392 research outputs found
NuSTAR and Suzaku observations of the hard state in Cygnus X-1: locating the inner accretion disk
We present simultaneous Nuclear Spectroscopic Telescope Array (NuSTAR ) and
Suzaku observations of the X-ray binary Cygnus X-1 in the hard state. This is
the first time this state has been observed in Cyg X-1 with NuSTAR, which
enables us to study the reflection and broad-band spectra in unprecedented
detail. We confirm that the iron line cannot be fit with a combination of
narrow lines and absorption features, and instead requires a relativistically
blurred profile in combination with a narrow line and absorption from the
companion wind. We use the reflection models of Garcia et al. (2014) to
simultaneously measure the black hole spin, disk inner radius, and coronal
height in a self-consistent manner. Detailed fits to the iron line profile
indicate a high level of relativistic blurring, indicative of reflection from
the inner accretion disk. We find a high spin, a small inner disk radius, and a
low source height, and rule out truncation to greater than three gravitational
radii at the 3{\sigma} confidence level. In addition, we find that the line
profile has not changed greatly in the switch from soft to hard states, and
that the differences are consistent with changes in the underlying reflection
spectrum rather than the relativistic blurring. We find that the blurring
parameters are consistent when fitting either just the iron line or the entire
broad-band spectrum, which is well modelled with a Comptonized continuum plus
reflection model.Comment: 12 pages, 7 figures, accepted for publication in Ap
Measuring Black Hole Spin using X-ray Reflection Spectroscopy
I review the current status of X-ray reflection (a.k.a. broad iron line)
based black hole spin measurements. This is a powerful technique that allows us
to measure robust black hole spins across the mass range, from the stellar-mass
black holes in X-ray binaries to the supermassive black holes in active
galactic nuclei. After describing the basic assumptions of this approach, I lay
out the detailed methodology focusing on "best practices" that have been found
necessary to obtain robust results. Reflecting my own biases, this review is
slanted towards a discussion of supermassive black hole (SMBH) spin in active
galactic nuclei (AGN). Pulling together all of the available XMM-Newton and
Suzaku results from the literature that satisfy objective quality control
criteria, it is clear that a large fraction of SMBHs are rapidly-spinning,
although there are tentative hints of a more slowly spinning population at high
(M>5*10^7Msun) and low (M<2*10^6Msun) mass. I also engage in a brief review of
the spins of stellar-mass black holes in X-ray binaries. In general,
reflection-based and continuum-fitting based spin measures are in agreement,
although there remain two objects (GROJ1655-40 and 4U1543-475) for which that
is not true. I end this review by discussing the exciting frontier of
relativistic reverberation, particularly the discovery of broad iron line
reverberation in XMM-Newton data for the Seyfert galaxies NGC4151, NGC7314 and
MCG-5-23-16. As well as confirming the basic paradigm of relativistic disk
reflection, this detection of reverberation demonstrates that future large-area
X-ray observatories such as LOFT will make tremendous progress in studies of
strong gravity using relativistic reverberation in AGN.Comment: 19 pages. To appear in proceedings of the ISSI-Bern workshop on "The
Physics of Accretion onto Black Holes" (8-12 Oct 2012). Revised version adds
a missing source to Table 1 and Fig.6 (IRAS13224-3809) and corrects the
referencing of the discovery of soft lags in 1H0707-495 (which were in fact
first reported in Fabian et al. 2009
High-density disc reflection spectroscopy of low-mass active galactic nuclei
The standard alpha-disc model predicts an anti-correlation between the
density of the inner accretion disc and the black hole mass times square of the
accretion rate, as seen in higher mass () active
galactic nuclei (AGNs). In this work, we test the predictions of the alpha-disc
model and study the properties of the inner accretion flow for the low-mass end
() of AGNs. We utilize a new high-density
disc reflection model where the density parameter varies from to cm and apply it to the broadband X-ray (0.3-10
keV) spectra of the low-mass AGN sample. The sources span a wide range of
Eddington fractions and are consistent with being sub-Eddington or
near-Eddington. The X-ray spectra reveal a soft X-ray excess below
keV which is well modeled by high-density reflection from an ionized accretion
disc of density cm on average. The results
suggest a radiation pressure-dominated disc with an average of 70% fraction of
the disc power transferred to the corona, consistent with that observed in
higher mass AGNs. We show that the disc density higher than cm
can result from the radiation pressure compression when the disc surface does
