Artikel zu "SGR1806-20 (I)"

(II)

(III)

(IV)

(V)

(MIV)

Magnetar (MIV)

SGR1806-20: detection of 7.5 second pulsations
MAGNETAR concept - Robert C. Duncan
Magnetare:- I (SGR & AXP) - II (Neutronensterne & Pulsare) -
All Magnetars more
K1 Bizarrer Stern besitzt Rekord-Magnetfeld
K1.2 Strahlenausbruch eines Sterns trifft die Erde
K2 Massive Stars in the SGR 1806-20 Cluster
K3 Artikel (I) zu "A tremendous flare from SGR1806-20"
K3.1 SGR 1806-20 and Its Compton Reflection from the Moon
K4 NASA Observes One of the Brightest Cosmic Explosions
K5.1 Artikel (II) zu "A tremendous flare from SGR1806-20"
K5.2 The distance of the 1806-20 cluster

Giant Burst Energies & Fluencies — :
SGR1806-20 : E_burst= 4 × 10⁴⁶ erg
flux F_ph = 10⁷ photons·cm^-2s^-1
fluence f_ph = 3.5 erg cm^-2 .
SGR0526-66: E_burst= 6 × 10⁴⁴ erg
SGR1900+14 : E_burst= 2 × 10⁴⁴ erg
animation: (Swift satellite and VLA)
Cosmic Explosion the Brightest in Recorded History
Literatur

SGR1806-20 (I)

Multiwavelength views: The 27 Dec 2004 flare from SGR1806-20
Image credit & Copyright: Robert Mallozzi (UAH) Galactic Magnetar Throws Giant Flare		Explanation [2005 February 21]: Was the brightest Galactic blast yet recorded a key to connecting two types of celestial explosions? Last December, a dense sheet of gamma rays only a few times wider than the Earth plowed through our Solar System, saturating satellites and noticeably reflecting off the Moon. A magnetar near our Galactic Center, the source of Soft Gamma Repeater (SGR) 1806-20, had unleashed its largest flare on record. The brightness and briefness of the tremendous explosion's initial peak made it look quite similar to another type of tremendous explosion if viewed from further away -- a short duration gamma-ray burst (GRB). Short duration GRBs are thought by many to be fundamentally different than their long duration GRB cousins that are likely related to distant supernovas. Illustrated above is a series of drawings depicting an outgoing explosion during the initial SGR spike. A fast moving wave of radiation is pictured shooting away from a central magnetar. The possible link between SGRs and GRBs should become better understood as more and similar events are detected by the Earth-orbiting Swift satellite.

K1 Bizarrer Stern besitzt Rekord-Magnetfeld

RXTE — 5.0 keV absorption line — B_s = 1.0x10¹⁵ G
	Authors: A.I. Ibrahim, S. Safi-Harb, J.H. Swank, W. Parke, S. Zane and R. Turolla
	Journal-ref: ApJ 574 (2002) L51 [astro-ph/0210513 ]
	Title: Discovery of Cyclotron Resonance Features in the Soft Gamma Repeater SGR 1806-20
Abstract: We report evidence of cyclotron resonance features from the Soft Gamma Repeater SGR 1806-20 in outburst, detected with the Rossi X-ray Timing Explorer in the spectrum of a long, complex precursor that preceded a strong burst. The features consist of a narrow 5.0 keV absorption line with modulation near its second and third harmonics (at 11.2 keV and 17.5 keV respectively). The line features are transient and are detected in the harder part of the precursor. The 5.0 keV feature is strong, with an equivalent width of ~ 500 eV and a narrow width of less than 0.4 keV. Interpreting the features as electron cyclotron lines in the context of accretion models leads to a large mass-radius ratio (M/R > 0.3 M_sun/km) that is inconsistent with neutron stars or that requires a low (5-7)x10¹¹ G magnetic field that is unlikely for SGRs. The line widths are also narrow compared with those of electron cyclotron resonances observed so far in X-ray pulsars. In the magnetar picture, the features are plausibly explained as ion cyclotron resonances in an ultra-strong magnetic field that have recently been predicted from magnetar candidates. In this view, the 5.0 keV feature is consistent with a proton cyclotron fundamental whose energy and width are close to model predictions. The line energy would correspond to a surface magnetic field of B_s = 1.0x10¹⁵ G for SGR 1806-20, in good agreement with that inferred from the spin-down measure in the source.

SGR 1806-20 — First measurement of the gravitational redshift, mass and radius of a magnetar.
	Authors: Alaa I. Ibrahim, Jean H. Swank, William Parke
	Journal-ref: ApJ 584 (2003) L17-L22 [astro-ph/0210515 ]
	Title: New Evidence for Proton Cyclotron Resonance in a Magnetar Strength Field from SGR 1806-20
Abstract: A great deal of evidence has recently been gathered in favor of the picture that Soft Gamma Repeaters and Anomalous X-Ray Pulsars are powered by ultra-strong magnetic fields (B_s > 10¹⁴ G; i.e. magnetars). Nevertheless, present determination of the magnetic field in such magnetar candidates has been indirect and model dependent. A key prediction concerning magnetars is the detection of ion cyclotron resonance features, which would offer a decisive diagnostic of the field strength. Here we present the detection of a 5 keV absorption feature in a variety of bursts from the Soft Gamma Repeater SGR 1806-20, confirming our initial discovery (Ibrahim et al. 2002) and establishing the presence of the feature in the source's burst spectra. The line feature is well explained as proton cyclotron resonance in an ultra-strong magnetic field, offering a direct measurement of SGR 1806-20's magnetic field (B_s ~ 10¹⁵ G) and a clear evidence of a magnetar. Together with the source's spin-down rate, the feature also provides the first measurement of the gravitational redshift, mass and radius of a magnetar.

Kosmischer Kraftprotz
Astronomen haben das stärkste bislang bekannte Magnetfeld im Universum nachgewiesen. Urheber ist eine seltsame, von gewaltigen Beben erschütterte Sternenleiche.

