587 research outputs found
Three Millisecond Pulsars in FERMI LAT Unassociated Bright Sources
We searched for radio pulsars in 25 of the non-variable, unassociated sources
in the Fermi LAT Bright Source List with the Green Bank Telescope at 820 MHz.
We report the discovery of three radio and gamma-ray millisecond pulsars (MSPs)
from a high Galactic latitude subset of these sources. All of the pulsars are
in binary systems, which would have made them virtually impossible to detect in
blind gamma-ray pulsation searches. They seem to be relatively normal, nearby
(<=2 kpc) millisecond pulsars. These observations, in combination with the
Fermi detection of gamma-rays from other known radio MSPs, imply that most, if
not all, radio MSPs are efficient gamma-ray producers. The gamma-ray spectra of
the pulsars are power-law in nature with exponential cutoffs at a few GeV, as
has been found with most other pulsars. The MSPs have all been detected as
X-ray point sources. Their soft X-ray luminosities of ~10^{30-31} erg/s are
typical of the rare radio MSPs seen in X-rays.Comment: Accepted for publication in ApJ Letter
Eight gamma-ray pulsars discovered in blind frequency searches of Fermi LAT data
We report the discovery of eight gamma-ray pulsars in blind frequency
searches using the LAT, onboard the Fermi Gamma-ray Space Telescope. Five of
the eight pulsars are young (tau_c10^36 erg/s), and
located within the Galactic plane (|b|<3 deg). The remaining three are older,
less energetic, and located off the plane. Five pulsars are associated with
sources included in the LAT bright gamma-ray source list, but only one, PSR
J1413-6205, is clearly associated with an EGRET source. PSR J1023-5746 has the
smallest characteristic age (tau_c=4.6 kyr) and is the most energetic
(Edot=1.1E37 erg/s) of all gamma-ray pulsars discovered so far in blind
searches. PSRs J1957+5033 and J2055+25 have the largest characteristic ages
(tau_c~1 Myr) and are the least energetic (Edot~5E33 erg/s) of the
newly-discovered pulsars. We present the timing models, light curves, and
detailed spectral parameters of the new pulsars. We used recent XMM
observations to identify the counterpart of PSR J2055+25 as XMMU
J205549.4+253959. In addition, publicly available archival Chandra X-ray data
allowed us to identify the likely counterpart of PSR J1023-5746 as a faint,
highly absorbed source, CXOU J102302.8-574606. The large X-ray absorption
indicates that this could be among the most distant gamma-ray pulsars detected
so far. PSR J1023-5746 is positionally coincident with the TeV source HESS
J1023-575, located near the young stellar cluster Westerlund 2, while PSR
J1954+2836 is coincident with a 4.3 sigma excess reported by Milagro at a
median energy of 35 TeV. Deep radio follow-up observations of the eight pulsars
resulted in no detections of pulsations and upper limits comparable to the
faintest known radio pulsars, indicating that these can be included among the
growing population of radio-quiet pulsars in our Galaxy being uncovered by the
LAT, and currently numbering more than 20.Comment: Submitted to Ap
First Observation of the Baryon and a New Measurement of the Mass
Using data recorded with the CLEO II and CLEO II.V detector configurations at
the Cornell Electron Storage Rings, we report the first observation and mass
measurement of the charmed baryon, and an updated measurement
of the mass of the baryon. We find
= 231.0 +- 1.1 +- 2.0 MeV, and
= 166.4 +- 0.2 +- 0.3 MeV, where the errors are
statistical and systematic respectively.Comment: 8 pages postscript, also available through
http://w4.lns.cornell.edu/public/CLN
Detection of 16 Gamma-Ray Pulsars Through Blind Frequency Searches Using the Fermi LAT
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 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.Comment: Corresponding authors: Michael Dormody, Paul S. Ray, Pablo M. Saz
Parkinson, Marcus Ziegle
Observation of New States Decaying into
Using 13.7 fb^{-1} of data recorded by the CLEO detector at CESR, we
investigate the spectrum of charmed baryons which decay into Lambda_c^+ pi^-
pi^+ and are more massive than the Lambda_{c1} baryons. We find evidence for
two new states: one is broad and has an invariant mass roughly 480 MeV above
that of the Lambda_c^+; the other is narrow with an invariant mass of 596 +- 1
+- 2 MeV above the Lambda_c^+ mass. These results are preliminary.Comment: 11 pages postscript, also available through
http://w4.lns.cornell.edu/public/CLN
Correlated /\c-/\cbar production in e+e- annihilations at sqrt{s}~10.5 GeV
Using 13.6/fb of continuum two-jet e+e- -> ccbar events collected with the
CLEO detector, we have searched for baryon number correlations at the primary
quark level. We have measured the likelihood for a /\c+ charmed baryon to be
produced in the hemisphere opposite a /\c- relative to the likelihood for a
/\c+ charmed baryon to be produced opposite an anticharmed meson Dbar; in all
cases, the reconstructed hadrons must have momentum greater than 2.3 GeV/c. We
find that, given a /\c- (reconstructed in five different decay modes), a /\c+
is observed in the opposite hemisphere (0.72+/-0.11)% of the time (not
corrected for efficiency). By contrast, given a Dbar in one hemisphere, a /\c+
is observed in the opposite hemisphere only (0.21+/-0.02)% of the time.
