 Artikel zu "Integral (ii)"
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(i)
(iii: SFXT)
(SGR)
AMsPSR (AMSP)
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Integral (ii)
K1.1 
New class of cosmic high energy accelerators
Ref.: Ubertini, P. et al.: ApJ 629, L109 (2005). 
Integral IGRJ18135–1751=HESS J1813–178: A new cosmic high energy accelerator from KeV to TeV. K1.2
X-ray binary IGR J16318-4848 in Norma
[20 October 2003] IGR J16318-4848
Erste Hinweise auf die mögliche Existenz einer unbekannten Klasse von kosmischen Gammastrahlen-Quellen gab es
schon im Oktober 2003, als "INTEGRAL" ein merkwürdiges Objekt mit dem Namen IGR J16318-4848 entdeckt hatte. Aus
den Daten von "INTEGRAL" sowie vom ESA-Röntgenobservatorium "XMM-Newton" konnte man schließen, dass man es
hierbei wahrscheinlich mit einem Doppelstern-System zu tun hatte, wobei es sich bei einem der Sterne um einen
Neutronenstern oder ein Schwarzes Loch handelt, dass in eine dicke Hülle aus kaltem Gas und Staub eingebettet ist.
INTEGRAL discovery of a bright, highly obscured galactic X-ray binary source IGR J16318-4848 in Norma.
NH ~ 2 × 1023 cm-2.
XMM-Newton: IGR J16320-4751 = AX J1631.9-4752
[Juni 2005]
Distribution of IGR sources
A list of all sources found by INTEGRAL.
X-ray binaries (where the compact object is a neutron star or black hole) can become strong hard X-rays emitters when accretion takes place. Among the ~300 known X-ray binaries in our Galaxy and the Magellanic clouds, a few systems show strong intrinsic photo-electric absorption: GX 301--2, Vela X--1, CI Cam. Moderate absorption was also detected in a few X-ray bursters. We report here on the discovery of IGR J1632, a Compton thick X-ray binary in which the X-ray obscuring matter has a column density as large as the inverse of the Thomson cross section. | |
opt. Suchbild zu IGR J1632 aus 3 Katalogen
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IGR J16320-4751 = AX J1631.9-4752
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ESA's Integral discovers hidden black holes
[20 October 2003] Integral, ESA's powerful gamma-ray space telescope, has discovered what seems to be
a new class of astronomical objects.
These are binary systems, probably including a black hole or a neutron star, embedded in a thick cocoon of cold gas. They have remained invisible so far to all other telescopes. Integral was launched one year ago to study the most energetic phenomena in the universe. |
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Image credit: ESA / Integral
An artist's impression of the mechanisms in an interacting binary system
Image credit: ESA / Integral
XMM-Newton spacecraft
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Integral detected the first of these objects, called IGR J16318-4848, on 29 January 2003. Although astronomers did not know its distance, they were sure it was in our Galaxy. Also, after some analysis, researchers concluded that the new object could be a binary system comprising a compact object, such as a neutron star or a black hole, and a very massive companion star.
When gas from the companion star is accelerated and swallowed by the more compact object, energy is released at all wavelengths, from the gamma rays through to visible and infrared light. About 300 binary systems like those are known to exist in our galactic neighbourhood and IGR J16318-4848 could simply have been one more. But something did not fit: why this particular object had not been discovered so far?
Astronomers, who have been observing the object regularly, guess that it had remained invisible because there must be a very thick shell of obscuring material surrounding it. If that was the case, only the most energetic radiation from the object could get through the shell; less-energetic radiation would be blocked. That could explain why space telescopes that are sensitive only to low-energy radiation had overlooked the object, while Integral, specialised in detecting very energetic emissions, did see it.
To test their theory, astronomers turned to ESA's XMM-Newton space observatory, which observes the sky in the X-ray wavelengths. As well as being sensitive to high-energy radiation, XMM-Newton is also able to check for the presence of obscuring material. Indeed, XMM-Newton detected this object last February, as well as the existence of a dense 'cocoon' of cold gas with a diameter of similar size to that of the Earth's orbit around the Sun.
This obscuring material forming the cocoon is probably 'stellar wind', namely gas ejected by the supermassive companion star. Astronomers think that this gas may be accreted by the compact black hole, forming a dense shell around it. This obscuring cloud traps most of the energy produced inside it.
The main author of these results, Roland Walter explained: "Only photons with the highest energies [above 10 keV] could escape from that cocoon. IGR J16318-4848 has therefore not been detected by surveys performed at lower energies, nor by previous gamma-ray missions that were much less sensitive than Integral."
| IGR J16318-4848 — | |
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Authors: R. Walter, J. Rodriguez, L. Foschini, J. de Plaa, S. Corbel, T. J.-L. Courvoisier, P. R. den Hartog, F. Lebrun, A. N. Parmar, J. A. Tomsick, P. Ubertini |
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Journal-ref: A&A 411 (2003) L427-L432 [astro-ph/0309536 ] |
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Title: INTEGRAL discovery of a bright highly obscured galactic X-ray binary source IGR J16318-4848 |
| Abstract:
INTEGRAL regularly scans the Galactic plane to search for new objects and in
particular for absorbed sources with the bulk of their emission above 10-20
keV. The first new INTEGRAL source was discovered on 2003 January 29, 0.5
degree from the Galactic plane and was further observed in the X-rays with
XMM-Newton. This source, IGR J16318-4848, is intrinsically strongly absorbed by
cold matter and displays exceptionally strong fluorescence emission lines. The
likely infrared/optical counterpart indicates that IGR J16318-4848 is probably
a High Mass X-Ray Binary neutron star or black hole enshrouded in a Compton
thick environment. Strongly absorbed sources, not detected in previous surveys,
could contribute significantly to the Galactic hard X-ray background between 10 and 200 keV.
INTRODUCTION
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The question now is to find out how many of these objects lurk in the Galaxy. XMM-Newton and Integral together
are the perfect tools to do the job. They have already discovered two more new sources embedded in obscuring
material. Future observations are planned.
