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Register a new userTen years of INTEGRAL observations of the hard X-ray emission from SGR 1900+14
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L. Ducci
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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 SGR 1806-20, the other persistent soft gamma-ray repeater for which a hard X-ray emission extending up to 150 keV has been reported.
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The International Gamma-Ray Astrophysics Laboratory (INTEGRAL) continues to successfully work in orbit after its launch in 2002. The mission provides the deepest ever survey of hard X-ray sources throughout the Galaxy at energies above 20 keV. We report on a catalogue of new hard X-ray source candidates based on the latest sky maps comprising 14 years of data acquired with the IBIS telescope onboard INTEGRAL in the Galactic Plane (|b|<17.5 deg). The current catalogue includes in total 72 hard X-ray sources detected at S/N>4.7 sigma and not known to previous INTEGRAL surveys. Among them, 31 objects have also been detected in the on-going all-sky survey by the BAT telescope of the Swift observatory. For 26 sources on the list, we suggest possible identifications: 21 active galactic nuclei, two cataclysmic variables, two isolated pulsars or pulsar wind nebulae, and one supernova remnant; 46 sources from the catalogue remain unclassified.
After nearly two years of quiescence, the soft gamma-ray repeater SGR 1900+14 again became burst-active on April 18 2001, when it emitted a large flare, preceded by few weak and soft short bursts. After having detected the X and gamma prompt emission of the flare, BeppoSAX pointed its narrow field X-ray telescopes to the source in less than 8 hours. In this paper we present an analysis of the data from this and from a subsequent BeppoSAX observation, as well as from a set of RossiXTE observations. Our data show the detection of an X-ray afterglow from the source, most likely related to the large hard X-ray flare. In fact, the persistent flux from the source, in 2-10 keV, was initially found at a level $sim$5 times higher than the usual value. Assuming an underlying persistent (constant) emission, the decay of the excess flux can be reasonably well described by a t$^{-0.9}$ law. A temporal feature - a $sim$half a day long bump - is observed in the decay light curve approximately one day after the burst onset. This feature is unprecedented in SGR afterglows. We discuss our results in the context of previous observations of this source and derive implications for the physics of these objects.
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 $E_{rot}sim 10^{52}textrm{ erg}$.
We report on the X-ray spectral properties of 10 short bursts from SGR1900+14 observed with the Narrow Field Instruments onboard BeppoSAX in the hours following the intermediate flare of 2001 April 18. Burst durations are typically shorter than 1 s, and often show significant temporal structure on time scales as short as $sim$10 ms. Burst spectra from the MECS and PDS instruments were fit across an energy range from 1.5 to above 100 keV. We fit several spectral models and assumed Nh values smaller than 5$times 10^{22}$ cm$^{-2}$, as derived from observations in the persistent emission. Our results show that the widely used optically thin thermal bremsstrahlung law provides acceptable spectral fits for energies higher than 15 keV, but severely overestimated the flux at lower energies. Similar behavior had been observed several years ago in short bursts from SGR 1806-20, suggesting that the rollover of the spectrum at low energies is a universal property of this class of sources. Alternative spectral models - such as two blackbodies or a cut-off power law - provide significantly better fits to the broad band spectral data, and show that all the ten bursts have spectra consistent with the same spectral shape.
Spectral and timing studies of Suzaku ToO observations of two SGRs, 1900+14 and 1806-20, are presented. The X-ray quiescent emission spectra were well fitted by a two blackbody function or a blackbody plus a power law model. The non-thermal hard component discovered by INTEGRAL was detected by the PIN diodes and its spectrum was reproduced by the power law model reported by INTEGRAL. The XIS detected periodicity P = 5.1998+/-0.0002 s for SGR 1900+14 and P = 7.6022+/-0.0007 s for SGR 1806-20. The pulsed fraction was related to the burst activity for SGR 1900+14.
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