Normalized to the total number of either /\c- or Dbar ``tags'', it is therefore
3.52+/-0.45+/-0.42 times more likely to find a /\c+ opposite a /\c- than a Dbar
meson. This enhancement is not observed in the JETSET 7.3 e+e- -> ccbar Monte
Carlo simulation.Comment: 19 pages, Latex, one figure separat
A Search for Charmless Decays
We have studied two-body charmless decays of the meson into the final
states , , , , , , and
using only decay modes with charged daughter particles. Using 9.7 million pairs collected with the CLEO detector, we place 90% confidence level
upper limits on the branching fractions, , depending
on final state and polarization.Comment: 8 pages postscript, also available through
http://w4.lns.cornell.edu/public/CLN
A Measurement of the Decay Asymmetry Parameters in \Xi_{c}^{0}\to \X^{-}\pi^{+}
Using the CLEO II detector at the Cornell Electron Storage Ring we have
measured the decay asymmetry parameter in the decay . We find , using the world average value of
we obtain . The physically allowed range of a decay
asymmetry parameter is . Our result prefers a negative value:
is at the 90% CL. The central value occupies the
middle of the theoretically expected range but is not yet precise enough to
choose between models.Comment: 10 pages postscript, also available through
http://w4.lns.cornell.edu/public/CLN
Study of exclusive two-body B0 meson decays to charmonium
We present a study of three B0 decay modes useful for time-dependent CP
asymmetry measurements. From a sample of 9.7 million B meson pairs collected
with the CLEO detector, we have reconstructed B0 -> J/psi K0S, B0 -> chi_c1
K0S, and B0 -> J/psi pi0 decays. The latter two decay modes have been observed
for the first time. We describe a K0S -> pi0 pi0 detection technique and its
application to the reconstruction of the decay B0 -> J/psi K0S. Combining the
results obtained using K0S -> pi+ pi- and K0S -> pi0 pi0 decays, we determine
Br(B0 -> J/psi K0) = (9.5 +- 0.8 +- 0.6)*10^-4, where the first uncertainty is
statistical and the second one is systematic.
We also obtain Br(B0 -> chi_c1 K0)= (3.9 +1.9/-1.3 +- 0.4)*10^-4 and Br(B0 ->
J/psi pi0) = (2.5 +1.1/-0.9 +- 0.2)*10^-5.Comment: 11 pages, 2 figures, submitted to Phys. Rev.
Measurement of the B0 and B+ meson masses from B0 -> psi(') K_S and B+ -> psi(') K+ decays
Using 9.6 million B meson pairs collected with the CLEO detector, we have
fully reconstructed 135 B0 -> psi(') K_S and 526 B+ -> psi(') K+ candidates
with very low background.
We fitted the psi(')K invariant mass distributions of these B meson
candidates and measured the masses of the neutral and charged B mesons to be
M(B0)=5279.1+-0.7[stat]+-0.3[syst] MeV/c^2 and
M(B+)=5279.1+-0.4[stat]+-0.4[syst] MeV/c^2. The precision is a significant
improvement over previous measurements.Comment: 2 typographic errors corrected; 11 pages, 2 figures; also available
through http://www.lns.cornell.edu/public/CLNS/CLEO.htm
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