K1.4
Multiwavelength IGR J16320-4751
| IGR J16320-4751/AX J1631.9-4752 — P = 1300 s | |
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Authors: J. Rodriguez, A. Bodaghee, P. Kaaret, J.A. Tomsick, E. Kuulkers, G. Malaguti, P.-O. Petrucci, C. Cabanac, M. Chernyakova, S. Corbel, S. Deluit, G. Di Cocco, K. Ebisawa, A. Goldwurm, G. Henri, F. Lebrun, A. Paizis, R. Walter, L. Foschini |
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Journal-ref: MNRAS 366 (2006) 274-282 [astro-ph/0511429 ] |
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Title: INTEGRAL and XMM-Newton observations of the X-ray pulsar IGR J16320-4751/AX J1631.9-4752 |
| Abstract:
We report on observations of the X-ray pulsar IGR J16320-4751 (a.k.a. AX J1631.9-4752) performed
simultaneously with INTEGRAL and XMM-Newton. We refine
the source position and identify the most likely infrared counterpart. Our
simultaneous coverage allows us to confirm the presence of X-ray pulsations at
~1300 s, that we detect above 20 keV with INTEGRAL for the first time. The
pulse fraction is consistent with being constant with energy, which is
compatible with a model of polar accretion by a pulsar. We study the spectral
properties of IGR J16320-4751 during two major periods occurring during the
simultaneous coverage with both satellites, namely a flare and a non-flare
period. We detect the presence of a narrow 6.4 keV iron line in both periods.
The presence of such a feature is typical of supergiant wind accretors such as
Vela X-1 or GX 301-2. We inspect the spectral variations with respect to the
pulse phase during the non-flare period, and show that the pulse is solely due
to variations of the X-ray flux emitted by the source and not to variations of the spectral parameters.
Our results are therefore compatible with the source being a pulsar in a High Mass X-ray Binary. We detect a soft excess appearing in the spectra as a blackbody with a temperature of ~0.07 keV. We discuss the origin of the X-ray emission in IGR J16320-4751: while the hard X-rays are likely the result of Compton emission produced in the close vicinity of the pulsar, based on energy argument we suggest that the soft excess is likely the emission by a collisionally energised cloud in which the compact object is embedded. INTRODUCTION
The INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL) was launched on October 17, 2002.
Since then, about 75 new sources have been discovered mainly with the IBIS telescope (Ubertini et al. 2003).
Because of its energy range (from 15 keV to ~ 1 MeV), its high angular resolution (12 arcmin),
good positional accuracy (down to ~ 0.5 arcmin for bright sources), and its unprecedented sensitivity between
20 and 200 keV, IBIS/ISGRI has allowed to discover many peculiar X-ray binaries characterized by a huge
equivalent absorption column density
( NH ), as high as a few times 1024 cm-2
in IGR J16318-4848 (Matt & Guainazzi 2003;Walter et al. 2003),
the first source discovered by INTEGRAL.
Due to the high absorption, most of these sources were not detected during previous soft X-ray scans of the Galaxy (see e.g. Kuulkers 2005 for a review). IGR J16320-4751 was detected on Feb. 1, 2003, with ISGRI as a hard X-ray source. The source was observed to vary significantly in the 15-40 keV energy range on time scales of ~ 1000 s, and was sometimes detected above 60 keV (Foschini et al. 2004). Inspection of the X-ray archives revealed that IGR J16320-4751 is the hard X-ray counterpart to AX J1631.9-4752, observed with ASCA in 1994 and 1997. Analysis of archival BeppoSAXWFC data showed that this source was persistent for at least 8 years. Soon after the discovery of IGR J16320-4751 by INTEGRAL, an XMM-Newton Target of Opportunity was triggered. This allowed us to obtain the most accurate X-ray position to date (Rodriguez et al. 2003), which in particular led to the identification of two possible infrared counterparts (Tomsick et al. 2003; Rodriguez et al. 2003) (hereafter source 1 and 2). From this analysis, we suggested that IGR J16320-4751 is probably a High Mass X-ray Binary (HMXB) hosting a neutron star (Rodriguez et al. 2003). This last point has been reinforced since the discovery of X-ray pulsations from this source in both XMM-Newton and ASCA observations (Lutovinov et al. 2005) with a pulse period of about 1300 s. | |
| — IGR J16318-4848 | |
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Author: Erik Kuulkers |
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Journal-ref: AIP 797 (2005) 402 [astro-ph/0504625 ] |
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Title: An absorbed view of a new class of INTEGRAL sources |
| Abstract:
The European gamma-ray observatory INTEGRAL has found a group of
hard X-ray sources which are highly absorbed, i.e., with column densities
higher than NH ~ 1023 cm-2.
with a red giant K-type companionHere I give an overview of this class of
INTEGRAL sources. The X-ray, as well as the optical/IR, properties of these
sources and their location in the sky suggest that they belong to the class of
high-mass X-ray binaries, some of them possibly long-period X-ray pulsars. The
donors in these binaries are most probably giant or supergiant stars.
I suggest that the soft X-ray spectrum below ~5 keV of IGR J16318-4848, as well as in several other X-ray binaries (e.g., XTE J0421+56), can be described by emission from a compact object which is strongly absorbed by a partionally ionised dense envelope. INTRODUCTION
References Ubertini, P., Lebrun, F., Di Cocco, G. et al. 2003, A&A, 411, L131 "IBIS: The Imager on-board INTEGRAL" Kuulkers, E. 2005, in “Interacting Binaries: Accretion, Evolution and Outcomes”, Eds. L.A. Antonelli, et al., Proc. of the Interacting Binaries Meeting of Cefalu, Italy, July 2004, AIP. | |
| IGR J16318-4848 — NH ~ 1 × 1024 cm-2 | |
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Authors: A. Ibarra, G. Matt, M. Guainazzi, E. Kuulkers, E. Jimenez-Bailon, J. Rodriguez, F. Nicastro, R. Walter |
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Journal-ref: A&A 465 (2007) 501 [astro-ph/0611343 ] |
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Title: The XMM-Newton/INTEGRAL monitoring campaign of IGR J16318-4848 |
| Abstract:
IGR J16318-4848 is the prototype and one of the more extreme examples of the
new class of highly obscured Galactic X-ray sources discovered by INTEGRAL.