Sie sind nur wenige Kilometer groß, extrem kompakt und besitzen vor allem ein ungeheuer starkes Magnetfeld: So genannte Magnetare zählen zu den exotischsten Objekten im Universum. Höchstens zehn solcher seltsamen Sternenleichen sind den Astronomen überhaupt bekannt, und ihre magnetischen Eigenschaften konnten bislang bloß indirekt bestimmt werden.
Jetzt ist es einem Forscherteam gelungen, das Feld eines solchen Monster-Magneten zu messen. Die Wissenschaftler um Alaa Ibrahim von der George Washington University haben energiereiche Strahlungsblitze analysiert, die von einer Quelle namens SGR 1806-20 im Sternbild Schütze ausgesandt wurden. Dieses Himmelsobjekt hatten Astrophysiker erst vor wenigen Jahren als Magnetar entlarvt.

Robert Mallozzi/ UA

Magnetar (Illustration): Stellare Beben in der Trümmerwolke

Aus Beobachtungen mit dem Nasa-Röntgensatelliten "Rossi X-ray Timing Explorer" konnten Ibrahim und seine Kollegen auf die magnetische Kraft von SGR 1806-20 schließen. Nach den Berechnungen der Forscher muss die Sternenleiche ein rund hundert Milliarden Tesla starkes Feld aufweisen. Zum Vergleich: Das Magnetfeld der Erde beträgt um die 50 Mikrotesla, das Feld weißer Zwerge erreicht etwa 30 k Tesla.
Damit besitzt der kosmische Kraftprotz das stärkste bislang bekannte Magnetfeld im Universum. Zudem übertrifft der jetzt ermittelte Wert deutlich die bisherigen Schätzungen. "Wenn sich dieser Magnetar so nah an der Erde befände wie der Mond, würde er die Moleküle in unserem Körper neu anordnen", erklärt Ibrahim. Glücklicherweise liegt SGR 1806-20 aber einige zehntausend Lichtjahre entfernt.
Bemerkbar gemacht hatten sich die merkwürdigen Objekte schon vor über 20 Jahren. Erstmals fielen sie 1979 auf, als mehrere Satelliten zeitgleich einen energiereichen Blitz im so genannten weichen Gammabereich registrierten. Nach und nach konnten die unregelmäßig auftretenden Strahlungsgewitter einzelnen Quellen zugeordnet werden. Die Wiederholungstäter erhielten den Namen "Soft Gamma-ray Repeater" (SGR).
Wie sich herausstellte, stimmt die Position von SGR 1806-20 mit der eines Supernova-Überrestes überein. Solche Trümmerwolken entstehen, wenn ein massiver Stern am Ende seiner Laufbahn explodiert. Während seine Hülle nach außen schießt, kann der Kern zu einem kompakten Neutronenstern kollabieren. Es war also wahrscheinlich, dass die Gammablitze von einer bizarren Unterart solcher Sternenleichen ausgesandt wurden.
Als Erklärung für die Ausbrüche schlugen Theoretiker 1992 die Existenz von Neutronensternen mit einem enormen Magnetfeld vor - das Magnetar-Modell war geboren. Die unvorstellbaren Kräfte würden, so die These, immer wieder die Oberfläche der rotierenden Sternenleiche aufreißen. Das bei solchen stellaren Beben herausgeschleuderte und im Magnetfeld gefangene Plasma könnte die beobachteten weichen Gammablitze hervorrufen.
Eine Bestätigung dieser Theorie ließ bis 1998 auf sich warten. Beim Vergleich verschiedener Strahlungsschübe von SGR 1806-20 stellten Forscher fest, dass sich ein regelmäßiges Pulsen im Nachleuchten der Ausbrüche über Jahre leicht verlangsamt hatte. Offensichtlich bremste tatsächlich ein gewaltiges Magnetfeld die Rotation des Neutronensterns. Dieses müsse, so die damalige indirekte Schätzung, in der Größenordnung von zehn Milliarden Tesla liegen.
Der direktere Nachweis gelang jetzt Ibrahim und Kollegen: Sie entdeckten im Spektrum der Ausbrüche von SGR 1806-20 verdächtige Dellen. Diese entstehen nach Ansicht der Wissenschaftler durch Protonen, die bei einem Beben des Magnetars freigesetzt und durch das immense Magnetfeld auf spiralförmige Bahnen gezwungen werden. Die von den Forschern gefundenen Merkmale entsprechen genau der Energie, die solche geladenen Teilchen in einem Feld von hundert Milliarden Tesla absorbieren würden.
Von dieser Messmethode erhofft sich das Team, dessen Ergebnisse in den "Astrophysical Journal Letters" erschienen sind, weitere Aufschlüsse über die noch kaum erforschten Magnetare. "Niemand würde solchen Objekten gerne nahe kommen", sagt Ibrahim. "Wir haben jetzt aber einen Weg gefunden, um aus der Ferne die Physik von Materie zu studieren, die sich unter dem Einfluss extremer Gravitation und enormen magnetischen Kräften befindet."

K1.2 SGR 1806-20 : Strahlenausbruch eines Sterns trifft die Erde

Image credit: RHESSI / Wind / Hurley et al.

Figure 1a.
RHESSI germanium detector data for the 27 December 2004 giant flare.
20-100 keV time history plotted with 0.5 s resolution. Zero seconds saturated the detectors within 1 ms . The detectors emerged from saturation on the falling edge 200 ms later and remained unsaturated after that.
The amplitude variations in the oscillatory phase appear to be real, and are not caused by any known instrumental effect.
Inset: time history of the precursor with 8 ms resolution.

Die Erde ist am 27. Dezember 2004 um halb elf Uhr nachts von einem gewaltigen Gamma- und Röntgenstrahlen-Ausbruch getroffen worden. Der Grund: Ein Neutronenstern setzte in einer Zehntelsekunde mehr Energie frei als die Sonne in 100.000 Jahren. Ein Ereignis, das nur einmal in Hunderten von Jahren vorkommt.

