685 research outputs found
Pulsar Results with the Fermi Large Area Telescope
The launch of the Fermi Gamma-ray Space Telescope has heralded a new era in
the study of gamma-ray pulsars. The population of confirmed gamma-ray pulsars
has gone from 6-7 to more than 60, and the superb sensitivity of the Large Area
Telescope (LAT) on Fermi has allowed the detailed study of their spectra and
light curves. Twenty-four of these pulsars were discovered in blind searches of
the gamma-ray data, and twenty-one of these are, at present, radio quiet,
despite deep radio follow-up observations. In addition, millisecond pulsars
have been confirmed as a class of gamma-ray emitters, both individually and
collectively in globular clusters. Recently, radio searches in the direction of
LAT sources with no likely counterparts have been highly productive, leading to
the discovery of a large number of new millisecond pulsars. Taken together,
these discoveries promise a great improvement in the understanding of the
gamma-ray emission properties and Galactic population of pulsars. We summarize
some of the results stemming from these newly-detected pulsars and their timing
and multi-wavelength follow-up observations.Comment: 21 pages, 9 figures, to appear in Proceedings of ICREA Workshop on
The High-Energy Emission from Pulsars and their Systems, Sant Cugat, Spain,
2010 April 12-16 (Springer
Multifrequency Strategies for the Identification of Gamma-Ray Sources
More than half the sources in the Third EGRET (3EG) catalog have no firmly
established counterparts at other wavelengths and are unidentified. Some of
these unidentified sources have remained a mystery since the first surveys of
the gamma-ray sky with the COS-B satellite. The unidentified sources generally
have large error circles, and finding counterparts has often been a challenging
job. A multiwavelength approach, using X-ray, optical, and radio data, is often
needed to understand the nature of these sources. This chapter reviews the
technique of identification of EGRET sources using multiwavelength studies of
the gamma-ray fields.Comment: 35 pages, 22 figures. Chapter prepared for the book "Cosmic Gamma-ray
Sources", edited by K.S. Cheng and G.E. Romero, to be published by Kluwer
Academic Press, 2004. For complete article and higher resolution figures, go
to: http://www.astro.columbia.edu/~muk/mukherjee_multiwave.pd
Discovery of x-ray pulsations from the integral source IGR J11014−6103
published_or_final_versio
Activated Magnetospheres of Magnetars
Like the solar corona, the external magnetic field of magnetars is twisted by
surface motions of the star. The twist energy is dissipated over time. We
discuss the theory of this activity and its observational status. (1) Theory
predicts that the magnetosphere tends to untwist in a peculiar way: a bundle of
electric currents (the "j-bundle") is formed with a sharp boundary, which
shrinks toward the magnetic dipole axis. Recent observations of shrinking hot
spots on magnetars are consistent with this behavior. (2) Continual discharge
fills the j-bundle with electron-positron plasma, maintaining a nonthermal
corona around the neutron star. The corona outside a few stellar radii strongly
interacts with the stellar radiation and forms a "radiatively locked" outflow
with a high e+- multiplicity. The locked plasma annihilates near the apexes of
the closed magnetic field lines. (3) New radiative-transfer simulations suggest
a simple mechanism that shapes the observed X-ray spectrum from 0.1 keV to 1
MeV: part of the thermal X-rays emitted by the neutron star are reflected from
the outer corona and then upscattered by the inner relativistic outflow in the
j-bundle, producing a beam of hard X-rays.Comment: 23 pages, 7 figures; review chapter in the proceedings of ICREA
Workshop on the High-Energy Emission from Pulsars and Their Systems, Sant
Cugat, Spain, April 201
Gamma Ray Pulsars: Multiwavelength Observations
High-energy gamma rays are a valuable tool for studying particle acceleration
and radiation in the magnetospheres of energetic pulsars. The seven or more
pulsars seen by instruments on the Compton Gamma Ray Observatory (CGRO) show
that: the light curves usually have double-peak structures (suggesting a broad
cone of emission); gamma rays are frequently the dominant component of the
radiated power; and all the spectra show evidence of a high-energy turnover.