A monitoring campaign on this source has been carried out by XMM-Newton and INTEGRAL, consisting in three simultaneous observations performed in February, March and August 2004. The long-term variability of the Compton-thick absorption and emission line complexes will be used to probe the properties of the circumstellar matter. A detailed timing and spectral analysis of the three observations is performed, along with the reanalysis of the XMM-Newton observation performed in February 2003. The results are compared with predictions from numerical radiative transfer simulations to derive the parameters of the circumstellar matter. Despite the large flux dynamic range observed (almost a factor 3 between observations performed a few months apart), the source remained bright (suggesting it is a persistent source) and Compton-thick (NH = 1.2 × 1024 cm-2). Large Equivalent Width (EW) emission lines from Fe Ka, Fe Kb and Ni Ka were present in all spectra. The addition of a Fe Ka Compton Shoulder improves the fits, especially in the 2004 observations. Sporadic occurrences of rapid X-ray flux risings were observed in three of the four observations. The Fe Ka light curve followed the continuum almost instantaneously, suggesting that the emission lines are produced by illumination of small-scale optically-thick matter around the high-energy continuum source. Using the iron line EW and Compton Shoulder as diagnostic of the geometry of the matter, we suggest that the obscuring matter is in a flattened configuration seen almost edge-on. | |
K1.5
IGR J17497-2821
| IGR J17497-2821 — NH ~ 4 × 1022 cm-2 | |
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Authors: J. Rodriguez, M. Cadolle Bel, J.A. Tomsick, S. Corbel, C. Brocksopp, A. Paizis, S.E. Shaw, A. Bodaghee |
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Journal-ref: ApJ 655 (2007) L97 [astro-ph/0611341 ] |
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Title: The discovery outburst of the X-ray transient IGR J17497-2821 observed with RXTE and ATCA |
| Abstract:
We report the results of a series of RXTE and ATCA observations of the
recently-discovered X-ray transient IGR J17497-2821. Our 3-200 keV PCA+HEXTE
spectral analysis shows very little variations over a period of ~10 days around the maximum of the outburst.
IGR J17497-2821 is found in a typical Low Hard State (LHS) of X-ray binaries (XRB), well represented by an absorbed Comptonized spectrum with an iron edge at about 7 keV. The high value of the absorption (NH ~ 4 × 1022 cm-2) suggests that the source is located at a large distance, either close to the Galactic center or beyond. The timing analysis shows no particular features, while the shape of the power density spectra is also typical of LHS of XRBs, with ~36% RMS variability. No radio counterpart is found down to a limit of 0.21 mJy at 4.80 GHz and 8.64 GHz. We discuss the properties of IGR J17497-2821 and by comparing them with those of other sources, we suggest that it is a black hole candidate. | |
| IGR J17497-2821 — BH with a red giant K-type companion | ||
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Authors: A. Paizis, M. A. Nowak, S. Chaty, J. Rodriguez, T. J.-L. Courvoisier, M. Del Santo, K. Ebisawa, R. Farinelli, P. Ubertini, J. Wilms | |
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Journal-ref: ApJL (2006) [astro-ph/0611344 ] | |
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Title: Hunting the nature of IGR J17497-2821 with X-ray and NIR observations | |
We extracted the most precise X-ray position of IGR J17497-2821, aJ2000 = 17h 49m 38''.037, dJ2000 = -28° 21' 17''.37 (90% uncertainty of 0.6"). We also report on optical and near infra-red photometric follow-up observations based on this position. With the multi-wavelength information at hand, we discuss the possible nature of the source proposing that IGR J17497-2821 is a low-mass X-ray binary, most likely hosting a black hole, with a red giant K-type companion. 1. Introduction
On 2006 September 17 a new hard-X ray transient, IGR J17497-2821 (Soldi et al. 2006), was discovered
by the IBIS telescope on-board INTEGRAL.
The source was first detected at a flux of about 25 mCrab in the 20–40 keV range and further observations indicated that IGR J17497-2821 was brightening with a 3–200 keV INTEGRAL spectrum well fitted by an absorbed power-law with G=1.93±0.05. Two days later, a Swift observations was performed and a Swift position at aJ2000 = 17h 49m 38''.1, dJ2000 = -28° 21' 16''.9 with uncertainty of 5''.3 radius (90% containment) was reported. The XRT spectrum was well fitted using an absorbed power-law with NH = (4.8 ± 0.3) × 1022 cm-2 and G=1.6 ± 0.1. 4. Discussion
IGR J17497-2821 is placed in the direction of the
Galactic center, (l,b)=(0°.9,-0°.4), and we observe a column density of about
NH = 5 × 1022 cm-2
that is higher than the galactic average value expected in the source direction,
NH = 1.5 × 1022 cm-2 (Dickey & Lockman 1990). This
can imply that there is an additional contribution from within the system.
Given the location in the sky and the high interstellar absorption, the
source is most likely at the distance of the Galactic center or beyond.
For our best fit model, assuming a distance of 8 kpc, we obtain an (un-absorbed) source luminosity of about LX(2–10 keV) = 4 × 1036 erg s-1, typical of X-ray binaries. The nature of the companion, i.e. Low Mass X-ray Binary (LMXB) versus High Mass X-ray Binary (HMXB) and of the compact object, i.e. Black Hole (BH) versus Neutron Star (NS) is still a matter of debate. The general X-ray properties seem to suggest that the source is a (transient) LMXB and the X-ray spectrum we obtain is compatible with a LMXB in the so-called low-hard state (LHS), cold (0.2 keV) disk emission plus power-law with G ~ 1.5. Regarding the nature of the compact object we note that up to now no pulsations or type-I X-ray bursts, that would point to presence of NS in the system, have been detected so no conclusive signature is currently available to infer the nature of the compact object. Our results are consistent with a cold (0.2 keV) disk around a BH of e.g. 10 solar masses at a distance of 8 kpc and also the power-law slope (G ~ 1.5) is typical of a BH in the low-hard state. Determining the nature of the compact object in a non-pulsating X-ray binary is one of the most intriguing questions still unresolved and IGR J17497-2821 is a good example of such a challenge. | ||
K2
The SGR 1806-20 signature on the Earth's magnetic field
Zum Thema | |
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Authors: Mioara Mandea, Georgios Balasis |
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Journal-ref: Geophys. J. Int. 167 (2006) [0710.2793 ] |
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Title: The SGR 1806-20 magnetar signature on the Earth's magnetic field |
| Abstract:
SGRs denote ``soft gamma-ray repeaters'', a small class of slowly spinning neutron
stars with strong magnetic fields. On 27 December 2004, a giant flare was
detected from magnetar SGR 1806-20.
