413 research outputs found
A new eclipsing binary system with a pulsating component detected by CoRoT
We report the discovery of CoRoT 102980178 (R.A.= 06:50:12.10, Dec.=
-02:41:21.8, J2000) an Algol-type eclipsing binary system with a pulsating
component (oEA). It was identified using a publicly available 55 day long
monochromatic lightcurve from the CoRoT initial run dataset (exoplanet field).
Eleven consecutive 1.26m deep total primary and the equal number of 0.25m deep
secondary eclipses (at phase 0.50) were observed. The following light elements
for the primary eclipse were derived: HJD_MinI= 2454139.0680 + 5.0548d x E. The
lightcurve modeling leads to a semidetached configuration with the photometric
mass ratio q=0.2 and orbital inclination i=85 deg. The out-of-eclipse
lightcurve shows ellipsoidal variability and positive O'Connell effect as well
as clear 0.01m pulsations with the dominating frequency of 2.75 c/d. The
pulsations disappear during the primary eclipses, which indicates the primary
(more massive) component to be the pulsating star. Careful frequency analysis
reveals the second independent pulsation frequency of 0.21 c/d and numerous
combinations of these frequencies with the binary orbital frequency and its
harmonics. On the basis of the CoRoT lightcurve and ground based multicolor
photometry, we favor classification of the pulsating component as a gamma
Doradus type variable, however, classification as an SPB star cannot be
excluded.Comment: 16 pages, 7 figures, 3 tables, accepted to Communications in
Asteroseismolog
Two active states of the narrow-line gamma-ray-loud AGN GB 1310+487
Context. Previously unremarkable, the extragalactic radio source GB 1310+487 showed a γ-ray flare on 2009 November 18, reaching a daily flux of ~ 10^(-6) photons cm^(-2) s^(-1) at energies E> 100 MeV and became one of the brightest GeV sources for about two weeks. Its optical spectrum shows strong forbidden-line emission while lacking broad permitted lines, which is not typical for a blazar. Instead, the spectrum resembles those of narrow emission-line galaxies.
Aims. We investigate changes in the object’s radio-to-GeV spectral energy distribution (SED) during and after the prominent γ-ray flare with the aim of determining the nature of the object and of constraining the origin of the variable high-energy emission.
Methods. The data collected by the Fermi and AGILE satellites at γ-ray energies; Swift at X-ray and ultraviolet (UV); the Kanata, NOT, and Keck telescopes at optical; OAGH and WISE at infrared (IR); and IRAM 30 m, OVRO 40 m, Effelsberg 100 m, RATAN-600, and VLBA at radio are analyzed together to trace the SED evolution on timescales of months.
Results. The γ-ray/radio-loud narrow-line active galactic nucleus (AGN) is located at redshift z = 0.638. It shines through an unrelated foreground galaxy at z = 0.500. The AGN light is probably amplified by gravitational lensing. The AGN SED shows a two-humped structure typical of blazars and γ-ray-loud narrow-line Seyfert 1 galaxies, with the high-energy (inverse-Compton) emission dominating by more than an order of magnitude over the low-energy (synchrotron) emission during γ-ray flares. The difference between the two SED humps is smaller during the low-activity state. Fermi observations reveal a strong correlation between the γ-ray flux and spectral index, with the hardest spectrum observed during the brightest γ-ray state. The γ-ray flares occurred before and during a slow rising trend in the radio, but no direct association between γ-ray and radio flares could be established.