not hold a strong magnetic pressure gradient. We find tentative evidence for a
drop in black hole spin at low-mass regimes.Comment: 20 pages, 10 figures, 6 tables. Accepted for publication in MNRA
The 1.5âMs observing campaign on IRAS 13224â3809 â I. X-ray spectral analysis
We present a detailed spectral analysis of the recent 1.5âMs XMMâNewton observing campaign on the narrow-line Seyfert 1 galaxy IRAS 13224â3809, taken simultaneously with 500âks of NuSTAR data. The X-ray light curve shows three flux peaks, registering at about 100 times the minimum flux seen during the campaign, and rapid variability with a time-scale of kiloseconds. The spectra are well fit with a primary power-law continuum, two relativistic-blurred reflection components from the inner accretion disc with very high iron abundance, and a simple blackbody-shaped model for the remaining soft excess. The spectral variability is dominated by the power-law continuum from a corona region within a few gravitational radii from the black hole. Additionally, blueshifted NeâX, MgâXII, SiâXIV, and SâXVI absorption lines are identified in the stacked low-flux spectrum, confirming the presence of a highly ionized outflow with velocity up to v = 0.267 and 0.225âc. We fit the absorption features with xstar models and find a relatively constant velocity outflow through the whole observation. Finally, we replace the bbody and supersolar abundance reflection models by fitting the soft excess successfully with the extended reflection model relxillD, which allows for higher densities than the standard relxill model. This returns a disc electron density n_e > 10^(18.7)âcm^(â3) and lowers the iron abundance from Z_(Fe) = 24^(+3)_(â4)Z_â with n-e = 10^(15) cm^(-3) to Z_(Fe) = 6.6^(+0.8)_(-2.1)Z_â
Neutrinos below 100 TeV from the southern sky employing refined veto techniques to IceCube data
Many Galactic sources of gamma rays, such as supernova remnants, are expected
to produce neutrinos with a typical energy cutoff well below 100 TeV. For the
IceCube Neutrino Observatory located at the South Pole, the southern sky,
containing the inner part of the Galactic plane and the Galactic Center, is a
particularly challenging region at these energies, because of the large
background of atmospheric muons. In this paper, we present recent advancements
in data selection strategies for track-like muon neutrino events with energies
below 100 TeV from the southern sky. The strategies utilize the outer detector
regions as veto and features of the signal pattern to reduce the background of
atmospheric muons to a level which, for the first time, allows IceCube
searching for point-like sources of neutrinos in the southern sky at energies
between 100 GeV and several TeV in the muon neutrino charged current channel.
No significant clustering of neutrinos above background expectation was
observed in four years of data recorded with the completed IceCube detector.
Upper limits on the neutrino flux for a number of spectral hypotheses are
reported for a list of astrophysical objects in the southern hemisphere.Comment: 19 pages, 17 figures, 2 table
Differential limit on the extremely-high-energy cosmic neutrino flux in the presence of astrophysical background from nine years of IceCube data
We report a quasi-differential upper limit on the extremely-high-energy (EHE)
neutrino flux above GeV based on an analysis of nine years of
IceCube data. The astrophysical neutrino flux measured by IceCube extends to
PeV energies, and it is a background flux when searching for an independent
signal flux at higher energies, such as the cosmogenic neutrino signal. We have
developed a new method to place robust limits on the EHE neutrino flux in the
presence of an astrophysical background, whose spectrum has yet to be
understood with high precision at PeV energies. A distinct event with a
deposited energy above GeV was found in the new two-year sample, in
addition to the one event previously found in the seven-year EHE neutrino
search. These two events represent a neutrino flux that is incompatible with
predictions for a cosmogenic neutrino flux and are considered to be an
astrophysical background in the current study. The obtained limit is the most
stringent to date in the energy range between and GeV. This result constrains neutrino models predicting a three-flavor
neutrino flux of $E_\nu^2\phi_{\nu_e+\nu_\mu+\nu_\tau}\simeq2\times 10^{-8}\
{\rm GeV}/{\rm cm}^2\ \sec\ {\rm sr}10^9\ {\rm GeV}$. A significant part
of the parameter-space for EHE neutrino production scenarios assuming a
proton-dominated composition of ultra-high-energy cosmic rays is excluded.Comment: The version accepted for publication in Physical Review
Book Reviews
