ABSTRACT
We present and analyse a new tidal disruption event (TDE), AT2017eqx at redshift z = 0.1089, discovered by Pan-STARRS and ATLAS. The position of the transient is consistent with the nucleus ...of its host galaxy; the spectrum shows a persistent blackbody temperature T ≳ 20 000 K with broad H i and He ii emission; and it peaks at a blackbody luminosity of L ≈ 1044 erg s−1. The lines are initially centred at zero velocity, but by 100 d, the H i lines disappear while the He ii develops a blueshift of ≳ 5000 km s−1. Both the early- and late-time morphologies have been seen in other TDEs, but the complete transition between them is unprecedented. The evolution can be explained by combining an extended atmosphere, undergoing slow contraction, with a wind in the polar direction becoming visible at late times. Our observations confirm that a lack of hydrogen a TDE spectrum does not indicate a stripped star, while the proposed model implies that much of the diversity in TDEs may be due to the observer viewing angle. Modelling the light curve suggests AT2017eqx resulted from the complete disruption of a solar-mass star by a black hole of ∼106.3 M⊙. The host is another Balmer-strong absorption galaxy, though fainter and less centrally concentrated than most TDE hosts. Radio limits rule out a relativistic jet, while X-ray limits at 500 d are among the deepest for a TDE at this phase.
ABSTRACT
We present the first X-ray observation at sub-arcsecond resolution of the high-redshift (z = 6.18) radio-loud quasar CFHQS J142952 + 544717 (J1429). The ∼100 net-count 0.3–7 keV spectrum ...obtained from ∼30 ks Chandra exposure is best fit by a single power-law model with a photon index Γ = 2.0 ± 0.2 and no indication of an intrinsic absorber, implying a 3.6–72 keV rest-frame luminosity $L_{\rm X}=(2.3^{+0.6}_{-0.5})\times 10^{46}$ erg s−1. We identify a second X-ray source at 30″ distance from J1429 position, with a soft (Γ ≃ 2.8) and absorbed (equivalent hydrogen column density NH < 13.4 × 1020 cm−2) spectrum, which likely contaminated J1429 spectra obtained in lower angular resolution observations. Based on the analysis of the Chandra image, the bulk of the X-ray luminosity is produced within the central ∼3 kpc region, either by the disc/corona system, or by a moderately aligned jet. In this context, we discuss the source properties in comparison with samples of low- and high-redshift quasars. We find indication of a possible excess of counts over the expectations for a point-like source in a 0.5″–1.5″ (∼3−8 kpc) annular region. The corresponding X-ray luminosity at J1429 redshift is 4 × 1045 erg s−1. If confirmed, this emission could be related to either a large-scale X-ray jet, or a separate X-ray source.
Abstract
We report the detection of extended X-ray emission from two high-redshift radio quasars. These quasars, J1405+0415 at
z
= 3.208 and J1610+1811 at
z
= 3.118, were observed in a Chandra ...snapshot survey selected from a complete sample of the radio-brightest quasars in the overlap area of the VLA-FIRST radio survey and the Sloan Digital Sky Survey. The extended X-ray emission is located along the line connecting the core to a radio knot or hotspot, favoring the interpretation of X-ray jets. The inferred rest-frame jet X-ray luminosities from 2 to 30 keV would be of order 10
45
erg s
−1
if emitted isotropically and without relativistic beaming. In the scenario of inverse Compton scattering of the cosmic microwave background (CMB), X-ray jets without a coincident radio counterpart may be common, and should be readily detectable to redshifts even beyond 3.2 due to the (1+
z
)
4
increase of the CMB energy density compensating for the (1+
z
)
−4
cosmological diminution of surface brightness. If these can be X-ray confirmed, they would be the second and third examples of quasar X-ray jets without detection of underlying continuous radio jets.
Jupiter's X‐ray Emission During the 2007 Solar Minimum Dunn, W. R.; Branduardi‐Raymont, G.; Carter‐Cortez, V. ...
