126 research outputs found
Preheating of the Universe by cosmic rays from primordial supernovae at the beginning of cosmic reionization
The 21-cm signal from the cosmic reionization epoch can shed light on the
history of heating of the primordial intergalactic medium (IGM) at z~30-10. It
has been suggested that X-rays from the first accreting black holes could
significantly heat the Universe at these early epochs. Here we propose another
IGM heating mechanism associated with the first stars. As known from previous
work, the remnants of powerful supernovae (SNe) ending the lives of massive
Population III stars could readily expand out of their host dark matter
minihalos into the surrounding IGM, aided by the preceeding photoevaporation of
the halo's gas by the UV radiation from the progenitor star. We argue that
during the evolution of such a remnant a significant fraction of the SN kinetic
energy can be put into low-energy (E<30 MeV) cosmic rays that will eventually
escape into the IGM. These subrelativistic cosmic rays could propagate through
the Universe and heat the IGM by ~10-100 K by z~15, before more powerful
reionization/heating mechanisms associated with the first galaxies and quasars
came into play. Future 21-cm observations could thus constrain the energetics
of the first supernovae and provide information on the magnetic fields in the
primordial IGM.Comment: 10 pages, 1 figure, accepted for publication in MNRA
Identification of X-ray lines in the spectrum of the arcsec-scale precessing jets of SS 433
The extended X-ray emission observed at arcsec scales along the propagation
trajectory of the precessing relativistic jets of the Galactic microquasar SS
433 features a broad emission line, with the position of the centroid being
significantly different for the approaching and receding jets (
and keV, respectively). These observed line positions are at
odds with the predictions of the kinematic model for any of the plausible
bright spectral lines in this band, raising the question of their
identification. Here we address this issue by taking into account time delays
of the emission coming from the receding regions of the jets relative to that
from the approaching ones, which cause a substantial phase shift and distortion
of the predicted line positions for the extended ( cm) emission
compared to the X-ray and optical lines observed from the central source
(emitted at distances cm and cm, respectively).
We demonstrate that the observed line positions are fully consistent with the
Fe XXVI Ly ( keV) line emerging from a region of size cm along the jet. This supports the idea that intensive
reheating of the jets up to temperatures keV takes place at these
distances, probably as a result of partial deceleration of the jets due to
interaction with the surrounding medium, which might cause collisions between
discrete dense blobs inside the jets.Comment: Astronomy Letters, in press; 9 pages, 7 figure
The intrinsic collective X-ray spectrum of luminous high-mass X-ray binaries
Using a sample of two hundred luminous (L_unabs>10^38 erg/s, where L_unabs is
the unabsorbed 0.25-8 keV luminosity) high-mass X-ray binary (HMXB) candidates
found with Chandra in 27 nearby galaxies, we have constructed the collective
X-ray spectrum of HMXBs in the local Universe per unit star formation rate,
corrected for observational biases associated with intrinsic diversity of HMXB
spectra and X-ray absorption in the interstellar medium. This spectrum is well
fit by a power law with a photon index Gamma=2.1+/-0.1 and is dominated by
ultraluminous X-ray sources with L_unabs>10^39 erg/s. Hard sources (those with
the 0.25-2 keV to 0.25-8 keV flux ratio of <0.6) dominate above ~2 keV, while
soft and supersoft sources (with the flux ratios of 0.6-0.95 and >0.95,
respectively) at lower energies. The derived spectrum probably represents the
angle-integrated X-ray emission of the near- and super-critically accreting
stellar mass black holes and neutron stars in the local Universe. It provides
an important constraint on supercritical accretion models and can be used as a
reference spectrum for calculations of the X-ray preheating of the Universe by
the first generations of X-ray binaries.Comment: 8 pages, 4 figues, accepted for publication in MNRA
Bright end of the luminosity function of high-mass X-ray binaries: contributions of hard, soft and supersoft sources
Using a spectral analysis of bright Chandra X-ray sources located in 27
nearby galaxies and maps of star-formation rate (SFR) and ISM surface densities
for these galaxies, we constructed the intrinsic X-ray luminosity function
(XLF) of luminous high-mass X-ray binaries (HMXBs), taking into account
absorption effects and the diversity of HMXB spectra. The XLF per unit SFR can
be described by a power law dN/d log L=2.0(L/10^39 erg/s)^(-0.6)
(M_Sun/yr)^(-1) from L=10^38 to 10^40.5 erg/s, where L is the unabsorbed
luminosity at 0.25-8 keV. The intrinsic number of luminous HMXBs per unit SFR
is a factor of ~2.3 larger than the observed number reported before. The
intrinsic XLF is composed of hard, soft and supersoft sources (defined here as
those with the 0.25-2 keV to 0.25-8 keV flux ratio of 0.95,
respectively) in ~2:1:1 proportion. We also constructed the intrinsic HMXB XLF
