217 research outputs found
The X-ray Properties of the Nearby Star-Forming Galaxy IC 342: The XMM-Newton View
We present the X-ray properties of IC342 using XMM-Newton. Thirty-five
sources are detected coincident with the disk of IC342 (more than tripling the
number known), of which ~31 are likely to be intrinsic to IC342. This
population shows a range of spectral properties and has an X-ray luminosity
function slope and infrared luminosity comparable to that of starburst galaxies
such as M82 and the Antennae, while its relative lack of extended X-ray
emission is similar to the properties of quiescent spirals. We do detect
long-term variability between this observation and the 1991 ROSAT and 1993/2000
ASCA observations for five sources. Notably, the second most luminous source
IC342 X-2 is is found to be in its the lowest luminosity state observed for X-2
to date, although the slope of the spectrum is intermediate between the
previously observed low/hard and high/soft states. IC342 X-1, on the other
hand, is found to be in an identical state to that observed in 2000 with ASCA.
Assuming X-1 is in an anomalous very high (VH) state, then either (1) X-1 has
remained in this state between 2000 and 2002, and is therefore the longest
duration VH-state binary ever observed, or (2) it was simply caught in a VH
state by chance in both the 2000 ASCA and 2002 XMM-Newton observations. We have
also confirmed the ROSAT HRI result that the nucleus of IC342 is made up of
both point-like and extended emission. The relative fluxes of the two spectral
components suggest that the nucleus is complex, with a soft extended component
contributing approximately half of the total luminosity. (Abridged)Comment: AJ in press (December 2003), 9 pages, 7 figures, 2 tables,
emulateapj.cls use
Modeling the Redshift Evolution of the Normal Galaxy X-ray Luminosity Function
Emission from X-ray binaries (XRBs) is a major component of the total X-ray
luminosity of normal galaxies, so X-ray studies of high redshift galaxies allow
us to probe the formation and evolution of X-ray binaries on very long
timescales. In this paper, we present results from large-scale population
synthesis models of binary populations in galaxies from z = 0 to 20. We use as
input into our modeling the Millennium II Cosmological Simulation and the
updated semi-analytic galaxy catalog by Guo et al. (2011) to self-consistently
account for the star formation history (SFH) and metallicity evolution of each
galaxy. We run a grid of 192 models, varying all the parameters known from
previous studies to affect the evolution of XRBs. We use our models and
observationally derived prescriptions for hot gas emission to create
theoretical galaxy X-ray luminosity functions (XLFs) for several redshift bins.
Models with low CE efficiencies, a 50% twins mass ratio distribution, a steeper
IMF exponent, and high stellar wind mass loss rates best match observational
results from Tzanavaris & Georgantopoulos (2008), though they significantly
underproduce bright early-type and very bright (Lx > 10d41) late-type galaxies.
These discrepancies are likely caused by uncertainties in hot gas emission and
SFHs, AGN contamination, and a lack of dynamically formed Low-mass XRBs. In our
highest likelihood models, we find that hot gas emission dominates the emission
for most bright galaxies. We also find that the evolution of the normal galaxy
X-ray luminosity density out to z = 4 is driven largely by XRBs in galaxies
with X-ray luminosities between 10d40 and 10d41 erg/s.Comment: Accepted into ApJ, 17 pages, 3 tables, 7 figures. Text updated to
address referee's comment
A Hard X-ray Study of the Normal Star-Forming Galaxy M83 with NuSTAR
We present results from sensitive, multi-epoch NuSTAR observations of the
late-type star-forming galaxy M83 (d=4.6 Mpc), which is the first investigation
to spatially resolve the hard (E>10 keV) X-ray emission of this galaxy. The
nuclear region and ~ 20 off-nuclear point sources, including a previously
discovered ultraluminous X-ray (ULX) source, are detected in our NuSTAR
observations. The X-ray hardnesses and luminosities of the majority of the
point sources are consistent with hard X-ray sources resolved in the starburst
galaxy NGC 253. We infer that the hard X-ray emission is most likely dominated
by intermediate accretion state black hole binaries and neutron star low-mass
X-ray binaries (Z-sources). We construct the X-ray binary luminosity function
(XLF) in the NuSTAR band for an extragalactic environment for the first time.
