415 research outputs found
XMM-Newton Slew Survey observations of the gravitational wave event GW150914
The detection of the first gravitational wave (GW) transient GW150914
prompted an extensive campaign of follow-up observations at all wavelengths.
Although no dedicated XMM-Newton observations have been performed, the
satellite passed through the GW150914 error box during normal operations. Here
we report the analysis of the data taken during these satellite slews performed
two hours and two weeks after the GW event. Our data cover 1.1 square degrees
and 4.8 square degrees of the final GW localization region. No credible X-ray
counterpart to GW150914 is found down to a sensitivity of 6E-13 erg/cm2/s in
the 0.2-2 keV band. Nevertheless, these observations show the great potential
of XMM-Newton slew observations for the search of the electromagnetic
counterparts of GW events. A series of adjacent slews performed in response to
a GW trigger would take <1.5 days to cover most of the typical GW credible
region. We discuss this scenario and its prospects for detecting the X-ray
counterpart of future GW detections.Comment: 6 pages, 3 figures, 2 tables. Accepted for publication in ApJ Letter
Behind the dust curtain: the spectacular case of GRB 160623A
We report on the X-ray dust-scattering features observed around the afterglow
of the gamma ray burst GRB 160623A. With an XMM-Newton observation carried out
~2 days after the burst, we found evidence of at least six rings, with angular
size expanding between ~2 and 9 arcmin, as expected for X-ray scattering of the
prompt GRB emission by dust clouds in our Galaxy. From the expansion rate of
the rings, we measured the distances of the dust layers with extraordinary
precision: 528.1 +\- 1.2 pc, 679.2 +\- 1.9 pc, 789.0 +\- 2.8 pc, 952 +\- 5 pc,
1539 +\- 20 pc and 5079 +\- 64 pc. A spectral analysis of the ring spectra,
based on an appropriate dust-scattering model (BARE-GR-B from Zubko et al.
2004}) and the estimated burst fluence, allowed us to derive the column density
of the individual dust layers, which are in the range 7x10^20-1.5x10^22 cm^-2.
The farthest dust-layer (i.e. the one responsible for the smallest ring) is
also the one with the lowest column density and it is possibly very extended,
indicating a diffuse dust region. The properties derived for the six
dust-layers (distance, thickness, and optical depth) are generally in good
agreement with independent information on the reddening along this line of
sight and on the distribution of molecular and atomic gas.Comment: 9 pages, 10 figures, 1 table; accepted for publication in MNRA
Simulating high-redshift galaxies
Recent observations have gathered a considerable sample of high redshift
galaxy candidates and determined the evolution of their luminosity function
(LF). To interpret these findings, we use cosmological SPH simulations
including, in addition to standard physical processes, a detailed treatment of
the Pop III-Pop II transition in early objects. The simulated high-z galaxies
match remarkably well the amplitude and slope of the observed LF in the
redshift range 5<z<10. The LF shifts towards fainter luminosities with
increasing redshift, while its faint-end slope keeps an almost constant value,
\alpha ~-2. The stellar populations of high-z galaxies have ages of 100-300
(40-130) Myr at z=5 (z=7-8), implying an early (z>9.4) start of their star
formation activity; the specific star formation rate is almost independent of
galactic stellar mass. These objects are enriched rapidly with metals and
galaxies identified by HST/WFC3 (M_UV < -18) show metallicities ~0.1 Zsun even
at z=7-8. Most of the simulated galaxies at z~7 (noticeably the smallest ones)
are virtually dust-free, and none of them has an extinction larger than E(B-V)
= 0.01. The bulk (50%) of the ionizing photons is produced by objects
populating the faint-end of the LF (M_UV < -16), which JWST will resolve up to
z=7.3. PopIII stars continue to form essentially at all redshifts; however, at
z=6 (z=10) the contribution of Pop III stars to the total galactic luminosity
is always less than 5% for M_UV < -17 (M_UV < -16). The typical high-z galaxies
closely resemble the GRB host galaxy population observed at lower redshifts,
strongly encouraging the use of GRBs to detect the first galaxies.Comment: 14 pages, 10 figures, MNRAS in pres
Perturbações do comportamento, vinculação, funcionamento familiar e práticas educativas parentais em jovens delinquentes
Dissertação de Mestrado apresentada ao ISPA - Instituto UniversitárioO objectivo deste trabalho é o estudo das perturbações do comportamento em
adolescentes delinquentes. O problema a estudar é a relação entre a qualidade da
vinculação às figuras parentais, as características do sistema familiar, a percepção das
práticas educativas parentais e as perturbações do comportamento.