The initial spike was followed by a hard-X-ray tail persisting for 380 s with a modulation period of 7.56 s. This event has received considerable attention, particularly in the astrophysics area. Its relevance to the geophysics community lies in the importance of investigating the effects of such an event on the near-earth electromagnetic environment. However, the signature of a magnetar flare on the geomagnetic field has not previously been investigated. Here, by applying wavelet analysis to the high-resolution magnetic data provided by the CHAMP satellite, a modulated signal with a period of 7.5 s over the duration of the giant flare appears in the observed data. Moreover, this event was detected by the energetic ion counters onboard the DEMETER satellite. | |
K2.1 Gamma-Blitz traf die Erde
Astrophysiker am MPE in Garching messen den bisher stärksten Strahlenausbruch eines Magnetars
Am 27. Dezember 2004 um 22:30:26 MEZ wurde die Erde von einer gewaltigen Wellenfront von Gamma- und
Röntgenstrahlung getroffen.
"Das spektakuläre Ereignis haben wir dem Magnetar mit dem Namen "SGR 1806-20" zu verdanken", erklärt Giselher Lichti. "Dieser Neutronenstern hat einen Durchmesser wie eine mittlere Großstadt und eine Masse vergleichbar mit der Sonne. Er erlitt eine gewaltige magnetische Instabilität, wobei sich sein starkes Magnetfeld in einen niedrigeren Energiezustand umorientierte", erklärt der Astrophysiker. "In den ersten 0.2 Sekunden wurde dadurch von diesem Objekt die gleiche Energiemenge emittiert wie von der Sonne in etwa einer Viertelmillion Jahren. Dieser Ausbruch war etwa 100-mal stärker als der bisher stärkste beobachtete Ausbruch (englisch burst) von einem Magnetar."
Magnetare sind Neutronensterne, deren Magnetfelder das 1.000fache des bei Neutronensternen üblichen Wertes aufweisen. Man schätzt, dass etwa zehn Prozent aller Neutronensterne zu dieser Sternklasse zählen. Neutronensterne entstehen beim Kollaps von Sternen einer bestimmten Gewichtsklasse bei einer Supernovaexplosion. Sie haben einen typischen Durchmesser von etwa 20 km und ein extrem starkes Magnetfeld der Größenordnung 1012 Gauß (Zum Vergleich: Das Magnetfeld der Erde hat eine Stärke von etwa einem Gauß), das sich als Folge der Gesetze der Elektrodynamik ergibt, wonach das Produkt aus Sternquerschnitt und Magnetfeld beim Kollaps des Vorläufersterns konstant bleibt. Das um den Faktor 1000 stärkere Magnetfeld eines neugeborenen Magnetars entsteht innerhalb weniger Sekunden durch einen komplexen Dynamoeffekt in seinem Inneren, verursacht durch Konvektion und schnelle Rotation.
 
Abb.: Magnetaresind Neutronensterne, deren Magnetfelder das 1.000fache des bei Neutronensternen üblichen Wertes aufweisen. Man schätzt, dass etwa zehn Prozent aller Neutronensterne zu dieser Sternklasse zählen. Neutronensterne entstehen beim Kollaps von Sternen einer bestimmten Gewichtsklasse bei einer Supernovaexplosion. Sie haben einen typischen Durchmesser von etwa 20 km und ein extrem starkes Magnetfeld der Größenordnung 1012 Gauß (Zum Vergleich: Das Magnetfeld der Erde hat eine Stärke von etwa einem Gauß), das sich als Folge der Gesetze der Elektrodynamik ergibt, wonach das Produkt aus Sternquerschnitt und Magnetfeld beim Kollaps des Vorläufersterns konstant bleibt. Soft Gamma Repeater SGR 1806-20 assoziiert mit SNR G10.0-0.3 d=15 kpc? P = 7.5s; P' = 10-10 s/s; B = 1014 Gauß Bild: R. Mallozzi/NASA |
Doch nicht nur der INTEGRAL - Satellit zeichnete das Ereignis auf. Die Wellenfront wurde noch von 13 anderen Röntgen- und Gammadetektoren im Weltraum gemessen, die zwischen Erde und Saturn Messungen durchführen. "Sogar der russische Coronas-F Satellit sah diesen Burst, obwohl er sich zur Zeit des Ereignisses hinter der Erde befand, er die direkte Strahlung von der Quelle also gar nicht messen konnte", erklärt Giselher Lichti. "Die Analyse der Ankunftszeiten ergab, dass das russische Instrument Gammastrahlen gemessen hatte, die von der Mondoberfläche reflektiert worden waren."
Wegen der Stärke des Bursts und seiner durchdringenden Strahlung konnten auch Detektoren die Wellenfront messen, die nicht auf die Stelle am Himmel gerichtet waren, von dem die Strahlung kam. Die Gammastrahlung durchdrang nämlich die Abschirmungen aus Metall oder Kristallen und brachte die Detektoren kurzzeitig in die Sättigung.
Ob das vom MPE gebaute Instrument auf dem Satelliten INTEGRAL in die Sättigung ging, muß noch geklärt werden. "Das Verhalten unseres Detektors unter so hohem Strahlungsfluss muss noch detaillierter untersucht werden, um eine genauere Abschätzung der gesamten Energieabstrahlung dieses Ereignisses zu erlauben", sagt Andreas von Kienlin, der das Instrument kalibriert und in Betrieb genommen hat.
"Der Ausbruch des Neutronensterns begann mit der Emission von energiereicher Gammastrahlung, die nur einen Bruchteil einer Sekunde dauerte, aber den Großteil der emittierten Energie enthielt. Dieser Ausbruch war gefolgt von einer schwächeren Gammaemission, die mehr als sechs Minuten andauerte und deren Intensität mit einer Periode von 7,56 Sekunden oszillierte. Diese Oszillation wird mit der bekannten Rotationsperiode des Neutronensterns in Verbindung gebracht", erklärt Andreas von Kienlin. "Unsere Messungen zeigten, dass die Energieverteilung der Gammaquanten des Ausbruchs charakteristisch für ein ultra-heißes thermisches Plasma ist", sagt Andreas von Kienlin. "Genau das, was wir von einem Magnetar erwarten, der leichte hochenergetische Teilchen ausstößt. Die meisten dieser Teilchen zerstrahlten offensichtlich in reine Gammastrahlen, die dann in den interstellaren Raum entwichen."
Die oszillierende Gammaemission stammt offenbar von übriggebliebenen Elektronen und Positronen, die im Magnetfeld des Magnetars eingeschlossen sind, vermuten die Astrophysiker. Die Theorie sagt vorher, dass solch ein heißer eingeschlossener Feuerball innerhalb von Minuten schrumpfen und verdampfen sollte. Seine Helligkeit scheint zu oszillieren, weil der Feuerball über das Magnetfeld an die Oberfläche des rotierenden Neutronensterns gebunden ist.
