866 research outputs found
X-ray monitoring of classical novae in the central region of M 31. II. Autumn and winter 2007/2008 and 2008/2009
[Abridged] Classical novae (CNe) represent the major class of supersoft X-ray
sources (SSSs) in the central region of our neighbouring galaxy M 31. We
performed a dedicated monitoring of the M 31 central region with XMM-Newton and
Chandra between Nov 2007 and Feb 2008 and between Nov 2008 and Feb 2009
respectively, in order to find SSS counterparts of CNe, determine the duration
of their SSS phase and derive physical outburst parameters. We systematically
searched our data for X-ray counterparts of CNe and determined their X-ray
light curves and spectral properties. We detected in total 17 X-ray
counterparts of CNe in M 31, only four of which were known previously. These
latter sources are still active 12.5, 11.0, 7.4 and 4.8 years after the optical
outburst. From the 17 X-ray counterparts 13 were classified as SSSs. Four novae
displayed short SSS phases (< 100 d). Based on these results and previous
studies we compiled a catalogue of all novae with SSS counterparts in M 31
known so far. We used this catalogue to derive correlations between the
following X-ray and optical nova parameters: turn-on time, turn-off time,
effective temperature (X-ray), t2 decay time and expansion velocity of the
ejected envelope (optical). Furthermore, we found a first hint for the
existence of a difference between SSS parameters of novae associated with the
stellar populations of the M 31 bulge and disk. Additionally, we conducted a
Monte Carlo Markov Chain simulation on the intrinsic fraction of novae with SSS
phase. This simulation showed that the relatively high fraction of novae
without detected SSS emission might be explained by the inevitably incomplete
coverage with X-ray observations in combination with a large fraction of novae
with short SSS states, as expected from the WD mass distribution. In order to
verify our results with an increased sample further monitoring observations are
needed.Comment: 31 pages, 23 figures, 10 tables; submitted to A&
Anharmonic magnetic deformation of self-assembled molecular nanocapsules
High magnetic fields were used to deform spherical nanocapsules,
self-assembled from bola-amphiphilic sexithiophene molecules. At low fields the
deformation -- measured through linear birefringence -- scales quadratically
with the capsule radius and with the magnetic field strength. These data
confirm a long standing theoretical prediction (W. Helfrich, Phys. Lett. {\bf
43A}, 409 (1973)), and permits the determination of the bending rigidity of the
capsules as (2.60.8) J. At high fields, an enhanced
rigidity is found which cannot be explained within the Helfrich model. We
propose a complete form of the free energy functional that accounts for this
behaviour, and allows discussion of the formation and stability of nanocapsules
in solution.Comment: 4 pages, 3 figures, accepted in Phys. Rev. Let
Deep XMM-Newton observations of the northern disc of M31. I. Source catalogue
We carried out new observations of two fields in the northern ring of M31
with XMM-Newton with two exposures of 100 ks each and obtained a complete list
of X-ray sources down to a sensitivity limit of ~7 x 10^34 erg s^-1 (0.5 - 2.0
keV). The major objective of the observing programme was the study of the hot
phase of the ISM in M31. The analysis of the diffuse emission and the study of
the ISM is presented in a separate paper. We analysed the spectral properties
of all detected sources using hardness ratios and spectra if the statistics
were high enough. We also checked for variability. We cross-correlated the
source list with the source catalogue of a new survey of the northern disc of
M31 carried out with Chandra and Hubble (Panchromatic Hubble Andromeda
Treasury, PHAT) as well as with other existing catalogues. We detected a total
of 389 sources, including 43 foreground stars and candidates and 50 background
sources. Based on the comparison to the Chandra/PHAT survey, we classify 24
hard X-ray sources as new candidates for X-ray binaries (XRBs). In total, we
identified 34 XRBs and candidates and 18 supernova remnants (SNRs) and
candidates. Three of the four brightest SNRs show emission mainly below 2 keV,
consistent with shocked ISM. The spectra of two of them also require an
additional component with a higher temperature. The SNR [SPH11] 1535 has a
harder spectrum and might suggest that there is a pulsar-wind nebula inside the
SNR. We find five new sources showing clear time variability. We also studied
the spectral properties of the transient source SWIFT J004420.1+413702, which
shows significant variation in flux over a period of seven months (June 2015 to
January 2016) and associated change in absorption. Based on the likely optical
counterpart detected in the Chandra/PHAT survey, the source is classified as a
low-mass X-ray binary.Comment: Accepted for publication in A&
The Fourth BATSE Gamma-Ray Burst Catalog (Revised)
The Burst and Transient Source Experiment (BATSE) on the Compton Gamma Ray
Observatory (CGRO) has triggered on 1637 cosmic gamma-ray bursts between 1991
April 19 and 1996 August 29. These events constitute the Fourth BATSE burst
catalog. The current version (4Br) has been revised from the version first
circulated on CD-ROM in September 1997 (4B) to include improved locations for a
subset of bursts that have been reprocssed using additional data. A significant
difference from previous BATSE catalogs is the inclusion of bursts from periods
when the trigger energy range differed from the nominal 50-300 keV. We present
tables of the burst occurrence times, locations, peak fluxes, fluences, and
durations. In general, results from previous BATSE catalogs are confirmed here
with greater statistical significance.Comment: 45 pages, 12 Postscript figures, accepted for publication in Ap. J.
Supp
A remarkable recurrent nova in M 31: The optical observations
Context. In late November 2013 a fifth eruption in five years of the M31 recurrent nova M31N 2008-12a was announced.
Aims. In this Letter we address the optical lightcurve and progenitor system of M31N 2008-12a.