A população estudada é constituída por 152 adolescentes entre os 12 - 21 anos.
Os dados recolheram-se em dois Centros Educativos de Lisboa do IRS -
Instituto de Reinserção Social e numa Escola Secundária de Lisboa.
As medidas utilizadas foram: Escala de Auto-Avaliação para Jovens – YSR que
avalia os problemas de comportamento, Kerns Security Scale - KSS, que avalia a
qualidade da vinculação ao pai e à mãe, separadamente, Inventory for Assessing
Memories of Paternal Rearing Behavior – EMBU-Forma A, que avalia a percepção das
práticas educativas parentais e Family Adaptability and Cohesion Evaluation Scale –
FACES III, que caracteriza o funcionamento familiar.
Neste estudo, verificou-se que os adolescentes delinquentes, institucionalizados
em centro educativo, apresentam mais problemas de comportamento do que os que
vivem em meio familiar “estável”; os adolescentes inseridos em meio familiar
apresentam valores mais elevados de segurança da vinculação (quer à mãe, quer ao pai),
do que os adolescentes delinquentes e ainda que os adolescentes em meio familiar têm
famílias cujo funcionamento familiar é mais flexível, que os adolescentes delinquentes;
estes sentem maior rejeição, mas também mais conforto emocional e superprotecção
que os adolescentes em meio familiar. Verificou-se que existe uma relação entre as
perturbações do comportamento, a segurança da vinculação, o funcionamento familiar e
a percepção das práticas educativas parentais.The aim of this work is the study of behavioral disorders in adolescent
offenders. The problem of this study is the relationship between quality of attachment to
parental figures, the characteristics of the family system, the perception of parenting
practices and behavior disorders.
The population studied was 152 adolescents aged between 12 and 21 years old.
Data was collected in two Lisbon‟s reformatories of IRS- Instituto de
Reinserção Social and also in a Lisbon‟s State School.
Measures used in this study were YSR – Youth Self Report, which evaluates
behavior disorders, Kerns Security Scale that evaluates the quality of attachment to
parents, separately, the Inventory for Assessing Memories of Paternal Rearing Behavior
– EMBU-A, that assesses the perceptions of parenting practices and Family Adaptability
and Cohesion Evaluation Scale – FACES III allows to characterize family functioning.
In this study, it was found that delinquent adolescents, institutionalized in the
reformatories, have more behavior problems than adolescents living in the “solid”
family; adolescents who lives in the family have higher levels of security (either to
mother or father) than delinquent adolescents and that adolescents placed in the family
have families whose family functioning is more flexible than the delinquent
adolescents, they feel greater rejection, but also more emotional comfort and
overprotection than teens that lives in the family. It was found that exist a relationship
between behavioral disorders, security of attachment, family functioning and
perceptions of parenting practices
Low-Mass Relics of Early Star Formation
The earliest stars to form in the Universe were the first sources of light,
heat and metals after the Big Bang. The products of their evolution will have
had a profound impact on subsequent generations of stars. Recent studies of
primordial star formation have shown that, in the absence of metals (elements
heavier than helium), the formation of stars with masses 100 times that of the
Sun would have been strongly favoured, and that low-mass stars could not have
formed before a minimum level of metal enrichment had been reached. The value
of this minimum level is very uncertain, but is likely to be between 10^{-6}
and 10^{-4} that of the Sun. Here we show that the recent discovery of the most
iron-poor star known indicates the presence of dust in extremely
low-metallicity gas, and that this dust is crucial for the formation of
lower-mass second-generation stars that could survive until today. The dust
provides a pathway for cooling the gas that leads to fragmentation of the
precursor molecular cloud into smaller clumps, which become the lower-mass
stars.Comment: Offprint of Nature 422 (2003), 869-871 (issue 24 April 2003
A method for quantifying the gamma-ray burst bias. Application in the redshift range of 0–1.1
International audienceContext. Long gamma-ray bursts (LGRBs) are related to the final stages of evolution of very massive stars. As such, they should follow the star formation rate (SFR) of galaxies. We can use them to probe for star-forming galaxies in the distant universe following this assumption. The relation between the rate of LGRBs in a given galaxy and its SFR (which we call the LGRB bias) may however be complex, as we have good indications that the LGRB hosts are not perfect analogues to the general population of star-forming galaxies. Aims. In this work, we try to quantify how the LGRB bias depends on physical parameters of their host galaxy, such as SFR or stellar mass. These trends may reveal more fundamental properties such as the role of the metallicity of LGRBs and of their progenitors .Methods. We propose an empirical method based on the comparison of stellar mass functions (and SFR distributions) of LGRB hosts and of star-forming galaxies to find how the bias depends on the stellar mass or the SFR.Results. By applying this method to a sample of LGRB hosts at redshifts lower than 1.1, where the properties of star-forming galaxies are fairly well established and where the properties of LGRB host galaxies can be deduced from observations (limiting ourselves to stellar masses higher than 109.25M⊙ and SFR higher than ~1.8 M⊙ yr-1), we find that the LGRB bias depends on both the stellar mass and SFR. We find that the bias decreases with the SFR; that is, we see no preference for highly star-forming galaxies, once we account for the higher number of massive stars in galaxies with larger SFR. We do not find any trend with the specific star formation rate (SSFR), but the dynamical range in SSFR in our study is narrow. Through an indirect method, we relate these trends to a possible decrease in the LGRBs rate / SFR ratio with the metallicity.Conclusions. The method we propose suggests trends that may be useful to constrain models of LGRB progenitors, showing a clear decrease in the LGRB bias with the metallicity. This is promising for the future as the number of LGRB hosts studied will increase
Short GRBs at the dawn of the gravitational wave era
We derive the luminosity function and redshift distribution of short Gamma
Ray Bursts (SGRBs) using (i) all the available observer-frame constraints (i.e.
