30 research outputs found
Temporal Variability of the X-ray Emission of the Crab Nebula Torus
We have analyzed five ROSAT HRI images of the Crab Nebula spanning the years
1991 to 1997 and have found significant changes in the emission structure of
the X-ray torus surrounding the pulsar. Certain regions increase in brightness
by about 20% over the six years, while others show decreases in surface
brightness. The origin of these changes is unclear, but a possible explanation
is that the bulk velocity of the synchrotron radiating electrons has decreased
on the order of 20% as well.Comment: 15 pages plus 6 figures, figure 1 and figure 6 are in color, to
appear in The Astrophysical Journal, Jan 1, 1999, Vol. 510, #
Optical spectroscopy of the radio pulsar PSR B0656+14
We have obtained the spectrum of a middle-aged PSR B0656+14 in the 4300-9000
AA range with the ESO/VLT/FORS2. Preliminary results show that at 4600-7000 AA
the spectrum is almost featureless and flat with a spectral index $\alpha_nu ~
-0.2 that undergoes a change to a positive value at longer wavelengths.
Combining with available multiwavelength data suggests two wide, red and blue,
flux depressions whose frequency ratio is about 2 and which could be the 1st
and 2nd harmonics of electron/positron cyclotron absorption formed at magnetic
fields ~10^8G in upper magnetosphere of the pulsar.Comment: 4 pages, 4 figures, To appear in Astrophysics and Space Science,
Proceedings of "Isolated Neutron Stars: from the Interior to the Surface",
eds. D. Page, R. Turolla and S. Zan
A Surprising Periodicity Detected During a Super-outburst of V844 Herculis by TESS
We identify a previously undetected periodicity at a frequency of
49.080.01 d (period of 29.340.01 minutes) during a
super-outburst of V844 Her observed by TESS. V844 Her is an SU UMa type
cataclysmic variable with an orbital period of 78.69 minutes, near the period
minimum. The frequency of this new signal is constant in contrast to the
superhump oscillations commonly seen in SU UMa outbursts. We searched without
success for oscillations during quiescence using MDM, TESS, and XMM-Newton
data. The lack of a periodic signal in the XMM light curve and the relatively
low X-ray luminosity of V844 Her suggests that it is not a typical IP. We
consider the possibility that the 29 min signal is the result of super-Nyquist
sampling of a Dwarf Nova Oscillation with a period near the 2-minute cadence of
the TESS data. Our analysis of archival AAVSO photometry from a 2006
super-outburst supports the existence of a 29 min oscillation, although a
published study of an earlier superoutburst did not detect the signal. We
compare the X-ray properties of V844 Her with short orbital period intermediate
polars (IP), V1025 Cen and DW Cnc. We conclude that the new signal is a real
photometric oscillation coming from the V844 Her system and that it is unlikely
to be an aliased high-frequency oscillation. The steady frequency of the new
signal suggests that its origin is related to an asynchronously rotating white
dwarf in V844 Her, although the precise mechanism producing the flux variations
remains unclear.Comment: 13 pages, 10 figures, accepted for publication in the Astrophysical
Journa
The Radio - 2 mm Spectral Index of the Crab Nebula Measured with GISMO
We present results of 2 mm observations of the Crab Nebula, obtained using
the Goddard-IRAM Superconducting 2 Millimeter Observer (GISMO) bolometer camera
on the IRAM 30 m telescope. Additional 3.3 mm observations with the MUSTANG
bolometer array on the Green Bank Telescope are also presented. The integrated
2 mm flux density of the Crab Nebula provides no evidence for the emergence of
a second synchrotron component that has been proposed. It is consistent with
the radio power law spectrum, extrapolated up to a break frequency of
log(nu_{b} [GHz]) = 2.84 +/- 0.29 or nu_{b} = 695^{+651}_{-336} GHz. The Crab
Nebula is well-resolved by the ~16.7" beam (FWHM) of GISMO. Comparison to radio
data at comparable spatial resolution enables us to confirm significant spatial
variation of the spectral index between 21 cm and 2 mm. The main effect is a
spectral flattening in the inner region of the Crab Nebula, correlated with the
toroidal structure at the center of the nebula that is prominent in the near-IR
through X-ray regime.Comment: Accepted for publication in the Ap
Six Years of Chandra Observations of Supernova Remnants
We present a review of the first six years of Chandra X-ray Observatory
observations of supernova remnants. From the official "first-light" observation
of Cassiopeia A that revealed for the first time the compact remnant of the
explosion, to the recent million-second spectrally-resolved observation that
revealed new details of the stellar composition and dynamics of the original
explosion, Chandra observations have provided new insights into the supernova
phenomenon. We present an admittedly biased overview of six years of these
observations, highlighting new discoveries made possible by Chandra's unique
capabilities.Comment: 82 pages, 28 figures, for the book Astrophysics Update
The Relation Between the Surface Brightness and the Diameter for Galactic Supernova Remnants
In this work, we have constructed a relation between the surface brightness
() and diameter (D) of Galactic C- and S-type supernova remnants
(SNRs). In order to calibrate the -D dependence, we have carefully
examined some intrinsic (e.g. explosion energy) and extrinsic (e.g. density of
the ambient medium) properties of the remnants and, taking into account also
the distance values given in the literature, we have adopted distances for some
of the SNRs which have relatively more reliable distance values. These
calibrator SNRs are all C- and S-type SNRs, i.e. F-type SNRs (and S-type SNR
Cas A which has an exceptionally high surface brightness) are excluded. The
Sigma-D relation has 2 slopes with a turning point at D=36.5 pc: (at 1
GHz)=8.4 D
WmHzster (for
WmHzster and D36.5 pc) and (at 1
GHz)=2.7 10 D
WmHzster (for
WmHzster and D36.5 pc). We discussed the theoretical
basis for the -D dependence and particularly the reasons for the change
in slope of the relation were stated. Added to this, we have shown the
dependence between the radio luminosity and the diameter which seems to have a