Ihren Ursprung hatte die Strahlung in einem Neutronenstern in etwa 15 kpc Entfernung, wie mehrere Forschungsorganisationen auf der Welt jetzt mitteilten. Die Wellenfront war dabei intensiver als der stärkste jemals gemessene Strahlungsausbruch unserer Sonne, berichteten Astrophysiker am MPE in Garching.
Das Ereignis wurde von Radioteleskopen auf der ganzen Welt und Satelliten im All beobachtet. Forscher in Australien berichteten, die Riesenexplosion des Neutronensterns SGR 1806-20 habe ihn für eine Zehntelsekunde heller als den Vollmond gemacht. Er sei damit das hellste Objekt außerhalb unseres Sonnensystems, das je ermittelt worden sei. Die Strahlung beeinträchtigte kurzzeitig auch die obere Schicht der Erdatmosphäre, berichtete die US-Raumfahrtbehörde Nasa.
Der Neutronenstern, der wegen seiner besonderen Eigenschaften auch als Magnetar bezeichnet werde, habe in einer Zehntelsekunde mehr Energie freigesetzt als die Sonne in 100.000 Jahren.
So ein Ereignis gebe es nur einmal in hundert oder tausend Jahren, erklärte Bryan Gaensler vom Harvard-Smithsonian Zentrum für Astrophysik, der die Forschungen am australischen Radioteleskop CSIRO leitete. "Wäre das zehn Lichtjahre von uns entfernt passiert, dann hätte es die Atmosphäre schwer beschädigt und möglicherweise zu einem Massensterben geführt. Glücklicherweise gibt es keine Neutronensterne in unserer Nähe." Der nächste bekannte Neutronenstern, der AXP 1E 2259+586, ist rund 4 kpc entfernt.
Unter den bekannten Millionen von Neutronensternen sind nur zwölf Magnetare. Neutronensterne sind eingestürzte Sonnen, die eine ungeheuer starke magnetische Strahlung, aber nur einen Durchmesser von rund 25 Kilometern haben.

K2 Massive Stars in the SGR 1806-20 Cluster

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	Authors: D.F. Figer, F. Najarro, T.R. Geballe, R.D. Blum, R.P. Kudritzki
	Journal-ref: ApJ 622 (2005) L49-L52 [astro-ph/0501560 ]
	Title: Massive Stars in the SGR 1806-20 Cluster
Abstract: We report the discovery of additional hot and massive stars in the cluster surrounding the soft gamma repeater SGR 1806-20, based upon UKIRT and Keck near-infrared spectroscopy. Of the newly identified stars, three are Wolf-Rayet stars of types WC8, WN6, and WN7, and a fourth star is an OB supergiant. These three stars, along with four previously discovered, imply a cluster age of ~3.0-4.5 Myr, based on the presence of WC stars and the absence of red supergiants. Assuming coevality, this age suggests that the progenitor of SGR 1806-20 had an initial mass greater than ~50 M. This is consistent with the suggestion that SGRs are post-supernovae end states of massive progenitors, and may suggest that only massive stars evolve into magnetars that produce SGRs. It also suggests that very massive stars can evolve into neutron stars, not just black holes, as recently predicted by theory. The cluster age also provides constraints on the very high mass object, LBV 1806-20. Massive stellar clusters are the birth sites of the most massive stars, and are proving grounds for theories of massive star formation, evolution, end states, and Galactic chemical enrichment. With the recent advent of sensitive infrared instrumentation, on ground and space based platforms, many massive clusters in the Galaxy are now just being discovered and investigated. At least two of these clusters contain soft gamma repeaters (SGRs), a rare phenomenon characterized by persistent and energetic bursts of gamma ray emission lasting up to several seconds and releasing ~ 10⁴⁰ erg s^-1 (Mazets, Golenetskij, & Guryan 1979; Mazets et al. 1979; Kouveliotou et al. 1998). Only four SGRs are known, three in the Galaxy and one in the SMC. Three of the SGRs are associated with massive stellar clusters. SGR 1806-20 is surrounded by a cluster of massive stars (Fuchs et al. 1999). Kulkarni et al. (1995) identified a luminous star that they claimed may be the infrared counterpart to SGR 1806-20, but Eikenberry et al. (2001) and Kaplan et al. (2002) determined that it is too far from the Chandra error box; no near-infrared counterpart has yet been found, even down to very faint magnitudes. van Kerkwijk et al. (1995) find that this star has characteristics similar to those of Luminous Blue Variables (LBVs), i.e. it has L > 10⁶M and a spectral type in the range O9-B2. Eikenberry et al. (2004) estimated an extremely high mass for LBV 1806-20, ~ 200 M; but Figer et al. (2004) have shown that it has double lines and thus may be binary. References Eikenberry, S. S., Garske, M. A., Hu, D., et al. 2001, ApJ 563, L133 Figer, D. F., Najarro, F., & Kudritzki, R. P. 2004, ApJ 610, L109 Kouveliotou C., Dieters S., Strohmayer T., et al. Nature 393, 235 (1998) Mazets, E.P., Golentskii, S.V., Ilinskii, V.N., Aptekar, R.L., & Guryan, I.A. 1979, Nature 282, 587 van Kerkwijk, M.H., Kulkarni, S.R.,Matthews, K., & Neugebauer, G. 1995, ApJ 444, L33

K3 A tremendous flare from SGR1806-20

Zum Thema 27 December 2004 — A tremendous flare from SGR1806-20 with implications for short-duration gamma-ray bursts
Magnetars (Theorie) A XMM-Newton View of the Soft g-ray Repeater SGR 1806-20	Cosmic Explosion the Brightest in Recorded History (Swift)

