3,322 research outputs found
Probing millisecond pulsar emission geometry using light curves from the Fermi Large Area Telescope
An interesting new high-energy pulsar sub-population is emerging following
early discoveries of gamma-ray millisecond pulsars (MSPs) by the Fermi Large
Area Telescope (LAT). We present results from 3D emission modeling, including
the Special Relativistic effects of aberration and time-of-flight delays and
also rotational sweepback of B-field lines, in the geometric context of polar
cap (PC), outer gap (OG), and two-pole caustic (TPC) pulsar models. In contrast
to the general belief that these very old, rapidly-rotating neutron stars (NSs)
should have largely pair-starved magnetospheres due to the absence of
significant pair production, we find that most of the light curves are best fit
by TPC and OG models, which indicates the presence of narrow accelerating gaps
limited by robust pair production -- even in these pulsars with very low
spin-down luminosities. The gamma-ray pulse shapes and relative phase lags with
respect to the radio pulses point to high-altitude emission being dominant for
all geometries. We also find exclusive differentiation of the current gamma-ray
MSP population into two MSP sub-classes: light curve shapes and lags across
wavebands impose either pair-starved PC (PSPC) or TPC / OG-type geometries. In
the first case, the radio pulse has a small lag with respect to the single
gamma-ray pulse, while the (first) gamma-ray peak usually trails the radio by a
large phase offset in the latter case. Finally, we find that the flux
correction factor as a function of magnetic inclination and observer angles is
typically of order unity for all models. Our calculation of light curves and
flux correction factor for the case of MSPs is therefore complementary to the
"ATLAS paper" of Watters et al. for younger pulsars.Comment: 51 pages, 23 figures, 3 tables; low-resolution figures; accepted for
publication by Ap
Modeling and Maximum Likelihood Fitting of Gamma-Ray and Radio Light Curves of Millisecond Pulsars Detected with Fermi
Pulsed gamma rays have been detected with the Fermi Large Area Telescope
(LAT) from more than 20 millisecond pulsars (MSPs), some of which were
discovered in radio observations of bright, unassociated LAT sources. We have
fit the radio and gamma-ray light curves of 19 LAT-detected MSPs in the context
of geometric, outer-magnetospheric emission models assuming the retarded vacuum
dipole magnetic field using a Markov chain Monte Carlo maximum likelihood
technique. We find that, in many cases, the models are able to reproduce the
observed light curves well and provide constraints on the viewing geometries
that are in agreement with those from radio polarization measurements.
Additionally, for some MSPs we constrain the altitudes of both the gamma-ray
and radio emission regions. The best-fit magnetic inclination angles are found
to cover a broader range than those of non-recycled gamma-ray pulsars.Comment: 4 pages, 3 figures, 2011 Fermi Symposium proceedings - eConf C110509
-- v2 corrects caption of Figure 1, v3 corrects missing fil
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