Journal of geophysical research. Space physics,
June 2020, 2020-06-00, 20200601, Letnik:
125, Številka:
6
Journal Article
Recenzirano
Odprti dostop
The 2007–2009 solar minimum was the longest of the space age. We present the first of two companion papers on Chandra and XMM‐Newton X‐ray campaigns of Jupiter through February–March 2007. We find ...that low solar X‐ray flux during solar minimum causes Jupiter's equatorial regions to be exceptionally X‐ray dim (0.21 GW at minimum; 0.76 GW at maximum). While the Jovian equatorial emission varies with solar cycle, the aurorae have comparably bright intervals at solar minimum and maximum. We apply atomic charge exchange models to auroral spectra and find that iogenic plasma of sulphur and oxygen ions provides excellent fits for XMM‐Newton observations. The fitted spectral S:O ratios of 0.4–1.3 are in good agreement with in situ magnetospheric S:O measurements of 0.3–1.5, suggesting that the ions that produce Jupiter's X‐ray aurora predominantly originate inside the magnetosphere. The aurorae were particularly bright on 24–25 February and 8–9 March, but these two observations exhibit very different spatial, spectral, and temporal behavior; 24–25 February was the only observation in this campaign with significant hard X‐ray bremsstrahlung from precipitating electrons, suggesting this may be rare. For 8–9 March, a bremsstrahlung component was absent, but bright oxygen O6+ lines and best‐fit models containing carbon, point to contributions from solar wind ions. This contribution is absent in the other observations. Comparing simultaneous Chandra ACIS and XMM‐Newton EPIC spectra showed that ACIS systematically underreported 0.45‐ to 0.6‐keV Jovian emission, suggesting quenching may be less important for Jupiter's atmosphere than previously thought. We therefore recommend XMM‐Newton for spectral analyses and quantifying opacity/quenching effects.
Key Points
Jupiter's equatorial X‐ray emission varies in accordance with solar cycle 24 but auroral power can be comparably bright at solar min and max
Charge exchange models provide good fits to aurora spectra retrieving S:O ratios of 0.4–1.3 agreeing with in situ magnetosphere measurements
We report systematic differences between Chandra ACIS and XMM‐Newton EPIC‐pn Jovian spectra and the impact of these on opacity and quenching
Abstract
We use new and archival Chandra observations of Cygnus A, totalling ∼1.9 Ms, to investigate the distribution and temperature structure of gas lying within the projected extent of the cocoon ...shock and exhibiting a rib-like structure. We confirm that the X-rays are dominated by thermal emission with an average temperature of around 4 keV, and have discovered an asymmetry in the temperature gradient, with the southwestern part of the gas cooler than the rest by up to 2 keV. Pressure estimates suggest that the gas is a coherent structure of single origin located inside the cocoon, with a mass of roughly 2 × 1010 M⊙. We conclude that the gas is debris resulting from disintegration of the cool core of the Cygnus A cluster after the passage of the jet during the early stages of the current epoch of activity. The 4 keV gas now lies on the central inside surface of the hotter cocoon rim. The temperature gradient could result from an offset between the centre of the cluster core and the Cygnus A host galaxy at the switch-on of current radio activity.
•We have detected 7 net x-rays in 174ksec from the Pluto system using Chandra.•This 1st KBO x-ray detection was at >99.95% significance & 0.60 > E >0.31keV.•The power represented by this signal is ...significant, 200 +200/-100 MW.•Charge-exchange between SW CNO ions & escaping Pluto neutrals could produce this.•Less likely is scattering of solar x-rays by haze particles in Pluto's atmosphere.
Using Chandra ACIS-S, we have obtained low-resolution imaging X-ray spectrophotometry of the Pluto system in support of the New Horizons flyby on 14 July 2015. Observations were obtained in a trial “seed” campaign conducted in one visit on 24 Feb 2014, and a follow-up campaign conducted soon after the New Horizons flyby that consisted of 3 visits spanning 26 Jul to 03 Aug 2015. In a total of 174 ksec of on-target time, in the 0.31 to 0.60keV passband, we measured 8 total photons in a co-moving 11×11 pixel2 box (the 90% flux aperture determined by observations of fixed background sources in the field) measuring ∼121,000×121,000 km2 (or ∼100×100 RPluto) at Pluto. No photons were detected from 0.60 to 1.0keV in this box during the same exposures. Allowing for background, we find a net signal of 6.8 counts and a statistical noise level of 1.2 counts, for a detection of Pluto in this passband at >99.95%confidence. The Pluto photons do not have the spectral shape of the background, are coincident with a 90% flux aperture co-moving with Pluto, and are not confused with any background source, so we consider them as sourced from the Pluto system. The mean 0.31 - 0.60keV X-ray power from Pluto is 200 +200/-100 MW, in the middle range of X-ray power levels seen for other known Solar System emission sources: auroral precipitation, solar X-ray scattering, and charge exchange (CXE) between solar wind (SW) ions and atmospheric neutrals. We eliminate auroral effects as a source, as Pluto has no known magnetic field and the New Horizons Alice UV spectrometer detected no airglow from Pluto during the flyby. Nano-scale atmospheric haze particles could lead to enhanced resonant scattering of solar X-rays from Pluto, but the energy signature of the detected photons does not match the solar spectrum and estimates of Pluto's scattered X-ray emission are 2 to 3 orders of magnitude below the 3.9±0.7×10−5cps found in our observations. Charge-exchange-driven emission from hydrogenic and heliogenic SW carbon, nitrogen, and oxygen (CNO) ions can produce the energy signature seen, and the 6×1025 neutral gas escape rate from Pluto deduced from New Horizons’ data (Gladstone et al. 2016) can support the ∼3.0 +3.0/-1.5 × 1024 X-ray photons/s emission rate required by our observations. Using the solar wind proton density and speed measured by the Solar Wind Around Pluto (SWAP) instrument in the vicinity of Pluto at the time of the photon emissions, we find a factor of 40 +40/-20 lower SW minor ions flowing planarly into an 11×11 pixel2, 90% flux box centered on Pluto than are needed to support the observed emission rate. Hence, the SW must be somehow significantly focused and enhanced within 60,000km (projected) of Pluto for this mechanism to work.