RHESSI and Wind — a rare 380 s long giant flare from SGR1806-20
	Authors: K. Hurley, S.E. Boggs, D. M. Smith, R.C. Duncan, R. Lin, A. Zoglauer, S. Krucker, G. Hurford, H. Hudson, C. Wigger, W. Hajdas, C. Thompson, I. Mitrofanov, A. Sanin, W. Boynton, C. Fellows, A. von Kienlin, G. Lichti, A. Rau, T. Cline
	Nature 434 (2005) 1098-1103[astro-ph/0502329 ]
	A tremendous flare from SGR1806-20 with implications for short-duration gamma-ray bursts Soft gamma-ray repeaters (SGRs) are X-ray stars which emit numerous short-duration (0.1 s) bursts of photons up to 100 keV during sporadic active periods. They are thought to be magnetars: neutron stars with observable emissions powered by magnetic dissipation. Here we report the detection of a rare 380 s long giant flare from SGR1806-20 on 27 December 2004, with energy greatly exceeding that of all previously-detected events. Its initial gamma-ray E_spike had a blackbody spectrum, characteristic of a relativistic pair/photon outflow. It carried away as much energy in 0.2 s as the Sun radiates in a quarter million years. This extreme energy suggests a catastrophic instability on a magnetar involving global crust failure and magnetic reconnection, perhaps with a significant large-scale untwisting of the magnetosphere. From a great distance this event would appear to be a short-duration, hard spectrum cosmic gamma-ray burst. We argue that this may partially explain the origin of one class of mysterious bursts. NASA's newly-commissioned Swift satellite is likely to detect extragalactic magnetars in significant numbers, opening up a new field of astronomical study.

On 27 December 2004, the International Gamma-Ray Astrophysics Laboratory (INTEGRAL) reported the detection of the third giant flare to date;
it was also observed by 4 other missions in the 3rd interplanetary network

of gamma-ray burst detectors:

Image credit: RHESSI / Wind / Hurley et al.

Figure 1b.
RHESSI germanium detector data for the 27 December 2004 giant flare.
Spectral temperature vs. time in the oscillatory phase.

Image credit: RHESSI / Wind / Hurley et al.

the High Energy Neutron Detector and Gamma Sensor Head aboard Mars Odyssey,
the solar-pointing Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI),
Wind, and
Swift.

It was preceded by a ~1 s long precursor. The precursor, which occurred 142 s before the giant flare, exhibited a rise time ~ 45 ms and a fall time ~ 150 ms. The profile (inset to Fig. 1a) can be described as roughly flattopped.
Although RHESSI measured time- and energy-tagged photons continuously, ‘clean’ spectra (that is, unabsorbed by intervening materials) were measured for short intervals only twice each 4.06 s spacecraft spin period during the oscillatory phase. Preliminary spectral analysis (3-100 keV), using the RHESSI on-axis response matrices, are generally consistent with a single temperature blackbody or optically thin thermal bremsstrahlung model; the blackbody temperatures have been plotted. The formal uncertainties are smaller than the data points and are not shown.
Its >3 keV keV-fluence was 1.8 × 10^-4 erg cm^-2, and its energy spectrum can be crudely approximated by an optically thin thermal bremsstrahlung function with kT~15 keV. For an assumed distance of 15 kpc, its luminosity was 4.6 × 10⁴² erg.
The initial peak of the giant flare had rise and fall times <1 ms and ~65 ms respectively, similar to those for the other giant flares. Its intensity was such that all X- and gamma-ray detectors were briefly driven into saturation, but measurements with the RHESSI particle detectors are consistent with a fluence above 30 keV of 1.36 ± 0.35 erg cm^-2, making this the most intense cosmic transient observed in over 25 years of monitoring. Its peak flux as observed at earth outshone even the brightest solar flares. The time-resolved energy spectrum is consistent with that of a cooling blackbody (figure 1b) whose average temperature is T_{_spike} = 175 ± 25 keV.
At 15 kpc, the energy would have been E_spike= 3.5 × 10⁴⁶ erg and the peak flux in the first 0.125 s would have been L_spike = 1.8 × 10⁴⁷ erg/s. Comparisons with previous giant flares are subject to numerous uncertainties due to the variety of instruments, energy ranges, and time resolutions, but this flare was over 100 times more energetic than any observed previously in our Galaxy.

K3.1 Giant Flare in SGR 1806-20 and Its Compton Reflection from the Moon

	S. Golenetskii, R.Aptekar, E. Mazets, V. Pal'shin, D. Frederiks on behalf of Konus-Wind and Helicon/Coronas-F teams, and T. Cline on behalf of the Konus-Wind team
	GCN GRB OBSERVATION REPORT 04/12/29
	Detection of the SGR 1806-20 giant outburst back-scattered by the Moon. We present an evidence of Helicon-Coronas-F detection of the giant outburst from SGR1806-20 which was scattered back from the Moon. At the time of the outburst SGR1806-20 was occulted by the Earth for Coronas-F. A short burst triggered Helicon at 21:30:29.303s UT on Dec 27. A time delay between Konus-Wind and Helicon-Coronas-F detections is -7.70 s. This value corresponds exactly to burst travelling time from the Wind to the Moon and back to the Coronas-F. The spectrum of the event detected by the Helicon is highly unusual. It looks like a broad assymetric line peaked at ~100 keV. Apparently such a shape corresponds to back-scattering peak of a huge initial pulse of the outburst. The fluence of event is about 7.5x10^-7 erg cm-2 in 25-400 keV range.

Image credit: Mazets et al.

Fig. 1.— Time history of the 2004 December 27 giant outburst recorded by the Konus-Wind detector in three energy windows G1 (16.5–65 keV), G2 (65–280 keV), and G3 (280–1060 keV), and the hardness ratio G2/G1. The moderate initial count rate growth to 10² – 10³ counts s^-1 transforms rapidly to an avalanche-type rise to levels > 5 × 10⁷ counts s^-1, which drives the detector to deep saturation for a time DT ~ 0.5 s. After the initial pulse intensity has dropped to ~ 10⁶ counts s^-1, the detector resumes operation to record the burst tail.

Image credit: Mazets et al.

Fig. 2.— A spectrum of the burst tail averaged over the pulsation period. The low-energy component is similar to spectra of SGR’s recurrent bursts with E_o ~ 30 keV. At high energies it exhibits a hard power-law component with g = 1.8±0.2. This two-component model is shown by the solid line.

