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Post Info TOPIC: LS5039
Blobrana


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RE: LS5039
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Title: On the origin of LS 5039 and PSR J1825-1446
Authors: J. Moldón, M. Ribó, J. M. Paredes, W. Brisken, V. Dhawan, M. Kramer, A. G. Lyne, B. W. Stappers

Context. The gamma-ray binary LS 5039 and the isolated pulsar PSR J1825-1446 were proposed to have been formed in the supernova remnant (SNR) G016.8-01.1.
Aims. We aim to obtain the Galactic trajectory of LS 5039 and PSR J1825-1446 to find their origin in the Galaxy, and in particular to check their association with SNR G016.8-01.1 to restrict their age.
Methods. By means of radio and optical observations we obtained the proper motion and the space velocity of the sources.
Results. The proper motion of PSR J1825-1446 corresponds to a transverse space velocity of 690 km/s at a distance of 5 kpc. Its Galactic velocity at different distances is not compatible with the expected Galactic rotation. The velocity and characteristic age of PSR J1825-1446 make it incompatible with SNR G016.8-01.1. There are no clear OB associations or SNRs crossing the past trajectory of PSR J1825-1446. We estimate the age of the pulsar to be 80-245 kyr, which is compatible with its characteristic age. The proper motion of LS 5039 is 7.09 and -8.82 mas/yr in right ascension and declination, respectively. The association of LS 5039 with SNR G016.8-01.1 is unlikely, although we cannot to discard it. The system would have had to be formed in the association Ser OB2 (at 2.0 kpc) if the age of the system is 1.0-1.2 Myr, or in the association Sct OB3 (distance 1.5-2 kpc) for an age of 0.1-0.2 Myr. If the system were not formed close to Ser OB2, the pseudo-synchronisation of the orbit would be unlikely.
Conclusions. PSR J1825-1446 is a high-velocity isolated pulsar ejected from the Galaxy. The distance to LS 5039, which needs to be constrained by future astrometric missions such as Gaia, is a key parameter for restricting its origin and age.

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Blobrana


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LS 5039
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Title: Mass and orbit constraints of the gamma-ray binary LS 5039
Authors: T. Szalai, G. E. Sarty, L. L. Kiss, J. M. Matthews, J. Vinkó, Cs. Kiss

We present the results of space-based photometric and ground-based spectroscopic observing campaigns on the gamma-ray binary LS 5039. The new orbital and physical parameters of the system are similar to former results, except we found a lower eccentricity. Our MOST-data show that any broad-band optical photometric variability at the orbital period is below the 2 mmag level. Light curve simulations support the lower value of eccentricity and imply that the mass of the compact object is higher than 1.8 solar masses.

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Blobrana


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Title: The modulation of the gamma-ray emission from the binary LS 5039
Authors: G. Dubus, B. Cerutti, G. Henri

Gamma-ray binaries, composed of a massive star and compact object, have been established as a new class of sources of very high energy (VHE) photons. The gamma-rays are produced by inverse Compton scattering of the stellar light by VHE electrons accelerated in the vicinity of the compact object. The VHE emission from LS 5039 displays an orbital modulation.
The inverse Compton spectrum depends on the angle between the incoming and outgoing photon in the electron rest frame. Since the angle at which an observer sees the star and electrons changes with the orbit, a phase dependence of the spectrum is expected. The phase-dependent spectrum of LS 5039 is calculated, assuming a continuous injection of electrons. The shape of the electron distribution depends on the injected power-law and on the magnetic field intensity.
Anisotropic scattering produces hard emission at inferior conjunction, when attenuation due to pair production of the VHE gamma-rays on star light is minimum. The computed lightcurve and spectra provide good fits to the HESS and EGRET observations, except at phases of maximum attenuation where pair cascade emission may be significant for HESS. Detailed predictions are made for a modulation in the GLAST energy range. The magnetic field intensity at periastron is 0.8 ±0.2 G.
Anisotropic inverse Compton scattering plays a major role in LS 5039. The derived magnetic field intensity, injection energy and slope suggest a rotation-powered pulsar wind nebula. Gamma-ray binaries are promising sources to study the environment of pulsars on small scales.

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Blobrana


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The first astronomical source of very high-energy gamma-ray pulses has been discovered by an international team of researchers. The gamma rays, which have energies greater than 100 giga electron volts (GeV), are at least 100 000 times more energetic than other known periodic signals. (Astronomy & Astrophysics in press).
The pulses are produced in binary star system called LS 5039, which is a well-known source of x-rays. Located in the constellation Scutum, LS 5039 comprises a massive "blue" star that is about 20 times larger than the Sun and an unknown compact object that could be a black hole or neutron star. The two objects are locked in a highly eccentric orbit.

