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تسجيل مستخدم جديدDiscovery of a magnetar associated with the Soft Gamma Repeater SGR 1900+14
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The soft-gamma repeater SGR 1900+14 became active again on June 1998 after a long period of quiescence; it remained at a low state of activity until August 1998, when it emitted a series of extraordinarily intense outbursts. We have observed the source with RXTE twice, during the onset of each active episode. We confirm the pulsations at the 5.16 s period reported earlier (Hurley et al. 1998b, Hurley et al. 1998 e) from SGR 1900+14. Here we report the detection of a secular spindown of the pulse period at an average rate of 1.1*10^{-10} s/s. In view of the strong similarities between SGRs, we attribute the spindown of SGR 1900+14 to magnetic dipole radiation, possibly accelerated by a quiescent flux, as in the case of SGR 1806-20 (Kouveliotou et al. 1998a). This allows an estimate of the pulsar dipolar magnetic field, which is 2-8*10^{14} G. Our results confirm that SGRs are magnetars.
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We present a systematic analysis of all the BeppoSAX data of SGR1900+14. The observations spanning five years show that the source was brighter than usual on two occasions: ~20 days after the August 1998 giant flare and during the 10^5 s long X-ray a
fterglow following the April 2001 intermediate flare. In the latter case, we explore the possibility of describing the observed short term spectral evolution only with a change of the temperature of the blackbody component. In the only BeppoSAX observation performed before the giant flare, the spectrum of the SGR1900+14 persistent emission was significantly harder and detected also above 10 keV with the PDS instrument. In the last BeppoSAX observation (April 2002) the flux was at least a factor 1.2 below the historical level, suggesting that the source was entering a quiescent period.
The Soft Gamma Repeater SGR 1900+14 entered a remarkable phase of activity during the summer of 1998. This activity peaked on August 27, 1998 when a giant periodic gamma-ray flare resembling the famous March 5, 1979 event from SGR 0526-66 was recorde
d. Two days later (August 29), a strong, bright burst was detected with RXTE and BATSE. This event reveals several similarities to the giant flares of August 27 and March 5, and shows a number of unique features not previously seen in SGR bursts. Unlike typically short SGR bursts, this event features a 3.5 s burst peak that was preceded by an extended (~ 1 s) complex precursor, and followed by a long (~ 1000 s) periodic tail modulated at the 5.16 s stellar rotation period. Spectral analysis shows a striking distinction between the spectral behavior of the precursor, burst peak and extended tail. While the spectrum during the peak is uniform, a significant spectral evolution is detected in both the precursor and tail emissions. Temporal behavior shows a sharp rise (~ 9.8 ms) at the event onset and a rapid cutoff (~ 17 ms) at the end of the burst peak. The tail pulsations show a simple pulse profile consisting of one 5.16 s peak that did not evolve with time. The spectral and temporal signatures of this event imply that the precursor, main peak, and extended tail are produced by different physical mechanisms. We discuss these features and their implications in the context of the magnetar model. The energetics of the August 29 event, and its close proximity to the August 27 flare, suggest that it is an `aftershock of the preceding giant flare. P.S. This is an abbreviated version of the original abstract.
Magnetars are a special class of slowly rotating neutron stars with extremely strong magnetic fields -- at least an order of magnitude larger than those of the normal radio pulsars. The potential evolutionary links and differences between these two t
ypes of objects are still unknown; recent studies, however, have provided circumstantial evidence connecting magnetars with very massive progenitor stars. Here we report the discovery of an infrared elliptical ring or shell surrounding the magnetar SGR 1900+14. The appearance and energetics of the ring are difficult to interpret within the framework of the progenitors stellar mass loss or the subsequent evolution of the supernova remnant. We suggest instead that a dust-free cavity was produced in the magnetar environment by the giant flare emitted by the source in August 1998. Considering the total energy released in the flare, the theoretical dust--destruction radius matches well with the observed dimensions of the ring. We conclude that SGR 1900+14 is unambiguously associated with a cluster of massive stars, thereby solidifying the link between magnetars and massive stars.
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 bur
sts 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 and the localization of this new SGR, and our infrared and Chandra X-ray observations. We also present a detailed temporal and spectral study of the two GBM bursts. SGR J0418+5729 is the second source discovered in the same region of the sky in the last year, the other one being SGR J0501+4516. Both sources lie in the direction of the galactic anti-center and presumably at the nearby distance of ~2 kpc (assuming they reside in the Perseus arm of our galaxy). The near-threshold GBM detection of bursts from SGR J0418+5729 suggests that there may be more such dim SGRs throughout our galaxy, possibly exceeding the population of bright SGRs. Finally, using sample statistics, we conclude that the implications of the new SGR discovery on the number of observable active magnetars in our galaxy at any given time is <10, in agreement with our earlier estimates.
Magnetar wind nebulae (MWNe), created by new-born millisecond magnetars, and magnetar giant flares are PeVatron candidates and even potential sources of ultra high energy ($E>10^{18} textrm{ eV}$) cosmic rays (UHECRs). Nonthermal high-energy (HE, $E>
100 textrm{ MeV}$) and very high-energy (VHE, $E>100 textrm{ GeV}$) $gamma$-ray emission from magnetars neighbourhoods should be a promising signature of acceleration processes. We investigate a possibility of explaining HE and VHE $gamma$-ray emission from the vicinity of the magnetar SGR 1900+14 by cosmic rays accelerated in a Supernova remnant of a magnetar-related Supernova and/or in a MWN. Simulation of the observed HE (the extended Fermi-LAT source 4FGL J1908.6+0915e) and VHE (the extended H.E.S.S. source candidate HOTS J1907+091 and the point-like HAWC TeV source 3HWC J1907+085) $gamma$-ray emission, spatially coincident with the magnetar SGR 1900+14, was carried out in the framework of hadronic (pp collisions with a subsequent pion decay) and leptonic (inverse Compton scattering of low energy background photons by ultrarelativistic electrons) models. We show that under reasonable assumptions about parameters of the circumstellar medium the observed $gamma$-ray emission of Fermi-LAT 4FGL J1908.6+0915e, H.E.S.S. HOTSJ1907+091 and 3HWC J1907+085 sources may be explained or at least considerably contributed by a (still undetected) magnetar-connected Hypernova remnant and/or a MWN created by new-born millisecond magnetar with a large reserve of rotational energy $E_{rot}sim 10^{52}textrm{ erg}$.
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