SGR 1806-20 — Compton scattered by the Moon
	Authors: E.P. Mazets, T.L. Cline, R.L. Aptekar, D.D. Frederiks, S.V. Golenetskii, V.N. Il'inskii, V.D. Pal'shin
	Journal-ref: astro-ph (2005) [astro-ph/0502541 ]
	The Konus-Wind and Helicon-Coronas-F detection of the giant gamma-ray flare from the soft gamma-ray repeater SGR 1806-20 The giant outburst from SGR 1806-20 was observed on 2004 December 27 by many spacecraft. This extremely rare event exhibits a striking similarity to the two giant outbursts thus far observed, on 1979 March 5 from SGR 0526-66 and 1998 August 27 from SGR 1900+14. All the three outbursts start with a short giant radiation pulse followed by a weaker tail. The tail pulsates with the period of neutron star rotation of ~5--8 s, to decay finally in a few minutes. The enormous intensity of the initial pulse proved to be far above the saturation level of the gamma-ray detectors, with the result that the most valuable data on the time structure and energy spectrum of the pulse is lost. At the time of the December 27 outburst, a Russian spacecraft Coronas-F with a gamma-ray spectrometer aboard was occulted by the Earth and could not see the outburst. It succeeded, however, in observing a weak reflected signal due to the gamma-rays Compton scattered by the Moon. This has been the first observation of a cosmic gamma-ray flare reflected from a celestial body. Here we report, that the detection of a weakened back-scattered initial pulse combined with direct observations by the Konus gamma-ray spectrometer on the Wind spacecraft permitted us to reliably reconstruct the intensity, time history, and energy spectra of the outburst.

—

Authors: D.D. Frederiks, S.V. Golenetskii, V.D. Palshin, R.L. Aptekar, V.N. Ilyinskii, F.P. Oleinik, E.P. Mazets, T.L. Cline

Journal-ref: Astronomy Letters 33 (2007) 1-18 [astro-ph/0612289

]

Title: Giant Flare in SGR 1806-20 and Its Compton Reflection from the Moon

Abstract:
We analyze the data obtained when the Konus-Wind gamma-ray spectrometer detected a giant flare in SGR 1806-20 on December 27, 2004. The flare is similar in appearance to the two known flares in SGR 0526-66 and SGR 1900+14 while exceeding them significantly in intensity.
The enormous X-ray and gamma-ray flux in the narrow initial pulse of the flare leads to almost instantaneous deep saturation of the gamma-ray detectors, ruling out the possibility of directly measuring the intensity, time profile, and energy spectrum of the initial pulse.
In this situation, the detection of an attenuated signal of Compton back-scattering of the initial pulse emission by the Moon with the Helicon gamma-ray spectrometer onboard the Coronas-F satellite was an extremely favorable circumstance.

                  Q_rad, erg   L_max, erg/s
Initial pulse     2.3 × 10⁴⁶  3.5 × 10⁴⁷
Pulsating tail    2.1 × 10⁴⁴  1.3 × 10⁴²
Recurrent bursts  10^39.5-42.5   10^41.3-42.3

Table 1.

Analysis of this signal has yielded the most reliable temporal, energy, and spectral characteristics of the pulse. The temporal and spectral characteristics of the pulsating flare tail have been determined from Konus-Wind data.
Its soft spectra have been found to contain also a hard power-law component extending to 10 MeV. A weak afterglow of SGR 1806-20 decaying over several hours is traceable up to 1 MeV. We also consider the overall picture of activity of SGR 1806-20 in the emission of recurrent bursts before and after the giant flare.

1. Introduction

The first two soft gamma repeaters, SGR 0526-66 (Mazets et al. 1979a; Golenteskii et al. 1984) and SGR 1900+14 (Mazets et al. 1979b), were discovered and localized in March 1979. The third SGR 1806-20 was discovered in 1983 (Atteia et al. 1987; Laros et al. 1987). And only in 1998 was the fourth SGR 1627-41 discovered (Woods et al. 1999). The situation with the possible fifth SGR 1801-23 (Cline et al. 2000) arouses scepticism, since only two soft bursts separated by an interval of several hours have been detected from this source.

1. SGR 0526-66

Giant flares, very rare events comparable in peak emission power in the source (~10^45-47 erg/s) to the luminosity of quasars, are the second, incomparably more impressive type of SGR activity. The giant flare of March 5, 1979, had remained a unique event for more than 19 years.

2. SGR 1900+14

On August 27, 1998, a giant flare came from SGR 1900+14.
All the main features of the flare in SGR 0526-66 manifested themselves in this flare: a narrow, very intense initial emission peak with a hard energy spectrum accompanied by a relatively weaker, spectrally soft tail that decayed for several minutes while pulsating (Mazets et al. 1999a; Hurley et al. 1999; Feroci et al. 1999).

3. SGR 1806-20

The third similar, but even more intense flare that came from SGR 1806-20 on December 27, 2004, was observed on many spacecraft equipped with X-ray and gamma-ray detectors: INTEGRAL, Mars Odyssey, Wind, Swift, RXTE, RHESSI, and others (Hurley et al. 2004; Mazets et al. 2004; Palmer et al. 2005; Hurley et al. 2005; Smith et al. 2005; Woods et al.2005).
The enormous intensity of the initial pulse of the flare led to detector overload and saturation. As a result, the pulse time profile, spectrum, and intensity could not be measured reliably. These characteristics have been estimated more reliably by analyzing information from the small charged-particle detectors designed to study low-energy plasma and mounted on the Geotail (Terasawa et al. 2005), RHESSI, and Wind (Hurley et al. 2005) spacecraft.