Methods. Optical imaging data of the 2013 eruption from the Liverpool Telescope, La Palma, and Danish 1.54m Telescope, La Silla, and archival Hubble Space Telescope near-IR, optical and near-UV data are astrometrically and photometrically analysed.
Results. Photometry of the 2013 eruption, combined with three previous eruptions, enabled construction of a template lightcurve of a very fast nova, t2 (V) ' 4 days. The archival data allowed recovery of the progenitor system in optical and near-UV data, indicating a red-giant secondary with bright accretion disk, or alternatively a system with a sub-giant secondary but dominated by a disk.
Conclusions. The eruptions of M31N 2008-12a, and a number of historic X-ray detections, indicate a unique system with a recurrence timescale of � 1 year. This implies the presence of a very high mass white dwarf and a high accretion rate. The recovered progenitor system is consistent with such an elevated rate of accretion.We encourage additional observations, especially towards the end of 2014
Recommended from our members
Validation of TES Methane with HIPPO Aircraft Observations: Implications for Inverse Modeling of Methane Sources
We validate satellite methane observations from the Tropospheric Emission Spectrometer (TES) with 151 aircraft vertical profiles over the Pacific from the HIAPER Pole-to-Pole Observation (HIPPO) program. We find that a collocation window of ±750 km and ±24 h does not introduce significant error in comparing TES and aircraft profiles. We validate both the TES standard product (V004) and an experimental product with two pieces of information in the vertical (V005). We determine a V004 mean bias of 65.8 ppb and random instrument error of 43.3 ppb. For V005 we determine a mean bias of 42.3 ppb and random instrument error of 26.5 ppb in the upper troposphere, and mean biases (random instrument errors) in the lower troposphere of 28.8 (28.7) and 16.9 (28.9) ppb at high and low latitudes respectively. Even when V005 cannot retrieve two pieces of information it still performs better than V004. An observation system simulation experiment (OSSE) with the GEOS-Chem chemical transport model (CTM) and its adjoint shows that TES V004 has only limited value for constraining methane sources. Our successful validation of V005 encourages its production as a standard retrieval to replace V004.Earth and Planetary Science
Theory of spiral wave dynamics in weakly excitable media: asymptotic reduction to a kinematic model and applications
In a weakly excitable medium, characterized by a large threshold stimulus,
the free end of an isolated broken plane wave (wave tip) can either rotate
(steadily or unsteadily) around a large excitable core, thereby producing a
spiral pattern, or retract causing the wave to vanish at boundaries. An
asymptotic analysis of spiral motion and retraction is carried out in this
weakly excitable large core regime starting from the free-boundary limit of the
reaction-diffusion models, valid when the excited region is delimited by a thin
interface. The wave description is shown to naturally split between the tip
region and a far region that are smoothly matched on an intermediate scale.
This separation allows us to rigorously derive an equation of motion for the
wave tip, with the large scale motion of the spiral wavefront slaved to the
tip. This kinematic description provides both a physical picture and exact
predictions for a wide range of wave behavior, including: (i) steady rotation
(frequency and core radius), (ii) exact treatment of the meandering instability
in the free-boundary limit with the prediction that the frequency of unstable
motion is half the primary steady frequency (iii) drift under external actions
(external field with application to axisymmetric scroll ring motion in
three-dimensions, and spatial or/and time-dependent variation of excitability),
and (iv) the dynamics of multi-armed spiral waves with the new prediction that
steadily rotating waves with two or more arms are linearly unstable. Numerical
simulations of FitzHug-Nagumo kinetics are used to test several aspects of our
results. In addition, we discuss the semi-quantitative extension of this theory
to finite cores and pinpoint mathematical subtleties related to the thin
interface limit of singly diffusive reaction-diffusion models
X-Ray Monitoring of Classical Novae in the Central Region of M31. I. June 2006 - March 2007
Context. Classical novae (CNe) have recently been reported to represent the major class of supersoft X-ray sources (SSSs) in the central region of our neighbour galaxy M 31. Aims. We carried out a dedicated monitoring of the M 31 central region with XMM-Newton and Chandra in order to find SSS coun-terparts of CNe, determine the duration of their SSS phase and derive physical outburst parameters. Methods. We systematically searched our data for X-ray counterparts of CNe and determined their X-ray light curves and spectral properties. Additionally, we determined luminosity upper limits for all novae from previous studies which are not detected anymore and for all CNe in our field of view with optical outbursts between May 2005 and March 2007. Results. We detected eight X-ray counterparts of CNe in M 31, four of which were not previously known. Seven sources can be classified as SSSs, one is a candidate SSS. Two SSSs are still visible more than nine years after the nova outburst, whereas two other nova counterparts show a short SSS phase of less than 150 days. Of the latter sources, M31N 2006-04a exhibits a short-time variable X-ray light curve with an apparent period of (1.6 ±0.3) h. This periodicity could indicate the binary period of the system. There is no X-ray detection for 23 out of 25 CNe which were within the field of view of our observations and had their outburst from about one year before the start of the monitoring until its end. From the 14 SSS nova counterparts known from previous studies, ten are not detected anymore. Additionally, we found four SSSs in our XMM-Newton data without a nova counterpart, one of which is a new source. Conclusions. Out of eleven SSSs detected in our monitoring, seven are counterparts of CNe. We therefore confirm the earlier finding that CNe are the major class of SSSs in the central region of M 31. We use the measured SSS turn-on and turn-offtimes to estimate the mass ejected in the nova outburst and the mass burned on the white dwarf. Classical novae with short SSS phases seem to be an important contributor to the overall population
- …