peak flux, fluence, peak energy and duration distributions) of the large
population of Fermi SGRBs and (ii) the rest-frame properties of a complete
sample of Swift SGRBs. We show that a steep with a>2.0
is excluded if the full set of constraints is considered. We implement a Monte
Carlo Markov Chain method to derive the and functions
assuming intrinsic Ep-Liso and Ep-Eiso correlations or independent
distributions of intrinsic peak energy, luminosity and duration. To make our
results independent from assumptions on the progenitor (NS-NS binary mergers or
other channels) and from uncertainties on the star formation history, we assume
a parametric form for the redshift distribution of SGRBs. We find that a
relatively flat luminosity function with slope ~0.5 below a characteristic
break luminosity ~3 erg/s and a redshift distribution of SGRBs
peaking at z~1.5-2 satisfy all our constraints. These results hold also if no
Ep-Liso and Ep-Eiso correlations are assumed. We estimate that, within ~200 Mpc
(i.e. the design aLIGO range for the detection of GW produced by NS-NS merger
events), 0.007-0.03 SGRBs yr should be detectable as gamma-ray events.
Assuming current estimates of NS-NS merger rates and that all NS-NS mergers
lead to a SGRB event, we derive a conservative estimate of the average opening
angle of SGRBs: ~3-6 deg. Our luminosity function implies an
average luminosity L~1.5 erg/s, nearly two orders of magnitude
higher than previous findings, which greatly enhances the chance of observing
SGRB "orphan" afterglows. Efforts should go in the direction of finding and
identifying such orphan afterglows as counterparts of GW events.Comment: 13 pages, 5 figures, 2 tables. Accepted for publication in Astronomy
& Astrophysics. Figure 5 and angle ranges corrected in revised versio
GRB 190114C: from prompt to afterglow?
GRB 190114C is the first gamma-ray burst detected at Very High Energies (VHE,
i.e. >300 GeV) by the MAGIC Cherenkov telescope. The analysis of the emission
detected by the Fermi satellite at lower energies, in the 10 keV -- 100 GeV
energy range, up to ~ 50 seconds (i.e. before the MAGIC detection) can hold
valuable information. We analyze the spectral evolution of the emission of GRB
190114C as detected by the Fermi Gamma-Ray Burst Monitor (GBM) in the 10 keV --
40 MeV energy range up to ~60 sec. The first 4 s of the burst feature a typical
prompt emission spectrum, which can be fit by a smoothly broken power-law
function with typical parameters. Starting on ~4 s post-trigger, we find an
additional nonthermal component, which can be fit by a power law. This
component rises and decays quickly. The 10 keV -- 40 MeV flux of the power-law
component peaks at ~ 6 s; it reaches a value of 1.7e-5 erg cm-2 s-1. The time
of the peak coincides with the emission peak detected by the Large Area
Telescope (LAT) on board Fermi. The power-law spectral slope that we find in
the GBM data is remarkably similar to that of the LAT spectrum, and the GBM+LAT
spectral energy distribution seems to be consistent with a single component.
This suggests that the LAT emission and the power-law component that we find in
the GBM data belong to the same emission component, which we interpret as due
to the afterglow of the burst. The onset time allows us to estimate the initial
jet bulk Lorentz factor Gamma_0 is about 500, depending on the assumed
circum-burst density.Comment: 7 pages, 2 figures, in press, accepted for publication in A&
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