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"Bignami, Giovanni"
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A variable absorption feature in the X-ray spectrum of a magnetar
The X-ray spectrum of the soft-γ-ray repeater SGR 0418+5729 is found to exhibit an absorption line, the properties of which depend strongly on the star’s rotational phase; this line is interpreted as a proton cyclotron feature and its energy implies a magnetic field ranging from 2 × 10
14
gauss to more than 10
15
gauss.
Spectral analysis of a rotating magnetar
The Milky Way object SGR 0418+5729, first observed in June 2009 as a soft-γ-ray repeater, is thought to be a magnetar, a type of neutron star with a powerful magnetic field. This paper reports the analysis of the X-ray spectrum of this exotic object. The spectrum has an absorption line that varies dramatically in magnitude according to the star's rotational phase. The authors interpret this line as a cyclotron absorption feature generated near the surface, and its energy implies a magnetic field in the region of 10
15
gauss.
Soft-γ-ray repeaters (SGRs) and anomalous X-ray pulsars (AXPs) are slowly rotating, isolated neutron stars that sporadically undergo episodes of long-term flux enhancement (outbursts) generally accompanied by the emission of short bursts of hard X-rays
1
,
2
. This behaviour can be understood in the magnetar model
3
,
4
,
5
, according to which these sources are mainly powered by their own magnetic energy. This is supported by the fact that the magnetic fields inferred from several observed properties
6
,
7
,
8
of SGRs and AXPs are greater than—or at the high end of the range of—those of radio pulsars. In the peculiar case of SGR 0418+5729, a weak dipole magnetic moment is derived from its timing parameters
9
, whereas a strong field has been proposed to reside in the stellar interior
10
,
11
and in multipole components on the surface
12
. Here we show that the X-ray spectrum of SGR 0418+5729 has an absorption line, the properties of which depend strongly on the star’s rotational phase. This line is interpreted as a proton cyclotron feature and its energy implies a magnetic field ranging from 2 × 10
14
gauss to more than 10
15
gauss.
Journal Article
Two Missions, One Microquasar
The detection of high-energy gamma rays is providing a better picture of the structure and dynamics of microquasars. It has been on the suspect list for more than 30 years, but now we know for sure, smoking gun and all, that x-ray source number 3 in the constellation of Cygnus (Cyg X-3) emits gamma rays. After many near (and wide-of-the-mark) misses, we now have incontrovertible evidence coming from two independent gamma-ray telescopes, AGILE ( 1 ) and Fermi ( 2 ), the latter reported on page 1512 of this issue.
Journal Article
Celebrating the 400th Anniversary of Telescope Astronomy
Since Galileo looked skyward 400 years ago, telescopes have evolved to provide a broader and deeper understanding of the universe. Science authors laboring under the oppressive yoke of refereeing should think back to the time when Galileo Galilei brought his manuscript to printer Baglioni in Venice at the end of February 1610. The referee for his Sidereus Nuncius —a short treatise based on his first observations made through a telescope—was to be the office of the Holy Inquisition. Galileo knew that those referees didn't simply reject what they didn't like: They might invite you in for a few questions. But that time he was in luck. On 1 March, the Venice Council, on advice of the local Inquisitor, gave its consent.
Journal Article