		Fig. 5.— Scheme illustrating the Konus-Wind and Helicon-Coronas-F observations of the giant flare. The leading edge of the flare from SGR 1806-20 arrives at Wind at time T_W, passes by the Earth at T_E=T_W+5.086 s, reaches the Moon and is reflected from it, and, finally, the reflected emission reaches the Helicon-Coronas-F detector at T_Cor=T_W+7.69 s. Image credit: Frederiks et al. (2007)

References
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Cline, T., et al. 2000, ApJ, 531, 407
Golentskii, S., Ilinskii, V., & Mazets, E. 1984, Nature, 307, 41
Hurley, K., et al. 1999, Nature, 397, 41
Hurley, K., et al. 2004, GCN Circ. 2921
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K4 Swift NASA Observes One of the Brightest Cosmic Explosions

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Swift — Gamma-Ray Observations of a Giant Flare from The Magnetar SGR 1806-20	Cosmic Explosion the Brightest in Recorded History (anim)

Image credit: NASA

Swift:
Cosmic Explosion the Brightest in Recorded History

Scientists detected a flash of light from across the Galaxy so powerful; it bounced off the moon and lit up the Earth's upper atmosphere. The flash was brighter than anything ever detected from beyond our Solar System, and it lasted over a tenth of a second.

NASA and European satellites and many radio telescopes detected the flash and its aftermath on December 27, 2004. NASA's Swift satellite and the National Science Foundation-funded Very Large Array (VLA) were two of many observatories that observed the event arising from neutron star SGR 1806-20. It is a unique neutron star called a magnetar, about 50,000 light years from Earth in the constellation Sagittarius.
The apparent magnitude was brighter than a full moon and all historical star explosions. The light was brightest in the gamma-ray energy range, far more energetic than visible light or X-rays and invisible to our eyes. "This might be an once-in-a-lifetime event for astronomers, as well as for the neutron star," said David Palmer.

He is lead author on a paper describing the Swift observation. "We know of only two other giant flares in the past 35 years, and the December event was 100 times more powerful," he added.

Bryan Gaensler is lead author on a report describing the VLA observation, which tracked the ejected material as it flew out into interstellar space. Other key scientific teams are associated with radio telescopes in Australia, The Netherlands, United Kingdom, India and the United States, as well as with NASA's High Energy Solar Spectroscopic Imager (RHESSI).
Neutron stars form from collapsed stars. They are dense, fast-spinning, highly magnetic, and only about 15 miles in diameter. Only about 12 magnetars are known (cf. AXP und SGR -

-) among the millions of regular neutron stars in our Galaxy and neighboring galaxies.
SGR 1806-20 is also a soft gamma repeater (SGR) because it randomly flares and releases gamma rays. Only four SGRs are known. The giant flare on SGR 1806-20 was millions to billions of times more powerful than typical SGR flares. For a tenth of a second, the giant flare unleashed more energy than the sun emits in 150,000 years. Magnetic fields around magnetars are responsible for SGR outbursts, but the details remain unclear.
"The next biggest flare ever seen from any soft gamma repeater was peanuts compared to this incredible December 27 event," Gaensler said. "Had this happened within 10 light years of us, it would have severely damaged our atmosphere. Fortunately, all the magnetars we know of are much farther away than this," he added.
During the 1980s scientists wondered whether gamma-ray bursts were star explosions from beyond our Galaxy or eruptions on nearby neutron stars.
By the late 1990s it became clear gamma-ray bursts did indeed originate far away. But the extraordinary giant flare on SGR 1806-20 reopens the debate, according to Dr. Chryssa Kouveliotou of NASA's Marshall Space Flight Center, Huntsville, Ala., who coordinated multiwavelength follow-up observations. A small percentage of short gamma-ray bursts, less than two seconds, could be from SGR flares.
"An answer to the short gamma-ray burst mystery could come any day now that Swift is in orbit", said Swift lead scientist Neil Gehrels.

K5 Artikel (II) zu "A tremendous flare from SGR1806-20"

GEOTAIL — the first 600 ms of the giant flare of SGR 1806-20

Authors: Toshio Terasawa, Yasuyuki Tanaka, Yasuhiro Takei, Nobuyuki Kawai, Atsumasa Yoshida, Ken'ichi Nomoto, Ichiro Yoshikawa, Yoshifumi Saito, Yasumasa Kasaba, Takeshi Takashima, Toshifumi Mukai, Hirotomo Noda, Toshio Murakami, Kyoko Watanabe, Yasushi Muraki, Takaaki Yokoyama, Masahiro Hoshino

Journal-ref:Nature 434 (2005) 1110-1111 [astro-ph/0502315

]

Title: Repeated injections of energy in the first 600 ms of the giant flare of SGR 1806-20

GEOTAIL / Terasawa et al.

Fig. 1.— Observed photon counts during the first 600 ms of the giant flare. NMCP (red squares) and NCEM (blue solid squares) show the counts of MCP and CEM instruments accumulated over a bin of 5.48 ms duration.

Abstract: The massive flare of 27 December 2004 from the soft gamma-ray repeater SGR 1806-20, a possible magnetar saturated almost all gamma-ray detectors meaning that the profile of the pulse was poorly characterized. An accurate profile is essential to determine physically what was happening at the source. Here we report the unsaturated gamma-ray profile for the first 600 ms of the flare, with a time resolution of 5.48 ms. The peak of the profile (of the order of 10⁷ photons cm^-2 s^-1) was reached 50 ms after the onset of the flare, and was then followed by a gradual decrease with superposed oscillatory modulations possibly representing repeated energy injections with 60-ms intervals. The implied total energy is comparable to the stored magnetic energy in a magnetar ( ~ 10⁴⁷ erg ) based on the dipole magnetic field intensity ( ~ 10¹⁵ G ), suggesting either that the energy release mechanism was extremely efficient or that the interior magnetic field is much stronger than the external dipole field.

INTRODUCTION

On December 27, 2004, plasma particle detectors on the GEOTAIL spacecraft detected an extremely strong signal of hard X-ray photons from the giant flare of SGR1806-20, a magnetar candidate. While practically all gamma-ray detectors on any satellites were saturated during the first ~500 ms interval after the onset, one of the particle detectors on GEOTAIL was not saturated and provided unique measurements of the hard X-ray intensity and the profile for the first 600 ms interval with 5.48 ms time resolution.
After ~50 ms from the initial rapid onset, the peak photon flux (integrated above ~50 keV) reached the order of F_ph = 10⁷ photons·cm^-2s^-1. Assuming an exp(-E/650 keV) energy spectrum, we estimate the peak energy flux to be F_ph = 31 erg cm^-2 s^-1 and the fluence (for 0-600 ms) to be f_ph = 3.5 erg cm^-2 . The implied energy release comparable to the magnetic energy stored in a magnetar (~10⁴⁷ ergs) suggests an extremely efficient energy release mechanism.

