SGR 0418+5729
Credit
X-ray: NASA/CXC/CSIC-IEEC/N.Rea et al;
Optical: Isaac Newton Group of Telescopes, La Palma/WHT;
Infrared:
NASA/JPL-Caltech; Illustration: NASA/CXC/M.Weiss
This graphic shows an exotic object in our galaxy called SGR 0418+5729 (SGR 0418 for short). As described in our press release, SGR 0418 is a magnetar, a type of neutron star that has a relatively slow spin rate and generates occasional large blasts of X-rays.
The only plausible source for the energy emitted in these outbursts
is the magnetic energy stored in the star. Most magnetars have extremely
high magnetic fields on their surface that are ten to a thousand times
stronger than for the average neutron star.
New data shows that SGR 0418 doesn't fit that pattern. It has a surface
magnetic field similar to that of mainstream neutron stars.
In the image on the left, data from NASA's Chandra X-ray Observatory
shows SGR 0418 as a pink source in the middle (mouse over the image
above). Optical data from the William Herschel telescope in La Palma and
infrared data from NASA's Spitzer Space Telescope are shown in red,
green and blue.
On the right is an artist's impression showing a close-up view of SGR
0418. This illustration highlights the weak surface magnetic field of
the magnetar, and the relatively strong, wound-up magnetic field lurking
in the hotter interior of the star. The X-ray emission seen with
Chandra comes from a small hot spot, not shown in the illustration. At
the end of the outburst this spot has a radius of only about 160 meters,
compared with a radius for the whole star of about 12 km.
The researchers monitored SGR 0418 for over three years using
Chandra, ESA's XMM-Newton as well as NASA's Swift and RXTE satellites.
They were able to make an accurate estimate of the strength of the
external magnetic field by measuring how its rotation speed changes
during an X-ray outburst. These outbursts are likely caused by fractures
in the crust of the neutron star precipitated by the buildup of stress
in the stronger magnetic field lying below the surface.
By modeling the evolution of the cooling of the neutron star and its
crust, as well as the gradual decay of its magnetic field, the
researchers estimated that SGR 0418 is about 550,000 years old. This
makes SGR 0418 older than most other magnetars, and this extended
lifetime has probably allowed the surface magnetic field strength to
decline over time. Because the crust weakened and the interior magnetic
field is relatively strong, outbursts could still occur.
The implications of this result for understanding supernova explosions and the number and evolution of magnetars is discussed in the press release.
SGR 0418 is located in the Milky Way galaxy at a distance of about 6,500 light years
from Earth. These new results on SGR 0418 appear online and will be
published in the June 10, 2013 issue of The Astrophysical Journal.
NASA's Marshall Space Flight Center in Huntsville, Ala., manages the
Chandra program for NASA's Science Mission Directorate in Washington.
The Smithsonian Astrophysical Observatory controls Chandra's science and
flight operations from Cambridge, Mass.
Fast Facts for SGR 0418+5729:
Scale:
Image is about 2 arcmin across (about 3 light years)
Category:
Neutron Stars/X-ray Binaries
Coordinates: (J2000)
RA 04h 18m 33.90s | Dec +57° 32' 22.90''
Constellation:
Camelopardalis
Observation Date:
3 pointings between Nov 2010 and Nov 2011
Observation Time:
45 hours 52 min (1 day 21 hours 52 min)
Obs. ID:
13148, 13235, 13236
Instrument:
ACISReferences: Rea, N. et al, 2013, ApJ in press; arXiv:1303.5579
Color Code: X-ray (Pink); Optical (Luminosity); Infrared (Red, Green, Blue)
Distance Estimate: About 6500 light years
Color Code: X-ray (Pink); Optical (Luminosity); Infrared (Red, Green, Blue)
Distance Estimate: About 6500 light years
