescale t_0 for the…
We calculate the diffuse high energy (TeV - PeV) neutrino emission from hyperflares of Soft-Gamma Repeaters (SGRs), like the hyperflare risen from \astrobj{SGR 1806-20} on December 27 of 2004, within the framework of the fireball model. The fireball model for gamma-ray bursts (GRBs) can explain well the main features of this hyperflare and the subsequent multi-frequency terglow emission. The expected rate, $\sim 20-100$ Gpc$^{-3}$day$^{-1}$, of such hyperflares is well in excess of the GRBs rate. Our result shows that the contribution to the diffuse TeV-PeV neutrino background from such hyperf…
Since its initial discovery, the Fast radio burst (FRB) FRB 121102 has been found to be repeating with millisecond-duration pulses. Very recently, 15 new bursts were detected by the Green Bank Telescope (GBT) during its continous monitoring observations. In this letter, we show that the burst energy distribution has a power law form which is very similar to the Gutenberg-Richter law of earthquakes. In addition, the waiting time of the burst has a Gaussian distribution, which is also a distinctive feature of earthquakes. These findings suggest that the repeating FRB pulses may originate from th…
We revisit the apparent correlation between soft X-ray band photon index and spin-down rate nudot previously reported for Anomalous X-ray Pulsars (AXPs) and Soft Gamma Repeaters (SGRs) by Marsden & White (2001). Our analysis, improved thanks to new source discoveries, better spectral parameter measurements in previously known sources, and the requirement of source quiescence for parameter inclusion, shows evidence for the previously noted trend, although with greater scatter. This trend supports the twisted magnetosphere model of magnetars although the scatter suggests that factors other than …
We study the fluence distributions of over 3040 bursts from SGR 1806-20 and over 1963 bursts from SGR 1900+14 using the complete set of observations available from the Rossi X-Ray Timing Explorer/Proportional Counter Array through March 2011. Cumulative event distributions are presented for both sources and are fitted with single and broken power laws as well as an exponential cutoff. The distributions are best fit by a broken power law with exponential cutoff, however the statistical significance of the cutoff is not high and the upper portion of the broken power law can be explained as the e…
In the fallback disk model for the persistent emission of Anomalous X-ray pulsars (AXPs) and soft gamma-ray repeaters (SGRs), the hard X-ray emission arises from bulk- and thermal Comptonization of bremsstrahlung photons, which are generated in the accretion column. The relatively low X-ray luminosity of these sources implies a moderate transverse optical depth to electron scattering, with photons executing a small number of shock crossings before escaping sideways. We explore the range of spectral shapes that can be obtained with this model and characterize the most important parameter depend…
SGR 0418+5729 is a transient Soft Gamma-ray Repeater which underwent a major outburst in June 2009, during which the emission of short bursts was observed. Its properties appeared quite typical of other sources of the same class until long-term X-ray monitoring failed to detect any period derivative. The present upper limit on $\dot P$ implies that the surface dipole field is $B_p\lesssim 7.5\times 10^{12}\ {\rm G}$ (Rea et al 2010), well below those measured in other Soft Gamma-ray Repeaters (SGRs) and in the Anomalous X-ray Pulsars (AXPs), a group of similar sources. Both SGRs and AXPs are c…
Several observations obtained in the last few years indicate that Soft Gamma-ray Repeaters (SGRs) and Anomalous X-ray Pulsars (AXPs) are basically a single class of isolated neutron stars. Their properties are well explained by the magnetar model, based on neutron stars powered by magnetic fields as high as 10^14 -10^15 G. Here I report some recent results obtained for the transient Soft Gamma-ray Repeater SGR 1627-41, that started a new outburst after about 10 years from the previous one, and for the Anomalous X-ray Pulsar 1E 1547.0-5408. The latter source recently showed a remarkable burstin…
SGR 1833-0832 was discovered on 2010 March 19 thanks to the Swift detection of a short hard X-ray burst and follow-up X-ray observations. Since then, it was repeatedly observed with Swift, Rossi X-ray Timing Explorer, and XMM-Newton. Using these data, which span about 225 days, we studied the long-term spectral and timing characteristics of SGR 1833-0832. We found evidence for diffuse emission surrounding SGR 1833-0832, which is most likely a halo produced by the scattering of the point source X-ray radiation by dust along the line of sight, and we show that the source X-ray spectrum is well d…