VLA — Discovery of a Radio Afterglow

Authors: B. M. Gaensler, C. Kouveliotou, J. D. Gelfand, G. B. Taylor, D. Eichler, R. A. M. J. Wijers, J. Granot, E. Ramirez-Ruiz, Y. E. Lyubarsky, R. W. Hunstead, D. Campbell-Wilson, A. J. van der Host, M. A. McLaughlin, R. P. Fender, M. A. Garrett, K. J. Newton-McGee, D. M. Palmer, N. Gehrels, P. M. Woods

Journal-ref: Nature 434 (2005) 1104-1106 [astro-ph/0502393

]

Title: An expanding radio nebula produced by a giant flare from the magnetar SGR 1806-20

Abstract: Soft gamma repeaters (SGRs) are "magnetars", a small class of slowly spinning neutron stars with extreme surface magnetic fields, ~10¹⁵ gauss. On 2004 December 27, a giant flare was detected from the magnetar SGR 1806-20, the third such event ever recorded. This burst of energy was detected by a variety of instruments and even caused an ionospheric disturbance in the Earth's upper atmosphere recorded around the globe. Here we report the detection of a fading radio afterglow produced by this outburst, with a luminosity 500 times larger than the only other detection of a similar source. From day 6 to day 19 after the flare from SGR 1806-20, a resolved, linearly polarized, radio nebula was seen, expanding at approximately a quarter the speed of light. To create this nebula, at least 4x10⁴³ ergs of energy must have been emitted by the giant flare in the form of magnetic fields and relativistic particles. The combination of spatially resolved structure and rapid time evolution allows a study in unprecedented detail of a nearby analog to supernovae and gamma-ray bursts.

VLA / Gaensler et al.

Radio Afterglowfrom the magnetar SGR 1806-20.
Radio emission from VLA J180839–202439 at 8.5 GHz. The figure shows the image of the source at three epochs. No source is seen in archival 8.5-GHz data from 1994 March. In the days after the giant flare, a bright but rapidly fading source is now seen at this position.

VLA, GMRT, NMA, and ATCA — measurements of the radio counterpart to SGR1806-20 as a function of frequency and time.
	Authors: P. B. Cameron, P. Chandra, A. Ray, S. R. Kulkarni, D. A. Frail, M. H. Wieringa, E. Nakar, E. S. Phinney, Atsushi Miyazaki, Masato Tsuboi, Sachiko Okumura, N. Kawai, K. M. Menten, F. Bertoldi
	Journal-ref: Nature 434 (2005) 1075-6 [astro-ph/0502428 ]
	Title: Discovery of a Radio Afterglow following the 27 December 2004 Giant Flare from SGR 1806-20
Abstract: Over a decade ago it was established that the remarkable high energy transients, known as soft gamma-ray repeaters (SGRs), were a Galactic population and originate from neutron stars with intense (~< 10¹⁵G) magnetic fields ("magnetars"). On 27 December 2004 a giant flare (fluence > 0.3 erg cm^-2) was detected from SGR 1806-20. Here we report the discovery of a fading radio counterpart ("afterglow"). We began a monitoring program from 0.2GHz to 100GHz and obtained a high resolution 21-cm radio spectrum which traces the intervening interstellar neutral Hydrogen clouds. From the analysis of the spectrum we argue that the source is located between 6.4 and 9.8 kpc and not at 12 kpc or 15 kpc. The revised distance relaxes the demands on the total energy of the explosion and, equally importantly, calls into question the relation between SGRs and massive star clusters. The radio source has similar properties as that observed from SGR 1900+14, although in both cases the rapid decay is puzzling. We suggest that this behaviour may result from changes in microphysics as the interstellar shock driven by the flare becomes transrelativistic. If so, SGRs are providing us with a new laboratory for studying strong astrophysical shocks in an interesting regime, the transrelavitistic regime.
	Title: Detection of a radio counterpart to the 27 December 2004 giant flare from SGR 1806-20. [revised]
Abstract: Analysis of the spectrum yields the first direct distance measurement of SGR 1806-20. The source is located at a distance greater than 6.4 kpc and we argue that it is nearer than 9.8 kpc. If true, our distance estimate lowers the total energy of the explosion and relaxes the demands on theoretical models. The energetics and the rapid decay of the radio source are not compatible with the afterglow model that is usually invoked for gamma-ray bursts. Instead we suggest that the rapidly decaying radio emission arises from the debris ejected during the explosion.

VLA — Radio Afterglow — Giant Flare from SGR 1806-20
	Authors: G. B. Taylor, J.D. Gelfand, B.M. Gaensler, J. Granot, C. Kouveliotou, R. P. Fender, E. Ramirez-Ruiz, D. Eichler, Y. E. Lyubarsky, M. Garrett, R. A. M. J. Wijers
	Journal-ref: ApJ 634 (2005) L93-L96 [astro-ph/0504363]
	Title: The Growth, Polarization, and Motion of the Radio Afterglow from the Giant Flare from SGR 1806-20
Abstract: The extraordinary giant flare (GF) of 2004 December 27 from the soft gamma repeater (SGR) 1806-20 was followed by a bright radio afterglow. We present an analysis of VLA observations of this radio afterglow from SGR 1806-20, consisting of previously reported 8.5 GHz data covering days 7 to 20 after the GF, plus new observations at 8.5 and 22 GHz from day 24 to 81. For a symmetric outflow, we find a deceleration in the expansion, from ~4.5 mas/day to <2.5 mas/day. The time of deceleration is roughly coincident with the rebrightening in the radio light curve, as expected to result when the ejecta from the GF sweeps up enough of the external medium, and transitions from a coasting phase to the Sedov-Taylor regime. The radio afterglow is elongated and maintains a 2:1 axis ratio with an average position angle of -40 degrees (north through east), oriented perpendicular to the average intrinsic linear polarization angle. We also report on the discovery of motion in the flux centroid of the afterglow, at an average velocity of 0.26 +/- 0.03 c (assuming a distance of 15 kpc) at a position angle of -45 degrees. This motion, in combination with the growth and polarization measurements, suggests an initially asymmetric outflow, mainly from one side of the magnetar.

