34 research outputs found
Benefits and Limitations of Web3
Web3 provides users and service providers several benefits not found in Web2.
However, despite the benefits provided, Web3 faces several obstacles that
prevent the paradigm from gaining widespread adoption. Developers should
understand the benefits and limitations of the technology in order to create
more accessible Web3 smart applications
Machine Learning for Detecting Malware in PE Files
The increasing number of sophisticated malware poses a major cybersecurity
threat. Portable executable (PE) files are a common vector for such malware. In
this work we review and evaluate machine learning-based PE malware detection
techniques. Using a large benchmark dataset, we evaluate features of PE files
using the most common machine learning techniques to detect malware
Feasibility Study of Lense-Thirring Precession in LS I +61303
Very recent analysis of the radio spectral index and high energy observations
have shown that the two-peak accretion/ejection microquasar model applies for
LSI+61303. The fast variations of the position angle observed with MERLIN and
confirmed by consecutive VLBA images must therefore be explained in the context
of the microquasar scenario. We calculate what could be the precessional period
for the accretion disk in LSI+61303 under tidal forces of the Be star
(P_{tidal-forces}) or under the effect of frame dragging produced by the
rotation of the compact object (P_{Lense-Thirring}). P_{tidal-forces}R_{tr}r_g$, where the Bardeen-Petterson effect
should align the midplane of the disk. For this truncated radius of the
accretion disk P_{Lense-Thirring} for a slow rotator results in a few days.
Therefore, Lense-Thirring precession induced by a slowly rotating compact
object could be compatible with the daily variations of the ejecta angle
observed in LSI+61303.Comment: 6 pages, 5 figures, accepted for publication in Astronomy and
Astrophysic
The 2022 Outburst of IGR J17091-3624: Connecting the exotic GRS 1915+105 to standard black hole X-ray binaries
While the standard X-ray variability of black hole X-ray binaries (BHXBs) is
stochastic and noisy, there are two known BHXBs that exhibit exotic
`heartbeat'-like variability in their light curves: GRS 1915+105 and IGR
J17091-3624. In 2022, IGR J17091-3624 went into outburst for the first time in
the NICER/NuSTAR era. These exquisite data allow us to simultaneously track the
exotic variability and the corresponding spectral features with unprecedented
detail. We find that as in typical BHXBs, the outburst began in the hard state,
then the intermediate state, but then transitioned to an exotic soft state
where we identify two types of heartbeat-like variability (Class V and a new
Class X). The flux-energy spectra show a broad iron emission line due to
relativistic reflection when there is no exotic variability, and absorption
features from highly ionized iron when the source exhibits exotic variability.
Whether absorption lines from highly ionized iron are detected in IGR
J17091-3624 is not determined by the spectral state alone, but rather is
determined by the presence of exotic variability; in a soft spectral state,
absorption lines are only detected along with exotic variability. Our finding
indicates that IGR J17091-3624 can be seen as a bridge between the most
peculiar BHXB GRS 1915+105 and `normal' BHXBs because it alternates between the
conventional and exotic behavior of BHXBs. We discuss the physical nature of
the absorbing material and exotic variability in light of this new legacy
dataset.Comment: 23 pages, 15 figures, 2 tables, accepted to be published in Ap
Highly-coherent quasi-periodic oscillations in the 'heartbeat' black hole X-ray binary IGR J17091-3624
IGR J17091-3624 is a black hole X-ray binary (BHXB), often referred to as the
'twin' of GRS 1915+105 because it is the only other known BHXB that can show
exotic 'heartbeat'-like variability that is highly structured and repeated.