The M83 XLF has a steeper XLF than the X-ray binary XLF in NGC 253, consistent
with previous measurements by Chandra at softer X-ray energies. The NuSTAR
integrated galaxy spectrum of M83 drops quickly above 10 keV, which is also
seen in the starburst galaxies NGC253, NGC 3310 and NGC 3256. The NuSTAR
observations constrain any AGN to be either highly obscured or to have an
extremely low luminosity of 10 erg/s (10-30 keV), implying it
is emitting at a very low Eddington ratio. An X-ray point source consistent
with the location of the nuclear star cluster with an X-ray luminosity of a few
times 10 erg/s may be a low-luminosity AGN but is more consistent with
being an X-ray binary.Comment: Accepted for publication in ApJ (25 pages, 17 figures
Spatially Resolving a Starburst Galaxy at Hard X-ray Energies: NuSTAR, Chandra, AND VLBA Observations of NGC 253
Prior to the launch of NuSTAR, it was not feasible to spatially resolve the
hard (E > 10 keV) emission from galaxies beyond the Local Group. The combined
NuSTAR dataset, comprised of three ~165 ks observations, allows spatial
characterization of the hard X-ray emission in the galaxy NGC 253 for the first
time. As a follow up to our initial study of its nuclear region, we present the
first results concerning the full galaxy from simultaneous NuSTAR, Chandra, and
VLBA monitoring of the local starburst galaxy NGC 253. Above ~10 keV, nearly
all the emission is concentrated within 100" of the galactic center, produced
almost exclusively by three nuclear sources, an off-nuclear ultraluminous X-ray
source (ULX), and a pulsar candidate that we identify for the first time in
these observations. We detect 21 distinct sources in energy bands up to 25 keV,
mostly consisting of intermediate state black hole X-ray binaries. The global
X-ray emission of the galaxy - dominated by the off-nuclear ULX and nuclear
sources, which are also likely ULXs - falls steeply (photon index >~ 3) above
10 keV, consistent with other NuSTAR-observed ULXs, and no significant excess
above the background is detected at E > 40 keV. We report upper limits on
diffuse inverse Compton emission for a range of spatial models. For the most
extended morphologies considered, these hard X-ray constraints disfavor a
dominant inverse Compton component to explain the {\gamma}-ray emission
detected with Fermi and H.E.S.S. If NGC 253 is typical of starburst galaxies at
higher redshift, their contribution to the E > 10 keV cosmic X-ray background
is < 1%.Comment: 20 pages, 14 figures, accepted for publication in Ap
AC Josephson effect in the long voltage-biased SINIS junction
Theory of non-stationary coherent effects is developed for
superconductor-normal-superconductor (SNS) structures with relatively strong
normal scattering on S/N interfaces (interface resistance is large compared to
intrinsic resistance of N metal). Analitical expressions are found for the
time-dependent anomalous Green functions induced in the N region under the
fixed-voltage-bias. The amplitude of the current oscillations is determined in
non-equilibrium conditions. Non-stationary correction to the distribution
function is calculated in high-temperature limit and found to be slowly
decreasing with the temperature, leading to the dominance of the
second-harmonic term in the Josepshon current at high temperatures and low
voltage.Comment: Final version accepted for publication in JETP Letters. Introduction
and discussion in the end of Sec.4 are extended, figure and few references
added, some numerical coefficients correcte
Super congruences and Euler numbers
Let be a prime. We prove that
, where E_0,E_1,E_2,... are Euler numbers. Our new approach is of
combinatorial nature. We also formulate many conjectures concerning super
congruences and relate most of them to Euler numbers or Bernoulli numbers.
Motivated by our investigation of super congruences, we also raise a conjecture
on 7 new series for , and the constant
(with (-) the Jacobi symbol), two of which are
and
\sum_{k>0}(15k-4)(-27)^{k-1}/(k^3\binom{2k}{k}^2\binom{3k}k)=K.$
The Radio - X-ray relation as a star formation indicator: Results from the VLA--E-CDFS Survey
In order to trace the instantaneous star formation rate at high redshift, and
hence help understanding the relation between the different emission mechanisms
related to star formation, we combine the recent 4 Ms Chandra X-ray data and
the deep VLA radio data in the Extended Chandra Deep Field South region. We
find 268 sources detected both in the X-ray and radio band. The availability of
redshifts for of the sources in our sample allows us to derive
reliable luminosity estimates and the intrinsic properties from X-ray analysis
for the majority of the objects. With the aim of selecting sources powered by
star formation in both bands, we adopt classification criteria based on X-ray
and radio data, exploiting the X-ray spectral features and time variability,
taking advantage of observations scattered across more than ten years. We
identify 43 objects consistent with being powered by star formation. We also
add another 111 and 70 star forming candidates detected only in the radio or