K5.2 The distance of the 1806-20 cluster

Cluster 1806-20 (G10.0-0.3) — d ~ 8.7 kpc
	Authors: J.L. Bibby, P.A. Crowther, J.P. Furness, J.S. Clark
	Journal-ref: MNRAS Letters (2008) [0802.0815 ]
	Title: A downward revision to the distance of the 1806-20 cluster and associated magnetar from Gemini near-Infrared spectroscopy
Abstract: We present H- and K-band spectroscopy of OB and Wolf-Rayet (WR) members of the Milky Way cluster 1806-20 (G10.0-0.3), to obtain a revised cluster distance of relevance to the 2004 giant flare from the SGR 1806-20 magnetar. From GNIRS spectroscopy obtained with Gemini South, four candidate OB stars are confirmed as late O/early B supergiants, while we support previous mid WN and late WC classifications for two WR stars. Based upon an absolute Ks-band magnitude calibration for B supergiants and WR stars, and near-IR photometry from NIRI at Gemini North plus archival VLT/ISAAC datasets, we obtain a cluster distance modulus of 14.7 ± 0.35 mag. The known stellar content of the 1806-20 cluster suggests an age of 3-5 Myr, from which theoretical isochrone fits infer a distance modulus of 14.7 ± 0.7 mag. Together, our results favour a distance modulus of 14.7 ± 0.4 mag (8.7 ± 1.5 kpc) to the 1806-20 cluster, which is significantly lower than the nominal 15 kpc distance to the magnetar. For our preferred distance, the peak luminosity of the December 2004 giant flare is reduced by a factor of three to L_peak ~ 7 × 10⁴⁶ erg s^-1, such that the contamination of BATSE short gamma ray bursts (GRB's) from giant flares of extragalactic magnetars is reduced to a few percent. We infer a magnetar progenitor mass of ~48 ± 10 M, in close agreement with that obtained recently for the magnetar in Westerlund 1. 1. Introduction To date only four examples of SGR’s are known, characterised by multiple, soft gamma-ray bursts, typically L_peak ~ 10⁴¹ erg s^-1 in peak luminosity, plus rare giant flares of L_peak ~ 10⁴⁵ erg s^-1 peak luminosity. One such giant flare, from SGR 1806–20 (Kouveliotou et al. 1998), was detected on 27 December 2004 by many satellites including the Burst Alert Telescope (BAT) on Swift (Palmer et al. 2005), and in January 2005 the radio afterglow was detected by Cameron et al. (2005) through VLA observations. 4. Discussion This distance represents a major downward revision to the current adopted magnetar distance of 15 kpc, suggesting a peak luminosity of ~ 7 × 10⁴⁶ erg s^-1 for the December 2004 giant flare. Hurley et al. (2005) argue that up to 40% of all BATSE short GRB’s could be giant flares from magnetars, if one was to adopt a 15 kpc distance to SGR 1806–20 and a frequency of giant flares of one per 30 yr per Milky Way galaxy. For the revised distance, perhaps only ~8% of BATSE short GRB’s have an origin in magnetar giant flares. References Cameron P. B. et al. 2005, Nature 434, 1112 Clark, J.S., Muno, M.P., et al., 2008, A&A 477, 147 Eikenberry, S.S. et al. 2004, ApJ, 616, 506 Kouveliotou C. et al. 1998, Nature 393, 235 Muno M.P. et al. 2006, ApJ, 636, L41 Palmer D.M. et al. 2005, Nature 434, 1107

Literatur zu "SGR 1806-20 (I)" (II)
G. B. Taylor, J.D. Gelfand, B.M. Gaensler, J. Granot, C. Kouveliotou, et al.	2005	ApJ 634, L93-L96	"The Growth, Polarization and Motion of the Radio Afterglow from the Giant Flare from SGR 1806-20 "
D.F. Figer, F. Najarro, T.R. Geballe, et al.	2005	ApJ 622, L49	"Massive Stars in the SGR 1806-20 Cluster"
B. M. Gaensler, C. Kouveliotou, J. D. Gelfand, et al.	2005	Nature 434, 1104-1106	"An expanding radio nebula produced by a giant flare from the magnetar SGR 1806-20"
K. Hurley, S.E. Boggs, D. M. Smith, R.C. Duncan, R. Lin, et al.	2005	Nature 434, 1098-1103	"A tremendous flare from SGR1806-20 with implications for short-duration gamma-ray bursts"
D. M. Palmer, S. Barthelmy, N. Gehrels, R. M. Kippen, et al.	2005	Nature 434, 1107-1109	"Gamma-Ray Observations of a Giant Flare from The Magnetar SGR 1806-20"
P. B. Cameron, P. Chandra, A. Ray, S. R. Kulkarni, D. A. Frail, et al.	2005	Nature 434, 1075-6	"Detection of a radio counterpart to the 27 December 2004 giant flare from SGR 1806-20"
Terasawa, T., Tanaka, Y, Takei, Y., et al.	2005	Nature 434, 1110-1111	"Repeated injections of energy in the first 600 ms of the giant flare of SGR 1806-20"
A.I. Ibrahim, S. Safi-Harb, J.H. Swank, W. Parke, S. Zane and R. Turolla	2002	ApJ 574, L51	"Discovery of Cyclotron Resonance Features in the Soft Gamma Repeater SGR 1806-20"
A.I. Ibrahim,J.H. Swank, W. Parke	2003	ApJ 584,L17-L22	"New Evidence for Proton Cyclotron Resonance in a Magnetar Strength Field from SGR 1806-20"

H. Heintzmann

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