502 research outputs found
On the anomalous X-ray afterglows of GRB 970508 and GRB 970828
Recently, BeppoSAX and ASCA have reported an unusual resurgence of soft X-ray
emission during the afterglows of GRB 970508 and GRB 970828, together with
marginal evidence for the existence of Fe-lines in both objects. We consider
the implications of the existence of a torus of iron-rich material surrounding
the sites of gamma ray bursts as would be expected in the SupraNova model; in
particular, we show that the fireball will quickly hit this torus, and bring it
to a temperature ~3x10^7 K. Bremsstrahlung emission from the heated up torus
will cause a resurgence of the soft X-ray emission with all expected
characteristics (flux level, duration and spectral hardening with time)
identical to those observed during the reburst. Also, thermal emission from the
torus will account for the observed iron line flux. These events are also
observable, for instance by new missions such as SWIFT, when beaming away from
our line sight makes us miss the main burst, as Fast (soft) X-ray Transients,
with durations ~10^3 s, and fluences ~10^-7-10^-4 erg cm^-2. This model
provides evidence in favor of the SupraNova model for Gamma Ray Bursts.Comment: To appear in MN Pink pages, MN-LateX, no figure
On gravitomagnetic precession around black holes
We compute exactly the Lense-Thirring precession frequency for point masses
in the Kerr metric, for arbitrary black hole mass and specific angular
momentum. We show that this frequency, for point masses at or close to the
innermost stable orbit, and for holes with moderate to extreme rotation, is
less than, but comparable to the rotation frequency. Thus, if the quasi
periodic oscillations (QPOs) observed in the modulation of the X-ray flux from
some black holes candidates are due to Lense-Thirring precession of orbiting
material, we predict that a separate, distinct QPO ought to be observed in each
object.Comment: Accepted for publication in MNRAS. MN-Latex, 2 figure
Iron line emission in X-ray afterglows
Recent observations of X-ray afterglows reveal the presence of a redshifted
Kalpha iron line in emission in four bursts. In GRB 991216, the line was
detected by the low energy grating of Chandra, which showed the line to be
broad, with a full width of ~15,000 km/s. These observations indicate the
presence of a >1 solar mass of iron rich material in the close vicinity of the
burst, most likely a supernova remnant. The fact that such strong lines are
observed less than a day after the trigger strongly limits the size of the
remnant, which must be very compact. If the remnant had the observed velocity
since the supernova explosion, its age would be less than a month. In this case
nickel and cobalt have not yet decayed into iron. We show how to solve this
paradox.Comment: 3 pages, to appear in the proceedings of the the 2nd Workshop on
Gamma-Ray Bursts in the Afterglow Era, Rome, Oct. 200
On the absorption feature in the prompt X-ray spectrum of GRB 990705
The absorption feature detected in the prompt X-ray emission of GRB 990705 bears important consequences. We investigate different production mechanisms and we conclude that the absorbing material cannot be very close to the burster and is likely to be moderately clumped. These properties challenge any model in which the burst explodes in coincidence with the core-collapse of a massive rotating star. We show that the straightforward interpretation of the absorption feature as a photoionization K edge of neutral iron faces a severe problem in that it requires a huge amount of iron in the close vicinity of the burster. We then discuss an alternative scenario, in which iron ions are kept in a high ionization state by the burst flux, and the absorption feature is produced by resonant scattering from hydrogen-like iron, broadened by a range outflow velocities. In this case the physical conditions and geometry of the absorbing material are fully consistent with the presence of a young supernova remnant surrounding the burst site at a radius R ~ 10^{16} cm. We finally discuss how this remnant might affect the generation of afterglows with a standard power-law flux decay
The prompt emission of GRB990712 with BeppoSAX: evidence of a transient X-ray emission feature
We report on the prompt X- and gamma-ray observations of GRB990712 with the
BeppoSAX Gamma-Ray Burst Monitor and Wide Field Camera No. 2. Due to Sun
constraints, we could not perform a follow-up observation with the BeppoSAX
Narrow Field Instruments. The light curve of the prompt emission shows two
pulses and a total duration of about 40s in X-rays. In gamma-rays the event is
even shorter. The 2-700 keV spectral emission with time shows a discontinuity
in the peak energy Ep of the E F(E) spectrum: Ep is above our energy passband
during the first pulse and goes down to ~10 keV during the second pulse.
Another peculiarity is noted in this event for the first time: the possible
evidence of a 2s duration emission feature during the tail of the first pulse.