0611251
Gamma ray intensity as a function of the orbital position of LS 5039. The signal is greatest at inferior conjunction when the compact body lies between the star and Earth.

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-- Edited by Blobrana at 00:53, 2006-12-02

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Blobrana


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Astronomers using the H.E.S.S. telescopes have discovered the first ever modulated signal from space in Very High Energy Gamma Rays – the most energetic such signal ever observed.
Regular signals from space have been known since the 1960s, when the first radio pulsar (nicknamed Little Green Men-1 for its regular nature) was discovered. This is the first time a signal has been seen at such high energies – 100,000 times higher than previously known - and is reported in the Journal Astronomy and Astrophysics.
The signal comes from a system called LS 5039 which was discovered by the H.E.S.S. team in 2005. LS5039 is a binary system formed of a massive blue star (20 times the mass of the Sun) and an unknown object, possibly a black hole. The two objects orbit each other at very short distance, varying between only 1/5 and 2/5 of the separation of the Earth from the Sun, with one orbit completed every four days.

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Blobrana


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(old news)
In a recent issue of Science Magazine, the High Energy Stereoscopic System (H.E.S.S.) team of international astrophysicists reports the discovery of another new type of very high energy (VHE) gamma ray source.

Gamma-rays are produced in extreme cosmic particle accelerators such as supernova explosions and provide a unique view of the high energy processes at work in the Milky Way. VHE gamma-ray astronomy is still a young field and H.E.S.S. is conducting the first sensitive survey at this energy range, finding previously unknown sources.


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The object that is producing the high energy radiation is thought to be a 'microquasar'. These objects consist of two stars in orbit around each other. One star is an ordinary star, but the other has used up all its nuclear fuel, leaving behind a compact corpse.
Depending on the mass of the star that produced it, this compact object is either a neutron star or a black hole, but either way its strong gravitational pull draws in matter from its companion star. This matter spirals down towards the neutron star or the black hole, in a similar way to water spiralling down a plughole.

However, sometimes the compact object receives more matter than it can cope with. The material is then squirted away from the system in a jet of matter moving at speeds close to that of light, resulting in a microquasar. Only a few such objects are known to exist in our galaxy and one of them, an object called LS5039, has now been detected by the H.E.S.S. team.


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In fact, the real nature LS5039 is something of a mystery. It is not clear what the compact object is. Some of the characteristics suggest it is a neutron star, some that it is a black hole. Not only that, but the jet isn't much of a jet; although it is moving at about 20% of the speed of light, which might seem a lot, in the context of these objects it's actually quite slow.

Nor is it clear how the gamma rays are being produced. As Dr. Guillaume Dubus of the Ecole Polytechnique points out "We really shouldn't have detected this object. Very high energy gamma rays emitted close to the companion star are more likely to be absorbed, creating a matter/antimatter cascade, than escape from the system."

"It's very exciting to have added another class of object to the growing catalogue of gamma ray sources. It's an intriguing object - it will take more observations to work out what is going on in there" - Dr Paula Chadwick of the University of Durham.

The H.E.S.S. array is ideal for finding new VHE gamma ray objects; because it's wide field of view (ten times the diameter of the Moon) means that it can survey the sky and discover previously unknown sources.

The results were obtained using the High Energy Stereoscopic System (H.E.S.S.) telescopes in Namibia, in South-West Africa. This system of four 13 m diameter telescopes is currently the most sensitive detector of VHE gamma-rays - radiation that is a million, million times more energetic than the visible light. These high energy gamma rays are quite rare even for relatively strong sources; only about one gamma ray per month hits a square metre at the top of the Earth's atmosphere. Also, since they are absorbed in the atmosphere, a direct detection of a significant number of the rare gamma rays would require a satellite of huge size.

The H.E.S.S. telescopes employ a trick - they use the atmosphere as detector medium. When gamma rays are absorbed in the air, they emit short flashes of blue light, named Cherenkov light, lasting a few billionths of a second. This light is collected by the H.E.S.S. telescopes with large mirrors and extremely sensitive cameras and can be used to create images of astronomical objects as they appear in gamma-rays.

The H.E.S.S. telescopes represent several years of construction effort by an international team of more than 100 scientists and engineers from Germany, France, the UK, Ireland, the Czech Republic, Armenia, South Africa and the host country Namibia. The instrument was inaugurated in September 2004 by the Namibian Prime Minister, Theo-Ben Guirab, and its first data have already resulted in a number of important discoveries, including the first astronomical image of a supernova shock wave at the highest gamma-ray energies.

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