2,123 research outputs found
The host galaxy of the z=2.4 radio-loud AGN MRC 0406-244 as seen by HST
We present multicolour Hubble Space Telescope images of the powerful z=2.4
radio galaxy MRC 0406-244 and model its complex morphology with several
components including a host galaxy, a point source, and extended nebular and
continuum emission. We suggest that the main progenitor of this radio galaxy
was a normal, albeit massive (M ~10^{11} solar masses), star-forming galaxy.
The optical stellar disc of the host galaxy is smooth and well described by a
S\'ersic profile, which argues against a recent major merger, however there is
also a point-source component which may be the remnant of a minor merger. The
half-light radius of the optical disc is constrained to lie in the range 3.5 to
8.2kpc, which is of similar size to coeval star forming galaxies.
Biconical shells of nebular emission and UV-bright continuum extend out from
the host galaxy along the radio jet axis, which is also the minor axis of the
host galaxy. The origin of the continuum emission is uncertain, but it is most
likely to be young stars or dust-scattered light from the AGN, and it is
possible that stars are forming from this material at a rate of
200^{+1420}_{-110} solar masses per year.Comment: Accepted for publication in MNRA
INTEGRAL observation of 3EG J1736-2908
The possible identification by INTEGRAL of the EGRET source 3EG J1736-2908
with the active galactic nucleus GRS 1734-292 is discussed. The latter was
discovered in 1990 and later identified with a Seyfert 1 galaxy. At the time of
the compilation of the 3rd EGRET Catalog, it was not considered as a possible
counterpart of the source 3EG J1736-2908, which remained unidentified. A
detailed multiwavelength study of the EGRET error circle is presented, by
including archival radio, soft- and hard-X observations, suggesting that GRS
1734-292 could be a likely counterpart of 3EG J1736-2908, even though this
poses very interesting questions about the production mechanisms of gamma-rays
with energies greater than 100 MeV.Comment: 6 pages, 3 figures. Accepted for publication on A&A Main Journa
A z~3 radio galaxy and its protocluster: evidence for a superstructure?
We present spectroscopic follow-up observations of Lyman Break Galaxies
(LBGs) selected in the field surrounding the radio galaxy MRC0316-257 at z~3.13
(0316). Robust spectroscopic redshifts are determined for 20 out of 24 objects.
Three of the spectroscopically confirmed galaxies have 3.12<z<3.13 indicating
that these objects reside in a protocluster structure previously found around
the radio galaxy. An additional 5 objects are found 1600 km/s blue-shifted with
respect to the main protocluster structure. This is in addition to three [OIII]
emitters found at this redshift in a previous study. This is further evidence
that a structure exists directly in front of the 0316 protocluster. We estimate
that the foreground structure is responsible for half of the surface
overdensity of LBGs found in the field as a whole. The foreground structure is
associated with a strong surface density peak 1.4 Mpc to the North-West of the
radio galaxy and a 2D Kolmogorov-Smirnov test indicates that the spatial
distributions of the 0316 and foreground galaxies differ at the 3 sigma level.
In addition, we compare the properties of protocluster, foreground structure
and field galaxies, but we find no significant differences. In terms of the
nature of the two structures, a merger scenario is a possible option. Simple
merger dynamics indicates that the observed relative velocity of 1600 km/s can
be reproduced if the two structures have masses of ~5x10^14 Msun and have
starting separations of around 2.5 to 3 Mpc. It is also possible that the
foreground structure is unrelated to the 0316 protocluster in which case the
two structures will not interact before z=0.Comment: 13 pages, 6 figures, accepted for publication in MNRA
GRB990510: on the possibility of a beamed X-ray afterglow
We discuss the prompt emission of the gamma-ray burst (GRB) 990510 and its
subsequent X-ray afterglow from 8.0 to 44.3 hrs after the prompt emission,
using observations with the Gamma-ray Burst Monitor and Narrow Field
Instruments on BeppoSAX. In the 40-700 keV band, GRB990510 had a fluence of
\~1.9x10^{-5}erg cm^{-2}, whereas it reached a peak flux of ~2.4x10^{-6}erg
cm^{-2} s^{-1}. The X-ray afterglow decay light curve can be satisfactorily
described by a single power law with index of -1.42+/-0.07. Both the X-ray and
optical behaviour of the afterglow can be explained by gamma-ray burst debris
expanding as a jet; we find that the cooling frequency is (fixed) between the
optical and X-ray wavelength bands.Comment: 16 pages, 4 figures, accepted for publication in the Astrophysical
Journa
The Kolmogorov-Smirnov test and its use for the identification of fireball fragmentation
We propose an application of the Kolmogorov-Smirnov test for rapidity
distributions of individual events in ultrarelativistic heavy ion collisions.