The feature is consistent with either a Gaussian profile with centroid energy
of 4.5 keV or a blackbody spectrum with kTbb ~1.3 keV. We discuss the possible
origin of the feature. The most attractive possibility is that we are observing
the thermal emission of a baryon-loaded expanding fireball, when it becomes
optically thin.Comment: 18 pages, 4 figures, published in The Astrophysical Journal Letters,
relevant changes in the Discussion (section 4) with respect to previous
versio
Variable broad lines and outflow in the weak blazar PBC J2333.9-2343
Indexación: Scopus; Scielo.Funding text #1
1Instituto de Física y Astronomía, Facultad de Ciencias, Universidad de Valparaíso, Gran Bretaña 1111, Playa Ancha, Valparaíso, Chile 2INAF – Istituto di Astrofisica e Planetologia Spaziali di Roma (IAPS-INAF), Via del Fosso del Cavaliere 100, I-00133 Roma, Italy 3INAF – Osservatorio Astronomico di Roma, via Frascati 33, I-00078 Monte Porzio Catone, Italy 4Excellence Cluster Universe, Technische Universität München, Boltzmannstr. 2, D-85748, Garching, Germany 5European Southern Observatory, Karl-Schwarzschild-Str 2, D-85748 Garching b. München, Germany 6Instituto Nacional de Astrofísica, Óptica y Electrónica, Apartado Postal 51-216, 72000 Puebla, México 7Argelander Institute for Astronomy, University of Bonn, Auf dem Hügel 71, D-53121 Bonn, Germany 8International Max Planck Research School of Astronomy and Astrophysics at the Universities of Bonn and Cologne, Auf dem Hügel 69, D-53121 Bonn, Germany 9INAF – Osservatorio di Astrofisica e Scienza dello Spazio, via Gobetti 93/3, I-40129 Bo...View all
Funding text #2
We acknowledge the referee, M. Villar Martín, for her comments and suggestions that helped to improve the paper. This work made use of data supplied by the UK Swift Science Data Centre at the University of Leicester, the NASA/IPAC extragalactic database (NED), the STARLIGHT code, and the IRAF software. Based upon observations carried out at the Observatorio Astronómico Nacional on the Sierra San Pedro Mártir (OAN-SPM), Baja California, México. LHG and FP acknowledge the ASI/INAF agreement number 2013-023-R1, LHG partial support from FONDECYT through grant 3170527, MP from ESSTI under the MoST, and from MINECO through research projects AYA2013-42227-P and AYA2016-76682-C3-1-P (AEI/FEDER, UE), LHG and SC from the Spanish grant AYA2013-42227-P, VC by CONACyT research grant 280789, EFJA from the Collaborative Research Center 956, subproject A1, funded by DFG, and GV from the DFG Cluster of Excellence ‘Origin and Structure of the Universe’ (www.universe-cluster.de).PBC J2333.9-2343 is a peculiar active nucleus with two giant radio lobes and a weak blazarlike nucleus at their centre. In this work we show new optical, ultraviolet (UV), and X-ray data taken from the San Pedro Mártir telescope, the New Technology Telescope, NTT/EFOSC2, and the Swift/XRT satellite. The source is highly variable at all frequencies, in particular the strongest variations are found in the broad Hα component with a flux increase of 61±4 per cent between 2009 and 2016, following the X-ray flux increase of 62±6 per cent between 2010 and 2016. We also detected a broad Hβ component in 2016, making the optical classification change from type 1.9 to type 1.8 in 1 yr. We have also detected a broad component of the [OIII]λ5007 line, which is blue-shifted and of high velocity, suggesting an origin from a highly disturbed medium, possibly an outflow. The line flux variability and broad widths are indicative of a jet that is, at least in part, responsible for the ionization of the broad line region (BLR) and narrow line region (NLR). © 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society.https://academic.oup.com/mnras/article-abstract/478/4/4634/4999938?redirectedFrom=fulltex
Dimensional Reduction of the 5D Kaluza-Klein Geodesic Deviation Equation
In the work of Kerner et al. (2001) the problem of the geodesic deviation in
a 5D Kaluza Klein background is faced. The 4D space-time projection of the
resulting equation coincides with the usual geodesic deviation equation in the
presence of the Lorenz force, provided that the fifth component of the
deviation vector satisfies an extra constraint which takes into account the
conservation along the path. The analysis was performed setting as a
constant the scalar field which appears in Kaluza-Klein model. Here we focus on
the extension of such a work to the model where the presence of the scalar
field is considered. Our result coincides with that of Kerner et al. when the
minimal case is considered, while it shows some departures in the
general case. The novelty due to the presence of is that the variation
of the between the two geodesic lines is not conserved during the motion;
an exact law for such a behaviour has been derived.Comment: 9 page
kHz Quasi Periodic Oscillations in Low Mass X-ray Binaries as Probes of General Relativity in the Strong Field Regime
We consider the interpretation of a pair of kHz Quasi Periodic Oscillations
(QPOs) in the Fourier spectra of two Low Mass X-Ray Binaries, Sco X-1 and
4U1608-52, hosting an old accreting neutron star. The observed frequency
difference of these QPOs decreaseas as their frequency increases, contrary to
simple beat frequency models, which predict a constant frequency difference. We
show that the behaviour of these QPOs is instead well matched in terms of the
fundamental frequencies (in the radial and azimuthal directions) for test
particle motion in the gravitational field of the neutron star, for reasonable
star masses, and nearly independent of the star spin. The radial frequency must
be much smaller than the azimuthal one, testifying that kHz QPOs are produced
close to the innermost stable orbit. These results are not reproduced through
the post--Newtonian (PN) approximation of General Relativity (GR). kHz QPOs
from X-ray binaries likely provide an accurate laboratory for strong field GR.Comment: to appear in Physical Review Letters, PRL Latex plus 2 figures in
standard PostScript forma
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