1,118 research outputs found
X-ray Lighthouses of the High-Redshift Universe. II. Further Snapshot Observations of the Most Luminous z>4 Quasars with Chandra
We report on Chandra observations of a sample of 11 optically luminous
(Mb<-28.5) quasars at z=3.96-4.55 selected from the Palomar Digital Sky Survey
and the Automatic Plate Measuring Facility Survey. These are among the most
luminous z>4 quasars known and hence represent ideal witnesses of the end of
the "dark age ''. Nine quasars are detected by Chandra, with ~2-57 counts in
the observed 0.5-8 keV band. These detections increase the number of X-ray
detected AGN at z>4 to ~90; overall, Chandra has detected ~85% of the
high-redshift quasars observed with snapshot (few kilosecond) observations. PSS
1506+5220, one of the two X-ray undetected quasars, displays a number of
notable features in its rest-frame ultraviolet spectrum, the most prominent
being broad, deep SiIV and CIV absorption lines. The average optical-to-X-ray
spectral index for the present sample (=-1.88+/-0.05) is steeper than
that typically found for z>4 quasars but consistent with the expected value
from the known dependence of this spectral index on quasar luminosity.
We present joint X-ray spectral fitting for a sample of 48 radio-quiet
quasars in the redshift range 3.99-6.28 for which Chandra observations are
available. The X-ray spectrum (~870 counts) is well parameterized by a power
law with Gamma=1.93+0.10/-0.09 in the rest-frame ~2-40 keV band, and a tight
upper limit of N_H~5x10^21 cm^-2 is obtained on any average intrinsic X-ray
absorption. There is no indication of any significant evolution in the X-ray
properties of quasars between redshifts zero and six, suggesting that the
physical processes of accretion onto massive black holes have not changed over
the bulk of cosmic time.Comment: 15 pages, 7 figures, accepted for publication in A
High-speed, multi-colour optical photometry of the anomalous X-ray pulsar 4U 0142+61 with ULTRACAM
We present high-speed, multi-colour optical photometry of the anomalous X-ray
pulsar 4U 0142+61, obtained with ULTRACAM on the 4.2-m William Herschel
Telescope. We detect 4U 0142+61 at magnitudes of i'=23.7+-0.1, g'=27.2+-0.2 and
u'>25.8, consistent with the magnitudes found by Hulleman et al.(2004) and
hence confirming their discovery of both a spectral break in the optical and a
lack of long-term optical variability. We also confirm the discovery of Kern &
Martin (2002) that 4U 0142+61 shows optical pulsations with an identical period
(~8.7 s) to the X-ray pulsations. The rms pulsed fraction in our data is
29+-8%, 5-7 times greater than the 0.2-8 keV X-ray rms pulsed fraction. The
optical and X-ray pulse profiles show similar morphologies and appear to be
approximately in phase with each other, the former lagging the latter by only
0.04+-0.02 cycles. In conjunction with the constraints imposed by X-ray
observations, the results presented here favour a magnetar interpretation for
the anomalous X-ray pulsars.Comment: 6 pages, 4 figures, accepted for publication in MNRA
Green Bank Telescope Observations of the Eclipse of Pulsar "A" in the Double Pulsar Binary PSR J0737-3039
We report on the first Green Bank Telescope observations at 427, 820 and 1400
MHz of the newly discovered, highly inclined and relativistic double pulsar
binary. We focus on the brief eclipse of PSR J0737-3039A, the faster pulsar,
when it passes behind PSR J0737-3039B. We measure a frequency-averaged eclipse
duration of 26.6 +/- 0.6 s, or 0.00301 +/- 0.00008 in orbital phase. The
eclipse duration is found to be significantly dependent on radio frequency,
with eclipses longer at lower frequencies. Specifically, eclipse duration is
well fit by a linear function having slope (-4.52 +/- 0.03) x 10^{-7}
orbits/MHz. We also detect significant asymmetry in the eclipse. Eclipse
ingress takes 3.51 +/- 0.99 times longer than egress, independent of radio
frequency. Additionally, the eclipse lasts (40 +/- 7) x 10^{-5} in orbital
phase longer after conjunction, also independent of frequency. We detect
significant emission from the pulsar on short time scales during eclipse in
some orbits. We discuss these results in the context of a model in which the
eclipsing material is a shock-heated plasma layer within the slower PSR
J0737-3039B's light cylinder, where the relativistic pressure of the faster
pulsar's wind confines the magnetosphere of the slower pulsar.Comment: 12 pages, 3 figure
The 2016 outburst of PSR J1119-6127: cooling & a spin-down dominated glitch
We report on the aftermath of a magnetar outburst from the young,
high-magnetic-field radio pulsar PSR J1119-6127 that occurred on 2016 July 27.
We present the results of a monitoring campaign using the Neil Gehrels Swift
X-ray Telescope, NuSTAR, and XMM-Newton. After reaching a peak luminosity of
~300 times the quiescent luminosity, the pulsar's X-ray flux declined by factor
of ~50 on a time scale of several months. The X-ray spectra are well described
by a blackbody and a hard power-law tail. After an initial rapid decline during
the first day of the outburst, we observe the blackbody temperature rising from
kT = 0.9 keV to 1.05 keV during the first two weeks of the outburst, before
cooling to 0.9 keV. During this time, the blackbody radius decreases
monotonically by a factor of ~4 over a span of nearly 200 days. We also report
a heretofore unseen highly pulsed hard X-ray emission component, which fades on
a similar timescale to the soft X-ray flux, as predicted by models of
relaxation of magnetospheric current twists. The previously reported spin-up
glitch which accompanied this outburst was followed by a period of enhanced and
erratic torque, leading to a net spin-down of Hz, a
factor of ~24 over-recovery. We suggest that this and other radiatively loud
magnetar-type glitch recoveries are dominated by magnetospheric processes, in
contrast to conventional radio pulsar glitch recoveries which are dominated by
internal physics.Comment: Submitted to Ap
- …