With the observation of high-energy astrophysical neutrinos by the IceCube Neutrino Observatory, interest has risen in models of PeV-mass decaying dark matter particles to explain the observed flux. We present two dedicated experimental analyses to test this hypothesis. One analysis uses 6 years of IceCube data focusing on muon neutrino âtrackâ events from the Northern Hemisphere, while the second analysis uses 2 years of âcascadeâ events from the full sky. Known background components and the hypothetical flux from unstable dark matter are fitted to the experimental data. Since no significant excess is observed in either analysis, lower limits on the lifetime of dark matter particles are derived: we obtain the strongest constraint to date, excluding lifetimes shorter than s at 90% CL for dark matter masses above 10 TeV
Search for transient optical counterparts to high-energy IceCube neutrinos with Pan-STARRS1
In order to identify the sources of the observed diffuse high-energy neutrino
flux, it is crucial to discover their electromagnetic counterparts. IceCube
began releasing alerts for single high-energy ( TeV) neutrino
detections with sky localisation regions of order 1 deg radius in 2016. We used
Pan-STARRS1 to follow-up five of these alerts during 2016-2017 to search for
any optical transients that may be related to the neutrinos. Typically 10-20
faint ( mag) extragalactic transients are found within the
Pan-STARRS1 footprints and are generally consistent with being unrelated field
supernovae (SNe) and AGN. We looked for unusual properties of the detected
transients, such as temporal coincidence of explosion epoch with the IceCube
timestamp. We found only one transient that had properties worthy of a specific
follow-up. In the Pan-STARRS1 imaging for IceCube-160427A (probability to be of
astrophysical origin of 50 %), we found a SN PS16cgx, located at 10.0'
from the nominal IceCube direction. Spectroscopic observations of PS16cgx
showed that it was an H-poor SN at z = 0.2895. The spectra and light curve
resemble some high-energy Type Ic SNe, raising the possibility of a jet driven
SN with an explosion epoch temporally coincident with the neutrino detection.
However, distinguishing Type Ia and Type Ic SNe at this redshift is notoriously
difficult. Based on all available data we conclude that the transient is more
likely to be a Type Ia with relatively weak SiII absorption and a fairly normal
rest-frame r-band light curve. If, as predicted, there is no high-energy
neutrino emission from Type Ia SNe, then PS16cgx must be a random coincidence,
and unrelated to the IceCube-160427A. We find no other plausible optical
transient for any of the five IceCube events observed down to a 5
limiting magnitude of mag, between 1 day and 25 days after
detection.Comment: 20 pages, 6 figures, accepted to A&
HEX-P: the High-Energy X-Ray Probe
The High-Energy X-ray Probe (HEX-P) is a next-generation high-energy X-ray observatory with broadband (2-200 keV) response that has 40 times the sensitivity of any previous mission in the 10-80 keV band and > 100 times the sensitivity of any previous mission in the 80-200 keV band. With this leap in observational capability, HEX-P will address a broad range of science objectives beyond any planned mission in the hard X-ray bandpass. HEX-P will probe the extreme environments around black holes and neutron stars, map the growth of supermassive black holes, and quantify the effect they have on their environments. HEX-P will resolve the hard X-ray emission from dense regions of our Galaxy to understand the high- energy source populations and investigate dark matter candidate particles through their decay channel signatures. If developed and launched on a timescale similar to Athena, the complementary abilities of the two missions will greatly enhance the Communitys ability to address the important science questions of the hot universe. HEX-P addresses science that is not planned by any flagship-class missions, and is beyond the capability of an Explorer-class mission
Intensive disc-reverberation mapping of Fairall 9 : 1st year of Swift & LCO monitoring
Funding: UK STFC grant ST/R000824/1 (KH).We present results of time-series analysis of the first year of the Fairall 9 intensive disc-reverberation campaign. We used Swift and the Las Cumbres Observatory global telescope network to continuously monitor Fairall 9 from X-rays to near-infrared at a daily to sub-daily cadence. The cross-correlation function between bands provides evidence for a lag spectrum consistent with the Ï â λ4/3 scaling expected for an optically thick, geometrically thin blackbody accretion disc. Decomposing the flux into constant and variable components, the variable component's spectral energy distribution is slightly steeper than the standard accretion disc prediction. We find evidence at the Balmer edge in both the lag and flux spectra for an additional bound-free continuum contribution that may arise from reprocessing in the broad-line region. The inferred driving light curve suggests two distinct components, a rapidly variable ( 100 days) component with an opposite lag to the reverberation signal.PostprintPeer reviewe
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