Conclusions. If the γ-ray flux is a mixture of synchrotron self-Compton and external Compton emission, the observed GeV spectral variability may result from varying relative contributions of these two emission components. This explanation fits the observed changes in the overall IR to γ-ray SED
Electric field formulation for thin film magnetization problems
We derive a variational formulation for thin film magnetization problems in
type-II superconductors written in terms of two variables, the electric field
and the magnetization function. A numerical method, based on this formulation,
makes it possible to accurately compute all variables of interest, including
the electric field, for any value of the power in the power law current-voltage
relation characterizing the superconducting material. For high power values we
obtain a good approximation to the critical state model solution. Numerical
simulation results are presented for simply and multiply connected films, and
also for an inhomogeneous film.Comment: 15 p., submitte
Chandra X-ray Observations of the Two Brightest Unidentified High Galactic Latitude Fermi-LAT gamma-ray Sources
We present Chandra ACIS-I X-ray observations of 0FGL J1311.9-3419 and 0FGL
J1653.4-0200, the two brightest high Galactic latitude (|b|>10 deg) gamma-ray
sources from the 3 month Fermi-LAT bright source list that are still
unidentified. Both were also detected previously by EGRET, and despite
dedicated multi-wavelength follow-up, they are still not associated with
established classes of gamma-ray emitters like pulsars or radio-loud active
galactic nuclei. X-ray sources found in the ACIS-I fields of view are
catalogued, and their basic properties are determined. These are discussed as
candidate counterparts to 0FGL J1311.9-3419 and 0FGL J1653.4-0200, with
particular emphasis on the brightest of the 9 and 13 Chandra sources detected
within their respective Fermi-LAT 95% confidence regions. Further follow-up
studies, including optical photometric and spectroscopic observations are
necessary to identify these X-ray candidate counterparts in order to ultimately
reveal the nature of these enigmatic gamma-ray objects.Comment: ApJ, accepted. 18 pages, 5 figure
3C 286: a bright, compact, stable, and highly polarized calibrator for millimeter-wavelength observations
(Context.) A number of millimeter and submillimeter facilities with linear
polarization observing capabilities have started operating during last years.
These facilities, as well as other previous millimeter telescopes and
interferometers, require bright and stable linear polarization calibrators to
calibrate new instruments and to monitor their instrumental polarization. The
current limited number of adequate calibrators implies difficulties in the
acquisition of these calibration observations. (Aims.) Looking for additional
linear polarization calibrators in the millimeter spectral range, in mid-2006
we started monitoring 3C 286, a standard and highly stable polarization
calibrator for radio observations. (Methods.) Here we present the 3 and 1 mm
monitoring observations obtained between September 2006 and January 2012 with
the XPOL polarimeter on the IRAM 30 m Millimeter Telescope. (Results.) Our
observations show that 3C 286 is a bright source of constant total flux with 3
mm flux density S_3mm = (0.91 \pm 0.02) Jy. The 3mm linear polarization degree
(p_3mm =[13.5\pm0.3]%) and polarization angle (chi_3mm
=[37.3\pm0.8]deg.,expressed in the equatorial coordinate system) are also
constant during the time span of our observations. Although with poorer time
sampling and signal-to-noise ratio, our 1 mm observations of 3C 286 are also
reproduced by a constant source of 1 mm flux density (S_1mm = [0.30 \pm 0.03]
Jy), polarization fraction (p_1mm = [14.4 \pm 1.8] %), and polarization angle
(chi_1mm = [33.1 \pm 5.7]deg.). (Conclusions.) This, together with the
previously known compact structure of 3C 286 -extended by ~3.5" in the sky-
allow us to propose 3C 286 as a new calibrator for both single dish and
interferometric polarization observations at 3 mm, and possibly at shorter
wavelengths.Comment: Accepted for publication in A&A. 7 pages, 4 figures, 8 tables.
Updated data sets with regard to previous version. New discussion about multi
frequency properties of the source. Section 3.3, Figures 3 and 4, and Tables
7 and 8 are ne
Parsec scale polarization properties of the TeV blazar Markarian 421
In this work we present a polarization analysis at radio frequencies of
Markarian 421, one of the closest (z=0.03) TeV blazars. The observations were
obtained, both in total and in polarized intensity, with the Very Long Baseline
Array (VLBA) at 15, 24, and 43 GHz throughout 2011, with one observation per
month (for a total of twelve epochs). We investigate the magnetic field
topology and the polarization structure on parsec scale and their evolution
with time. We detect polarized emission both in the core and in the jet region,
and it varies with frequency, location and time. In the core region we measure
a mean fractional polarization of about 1-2%, with a peak of about 4% in March
at 43 GHz; the polarization angle is almost stable at 43 GHz, but it shows
significant variability in the range 114-173 deg at 15 GHz. In the jet region
the polarization properties show a more stable behavior; the fractional
polarization is about 16% and the polarization angle is nearly perpendicular to
the jet axis. The higher EVPA variability observed at 15 GHz is due both to a
variable Faraday rotation effect and to opacity. The residual variability
observed in the intrinsic polarization angle, together with the low degree of
polarization in the core region, could be explained with the presence of a
blend of variable cross-polarized subcomponents within the beam.Comment: 6 pages, 4 figures, proceedings of the 12th European VLBI Network
Symposium and Users Meeting (7-10 October 2014, Cagliari, Italy
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