Die riesige Energiemenge des Ausbruchs vom 27. Dezember 2004 legt eine neue Lösung für ein altes Problem der Gammastrahlen - Burstastronomie nahe: Es handelt sich um die Frage nach den Quellen dieser sogenannten "Short-Duration Gamma-Ray Bursts". In den letzten 35 Jahren hat man Hunderte von kurzen (weniger als zwei Sekunden) mysteriösen Blitzen von hochenergetischer Strahlung aus den Tiefen des Raumes gemessen, ohne dass man weiß, woher diese gemessene Strahlung kommt. Eine Hypothese besagt, dass diese Strahlung bei der Verschmelzung von zwei kompakten Objekten (z. B. von zwei Neutronensternen oder einem Neutronenstern mit einem Schwarzen Loch) entstehen könnte. Die neuen Beobachtungen lassen nun eine weitere Interpretation der Beobachtungen zu: Es könnte sich dabei nämlich zum Teil um Ausbrüche wie dem am 27. Dezember beobachteten handeln. Diese Idee wird von Kevin Hurley und seinem Team vorgeschlagen. Danach können solche kurzen Ausbrüche auf Grund ihrer Intensität von sehr fernen Galaxien beobachtet werden. Ein Ereignis mit der vor kurzem gemessenen Stärke könnte bis zu Entfernungen von einigen Hundertmillionen Lichtjahren beobachtet werden. "Da sich in diesem Entfernungsbereich viele Galaxien befinden, müsste man solche Ereignisse häufig sehen. Man könnte damit also die Beobachtungen zu einem großen Teil, wenn nicht sogar ganz, erklären", meint Giselher Lichti.
Wie kann man sich nun den enormen Energieausstoß von einem solchen Magnetar erklären? Die Erfinder des Magnetar-Modells, die Theoretiker Robert Duncan (Universtät von Texas, Austin) und Christopher Thompson (Canadian Institute of Theoretical Astrophysics, Toronto), schlagen folgendes Szenario vor, um den gigantischen Energieausstoß bei einem solchen Flare erklären zu können. Um ihre Idee verstehen zu können, muss man sich erst einmal das ungeheuer starke Magnetfeld eines Magnetars bewusst machen, das um einen Faktor 1000 stärker ist als das eines normalen Neutronensterns. In solchen starken Feldern wird z. B. ein Wasserstoffatom so stark deformiert, dass es nadelförmig wird (~200 mal schmäler als lang). So ein Stern hat tief in seinem Inneren ein stark verdrilltes Magnetfeld, dessen Magnetfeldlinien sich wie eine Uhrfeder um die Rotationsachse winden. Sein äußeres Magnetfeld jedoch ähnelt mehr oder weniger dem eines Dipols eines Stabmagneten (vergleichbar dem Erdmagnetfeld).
Man glaubt, dass das verdrillte innere Magnetfeld das Überbleibsel der schnellen Rotation ist, die der Neutronenstern bei seiner Entstehung mitbekam. Es enthält den größten Teil der magnetischen Energie des Sterns. Dieses Magnetfeld übt eine Kraft auf die ein Kilometer dicke Kruste des Sterns mit einem Radius von zehn Kilometer aus und verschiebt diese. Das hat zum einen zur Folge, dass sich das äußere Magnetfeld verdrillt und zum anderen, dass starke Ladungsströme um den Stern fließen. Wenn sich die Magnetfelder immer stärker verdrillen, dann lassen diese Ströme den Stern hell im niederenergetischen Gammabereich aufscheinen. Die Verdrillung des äußeren Magnetfeldes beeinflusst auch die Rotation des Sterns und führt zu einer stärkeren Abbremsung.
Das scheint auch mit dem Magnetar SGR 1806-20 passiert zu sein. Von März 2004 bis zum Ausbruch im Dezember hat SGR 1806-20 viele einzelne schwache Ausbrüche gezeigt, die auf eine Verschiebung der Kruste hindeuteten. SGR 1806-20 wurde also immer heller im Gammalicht, mit Emission von immer mehr harten Gammaphotonen und einer stärkeren Abbremsung. Alle diese Messungen deuteten darauf hin, dass sich das äußere Magnetfeld mehr und mehr verdrillte. In dem Modell für den Ausbruch vom 27. Dezember von Duncan und Thompson wurde die Verdrillung so stark, dass der Stern mit seiner Kruste instabil wurde. Die Spannung des äußeren Magnetfelds hat sich dann in einem enormen Ausbruch entladen und es dann in einem niedrigeren und unverdrillten Zustand neu angeordnet.
Zur Zeit des Ausbruchs war der Magnetar nur fünf Grad von der Sonne entfernt. Er befindet sich in der Konstellation Sagittarius, in der Nähe des galaktischen Zentrums. Mit Hilfe des interplanetaren Netzwerkes, einem Zusammenschluss von mehreren Satellitenmissionen, gelang es Kevin Hurley mittels Triangulation die Position des Ausbruchs mit dem Magnetar SGR 1806-20 zu identifizieren. Die Position wurde von Radioastronomen des Very-Large Array - Teleskops in Socorro, New Mexico, durch Messung eines schwächer werdenden Nachleuchtens bei Radiowellen bestätigt. Die Beobachtung dieses Nachleuchtens liefert außerdem wichtige Informationen über den Explosionsmechanismus und wird zu einem besseren Verständnis des beobachteten Phänomens beitragen.
"Für das Leben auf der Erde bestand durch den Magnetar-Ausbruch jedoch keine Gefahr, da die Atmosphäre für diese Art von Strahlung undurchsichtig ist. Diese Strahlung ionisiert die Atome der Hochatmosphäre und wird dabei absorbiert.", gibt Giselher Lichti Entwarnung.
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Literatur zu "SGR1806-20" | |||
orig. Artikel |
orig. Nature Paper |
und
Konus Preprint
K2.2 Soft Gamma-Ray Repeater SGR 1806-20
| SGR 1806-20 — a very bright outburst on October 5 2004 | |
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Authors: D. Götz, S. Mereghetti, S. Molkov, K. Hurley, I.F. Mirabel, R. Sunyaev, G. Weidenspointner, S. Brandt, M. Del Santo, M. Feroci, E. Gogus, A. von Kienlin, M. van der Klis, C. Kouveliotou, N. Lund, G. Pizzichini, P. Ubertini, C. Winkler, P.M. Woods |
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Journal-ref: A&A 445 (2006) 313-321 [astro-ph/0508615 ] |
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Title: Two years of INTEGRAL monitoring of the Soft Gamma-Ray Repeater SGR 1806-20: from quiescence to frenzy |
| Abstract:
SGR 1806-20 has been observed for more than 2 years with the
INTEGRAL satellite. In this period the source went from a quiescent state into a very active one
culminating in a giant flare on December 27 2004. Here we report on the properties of all the short
bursts detected with INTEGRAL before the giant flare. We derive their number-intensity distribution
and confirm the hardness-intensity correlation for the bursts found by Götz et al. (2004a).
