112 research outputs found
A ZZ Ceti white dwarf in SDSS J133941.11+484727.5
We present time-resolved spectroscopy and photometry of the cataclysmic
variable (CV) SDSSJ133941.11+484727.5 (SDSS1339) which has been discovered in
the Sloan Digital Sky Survey Data Release 4. The orbital period determined from
radial velocity studies is 82.524(24)min, close to the observed period minimum.
The optical spectrum of SDSS1339 is dominated to 90% by emission from the white
dwarf. The spectrum can be successfully reproduced by a three-component model
(white dwarf, disc, secondary) with Twd=12500K for a fixed log g=8.0, d=170pc,
and a spectral type of the secondary later than M8. The mass transfer rate
corresponding to the optical luminosity of the accretion disc is very
low,~1.7x10^-13Msun/yr. Optical photometry reveals a coherent variability at
641s with an amplitude of 0.025mag, which we interpret as non-radial pulsations
of the white dwarf. In addition, a long-period photometric variation with a
period of either 320min or 344min and an amplitude of 0.025mag is detected,
which bears no apparent relation with the orbital period of the system. Similar
long-period photometric signals have been found in the CVs
SDSSJ123813.73-033933.0, SDSSJ204817.85-061044.8, GW Lib and FS Aur, but so far
no working model for this behaviour is available.Comment: MNRAS, in press, 8 pages, 10 figures, some figures downgraded to meet
the file size constraint of arxiv.or
The July 2010 outburst of the NLS1 PMN J0948+0022
We report about the multiwavelength campaign on the Narrow-Line Seyfert 1
(NLS1) Galaxy PMN J0948+0022 (z = 0.5846) performed in 2010 July-September and
triggered by high activity as measured by Fermi/LAT. The peak luminosity in the
0.1-100 GeV energy band exceeded, for the first time in this type of source,
the value of 10^48 erg/s, a level comparable to the most powerful blazars. The
comparison of the spectral energy distribution of the NLS1 PMN J0948+0022 with
that of a typical blazar - like 3C 273 - shows that the power emitted at gamma
rays is extreme.Comment: 2011 Fermi Symposium proceedings - eConf C11050
Radio and gamma-ray follow-up of the exceptionally high activity state of PKS 1510-089 in 2011
We investigate the radio and gamma-ray variability of the flat spectrum radio
quasar PKS 1510-089 in the time range between 2010 November and 2012 January.
In this period the source showed an intense activity, with two major gamma-ray
flares detected in 2011 July and October. During the latter episode both the
gamma-ray and the radio flux density reached their historical peak.
Multiwavelength analysis shows a rotation of about 380 deg of the optical
polarization angle close in time with the rapid and strong gamma-ray flare in
2011 July. An enhancement of the optical emission and an increase of the
fractional polarization both in the optical and in radio bands is observed
about three weeks later, close in time with another gamma-ray outburst. On the
other hand, after 2011 September a huge radio outburst has been detected, first
in the millimeter regime followed with some time delay at centimeter down to
decimeter wavelengths. This radio flare is characterized by a rising and a
decaying stage, in agreement with the formation of a shock and its evolution,
as a consequence of expansion and radiative cooling. If the gamma-ray flare
observed in 2011 October is related to this radio outburst, then this strongly
indicates that the region responsible for the gamma-ray variability is not
within the broad line, but a few parsecs downstream along the jet.Comment: 14 pages, 12 figures, accepted for publication in MNRA
The first gamma-ray outburst of a Narrow-Line Seyfert 1 Galaxy: the case of PMN J0948+0022 in July 2010
