ABSTRACT
Pulsars are rapidly rotating, highly magnetized neutron stars emitting radiation across the electromagnetic spectrum. Although there are more than 1800 known radio pulsars, until recently only seven were observed to pulse in gamma rays, and these were all discovered at other wavelengths. The Fermi Large Area Telescope (LAT) makes it possible to pinpoint neutron stars through their gamma-ray pulsations. We report the detection of 16 gamma-ray pulsars in blind frequency searches using the LAT. Most of these pulsars are coincident with previously unidentified gamma-ray sources, and many are associated with supernova remnants. Direct detection of gamma-ray pulsars enables studies of emission mechanisms, population statistics, and the energetics of pulsar wind nebulae and supernova remnants.
ABSTRACT
Pulsars are born with subsecond spin periods and slow by electromagnetic braking for several tens of millions of years, when detectable radiation ceases. A second life can occur for neutron stars in binary systems. They can acquire mass and angular momentum from their companions, to be spun up to millisecond periods and begin radiating again. We searched Fermi Large Area Telescope data for pulsations from all known millisecond pulsars (MSPs) outside of globular clusters, using rotation parameters from radio telescopes. Strong gamma-ray pulsations were detected for eight MSPs. The gamma-ray pulse profiles and spectral properties resemble those of young gamma-ray pulsars. The basic emission mechanism seems to be the same for MSPs and young pulsars, with the emission originating in regions far from the neutron star surface.
ABSTRACT
Observations with the Newton X-ray Multimirror Mission satellite show a strong periodic modulation at 6.67 +/- 0.03 hours of the x-ray source at the center of the 2000-year-old supernova remnant RCW 103. No fast pulsations are visible. If genetically tied to the supernova remnant, the source could either be an x-ray binary, composed of a compact object and a low-mass star in an eccentric orbit, or an isolated neutron star. In the latter case, the combination of its age and period would indicate that it is a peculiar magnetar, dramatically slowed down, possibly by a supernova debris disc. Both scenarios require nonstandard assumptions about the formation and evolution of compact objects in supernova explosions.
ABSTRACT
Isolated neutron stars are seen in x-rays through their nonthermal and/or surface thermal emissions. X-ray Multimirror Mission-Newton observations of the Geminga pulsar show a 43-electron volt spectrum from the whole neutron star surface, as well as a power-law component above 2 kiloelectron volts. In addition, we have detected a hot (170 electron volts) thermal emission from an approximately 60-meter-radius spot on the pulsar's surface. Such a thermal emission, only visible at selected phase intervals, may be coming from polar hot spot(s), long thought to exist as a result of heating from magnetospheric accelerated particles. It may provide the missing link between the x-ray and gamma-ray emission of the pulsar.
ABSTRACT
We report the X-ray Multimirror Mission-Newton European Photon Imaging Camera observation of two elongated parallel x-ray tails trailing the pulsar Geminga. They are aligned with the object's supersonic motion, extend for approximately 2', and have a nonthermal spectrum produced by electron-synchrotron emission in the bow shock between the pulsar wind and the surrounding medium. Electron lifetime against synchrotron cooling matches the source transit time over the x-ray features' length. Such an x-ray detection of a pulsar bow shock (with no Halpha emission) allows us to gauge the pulsar electron injection energy and the shock magnetic field while constraining the angle of Geminga's motion and the local matter density.
ABSTRACT
Isolated neutron stars are highly magnetized, fast-rotating objects that form as an end point of stellar evolution. They are directly observable in X-ray emission, because of their high surface temperatures. Features in their X-ray spectra could in principle reveal the presence of atmospheres, or be used to estimate the strength of their magnetic fields through the cyclotron process, as is done for X-ray binaries. Almost all isolated neutron star spectra observed so far appear as featureless thermal continua. The only exception is 1E1207.4-5209 (refs 7-9), where two deep absorption features have been detected, but with insufficient definition to permit unambiguous interpretation. Here we report a long X-ray observation of the same object in which the star's spectrum shows three distinct features, regularly spaced at 0.7, 1.4 and 2.1 keV, plus a fourth feature of lower significance, at 2.8 keV. These features vary in phase with the star's rotation. The logical interpretation is that they are features from resonant cyclotron absorption, which allows us to calculate a magnetic field strength of 8 x 10(10) G, assuming the absorption arises from electrons.