Our sample includes a very bright outburst that occurred on October 5 2004, during which over one hundred bursts were emitted in 10 minutes, involving an energy release of 3 x 1042 erg. We present a detailed analysis of it and discuss our results in the framework of the magnetar model. INTRODUCTION
SGR 1806–20 is currently one of the most active Soft Gamma-ray Repeaters. These sources (see Hurley (2000),
Woods & Thompson (2004) for recent reviews) were discovered by their recurrent emission of soft (<100 keV)
gamma-ray bursts. They undergo sporadic, unpredictable periods of activity, which last days to months, often
followed by long periods (up to years or decades) during which no bursts are detected. These recurrent bursts
have typical durations of ~0.1 s and luminosities in the range
Lo = 3 × 1039-42 erg s-1.
Occasionally, SGRs also emit giant flares that last up to a few hundred seconds
and exhibit remarkable pulsations that reveal their spin
periods (e.g. Mazets et al. (1979), Hurley et al. (1999), Hurley et al. (2005)).
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These results can be explained in the framework of a recent evolution of the magnetar model:
Lyutikov (2003) explains SGR bursts as generated by loss of magnetic equilibrium
in the magnetosphere, in close analogy to solar flares: new current-carrying magnetic flux tubes
rise continuously into the magnetosphere, driven by the deformations of the neutron star crust.
This in turn generates an increasingly complicated magnetic field structure, which
at some point becomes unstable to resistive reconnection.
During these reconnection events, some of the magnetic energy carried by the currents associated
with the magnetic flux tubes is dissipated. The large event described here can be explained by the
simultaneous presence of different active regions (where the flux emergence is especially
active) in the magnetosphere of the neutron star.
In fact, a long outburst with multiple components is explained as the result of numerous avalanche-type
reconnection events, as reconnection at one point may trigger reconnection at other points.
This explains the fact that the outburst seems to be composed by the sum of several
short bursts. This kind of event might indicate a particularly complicated phase of the magnetic field
structure which eventually led to a global restructuring of the whole magnetosphere with the emission of
the giant flare on December 27. This mode also suggests that short events are due to reconnection, while
longer events have in addition a large contribution from the surface, heated by the
precipitating particles, and are harder. This may explain the generally harder spectra observed.
Thus events like these release a small (compared to giant flares) fraction of the energy stored in the
twisted magnetic field of the neutron star, not allowing the magnetic field to decay significantly.
K3.1 Multiwavelength IGR J16283-4838
| IGR J16283-4838 — NH = 0.4 - 1.7 x 1023 cm-2 | |||
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Authors: V. Beckmann, J. A. Kennea, C. Markwardt, A. Paizis, S. Soldi, J. Rodriguez, S. D. Barthelmy, D. N. Burrows, M. Chester, N. Gehrels, N. Mowlavi, J. Nousek | ||
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Journal-ref: ApJ 631 (2005) 506-510 [astro-ph/0506170 ] | ||
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Title: Swift, INTEGRAL, RXTE, and Spitzer reveal IGR J16283-4838 | ||
| Abstract:
We present the first combined study of the recently discovered source IGR J16283-4838
with Swift, INTEGRAL, and RXTE. The source, discovered by INTEGRAL on April 7, 2005,
shows a highly absorbed
(variable NH = 0.4 - 1.7 x 1023 cm-2) and flat (photon index = 1) spectrum in the Swift/XRT and RXTE/PCA data. No optical counterpart is detectable (V > 20 mag), but a possible infrared counterpart within the Swift/XRT error radius is detected in the 2MASS and Spitzer/GLIMPSE survey. The observations suggest that IGR J16283-4838 is a high mass X-ray binary containing a neutron star embedded in Compton thick material. This makes IGR J16283-4838 a member of the class of highly absorbed HMXBs, discovered by INTEGRAL. INTRODUCTION
The dense molecular clouds lead to strong star formation activity, which also results in the formation of binary systems, and subsequently to X-ray binary systems. These objects show X-ray flares and outbursts because of accretion processes onto the compact object. At the same time, the gas and dust of the spiral arms absorb most of the emission in the optical to soft X-ray regime below 10 keV. In addition, dense absorbing atmospheres around the object make the detection of these sources even more difficult. The hard X-ray and soft gamma-ray mission INTEGRAL operates at energies above 20 keV. With the large field of view of the main instruments, the imager IBIS and the spectrograph SPI, and its observing program focussed on the Galactic plane and center, INTEGRAL is a powerful tool to discover highly absorbed sources (NH > 1023 cm-2) in the Galactic plane. So far a handful of those enigmatic objects has been found since the launch of INTEGRAL in October 2002 Six of those sources have been published so far:
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IGR J16318-4848 (NH ~ 19 × 1023 cm-2),
Distribution of IGR sources
For a list of all sources found by INTEGRAL see:
.
[13 July 2005] Three satellites needed to bring out ‘shy star’
An international team of scientists has uncovered a rare type of neutron star
so elusive that it took three satellites to identify it.
Credits: NASA/Dana Berry
This artist's impression illustrates neutron star IGR J16283-4838 flaring.
This is due to the matter accreted from its companion star.
Credits: NASA/Dana Berry
Artist's impression of neutron star IGR J16283-4838 orbiting its companion star.
Matter flowing from the companion to the neutron star, attracted by strong gravity,
occasionally flares up in X-ray and gamma-ray light.
Such flares last only for a few days or weeks but reveal the location of an otherwise dim system.
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The neutron star, called IGR J16283-4838, is an ultra-dense ‘ember’ of an exploded star and was first seen by Integral on 7 April 2005. This neutron star is about 8 kpc away, in a ‘double hiding place’. This means it is deep inside the spiral arm Norma of our Milky Way galaxy, obscured by dust, and then buried in a two-star system enshrouded by dense gas.
