596 research outputs found
Is the Fuzziness of GRB970228 constant?
In view of the data gathered in September 1997, we review the flux values
collected so far for the "fuzziness" seen in the optical counterpart of
GRB970228. Comparison between the ground based data collected in March and the
data of September 1997 suggests a fading of the fuzz. Given the diversity of
the data in hand, the magnitude of the effect and its significance are not easy
to quantify. Only new images, both from the ground and with the Space
Telescope, directly comparable to the old ones could settle this problem.Comment: 6 pages, Latex, 6 postscript figures, 1 postscript table Proceedings
of the 4th Huntsville Gammma-Ray Burst Symposiu
The near-infrared detection of PSR B0540-69 and its nebula
The ~1700 year old PSR B0540-69 in the LMC is considered the twin of the Crab
pulsar because of its similar spin parameters, magnetic field, and energetics.
Its optical spectrum is fit by a power-law, ascribed to synchrotron radiation,
like for the young Crab and Vela pulsars. nIR observations, never performed for
PSR B0540-69, are crucial to determine whether the optical power-law spectrum
extends to longer wavelengths or a new break occurs, like it happens for both
the Crab and Vela pulsars in the mIR, hinting at an even more complex particle
energy and density distribution in the pulsar magnetosphere. We observed PSR
B0540-69 in the J, H, and Ks bands with the VLT to detect it, for the first
time, in the nIR and characterise its optical-to-nIR spectrum. To disentangle
the pulsar emission from that of its pulsar wind nebula (PWN), we obtained
high-spatial resolution adaptive optics images with NACO. We could clearly
identify PSR B0540-69 in our J, H, and Ks-band images and measure its flux
(J=20.14, H=19.33, Ks=18.55, with an overall error of +/- 0.1 magnitudes in
each band). The joint fit to the available optical and nIR photometry with a
power-law spectrum gives a spectral index alpha=0.70 +/-0.04. The comparison
between our NACO images and HST optical ones does not reveal any apparent
difference in the PWN morphology as a function of wavelength. The PWN
optical-to-nIR spectrum is also fit by a single power-law, with spectral index
alpha=0.56+/- 0.03, slightly flatter than the pulsar's. Using NACO at the VLT,
we obtained the first detection of PSR B0540-69 and its PWN in the nIR. Due to
the small angular scale of the PWN (~4") only the spatial resolution of the
JWST will make it possible to extend the study of the pulsar and PWN spectrum
towards the mid-IR.Comment: 11 pages, 10 figures, Accepted for publication on Astronomy and
Astrophysic
Neutrons from Piezonuclear Reactions
We report the results obtained by cavitating water solutions of iron salts
(iron chloride and iron nitrate) with different concentrations at different
ultrasound powers. In all cases we detected a neutron radiation well higher
than the background level. The neutron production is perfectly reproducible and
can at some extent be controlled. These evidences for neutron emission
generated by cavitation support some preliminary clues for the possibility of
piezonuclear reactions (namely nuclear reactions induced by pressure and shock
waves) obtained in the last ten years. We have been able for the first time to
state some basic features of such a neutron emission induced by cavitation,
namely: 1) a marked threshold behavior in power, energy and time; 2) its
occurring without a concomitant production of gamma radiation.Comment: 8 figures; we added some more important references; we replaced some
figures with more detailed ones; we added more comprehensive details which
could not be desclosed before as part of private patents which have been
published no
HST and VLT observations of the neutron star 1E 1207.4-5209
1E 1207.4-5209, the peculiar Central Compact object in the G296.5+10.0
supernova remnant, has been proposed to be an "anti-magnetar" - a young neutron
star born with a weak dipole field. Accretion, possibly of supernova fallback
material, has also been invoked to explain a large surface temperature
anisotropy as well as the generation of peculiar cyclotron absorption features
superimposed to its thermal spectrum. Interestingly enough, a faint
optical/infrared source was proposed as a possible counterpart to 1E
1207.4-5209, but later questioned, based on coarse positional coincidence.
Considering the large offset of 1E 1207.4-5209 with respect to the center of
its host supernova remnant, the source should move at ~70 mas/yr. Thus, we
tested the association by measuring the proper motion of the proposed optical
counterpart. Using HST observations spanning 3.75 years, we computed a 3 sigma
upper limit of 7 mas/yr. Absolute astrometry on the same HST data set also
places the optical source significantly off the 99% confidence Chandra
position. This allows us to safely rule out the association. Using the HST data
set, coupled to ground-based observations collected at the ESO/VLT, we set the
deepest limits ever obtained to the optical/infrared emission from 1E
1207.4-5209. By combining such limits to the constraints derived from X-ray
timing, we rule out accretion as the source of the thermal anisotropy of the
neutron star.Comment: 8 pages, 3 figures. Accepted for publication in Astronomy &
Astrophysic
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