The test is particularly suitable to recognise non-statistical differences
between the events. Thus when applied to a narrow centrality class it could
indicate differences between events which would not be expected if all events
evolve according to the same scenario. In particular, as an example we assume
here a possible fragmentation of the fireball into smaller pieces at the
quark/hadron phase transition. Quantitative studies are performed with a Monte
Carlo model capable of simulating such a distribution of hadrons. We conclude
that the Kolmogorov-Smirnov test is a very powerful tool for the identification
of the fragmentation process.Comment: 9 pages, 10 figure
Discovery of luminous pulsed hard X-ray emission from anomalous X-ray pulsars 1RXS J1708-4009, 4U 0142+61 and 1E 2259+586 by INTEGRAL and RXTE
We report on the discovery of hard spectral tails for energies above 10 keV
in the total and pulsed spectra of anomalous X-ray pulsars 1RXS J1708-4009, 4U
0142+61 and 1E 2259+586 using RXTE PCA (2-60 keV) and HEXTE (15-250 keV) data
and INTEGRAL IBIS ISGRI (20-300 keV) data. Improved spectral information on 1E
1841-045 is presented. The pulsed and total spectra measured above 10 keV have
power-law shapes and there is so far no significant evidence for spectral
breaks or bends up to ~150 keV. The pulsed spectra are exceptionally hard with
indices measured for 4 AXPs approximately in the range -1.0 -- 1.0. We also
reanalyzed archival CGRO COMPTEL (0.75-30 MeV) data to search for signatures
from our set of AXPs. No detections can be claimed, but the obtained
upper-limits in the MeV band indicate that for 1RXS J1708-4009, 4U 0142+61 and
1E 1841-045 strong breaks must occur somewhere between 150 and 750 keV.Comment: Accepted for publication in ApJ; 19 pages; 4 Tables; 15 Figures (6
color
XMM-Newton spectral and timing analysis of the faint millisecond pulsars PSR J0751+1807 and PSR J1012+5307
We present XMM-Newton MOS imaging and PN timing data of the faint millisecond
pulsars PSR J0751+1807 and PSR J1012+5307. We find 46 sources in the MOS field
of view of PSR J0751+1807 searching down to an unabsorbed flux limit of 3 x
10^-15 ergs cm^-2 s^-1 (0.2-10.0 keV). We present, for the first time, the
X-ray spectra of these two faint millisecond pulsars. We find that a power law
model best fits the spectrum of PSR J0751+1807, Gamma=1.59+/-0.20, with an
unabsorbed flux of 4.4 x 10^-14 ergs cm^-2 s^-1 (0.2-10.0 keV). A power law is
also a good description of the spectrum of PSR J1012+5307, Gamma=1.78+/-0.36,
with an unabsorbed flux of 1.2 x 10^-13 ergs cm^-2 s^-1 (0.2-10.0 keV).
However, a blackbody model can not be excluded as the best fit to this data. We
present some evidence to suggest that both of these millisecond pulsars show
pulsations in this X-ray band. We find some evidence for a single broad X-ray
pulse for PSR J0751+1807 and we discuss the possibility that there are two
pulses per spin period for PSR J1012+5307.Comment: 8 pages, 9 figures, accepted for publication in Astronomy &
Astrophysic
The Gamma-Ray Blazar Content of the Northern Sky
Using survey data, we have re-evaluated the correlation of flat spectrum
radio sources with EGRET sources in the Northern sky. A likelihood analysis
incorporating the radio and X-ray properties and the Gamma-ray source
localization is used to gauge the reliability of associations and to search for
counterparts of previously unidentified EGRET sources. Above |b|=10deg, where
the classification is complete, we find that 70% of the Northern EGRET sources
have counterparts similar to the bright EGRET blazars. For several of these we
identify known blazar counterparts more likely than the earlier proposed 3EG
association; for ~20 we have new identifications. Spectroscopic confirmation of
these candidates is in progress and we have found flat spectrum radio quasars
and BL Lac counterparts with redshifts as high as 4. We also find strong
evidence for a set of 28 objects with no plausible counterpart like the known
EGRET Blazars. These thus represent either a new extragalactic population or a
population of Galactic objects with a large scale height. The survey has been
extended into the plane, where we find several new blazar candidates; the bulk
of the sources are, however, Galactic. Looking ahead to the GLAST era we
predict that several of the present 3EG sources are composite and that higher
resolution data will break these into multiple Blazar IDs.Comment: 13 pages, 6 figures, submitted to Ap
The study of neutron star magnetospheres with LOFT
This is a White Paper in support of the mission concept of the Large
Observatory for X-ray Timing (LOFT), proposed as a medium-sized ESA mission. We
discuss the potential of LOFT for the study of magnetospheres of isolated
neutron stars. For a summary, we refer to the paper.Comment: White Paper in Support of the Mission Concept of the Large
Observatory for X-ray Timin
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