182 research outputs found
A view of PKS 2155-304 with XMM-Newton Reflection Grating Spectrometers
We present the high resolution X-ray spectrum of the BL Lac object PKS
2155-304 taken with the RGS units onboard XMM-Newton in November 2000. We
detect a OVII Kalpha resonant absorption line from warm/hot local gas at 21.59A
(~4.5 sigma detection). The line profile is possibly double peaked. We do not
confirm the strong 20.02 A absorption line seen with Chandra and interpreted as
z~0.05 OVIII Kalpha. A 3sigma upper limit of 14 mA on the equivalent width is
set. We also detect the ~23.5 A interstellar OI 1s-->2p line and derive a
factor <=1.5 subsolar O/H ratio in the ISM along PKS 2155-304 line of sight.Comment: 13 pages, 5 figures, 3 tables, emulateapj style. Accepted by Ap
What can we learn from multi-objective meta-optimization of Evolutionary Algorithms in continuous domains?
Properly configuring Evolutionary Algorithms (EAs) is a challenging task made difficult by many different details that affect EAs' performance, such as the properties of the fitness function, time and computational constraints, and many others. EAs' meta-optimization methods, in which a metaheuristic is used to tune the parameters of another (lower-level) metaheuristic which optimizes a given target function, most often rely on the optimization of a single property of the lower-level method. In this paper, we show that by using a multi-objective genetic algorithm to tune an EA, it is possible not only to find good parameter sets considering more objectives at the same time but also to derive generalizable results which can provide guidelines for designing EA-based applications. In particular, we present a general framework for multi-objective meta-optimization, to show that "going multi-objective" allows one to generate configurations that, besides optimally fitting an EA to a given problem, also perform well on previously unseen ones
Prediction of hearing recovery in sudden deafness treated with intratympanic steroids
The present study aims to obtain a probability model allowing the prediction of the auditory recovery in patients affected by sudden sensorineural hearing loss treated exclusively with intratympanic steroids. A monocentric retrospective chart review of three-hundred eighty-one patients has been performed. A Probit model was used to investigate the correlation between the success of the treatment (marked or total recovery according to Furuashi's criteria), and the delay between the onset of disease and the beginning of therapy. The age of the patients and the audiometric curve shapes were included in the analysis. Results show that delay is negatively correlated with the variable success. Considering the entire sample, each day of delay decreases by 3% the probability of success. The prediction model shows that for every day that passes from the onset of the disease the probability of success declines in absence of the medical treatment, hence we conclude that early treatment is strongly recommended
The Effects of Periodically Gapped Time Series on Cross-correlation Lag Determinations
The three bright TeV blazars Mrk 421, Mrk 501 and PKS 2155-404 are highly
variable in synchrotron X-ray emission. In particular, these sources may
exhibit variable time lags between flux variations at different X-ray energy
bands. However, there are a number of issues that may significantly bias lag
determinations. Edelson et al. (2001) recently proposed that the lags on
timescales of hours, discovered by ASCA and BeppoSAX, could be an artifact of
periodic gaps in the light curves introduced by the Earth occultation every
\~1.6 hr. Using Monte Carlo simulations, in this paper we show that the lags
over timescales of hours can not be the spurious result of periodic gaps, while
periodic gaps indeed introduces uncertainty larger than what present in the
evenly sampled data. The results also show that time lag estimates can be
substantially improved by using evenly sampled light curves with large lag to
bin-size ratio. Furthermore, we consider an XMM-Newton observation without
interruptions and re-sample the light curves using the BeppoSAX observing
windows, and then repeat the same cross correlation function (CCF) analysis on
both the real and fake data. The results also show that periodic gaps in the
light curves do not significantly distort the CCF characters, and indeed the