We report on a multiwavelength campaign on the radio-loud Narrow-Line Seyfert
1 (NLS1) Galaxy PMN J0948+0022 (z=0.5846) performed in 2010 July-September and
triggered by a high-energy gamma-ray outburst observed by the Large Area
Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope. The peak flux in
the 0.1-100 GeV energy band exceeded, for the first time in this type of
source, the value of 10^-6 ph cm^-2 s^-1, corresponding to an observed
luminosity of 10^48 erg s^-1. Although the source was too close to the Sun
position to organize a densely sampled follow-up, it was possible to gather
some multiwavelength data that confirmed the state of high activity across the
sampled electromagnetic spectrum. The comparison of the spectral energy
distribution of the NLS1 PMN J0948+0022 with that of a typical blazar - like 3C
273 - shows that the power emitted at gamma rays is extreme.Comment: 8 pages, 7 figures, 2 tables. Accepted for the publication on MNRAS
Main Journal. Typo in bibliography correcte
The Structure and Dynamics of the Upper Chromosphere and Lower Transition Region as Revealed by the Subarcsecond VAULT Observations
The Very high Angular resolution ULtraviolet Telescope (VAULT) is a sounding
rocket payload built to study the crucial interface between the solar
chromosphere and the corona by observing the strongest line in the solar
spectrum, the Ly-a line at 1216 {\AA}. In two flights, VAULT succeeded in
obtaining the first ever sub-arcsecond (0.5") images of this region with high
sensitivity and cadence. Detailed analyses of those observations have
contributed significantly to new ideas about the nature of the transition
region. Here, we present a broad overview of the Ly-a atmosphere as revealed by
the VAULT observations, and bring together past results and new analyses from
the second VAULT flight to create a synthesis of our current knowledge of the
high-resolution Ly-a Sun. We hope that this work will serve as a good reference
for the design of upcoming Ly-a telescopes and observing plans.Comment: 28 pages, 11 figure
Multiwavelength Intraday Variability of the BL Lac S5 0716+714
We report results from a 1 week multi-wavelength campaign to monitor the BL
Lac object S5 0716+714 (on December 9-16, 2009). In the radio bands the source
shows rapid (~ (0.5-1.5) day) intra-day variability with peak amplitudes of up
to ~ 10 %. The variability at 2.8 cm leads by about 1 day the variability at 6
cm and 11 cm. This time lag and more rapid variations suggests an intrinsic
contribution to the source's intraday variability at 2.8 cm, while at 6 cm and
11 cm interstellar scintillation (ISS) seems to predominate. Large and
quasi-sinusoidal variations of ~ 0.8 mag were detected in the V, R and I-bands.
The X-ray data (0.2-10 keV) do not reveal significant variability on a 4 day
time scale, favoring reprocessed inverse-Compton over synchrotron radiation in
this band. The characteristic variability time scales in radio and optical
bands are similar. A quasi-periodic variation (QPO) of 0.9 - 1.1 days in the
optical data may be present, but if so it is marginal and limited to 2.2
cycles. Cross-correlations between radio and optical are discussed. The lack of
a strong radio-optical correlation indicates different physical causes of
variability (ISS at long radio wavelengths, source intrinsic origin in the
optical), and is consistent with a high jet opacity and a compact synchrotron
component peaking at ~= 100 GHz in an ongoing very prominent flux density
outburst. For the campaign period, we construct a quasi-simultaneous spectral
energy distribution (SED), including gamma-ray data from the FERMI satellite.