slope close to zero up to about D=36.5 pc. We have also adopted distance and
diameter values for all of the observed Galactic SNRs by examining all the
available distance values presented in the literature together with the
distances found from our -D relation.Comment: 45 pages, 2 figures, accepted for publication in Astronomical and
Astrophysical Transaction
Human Analogue Safe Haven Effect of the Owner : Behavioural and Heart Rate Response to Stressful Social Stimuli in Dogs
The secure base and safe haven effects of the attachment figure are central features of the human attachment theory. Recently, conclusive evidence for human analogue attachment behaviours in dogs has been provided, however, the owner’s security-providing role in danger has not been directly supported. We investigated the relationship between the behavioural and cardiac response in dogs (N = 30) while being approached by a threatening stranger in separation vs. in the presence of the owner, presented in a balanced order. Non-invasive telemetric measures of heart rate (HR) and heart rate variability (HRV) data during the threatening approaches was compared to periods before and after the encounters. Dogs that showed distress vocalisation during separation (N = 18) and that growled or barked at the stranger during the threatening approach (N = 17) were defined as behaviourally reactive in the given situation. While characteristic stress vocalisations were emitted during separations, the absence of the owner did not have an effect on dogs’ mean HR, but significantly increased the HRV. The threatening approach increased dogs’ mean HR, with a parallel decrease in the HRV, particularly in dogs that were behaviourally reactive to the encounter. Importantly, the HR increase was significantly less pronounced when dogs faced the stranger in the presence of the owner. Moreover, the test order, whether the dog encountered the stranger first with or without its owner, also proved important: HR increase associated with the encounter in separation seemed to be attenuated in dogs that faced the stranger first in the presence of their owner. We provided evidence for human analogue safe haven effect of the owner in a potentially dangerous situation. Similarly to parents of infants, owners can provide a buffer against stress in dogs, which can even reduce the effect of a subsequent encounter with the same threatening stimuli later when the owner is not present
Exposure to a dog elicits different cardiovascular and behavioral effects in pregnant and lactating goats
Behavioural indicators of welfare in farmed fish
Behaviour represents a reaction to the environment as fish perceive it and is therefore a key element of fish welfare. This review summarises the main findings on how behavioural changes have been used to assess welfare in farmed fish, using both functional and feeling-based approaches. Changes in foraging behaviour, ventilatory activity, aggression, individual and group swimming behaviour, stereotypic and abnormal behaviour have been linked with acute and chronic stressors in aquaculture and can therefore be regarded as likely indicators of poor welfare. On the contrary, measurements of exploratory behaviour, feed anticipatory activity and reward-related operant behaviour are beginning to be considered as indicators of positive emotions and welfare in fish. Despite the lack of scientific agreement about the existence of sentience in fish, the possibility that they are capable of both positive and negative emotions may contribute to the development of new strategies (e. g. environmental enrichment) to promote good welfare. Numerous studies that use behavioural indicators of welfare show that behavioural changes can be interpreted as either good or poor welfare depending on the fish species. It is therefore essential to understand the species-specific biology before drawing any conclusions in relation to welfare. In addition, different individuals within the same species may exhibit divergent coping strategies towards stressors, and what is tolerated by some individuals may be detrimental to others. Therefore, the assessment of welfare in a few individuals may not represent the average welfare of a group and vice versa. This underlines the need to develop on-farm, operational behavioural welfare indicators that can be easily used to assess not only the individual welfare but also the welfare of the whole group (e. g. spatial distribution). With the ongoing development of video technology and image processing, the on-farm surveillance of behaviour may in the near future represent a low-cost, noninvasive tool to assess the welfare of farmed fish.Fundação para a Ciência e Tecnologia, Portugal [SFRH/BPD/42015/2007]info:eu-repo/semantics/publishedVersio
Behavioural responses to unexpected changes in reward quality
Successive negative contrast (SNC) effects are changes in anticipatory or consummatory behaviour
when animals unexpectedly receive a lower value reward than they have received previously. SNC
effects are often assumed to reflect frustration and appear to be influenced by background affective
state. However, alternative explanations of SNC, such as the functional-search hypothesis, do not
necessarily imply an aversive affective state. We tested 18 dogs in a SNC paradigm using a patch
foraging task. Dogs were tested in two conditions, once with the low value reward in all of five trials
(unshifted) and once when reward value was altered between high and low (shifted). Following a
reward downshift, subjects showed a SNC effect by switching significantly more often between
patches compared to the unshifted condition. However, approach latency, foraging time and quantity
consumed did not differ between conditions, suggesting non-affective functional search behaviour
rather than frustration. There was no relationship between strength of SNC and anxiety-related
behaviours as measured in a novel object test and a personality questionnaire (C-BARQ). However,
associations with the C-BARQ scores for Trainability and Stranger directed aggression suggest a
possible link with behavioural flexibility and coping style. While reward quality clearly affects incentive
motivation, the relationship between SNC, frustration and background affective state requires further
exploration