X-ray band, respectively. We find a clear linear correlation between radio and
X-ray luminosity in star forming galaxies over three orders of magnitude and up
to . We also measure a significant scatter of the order of 0.4 dex,
higher than that observed at low redshift, implying an intrinsic scatter
component. The correlation is consistent with that measured locally, and no
evolution with redshift is observed. Using a locally calibrated relation
between the SFR and the radio luminosity, we investigate the L_X(2-10keV)-SFR
relation at high redshift. The comparison of the star formation rate measured
in our sample with some theoretical models for the Milky Way and M31, two
typical spiral galaxies, indicates that, with current data, we can trace
typical spirals only at z<0.2, and strong starburst galaxies with
star-formation rates as high as , up to .Comment: 21 pages, 10 figures, 5 table
The X-Ray Star Formation Story as Told by Lyman Break Galaxies in the 4 Ms CDF-S
We present results from deep X-ray stacking of {gt}4000 high-redshift galaxies from z {ap} 1 to 8 using the 4 Ms Chandra Deep Field-South data, the deepest X-ray survey of the extragalactic sky to date. The galaxy samples were selected using the Lyman break technique based primarily on recent Hubble Space Telescope ACS and WFC3 observations. Based on such high specific star formation rates (sSFRs): log SFR/M {gt} -8.7, we expect that the observed properties of these Lyman break galaxies (LBGs) are dominated by young stellar populations. The X-ray emission in LBGs, eliminating individually detected X-ray sources (potential active galactic nucleus), is expected to be powered by X-ray binaries and hot gas. We find, for the first time, evidence of evolution in the X-ray/SFR relation. Based on X-ray stacking analyses for z {lt} 4 LBGs (covering ~{}90% of the universe's history), we find that the 2-10 keV X-ray luminosity evolves weakly with redshift (z) and SFR as log L = 0.93log (1 + z) + 0.65log SFR + 39.80. By comparing our observations with sophisticated X-ray binary population synthesis models, we interpret that the redshift evolution of L /SFR is driven by metallicity evolution in high mass X-ray binaries, likely the dominant population in these high sSFR galaxies. We also compare these models with our observations of X-ray luminosity density (total 2-10 keV luminosity per Mpc) and find excellent agreement. While there are no significant stacked detections at z {gt}~{} 5, we use our upper limits from 5 {lt}~{} z {lt}~{} 8 LBGs to constrain the supermassive black hole accretion history of the universe around the epoch of reionization
Formation of Super-Earths
Super-Earths are the most abundant planets known to date and are
characterized by having sizes between that of Earth and Neptune, typical
orbital periods of less than 100 days and gaseous envelopes that are often
massive enough to significantly contribute to the planet's overall radius.
Furthermore, super-Earths regularly appear in tightly-packed multiple-planet
systems, but resonant configurations in such systems are rare. This chapters
summarizes current super-Earth formation theories. It starts from the formation
of rocky cores and subsequent accretion of gaseous envelopes. We follow the
thermal evolution of newly formed super-Earths and discuss their atmospheric
mass loss due to disk dispersal, photoevaporation, core-cooling and collisions.
We conclude with a comparison of observations and theoretical predictions,
highlighting that even super-Earths that appear as barren rocky cores today
likely formed with primordial hydrogen and helium envelopes and discuss some
paths forward for the future.Comment: Invited review accepted for publication in the 'Handbook of
Exoplanets,' Planet Formation section, Springer Reference Works, Juan Antonio
Belmonte and Hans Deeg, Ed
A Focused, Hard X-ray Look at Arp 299 with NuSTAR
We report on simultaneous observations of the local starburst system Arp 299
with NuSTAR and Chandra, which provides the first resolved images of this
galaxy up to energies of ~ 45 keV. Fitting the 3-40 keV spectrum reveals a
column density of ~ 4 x10^{24} cm^{-2}, characteristic of a
Compton-thick AGN, and a 10-30 keV luminosity of 1.2x 10^{43} ergs s^{-1}. The
hard X-rays detected by NuSTAR above 10 keV are centered on the western
nucleus, Arp 299-B, which previous X-ray observations have shown to be the
primary source of neutral Fe-K emission. Other X-ray sources, including Arp
299-A, the eastern nucleus which is also thought to harbor an AGN, as well as
X-ray binaries, contribute to the 10-20 keV emission from the
Arp 299 system. The lack of significant emission above 10 keV other than that
attributed to Arp 299-B suggests that: a) any AGN in Arp 299-A must be heavily
obscured ( > 10^{24} cm^{-2}) or have a much lower luminosity than
Arp 299-B and b) the extranuclear X-ray binaries have spectra that cut-off
above ~10 keV. Such soft spectra are characteristic of ultraluminous X-ray
(ULX) sources observed to date by NuSTAR.Comment: 9 pages; accepted for publication in Astrophysical Journa
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