We obtain lower limits for the relativistic Doppler-boosting of delta >= 12-26,
which for a BL\,Lac type object, is remarkably high.Comment: 16 pages, 15 figures, table 2; Accepted for Publication in MNRA
The first gamma-ray outburst of a narrow-line Seyfert 1 galaxy: the case of PMN J0948+0022 in 2010 July
We report on a multiwavelength campaign for the radio-loud narrow-line Seyfert 1 (NLS1) galaxy PMN J0948+0022 (z= 0.5846) performed in 2010 July-September and triggered by a high-energy Îł-ray outburst observed by the Large Area Telescope onboard the Fermi Gamma-ray Space Telescope. The peak flux in the 0.1-100 GeV energy band exceeded, for the first time in this type of source, the value of âŒ10â6 photon cmâ2 sâ1, corresponding to an observed luminosity of âŒ1048 erg sâ1. Although the source was too close to the Sun position to organize a densely sampled follow-up, it was possible to gather some multiwavelength data that confirmed the state of high activity across the sampled electromagnetic spectrum. The comparison of the spectral energy distribution of the NLS1 PMN J0948+0022 with that of a typical blazar - such as 3C 273 - shows that the power emitted at Îł-rays is extrem
Simultaneous Planck, Swift, and Fermi observations of X-ray and gamma-ray selected blazars
We present simultaneous Planck, Swift, Fermi, and ground-based data for 105
blazars belonging to three samples with flux limits in the soft X-ray, hard
X-ray, and gamma-ray bands. Our unique data set has allowed us to demonstrate
that the selection method strongly influences the results, producing biases
that cannot be ignored. Almost all the BL Lac objects have been detected by
Fermi-LAT, whereas ~40% of the flat-spectrum radio quasars (FSRQs) in the
radio, soft X-ray, and hard X-ray selected samples are still below the
gamma-ray detection limit even after integrating 27 months of Fermi-LAT data.
The radio to sub-mm spectral slope of blazars is quite flat up to ~70GHz, above
which it steepens to ~-0.65. BL Lacs have significantly flatter spectra
than FSRQs at higher frequencies. The distribution of the rest-frame
synchrotron peak frequency (\nupS) in the SED of FSRQs is the same in all the
blazar samples with =10^13.1 Hz, while the mean inverse-Compton peak
frequency, , ranges from 10^21 to 10^22 Hz. The distributions of \nupS
and of \nupIC of BL Lacs are much broader and are shifted to higher energies
than those of FSRQs and strongly depend on the selection method. The Compton
dominance of blazars ranges from ~0.2 to ~100, with only FSRQs reaching values
>3. Its distribution is broad and depends strongly on the selection method,
with gamma-ray selected blazars peaking at ~7 or more, and radio-selected
blazars at values ~1, thus implying that the assumption that the blazar power
is dominated by high-energy emission is a selection effect. Simple SSC models
cannot explain the SEDs of most of the gamma-ray detected blazars in all
samples. The SED of the blazars that were not detected by Fermi-LAT may instead
be consistent with SSC emission. Our data challenge the correlation between
bolometric luminosity and \nupS predicted by the blazar sequence.Comment: Version accepted by A&A. Joint Planck, Swift, and Fermi
collaborations pape
Fermi Large Area Telescope Observations of Misaligned AGN
Analysis is presented on 15 months of data taken with the Large Area
Telescope (LAT) on the Fermi Gamma-ray Space Telescope for 11 non-blazar AGNs,
including 7 FRI radio galaxies and 4 FRII radio sources consisting of 2 FRII
radio galaxies and 2 steep spectrum radio quasars. The broad line FRI radio
galaxy 3C 120 is reported here as a gamma-ray source for the first time. The
analysis is based on directional associations of LAT sources with radio sources
in the 3CR, 3CRR and MS4 (collectively referred to as 3C-MS) catalogs. Seven of
the eleven LAT sources associated with 3C-MS radio sources have spectral
indices larger than 2.3 and, except for the FRI radio galaxy NGC 1275 that
shows possible spectral curvature, are well described by a power law. No
evidence for time variability is found for any sources other than NGC 1275. The
gamma-ray luminosities of FRI radio galaxies are significantly smaller than
those of BL Lac objects detected by the LAT, whereas the gamma-ray luminosities
of FRII sources are quite similar to those of FSRQs, which could reflect
different beaming factors for the gamma-ray emission. A core dominance study of
the 3CRR sample indicate that sources closer to the jet axis are preferentially
detected with the Fermi-LAT, insofar as the gamma-ray--detected misaligned AGNs
have larger core dominance at a given average radio flux. The results are
discussed in view of the AGN unification scenario.Comment: 28 pages, 8 figures, 2 tables. Accepted for publication in The
Astrophysical Journa
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