“We are always hunting for new sources,” said Simona Soldi, who first saw the neutron star. “It is exciting to find something so elusive. How many more sources like this are out there?”
Neutron stars are the core remains of ‘supernovae’, exploded stars once about ten times as massive as our Sun. They contain about a Sun's worth of mass compacted into a sphere about 20 kilometres across.
“Our Galaxy’s spiral arms are loaded with neutron stars, black holes and other exotic objects, but the problem is that the spiral arms are too dusty to see through,” said Dr Volker Beckmann at NASA Goddard Spaceflight Centre, lead author of the combined results.
“The right combination of X-ray and gamma-ray telescopes could reveal what is hiding there, and provide new clues about the true star formation rate in our Galaxy,” he added.
Because the Integral scientists could not immediately decipher the nature of the object, they enlisted the help of NASA's Rossi X-ray Timing Explorer and the newly launched Swift satellite to observe it in different wavelengths.
Because gamma rays are hard to focus into sharp images, the science team then used the X-ray telescope on Swift to determine a precise location. In mid April 2005, Swift confirmed that the light was ‘highly absorbed’, which means the binary system was filled with dense gas from the stellar wind of the companion star.
Later the scientists used the Rossi Explorer to observe the source as it faded away. This observation revealed a familiar light signature, clinching the case for a fading high-mass X-ray binary with a neutron star.
IGR J16283-4838 is the seventh so-called ‘highly absorbed’, or hidden neutron star to be identified. Neutron stars, created from fast-burning massive stars, are intrinsically tied to star formation rates. They are also energetic ‘beacons’ in regions too dusty to study in detail otherwise. As more and more are discovered, new insights about what is happening in the Galaxy's spiral arms begin to emerge.
IGR J16283-4838 revealed itself with an ‘outburst’ on or near its surface. Neutron stars such as IGR J16283-4838 are often part of binary systems, orbiting a normal star. Occasionally, gas from the normal star, lured by gravity, crashes onto the surface of the neutron star and releases a great amount of energy. These outbursts can last for weeks before the system returns to dormancy for months or years.
Integral, the Rossi Explorer and Swift all detect X-rays and gamma rays, which are far more energetic than the visible light that our eyes detect. Yet each satellite has different capabilities. Integral has a large field of view, enabling it to scan our Milky Way galaxy for neutron stars and black hole activity.
Swift contains a high-resolution X-ray telescope, which allowed scientists to zoom in on IGR J16283-4838. The Rossi Explorer has a timing spectrometer, a device used to uncover properties of the light source, such as speed and rapid variations in the order of milliseconds.
K3.2 Multiwavelength IGR J16393-4643
| IGR J16393-4643 — HMXB — P = 912 s — NH = 2.5 × 1023 cm-2 | ||
|
Authors: A. Bodaghee, R. Walter, J.A. Zurita Heras, A.J. Bird, T.J.-L. Courvoisier, A. Malizia, R. Terrier, P. Ubertini | |
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Journal-ref: A&A 447 (2006) 1027-1034 [astro-ph/0510112 ] | |
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Title: IGR J16393-4643: a new heavily-obscured X-ray pulsar | |
| Abstract:
An analysis of the high-energy emission from IGR J16393-4643 (=AX
J1639.0-4642) is presented using data from INTEGRAL and XMM-Newton. The source
is persistent in the 20-40 keV band at an average flux of 5.1x10^-11
ergs/cm2/s, with variations in intensity by at least an order of magnitude. A
pulse period of 912.0 s was discovered in the ISGRI and EPIC light
curves. The source spectrum is a strongly-absorbed
(NH = 2.5 × 1023 cm-2) power law that features
a high-energy cutoff above 10 keV.
Two iron emission lines at 6.4 and 7.1 keV, an iron absorption edge >7.1 keV, and a soft excess emission of 7x10^-15 ergs/cm2/s between 0.5-2 keV, are detected in the EPIC spectrum. The shape of the spectrum does not change with the pulse. Its persistence, pulsation, and spectrum place IGR J16393-4643 among the class of heavily-absorbed HMXBs. The improved position from EPIC is R.A. (J2000)=16:39:05.4 and Dec.=-46:42:12 (4" uncertainty) which is compatible with that of 2MASS J16390535-4642137.
1. Introduction
The INTEGRAL core program routinely devotes observation time to Galactic Plane Scans (GPS)
and Galactic Centre Deep Exposures (GCDE). These numerous snapshots of the Milky Way can be assembled into
mosaic images of long exposure time (~1 Ms). This gamma-ray view of the galaxy, as collected by ISGRI, enabled
Bird et al. (2004) to detect 123 sources at a significance above 6s.
Around 20 of these sources are of unknown origin. A good portion of these new sources probably belong to the class of heavily-absorbed High Mass Xray Binaries (HMXBs) that are concentrated along the galactic plane and in the spiral arms. High-Mass X-ray Binaries are composed of a compact object such as a neutron star or a black hole that orbits a massive stellar companion. Depending on the type of companion, known HMXBs can be divided into two groups. Most HMXBs classified by Liu et al. (2000) contain a Be star. These systems are usually transient sources with hard spectra. The compact object has a wide orbit which mostly keeps it away from the Be star and its disk. Outbursts in these systems are due primarily to the compact object approaching the star and accreting matter from the slow, dense stellar wind. The second group of HMXBs features an O or B supergiant star. The orbit of the compact object places it well within the stellar wind, so material from the supergiant can be fed directly to the compact object through Bondi accretion, or it can pass to the compact object via an accretion disk. The latter mechanism is typically found in bright X-ray binaries in which the Roche lobe overflow of gas from the OB star supercedes the flow of accreting matter. For less luminous binaries, the OB star does not fill its Roche lobe and the behaviour of the X-ray source is determined predominantly by the stellar wind. X-ray emission in supergiant HMXB systems is usually persistent, with flares stemming from inhomogeneities in the wind. Neutron stars with strong magnetic fields develop a hot spot for accretion which can result in a pulsation. References Bird, A. J., Barlow, E. J., Bassani, L., et al. 2004, ApJ, 607, L33 | ||
| IGR J16393-4643 — HMXB — Prot = 912 s — Porb = 3.6875 d — e < 0.25 | ||
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Authors: T.W.J. Thompson, J.A. Tomsick, R.E. Rothschild, J.J.M. in't Zand, R. Walter | |
|
Journal-ref: ApJ 649 (2006) 373 [astro-ph/0605657 ] | |
|
Title: Orbital Parameters for the X-ray Pulsar IGR J16393-4643 | |
Abstract:
With recent and archival Rossi X-Ray Timing Explorer (RXTE) X-ray
measurements of the heavily obscured X-ray pulsar IGR J16393-4643, we carried
out a pulse timing analysis to determine the orbital parameters. Assuming a
circular orbit, we phase-connected data spanning over 1.5 years. The most
likely orbital solution has
 a projected semi-major axis of 43 ± 2 lt-s and
an orbital period of 3.6875 ± 0.0006 days.