Soft gamma-ray repeaters and anomalous X-ray pulsars are a small (but growing) group of X-ray sources characterized by the emission of short bursts and by a large variability in their persistent flux. They are believed to be magnetars, i.e. neutron stars powered by extreme magnetic fields 1E14-1E15 G). We found evidence for a magnetar with a low magnetic field, SGR 0418+5729, recently detected after it emitted bursts similar to those of soft gamma-ray repeaters. New X-ray observations show that its dipolar magnetic field cannot be greater than 8E12 G, well in the range of ordinary radio pulsar…
The soft gamma-ray repeater candidate SGR 0755$-$2933 was discovered in 2016 by Swift/BAT, which detected a short ($\sim$30 ms) powerful burst typical of magnetars. To understand the nature of the source, we present here an analysis of follow-up observations of the tentative soft X-ray counterpart of the source obtained with Swift/XRT, NuSTAR and Chandra. From our analysis we conclude that, based on the observed counterpart position and properties, it is actually not a soft gamma ray repeater but rather a new high mass X-ray binary. We suggest to refer to it as 2SXPS J075542.5$-$293353. We con…
The statistical properties of the soft gamma repeater SGR J1550--5418 are investigated carefully. We find that the cumulative distributions of fluence, peak flux and duration can be well fitted by a bent power law, while the cumulative distribution of waiting time follows a simple power law. In particular, the probability density functions of fluctuations of fluence, peak flux, and duration have a sharp peak and fat tails, which can be well fitted by a $q$-Gaussian function. The $q$ values keep approximately steady for different scale intervals, indicating a scale-invariant structure of soft g…
We study the statistical properties of the soft gamma repeater SGR 1935+2154. We find that the cumulative distributions of duration, waiting time, fluence and flux can be well fitted by bent power law. In addition, the probability density functions of fluctuations of duration, waiting time, fluence and flux well follow the Tsallis $q$-Gaussian distribution. The $q$ values keep steady for different temporal scale intervals, indicating a scale-invariant structure of the bursts. Those features are very similar to the property of the repeating fast radio burst FRB 121102, indicating the underlying…
Gamma-ray Bursts (GRBs) are bursts of $γ$-rays generated from relativistic jets launched from catastrophic events such as massive star core collapse or binary compact star coalescence. Previous studies suggested that GRB emission is erratic, with no noticeable memory in the central engine. Here we report a discovery that similar light curve patterns exist within individual bursts for at least some GRBs. Applying the Dynamic Time Warping (DTW) method, we show that similarity of light curve patterns between pulses of a single burst or between the light curves of a GRB and its X-ray flare can be …
Soft gamma repeaters and anomalous X-ray pulsars are believed to be magnetars, i.e. neutron stars powered by extreme magnetic fields, B~10^(14)-10^(15) Gauss. The recent discovery of a soft gamma repeater with low magnetic field (< 7.5x10^(12) Gauss), SGR 0418+5729, which shows bursts similar to those of SGRs, implies that a high surface dipolar magnetic field might not be necessary for magnetar-like activity. We show that the quiescent and bursting properties of SGR 0418+5729 find natural explanations in the context of low-magnetic field Quark-Nova (detonative transition from a neutron star t…
There are insufficient catastrophic events (collapse, explosion or merger of stars or compact objects) to explain the cosmologically local rate of apparently non-repeating FRB if each such catastrophic event produces a single FRB. Unless produced by some novel and unsuspected but comparatively frequent event, apparently non-repeating FRB must actually repeat many times in the lifetimes of their sources. Yet no such infrequent repetitions (in contrast to the frequent activity of FRB known to repeat) have been observed, constraining their repetition rates and active lifetimes. The absence of mor…
This paper reports the analysis procedure and results of simultaneous spectral fits of the Suzaku archive data for Sagittarius (Sgr) A East and the nearby Galactic center X-ray emission (GCXE). The results are that the mixed-morphology supernova remnant Sgr A East has a recombining plasma (RP) with Cr and Mn He$α$ lines, and a power-law component (PL) with an Fe I K$α$ line. The nearby GCXE has a $\sim$1.5-times larger surface brightness than the mean GCXE far from Sgr A East, although the spectral shape is almost identical. Based on these results, we interpret that the origins of the RP and t…