CCF peak ranges of the real and fake data overlap. Therefore, the lags
discovered by ASCA and BeppoSAX are not due to periodic gaps in the light
curves.Comment: 13 pages, 6 figures, accepted for publication in Ap
An XMM-Newton observation of the massive, relaxed galaxy cluster ClJ1226.9+3332 at z=0.89
A detailed X-ray analysis of an XMM-Newton observation of the high-redshift
(z=0.89) galaxy cluster ClJ1226.9+3332 is presented. The X-ray temperature is
found to be 11.5{+1.1}{-0.9}keV, the highest X-ray temperature of any cluster
at z>0.6. In contrast to MS1054-0321, the only other very hot cluster currently
known at z>0.8, ClJ1226.9+3332 features a relaxed X-ray morphology, and its
high overall gas temperature is not caused by one or several hot spots. The
system thus constitutes a unique example of a high redshift, high temperature,
relaxed cluster, for which the usual hydrostatic equilibrium assumption, and
the X-ray mass is most reliable. A temperature profile is constructed (for the
first time at this redshift) and is consistent with the cluster being
isothermal out to 45% of the virial radius. Within the virial radius
(corresponding to a measured overdensity of a factor of 200), a total mass of
(1.4+/-0.5)*10^15 M_solar is derived, with a gas mass fraction of 12+/-5%. The
bolometric X-ray luminosity is (5.3+/-0.2)*10^45 erg/s. The probabilities of
finding a cluster of this mass within the volume of the discovery X-ray survey
are 8*10^{-5} for Omega_M=1 and 0.64 for Omega_M=0.3, making Omega_M=1 highly
unlikely. The entropy profile suggests that entropy evolution is being
observed. The metal abundance (of Z=0.33{+0.14}{-0.10} Z_solar), gas mass
fraction, and gas distribution are consistent with those of local clusters;
thus the bulk of the metals were in place by z=0.89.Comment: 13 pages, 8 figures. Accepted for publication in MNRA
An Extreme Ultraviolet Explorer Atlas of Seyfert Galaxy Light Curves: Search for Periodicity
The Deep Survey instrument on the Extreme Ultraviolet Explorer satellite
(EUVE) obtained long, nearly continuous soft X-ray light curves of 5-33 days
duration for 14 Seyfert galaxies and QSOs. We present a uniform reduction of
these data, which account for a total of 231 days of observation. Several of
these light curves are well suited to a search for periodicity or QPOs in the
range of hours to days that might be expected from dynamical processes in the
inner accretion disk around ~10^8 M_sun black holes. Light curves and
periodograms of the three longest observations show features that could be
transient periods: 0.89 days in RX J0437.4-4711, 2.08 days in Ton S180, and 5.8
days in 1H 0419-577. The statistical significance of these signals is estimated
using the method of Timmer & Konig (1995), which carefully takes into account
the red-noise properties of Seyfert light curves. The result is that the
signals in RX J0437.4-4711 and Ton S180 exceed 95% confidence with respect to
red noise, while 1H 0419-577 is only 64% significant. These period values
appear unrelated to the length of the observation, which is similar in the
three cases, but they do scale roughly as the luminosity of the object, which
would be expected in a dynamical scenario if luminosity scales with black hole
mass.Comment: 26 pages, 9 figures, accepted by Ap
Constraining the black hole mass and accretion rate in the narrow-line Seyfert 1 RE J1034+396
We present a comprehensive study of the spectrum of the narrow-line Seyfert 1
galaxy RE J1034+396, summarizing the information obtained from the optical to
X-rays with observations from the William Herschel 4.2m Telescope (WHT), the
Hubble Space Telescope, the Extreme UltraViolet Explorer, ROSAT, ASCA and
BeppoSAX. The BeppoSAX spectra reveal a soft component which is
well-represented by two blackbodies with kT of about 60 eV and 160 eV,
mimicking that expected from a hot, optically-thick accretion disc around a
low-mass black hole. This is borne out by our modeling of the optical to X-ray
nuclear continuum, which constrains the physical parameters of a NLS1 for the
first time. The models demonstrate that RE J1034+396 is likely to be a system
with a nearly edge-on accretion disk (60 to 75 degrees from the disk axis),
accreting at nearly Eddington rates (0.3 to 0.7 L_edd) onto a low mass (about 2
million solar masses) black hole (abridged).Comment: ApJ accepte
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