This implies a mass function of f(M) = 6.5
± 1.1 M and confirms that this
INTEGRAL source is a High Mass X-ray
Binary (HMXB) system.
By including eccentricity in the orbital model, we find e < 0.25 at the 2 sigma level. The 3.7 day orbital period and the previously known ~910 s pulse period place the system in the region of the Corbet diagram populated by supergiant wind accretors, and the low eccentricity is also consistent with this type of system. Finally, it should be noted that although the 3.7 day solution is the most likely one, we cannot completely rule out two other solutions with orbital periods of 50.2 and 8.1 days. INTRODUCTION
their location in the Norma region and high intrinsic absorption. They are believed to be HMXBs and IGR J16393-4643 (l = 338.0°, b = 0.1°) is probably a member of this class. That this system may be a HMXB has also been suggested by Sugizaki et al. (2001) and Combi et al. (2004) due to the huge hydrogen column density towards the source, the hard spectral index (0.7–10 keV band), and its flux variability. Using 15–40 keV INTEGRAL ISGRI data spanning about 54 days, the pulse period was measured to be 912.0 ± 0.1 s with a pulse fraction of 54 ± 24%. | ||
K3.3 Multiwavelength IGR J2018+4043
| IGR J2018+4043 — NH = 6 × 1022 cm-2 | |
|
Authors: A.M. Bykov, A.M. Krassilchtchikov, Yu.A. Uvarov, J.A. Kennea, G.G.Pavlov, G.M.Dubner, E.B.Giacani, H.Bloemen, W.Hermsen, J.Kaastra, F.Lebrun, M.Renaud, R.Terrier, M.DeBecker, G.Rauw, J.-P.Swings |
|
Journal-ref: ApJ 649 (2006) L21-L24 [astro-ph/0609676 ] |
|
Title: On the nature of the hard X-ray source IGR J2018+4043 |
| Abstract:
We found a very likely counterpart to the recently discovered hard
X-ray source IGR J2018+4043 in the multi-wavelength observations of the source
field. The source, originally discovered in the 20-40 keV band, is now
confidently detected also in the 40-80 keV band, with a flux of
fX(40-80 keV) = (1.4 ± 0.4) x 10-11 erg cm-2 s-1. A 5 ks Swift observation of the IGR J2018+4043 field revealed a hard point-like source with the observed flux of fX(0.5-10 keV) = (3.4 ± 0.7) x 10-12 erg cm-2 s-1 (90% confidence level) at alpha = 20h18m38.55s, delta = +40d41m00.4s (with a 4.2" uncertainty). The combined Swift-INTEGRAL spectrum can be described by an absorbed power-law model with photon index G = 1.3 ± 0.2 and NH = 6 × 1022 cm-2. In archival optical and infrared data we found a slightly extended and highly absorbed object at the Swift source position. There is also an extended VLA 1.4 GHz source peaked at a beam-width distance from the optical and X-ray positions. The observed morphology and multiwavelength spectra of IGR J2018+4043 are consistent with those expected for an obscured accreting object, i.e. an AGN or a Galactic X-ray binary. The identification suggests possible connection of IGR J2018+4043 to the bright gamma-ray source GEV J2020+4023 (3EG J2020+4017) detected by COS B and CGRO EGRET in the gamma-Cygni SNR field. | |
| Literatur zu "IGR sources" | |||
| J. Rodriguez, J.A. Tomsick, L. Foschini, R. Walter, A. Goldwurm, S. Corbel, P. Kaaret | 2003 | A&A 407, L41 |
"An XMM Observation of IGR J16320-4751=AX J1631.9-4752"
|
| R. Walter, J. Rodriguez, L. Foschini, J. de Plaa, S. Corbel, T.J.-L. Courvoisier, P.R. den Hartog, F. Lebrun, et al. | 2003 | A&A 411, L427-32 |
"INTEGRAL discovery of a bright highly obscured galactic X-ray binary source IGR J16318-4848"
|
| J. Rodriguez, C. Cabanac, D.C. Hannikainen, V. Beckmann, S.E. Shaw, J. Schultz | 2005 | A&A 432, 235 |
"Unveiling the Nature of the High Energy Source IGR J19140+0951"
|
| J. Albert, et al, MAGIC collaboration | 2006 | ApJ 637, L41 |
"HESS J1813-178 — no longer an unidentified TeV source"
|
| D. Götz, S. Mereghetti, S. Molkov, K. Hurley, et al. | 2006 | A&A 445, 313-321 |
"Two years of INTEGRAL monitoring of SGR 1806-20: from quiescence to frenzy"
|
| V. Beckmann, J. A. Kennea, C. Markwardt, et al. | 2005 | ApJ 631, 506-510 |
"Swift, INTEGRAL, RXTE, and Spitzer reveal IGR J16283-4838"
|
| A. Bodaghee, R. Walter, J.A. Zurita Heras, et al. | 2006 | A&A 447, 1027-34 |
"IGR J16393-4643: a new heavily-obscured X-ray pulsar"
|
| A.M. Bykov, A.M. Krassilchtchikov, Yu.A. Uvarov, et al. | 2006 | ApJ 649, L21-L24 |
"On the nature of the hard X-ray source IGR J2018+4043"
|
| T.W.J. Thompson, J.A. Tomsick, R.E. Rothschild, et al. | 2006 | ApJ 649, 373 |
"Orbital Parameters for the X-ray Pulsar IGR J16393-4643"
|
| A. Ibarra, G. Matt, M. Guainazzi, et al. | 2007 | A&A 465, 501 |
"The XMM-Newton/INTEGRAL monitoring campaign of IGR J16318-4848"
|
| J. Rodriguez, M. Cadolle Bel, J.A. Tomsick, et al. | 2007 | ApJ 655, L97 |
"The discovery outburst of the X-ray transient IGR J17497-2821 observed with RXTE and ATCA"
|
 | H. Heintzmann | ( Eintrag vom 16.3.2008) |
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