We have analyzed the long-term evolution and the X-ray outburst light curve of SGR 0501+4516 in the frame of the fallback disc model. We have shown that the X-ray luminosity, period and period derivative of this typical soft gamma repeater can be achieved by a neutron star with a large range of initial disc masses provided that the source has a magnetic dipole field of ~ 1.4 x 10^{12} G on the pole of the star. At present, the star is accreting matter from the disc, which has an age ~ 3 x 10^4 yr, and will remain in the accretion phase until t ~ 2 - 5 x 10^5 yr depending on the initial disc ma…
The recent discovery of the "weak field, old magnetar", the soft gamma repeater SGR 0418+5729, whose dipole magnetic field is less than 7.5 \times 10^{12} G, has raised perplexing questions: How can the neutron star produce SGR-like bursts with such a low magnetic field? What powers the observed X-ray emission when neither the rotational energy nor the magnetic dipole energy are sufficient? These observations, that suggest either a much larger energy reservoir or a much younger true age (or both), have renewed the interest in the evolutionary sequence of magnetars. We examine, here, a phenomen…
Fast radio bursts (FRB) are enigmatic powerful single radio pulses with durations of several milliseconds and high brightness temperatures suggesting coherent emission mechanism. For the time being a number of extragalactic FRBs have been detected in the high-frequency radio band including repeating ones. The most plausible explanation for these phenomena is magnetar hyperflares. The first observational evidence of this scenario was obtained in April 2020 when an FRB was detected from the direction of the Galactic magnetar and soft gamma repeater SGR1935+2154. The FRB was preceded with a numbe…
We report on recent results obtained thanks to Target of Opportunity observations of the two galactic sources SGR 1627-41 and 1E 1547-5408. These two transient sources present several similarities which support the interpretation of Anomalous X-ray Pulsars and Soft Gamma-ray Repeaters as a single class of strongly magnetized neutron stars.
We report on the results from our deep Chandra observation (120 ks) of the supernova remnant (SNR) N49 and soft Gamma-ray repeater (SGR) 0526-66 in the Large Magellanic Cloud. We firmly establish the detection of an ejecta "bullet" beyond the southwestern boundary of N49. The X-ray spectrum of the bullet is distinguished from that of the main SNR shell, showing significantly enhanced Si and S abundances. We also detect an ejecta feature in the eastern shell, which shows metal overabundances similar to those of the bullet. If N49 was produced by a core-collapse explosion of a massive star, the …
A close high-mass binary system consisting of a neutron star (NS) and a massive OB supergiant companion is expected to lead to a TZO structure, which consists of a NS core and a stellar envelope. We use the scenario machine program to calculate the formation tracks of TZOs in close high mass NS binaries and their subsequent evolution. We propose and demonstrate that the explosion and instant contraction of a TZO structure leave its stellar remnant as a soft gamma ray repeater and an anomalous X-ray pulsar respectively.
We analyzed temporal and spectral properties, focusing on the short bursts, for three anomalous X-ray pulsars (AXPs) and soft gamma repeaters (SGRs), including SGR 1806-20, 1E 1048-5937 and SGR 0501+4516. Using the data from XMM-Newton, we located the short bursts by Bayesian blocks algorithm. The short bursts' duration distributions for three sources were fitted by two lognormal functions. The spectra of shorter bursts ($< 0.2~\rm s$) and longer bursts ($\geq 0.2~\rm s$) can be well fitted in two blackbody components model or optically thin thermal bremsstrahlung model for SGR 0501+4516. We a…
The discovery of quasi-periodic oscillations (QPOs) in magnetar giant flares has opened up prospects for neutron star asteroseismology. The scarcity of giant flares makes a search for QPOs in the shorter, far more numerous bursts from Soft Gamma Repeaters (SGRs) desirable. In Huppenkothen et al (2013), we developed a Bayesian method for searching for QPOs in short magnetar bursts, taking into account the effects of the complicated burst structure, and have shown its feasibility on a small sample of bursts. Here, we apply the same method to a much larger sample from a burst storm of 286 bursts …
Soft gamma repeaters and anomalous x-ray pulsars form a rapidly increasing group of x-ray sources exhibiting sporadic emission of short bursts. They are believed to be magnetars, i.e. neutron stars powered by extreme magnetic fields, B~10^{14}-10^{15} Gauss. We report on a soft gamma repeater with low magnetic field, SGR 0418+5729, recently detected after it emitted bursts similar to those of magnetars. X-ray observations show that its dipolar magnetic field cannot be greater than 7.5x10^{12} Gauss, well in the range of ordinary radio pulsars, implying that a high surface dipolar magnetic fiel…