Here we report on observations of IGR J17091-3624 from its 2022 outburst, where
we detect an unusually coherent quasi-periodic oscillation (QPO) when the
broadband variability is low (total fractional rms 6%) and the
spectrum is dominated by the accretion disk. Such spectral and variability
behavior is characteristic of the soft state of typical BHXBs (i.e., those that
do not show heartbeats), but we also find that this QPO is strongest when there
is some exotic heartbeat-like variability (so-called Class V variability). This
QPO is detected at frequencies between 5 and 8 Hz and has Q-factors (defined as
the QPO frequency divided by the width) 50, making it one of the most
highly coherent low-frequency QPO ever seen in a BHXB. The extremely high Q
factor makes this QPO distinct from typical low-frequency QPOs that are
conventionally classified into Type-A/B/C QPOs. Instead, we find evidence that
archival observations of GRS 1915+105 also showed a similarly high-coherence
QPO in the same frequency range, suggesting that this unusually coherent and
strong QPO may be unique to BHXBs that can exhibit 'heartbeat'-like
variability.Comment: 11 pages, 10 figures, 2 tables, accepted to be published in Ap
X-ray Reverberation Mapping of Ark 564 using Gaussian Process Regression
Ark 564 is an extreme high-Eddington Narrow-line Seyfert 1 galaxy, known for
being one of the brightest, most rapidly variable soft X-ray AGN, and for
having one of the lowest temperature coronae. Here we present a 410-ks NuSTAR
observation and two 115-ks XMM-Newton observations of this unique source, which
reveal a very strong, relativistically broadened iron line. We compute the
Fourier-resolved time lags by first using Gaussian processes to interpolate the
NuSTAR gaps, implementing the first employment of multi-task learning for
application in AGN timing. By fitting simultaneously the time lags and the flux
spectra with the relativistic reverberation model RELTRANS, we constrain the
mass at , although additional components
are required to describe the prominent soft excess in this source. These
results motivate future combinations of machine learning, Fourier-resolved
timing, and the development of reverberation models.Comment: 19 pages, 9 figures. Accepted for publication in The Astrophysical
Journa
The 2022 outburst of IGR J17091–3624: connecting the exotic GRS 1915+105 to standard black hole x-ray binaries
While the standard X-ray variability of black hole X-ray binaries (BHXBs) is stochastic and noisy, there are two known BHXBs that exhibit exotic “heartbeat”-like variability in their lightcurves: GRS 1915+105 and IGR J17091-3624. In 2022, IGR J17091-3624 went into outburst for the first time in the NICER/NuSTAR era. These exquisite data allow us to simultaneously track the exotic variability and the corresponding spectral features with unprecedented detail. We find that as in typical BHXBs, the outburst began in the hard state, then continued in the intermediate state, but then transitioned to an exotic soft state, where we identify two types of heartbeat-like variability (Class V and a new Class X). The flux energy spectra show a broad iron emission line due to relativistic reflection when there is no exotic variability, and absorption features from highly ionized iron when the source exhibits exotic variability. Whether absorption lines from highly ionized iron are detected in IGR J17091-3624 is not determined by the spectral state alone, but rather is determined by the presence of exotic variability; in a soft spectral state, absorption lines are only detected along with exotic variability. Our finding indicates that IGR J17091-3624 can be seen as a bridge between the most peculiar BHXB GRS 1915+105 and “normal” BHXBs, because it alternates between the conventional and exotic behaviors of BHXBs. We discuss the physical nature of the absorbing material and exotic variability in light of this new legacy data set.</p
The 2022 Outburst of IGR J17091–3624: Connecting the Exotic GRS 1915+105 to Standard Black Hole X-Ray Binaries
While the standard X-ray variability of black hole X-ray binaries (BHXBs) is stochastic and noisy, there are two known BHXBs that exhibit exotic “heartbeat”-like variability in their lightcurves: GRS 1915+105 and IGR J17091–3624. In 2022, IGR J17091–3624 went into outburst for the first time in the NICER/NuSTAR era. These exquisite data allow us to simultaneously track the exotic variability and the corresponding spectral features with unprecedented detail. We find that as in typical BHXBs, the outburst began in the hard state, then continued in the intermediate state, but then transitioned to an exotic soft state, where we identify two types of heartbeat-like variability ( Class V and a new Class X ). The flux energy spectra show a broad iron emission line due to relativistic reflection when there is no exotic variability, and absorption features from highly ionized iron when the source exhibits exotic variability. Whether absorption lines from highly ionized iron are detected in IGR J17091–3624 is not determined by the spectral state alone, but rather is determined by the presence of exotic variability; in a soft spectral state, absorption lines are only detected along with exotic variability. Our finding indicates that IGR J17091–3624 can be seen as a bridge between the most peculiar BHXB GRS 1915+105 and “normal” BHXBs, because it alternates between the conventional and exotic behaviors of BHXBs. We discuss the physical nature of the absorbing material and exotic variability in light of this new legacy data set