in the soft X-ray band (0.25-2 keV). Here, the numbers of hard, soft and
supersoft sources prove to be nearly equal. The cumulative present-day 0.25-2
keV emissivity of HMXBs with luminosities between 10^38 and 10^40.5 erg/s is ~5
10^39 erg/s (M_Sun/yr)^(-1), which may be relevant for studying the X-ray
preheating of the early Universe.Comment: 37 pages, 40 figures, accepted for publication in MNRA
Stellar tidal disruption candidates found by cross-correlating the ROSAT Bright Source Catalogue and XMM-Newton observations
We performed a systematic search for stellar tidal disruption events (TDE) by
looking for X-ray sources that were detected during the ROSAT All Sky Survey
and faded by more than an order of magnitude over the next two decades
according to XMM-Newton serendipitous observations. Besides a number of highly
variable persistent X-ray sources (like active galactic nuclei and cataclysmic
variables), we found three sources that are broadly consistent with the TDE
scenario: 1RXS J114727.1+494302, 1RXS J130547.2+641252, and 1RXS
J235424.5-102053. A TDE association is also acceptable for the fourth source,
1RXS J112312.7+012858, but an AGN origin cannot be ruled out either. This
statistics implies a TDE rate of yr per
galaxy in the Universe within , which is broadly consistent with
the estimates of the TDE rate in the more local Universe obtained previously.Comment: Accepted for publication in MNRAS; 13 pages, 9 figures, 4 table
Impact of ultraluminous X-ray sources on photoabsorption in the first galaxies
In the local Universe, integrated X-ray emission from high-mass X-ray
binaries (HMXBs) is dominated by the brightest ultraluminous X-ray sources
(ULXs) with luminosity >10^40 erg/s. Such rare objects probably also dominated
the production of X-rays in the early Universe. We demonstrate that a ULX with
Lx~10^40-10^41 erg/s (isotropic-equivalent luminosity in the 0.1-10 keV energy
band) shining for ~10^5 years (the expected duration of a supercritically
accreting phase in HMXBs) can significantly ionise the ISM in its host dwarf
galaxy of total mass M~10^7-10^8 Msun and thereby reduce its opacity to soft
X-rays. As a result, the fraction of the soft X-ray (below 1 keV) radiation
from the ULX escaping into the intergalactic medium (IGM) can increase from
~20-50% to ~30-80% over its lifetime. This implies that HMXBs can induce a
stronger heating of the IGM at z>10 compared to estimates neglecting the ULX
feedback on the ISM. However, larger galaxies with M>3 x 10^8 Msun could not be
significantly ionised even by the brightest ULXs in the early Universe. Since
such galaxies probably started to dominate the global star-formation rate at
z<10, the overall escape fraction of soft X-rays from the HMXB population
probably remained low, <30%, at these epochs.Comment: 13 pages, 11 figures, accepted for publication in MNRA
NuSTAR and XMM-Newton observations of the ultraluminous X-ray source NGC 5643 X-1
We present a high-quality hard X-ray spectrum of the ultraluminous X-ray
source (ULX) NGC 5643 X-1 measured with NuSTAR in May-June 2014. We have
obtained this spectrum by carefully separating the signals from the ULX and
from the active nucleus of its host galaxy NGC 5643 located 0.8 arcmin away.
Together with long XMM-Newton observations performed in July 2009 and August
2014, the NuSTAR data confidently reveal a high-energy cutoff in the spectrum
of NGC 5643 X-1 above ~10 keV, which is a characteristic signature of ULXs. The
NuSTAR and XMM-Newton data are consistent with the source having a constant
luminosity ~1.5E40 erg/s (0.2-12 keV) in all but the latest observation (August
2014) when it brightened to ~3E40 erg/s. This increase is associated with the
dominant, hard spectral component (presumably collimated emission from the
inner regions of a supercritical accretion disc), while an additional, soft
component (with a temperature ~0.3 keV if described by multicolor disk
emission), possibly associated with a massive wind outflowing from the disk, is
also evident in the spectrum but does not exhibit significant variability.Comment: 8 pages, 3 figures, 4 tables, Accepted for publication in MNRA
Preheating of the early Universe by radiation from high-mass X-ray binaries
Using a reliably measured intrinsic (i.e. corrected for absorption effects)
present-day luminosity function of high-mass X-ray binaries (HMXBs) in the
0.25-2 keV energy band per unit star-formation rate, we estimate the preheating
of the early Universe by soft X-rays from such systems. We find that X-ray
irradiation, mainly executed by ultraluminous and supersoft ultraluminous X-ray
sources with luminosity L> 10^39 erg/s, could significantly heat (T>T_cmb,
where T_cmb is the temperature of the cosmic microwave background) the
intergalactic medium by z~10 if the specific X-ray emissivity of the young
stellar population in the early Universe was an order of magnitude higher than
at the present epoch (which is possible due to the low metallicity of the first
galaxies) and the soft X-ray emission from HMXBs did not suffer strong
absorption within their galaxies. This makes it possible to observe the 21 cm
line of neutral hydrogen in emission from redshifts z<10.Comment: 9 pages, 4 figures, accepted for publication in Astronomy Letter
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