Magnetar, pretending to be a pulsar, has puzzled astronomers
Using several large radio telescopes located on different continents, managed to clarify some of the amazing details of the "life" of a unique facility, opened in 2003 X-ray Observatory NASA Rossi (as transient anomalous X-ray pulsars) and the designation XTE J1810-197. Expected that XTE J1810-197 is a single rotating neutron star, which has a high-powered magnetic field — the so-called magnetars (magnetar).
However, despite the fact that all magnetars represent a very small class of objects, XTE J1810-197 and of magnetars was truly unique, capable of such tricks, which previously no other magnetar were observed. The strange behavior of this object may force astronomers to rethink some theories related to radio pulsars (another class of objects associated with neutron stars) and promises to bring a new understanding of the physics of the most extreme objects in our galaxy. August 24 released the corresponding article in the scientific journal Nature (vol 442, pp 892-895), it can be found also on arXiv.org.
Neutron stars — are the remnants of massive stars that exploded as supernovae. Their mass is the mass of our Sun, but they are compressed to a diameter of about 20 kilometers and have a density greater than the density of an atomic nucleus (in fact, they are so super-giant nuclei are). "Normal" pulsar — a neutron star emitting a "beacon mode" beams of radio waves from the areas of their magnetic poles. If the Earth falls into a rotating beam of radio waves, astronomers can capture radiation from the pulsar with radio telescopes. Since the discovery of the first pulsar in 1967, scientists have been able to find about 1,700 of these radio sources.
All pulsars characterized by a very strong magnetic field, but about a dozen famous earthlings neutron stars have magnetic fields are 100-1000 times stronger than typical pulsars. These are the magnetars, for observers manifested as anomalous X-ray pulsars (RPA English terms — anomalous X-ray pulsars — AXPs) and soft-recurring sources of gamma-ray bursts (MPG, soft gamma repeaters — SGRs, discovered by Soviet scientists in the late 1970s -s). "The magnetic field of a magnetar immediately launched any aircraft carrier so that it points to the north, like a compass needle, which affects the magnetic field of our Earth," — says David Helfand (David Helfand), Columbia University (Columbia University) in New York, who participated in these studies. Indeed magnetar field a thousand trillion (1015) times the Earth (1014 gauss in comparison with terrestrial 0.5 gauss).
Magnetar, in question, is about 10 thousand light-years from Earth in the constellation of Sagittarius (in this constellation is our galactic center, but it is "cut and cut" — it is in the 26 thousand light-years), and he regularly emits powerful radio pulses in the same way as any "decent" pulsar, which has its own magnetic field is much weaker. The usual magnetar would be visible only in X-rays, and only occasionally would show up as a very weak source in the optical and infrared light.
"No one ever checked the radio pulses of magnetars. General, we think that it is unable to magnetars, — said the head of the US-Australian research team, Fernando Camilo (Fernando Camilo) of Columbia University. — This facility will allow us to learn new things about the physics of magnetars, the that we never otherwise would not know. "
The fact that XTE J1810-197 can emit radio waves, it was reported in 2004 (this is shown by Jules Alpern (Jules Halpern) from Columbia University and his colleagues, who worked with the radio telescope VLA (Very Large Array) in New Mexico.) But in March of this year, Camilo and his staff engaged in a detailed study of the radio emission is through the East Australian radio Parkes, owned by CSIRO (Commonwealth Scientific and Industrial Research Organisation) — Social Organization Scientific and Industrial Research (later joined the project radio telescopes Robert C. Byrd Green Bank Telescope, Very Long Baseline Array (VLBA) and a host of other instruments in Australia, USA and Europe).
Immediately have found surprisingly powerful radio pulses followed every 5.54 seconds, which corresponded previously identified rotation period of the neutron star (and thus was denied an earlier suggestion that the radio waves could emit a cloud of particles ejected from the neutron star in an X-ray flare).
However, XTE J1810-197 is not limited, it is also a powerful transmitter at frequencies up to 140 GHz, which is the highest frequency ever recorded in the case of radio pulsars. In addition, in contrast to all the "normal" pulsar radio pulses of magnetars power and their shape varies from day to day. These variations are likely to suggest that the magnetic fields surrounding the pulsar, also subject to material changes. Expected to soon as the power pulses of the strange magnetar change at all wavelengths, including radio frequency range (ie, reduced to a level that preceded the 2003, however, when it will happen, just not yet known — maybe six months, maybe half a century ).
"For me, one of the most exciting features of this radiation is that its spectrum has a clear plateau, — says Camilo. — This means that the brightness is constant for all the observed frequencies from 350 MHz to 140 GHz. A typical pulsar at the highest frequencies would radiate about 15,000 times smaller than the low … "(At this time it is the brightest of all the neutron star, known to astronomers.)
The most influential theory for describing the behavior of the anomalous x-ray sources and the birth of soft gamma repeaters bursts, is now considered one that was created in 1992 by Canadian Christopher Thompson (Christopher Thompson) and the American Robert Duncan (Robert Duncan). These theorists have linked magnetar flare activity with reconnection of magnetic field lines in the magnetosphere, they (as it was considered initially) or external solid crust floating on top of superfluid "ingot".
It is assumed that the outer layers of neutron stars, the neutrons and protons can form a "normal" atoms (in the center of the quasar, they are pressed together enormous pressure so radically that there is a "socialization" of the electron shells and nuclei). Heavy duty magnetic field korezhit (pulling), these atoms on the surface so that they form a kind of kvazipolimernye threads interwoven with each other and form a sort of carpet covering the entire surface of the magnetosphere (also talk about penetrating this substance a single relativistic electron Fermi sea, well, deeper "swollen" form the core of the neutron "nuclear pasta" and "nuclear lasagna" — nuclear spaghetti and lasagna, — freezes thick branches and plates).
Perhaps it was sporadic restructuring fragments remix "hooked" to them the magnetic field lines (as in the plasma during solar flares) and leads to massive emissions of radiation. Alternative theory links the activity of "magnetars" with the presence of accretion disks of completely destroyed or companions of material ejected during the explosion. The work of Camilo and his colleagues write that their observations preclude alternative accretion models for AXPs.
"In any case, this discovery brings a rare" beast "- magnetar — a much more common radio pulsars and will certainly help us to put some order in all of this" zoo "of neutron stars," — said Dr. Camilo.
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