For all the known gamma-ray pulsars, multiwavelength observations and
theoretical models based on such observations offer the prospect of gaining a
broad understanding of these rotating neutron stars. The Gamma-ray Large Area
Space Telescope (GLAST), now in planning for a launch in 2007, will provide a
major advance in sensitivity, energy range, and sky coverage.Comment: To appear in Cosmic Gamma Ray Sources, Kluwer ASSL Series, Edited by
K.S. Cheng and G.E. Romer
Transient pulsed radio emission from a magnetar
Anomalous X-ray pulsars (AXPs) are slowly rotating neutron stars with very
bright and highly variable X-ray emission that are believed to be powered by
ultra-strong magnetic fields of >1e14 G, according to the 'magnetar' model. The
radio pulsations that have been observed from more than 1,700 neutron stars
with weaker magnetic fields have never been detected from any of the dozen
known magnetars. The X-ray pulsar XTE J1810-197 was revealed (in 2003) as the
first AXP with transient emission when its luminosity increased 100-fold from
the quiescent level; a coincident radio source of unknown origin was detected
one year later. Here we show that XTE J1810-197 emits bright, narrow, highly
linearly polarized radio pulses, observed at every rotation, thereby
establishing that magnetars can be radio pulsars. There is no evidence of radio
emission before the 2003 X-ray outburst (unlike ordinary pulsars, which emit
radio pulses all the time), and the flux varies from day to day. The flux at
all radio frequencies is approximately equal -- and at >20 GHz XTE J1810-197 is
currently the brightest neutron star known. These observations link magnetars
to ordinary radio pulsars, rule out alternative accretion models for AXPs, and
provide a new window into the coronae of magnetars.Comment: accepted by Nature; some new data and significantly revised
discussio
X-ray emission from isolated neutron stars
X-ray emission is a common feature of all varieties of isolated neutron stars
(INS) and, thanks to the advent of sensitive instruments with good
spectroscopic, timing, and imaging capabilities, X-ray observations have become
an essential tool in the study of these objects. Non-thermal X-rays from young,
energetic radio pulsars have been detected since the beginning of X-ray
astronomy, and the long-sought thermal emission from cooling neutron star's
surfaces can now be studied in detail in many pulsars spanning different ages,
magnetic fields, and, possibly, surface compositions. In addition, other
different manifestations of INS have been discovered with X-ray observations.
These new classes of high-energy sources, comprising the nearby X-ray Dim
Isolated Neutron Stars, the Central Compact Objects in supernova remnants, the
Anomalous X-ray Pulsars, and the Soft Gamma-ray Repeaters, now add up to
several tens of confirmed members, plus many candidates, and allow us to study
a variety of phenomena unobservable in "standard'' radio pulsars.Comment: Chapter to be published in the book of proceedings of the 1st Sant
Cugat Forum on Astrophysics, "ICREA Workshop on the high-energy emission from
pulsars and their systems", held in April, 201
Improving Ethical Review of Research Involving Incentives for Health Promotion
Alex London and colleagues propose new ethical frameworks for evaluating the risks associated with research in which financial or other incentives are used to promote healthy behavior
Multiwavelength monitoring and X-ray brightening of Be X-ray binary PSR J2032+4127/MT91 213 on its approach to periastron
The radio and gamma-ray pulsar PSR J2032+4127 was recently found to be in a decades-long orbit with the Be star MT91 213, with the pulsar moving rapidly towards periastron. This binary shares many similar characteristics with the previously unique binary system PSR B1259−63/LS 2883. Here, we describe radio, X-ray, and optical monitoring of PSR J2032+4127/MT91 213. Our extended orbital phase coverage in radio, supplemented with Fermi LAT gamma-ray data, allows us to update and refine the orbital period to 45–50 yr and time of periastron passage to 2017 November. We analyse archival and recent Chandra and Swift observations and show that PSR J2032+4127/MT91 213 is now brighter in X-rays by a factor of ∼70 since 2002 and ∼20 since 2010. While the pulsar is still far from periastron, this increase in X-rays is possibly due to collisions between pulsar and Be star winds. Optical observations of the Hα emission line of the Be star suggest that the size of its circumstellar disc may be varying by ∼2 over time-scales as short as 1–2 months. Multiwavelength monitoring of PSR J2032+4127/MT91 213 will continue through periastron passage, and the system should present an interesting test case and comparison to PSR B1259−63/LS 2883
Detection of the pairwise kinematic Sunyaev-Zel'dovich effect with BOSS DR11 and the Atacama Cosmology Telescope
We present a new measurement of the kinematic Sunyaev-Zeldovich effect using
data from the Atacama Cosmology Telescope (ACT) and the Baryon Oscillation
Spectroscopic Survey (BOSS). Using 600 square degrees of overlapping sky area,
we evaluate the mean pairwise baryon momentum associated with the positions of
50,000 bright galaxies in the BOSS DR11 Large Scale Structure catalog. A
non-zero signal arises from the large-scale motions of halos containing the
sample galaxies. The data fits an analytical signal model well, with the
optical depth to microwave photon scattering as a free parameter determining
the overall signal amplitude. We estimate the covariance matrix of the mean
pairwise momentum as a function of galaxy separation, using microwave sky
simulations, jackknife evaluation, and bootstrap estimates. The most
conservative simulation-based errors give signal-to-noise estimates between 3.6
and 4.1 for varying galaxy luminosity cuts. We discuss how the other error
determinations can lead to higher signal-to-noise values, and consider the
impact of several possible systematic errors. Estimates of the optical depth
from the average thermal Sunyaev-Zeldovich signal at the sample galaxy
positions are broadly consistent with those obtained from the mean pairwise
momentum signal.Comment: 15 pages, 8 figures, 2 table
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