Using Chandra ACIS-S, we have obtained imaging Xray spectrophotometry of the Pluto system in support of the New Horizons flyby on 14 July 2015. 174 ksec of observations were obtained on 4 visits in ...Feb 2014 to Aug 2015. We measured a net signal of 6.8 counts and a noise level of 1.2 counts in a comoving 11 x 11 pixel box (100 x 100 R_Pluto) in the 0.31 to 0.60 keV passband for a detection at > 99.95 C.L. The Pluto photons do not match the background spectrum, are coincident with a 90% flux aperture comoving with Pluto, and are not sky source confused. The mean 0.31 to 0.60 keV Xray power from Pluto is 200 MW, in the midrange of Xray power levels seen for known solar system emission sources: auroral precipitation, solar Xray scattering, and charge exchange (CXE) between solar wind (SW) ions & atmospheric neutrals. We eliminate auroral effects as a source, as Pluto has no known magnetic field & the New Horizons Alice UV spectrometer detected no airglow from Pluto during the flyby. Nano-scale atmospheric haze particles could lead to enhanced resonant scattering of solar X-rays from Pluto, but the energy signature of the detected photons does not match the solar spectrum and estimates of Plutos scattered Xray emission are > 100 times below the 3.9e-5 cps found in our observations. CXE emission from SW carbon, nitrogen, and oxygen ions can produce the energy signature seen, and the 6e25 neutral gas escape rate from Pluto deduced from New Horizons data can support the 3.0e24 Xray photons/sec emission rate required by our observations. Using the SW proton density and speed measured by the Solar Wind Around Pluto (SWAP) instrument in the vicinity of Pluto at the time of the photon emissions, we find too few SW minor ions flowing into the 11 x 11 pixel box centered on Pluto than are needed to support the observed emission rate unless the SW is significantly focused and enhanced in this region.
We present the first X-ray observation at sub-arcsecond resolution of the
high-redshift ($z=6.18$) radio-loud quasar CFHQS J142952+544717 (J1429). The
~100 net-count 0.3-7 keV spectrum obtained from ...$\sim 30$ ksec Chandra exposure
is best fit by a single power-law model with a photon index $\Gamma=2.0\pm0.2$
and no indication of an intrinsic absorber, implying a 3.6-72 keV rest-frame
luminosity $L_{\rm X}=(2.3^{+0.6}_{-0.5})\times10^{46}$ erg s$^{-1}$. We
identify a second X-ray source at 30 arcsec, distance from J1429 position, with
a soft ($\Gamma\simeq 2.8$) and absorbed (equivalent hydrogen column density
$N_{\rm H} <13.4\times 10^{20}$ cm$^{-2}$) spectrum, which likely contaminated
J1429 spectra obtained in lower angular resolution observations. Based on the
analysis of the Chandra image, the bulk of the X-ray luminosity is produced
within the central $\sim 3$ kpc region, either by the disk/corona system, or by
a moderately aligned jet. In this context, we discuss the source properties in
comparison with samples of low- and high-redshift quasars. We find indication
of a possible excess of counts over the expectations for a point-like source in
a 0.5 arcsec-1.5 arcsec ($\sim 3-8$ kpc) annular region. The corresponding
X-ray luminosity at J1429 redshift is $4\times 10^{45}$ erg s$^{-1}$. If
confirmed, this emission could be related to either a large-scale X-ray jet, or
a separate X-ray source.
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