815 research outputs found
X-ray Variability and Emission Process of the Radio Jet in M87
We monitored the M87 jet with the ACIS-S detector on Chandra with 5
observations between 2002 Jan and 2002 Jul. Our goal was to determine the
presence and degree of variability in morphology, intensity, and spectral
parameters. We find strong variability of the core and HST-1, the knot lying
0.8" from the core. These observations were designed to constrain the X-ray
emission process: whereas synchrotron emission would necessitate the presence
of extremely high energy electrons with a halflife of a few years or less,
inverse Compton emission from a relativistic jet would arise from low energy
electrons with very long halflives. Currently, all indications point to a
synchrotron process for the X-ray emission from the M87 jet. We give key
parameters for a ``modest beaming'' synchrotron model.Comment: 4 pages with 2 embedded figures (1 in color). To be published in the
proceedings of the Bologna Jet Workshop "The Physics of Relativistic Jets in
the CHANDRA and XMM Era", 23-27 September 2002, Brunetti, Harris, Sambruna,
and Setti, editors. 2003, New Ast. Re
Month-Timescale Optical Variability in the M87 Jet
A previously inconspicuous knot in the M87 jet has undergone a dramatic
outburst and now exceeds the nucleus in optical and X-ray luminosity.
Monitoring of M87 with the Hubble Space Telescope and Chandra X-ray Observatory
during 2002-2003, has found month-timescale optical variability in both the
nucleus and HST-1, a knot in the jet 0.82'' from the nucleus. We discuss the
behavior of the variability timescales as well as spectral energy distribution
of both components. In the nucleus, we see nearly energy-independent
variability behavior. Knot HST-1, however, displays weak energy dependence in
both X-ray and optical bands, but with nearly comparable rise/decay timescales
at 220 nm and 0.5 keV. The flaring region of HST-1 appears stationary over
eight months of monitoring. We consider various emission models to explain the
variability of both components. The flares we see are similar to those seen in
blazars, albeit on longer timescales, and so could, if viewed at smaller
angles, explain the extreme variability properties of those objects.Comment: 4 pages, 3 figures, ApJ Lett., in pres
Determination of the intrinsic velocity field in the M87 jet
A new method to estimate the Doppler beaming factor of relativistic
large-scale jet regions is presented. It is based on multiwaveband fitting to
radio-to-X-ray continua with synchrotron spectrum models. Combining our method
with available observational data of proper motions, we derive the intrinsic
velocity as well as the viewing angles to the line of sight for eight knotty
regions down the M87 jet. The results favor the 'modest beaming' scenario along
the jet, with Doppler factors varying between 2-5. The inner jet of M87 suffers
sharp deceleration, and the intrinsic speed remains roughly constant down the
outer jet. The orientation of the inner jet regions is fully consistent with
the result of 10deg-19deg to the line of sight suggested by previous Hubble
Space Telescope (HST) proper motion studies of the M87 jet. The outer jet,
however, shows systematic deflection off the inner jet to much smaller
inclination (<<10deg). Further calculation of knot A suggests this deflection
can be regarded as evidence that the outer jet suffers some departure from
equipartition. The nucleus region of the M87 jet should have a viewing angle
close to its first knot HST-1, i.e. ~15deg, which favors the idea that M87 may
be a misaligned blazar. This work provides some hints about the overall
dynamics of this famous extragalactic jet.Comment: 11 pages, 3 figures, 4 tables, MNRAS, 2009, in pres
X-ray Emission Processes in Extragalactic Jets, Lobes and Hot Spots
This paper is a brief review of the processes responsible for X-ray emission
from radio jets, lobes and hot spots. Possible photons in inverse Compton
scattering models include the radio synchrotron radiation itself (i.e.
synchrotron self-Compton [SSC] emission), the cosmic microwave background
(CMB), the galaxy starlight and radiation from the active nucleus. SSC emission
has been detected from a number of hot spots. Scattering of the CMB is expected
to dominate for jets (and possibly hot spots) undergoing bulk relativistic
motion close to the direction towards the observer. Scattering of infrared
radiation from the AGN should be observable from radio lobes, especially if
they are close to the active nucleus. Synchrotron radiation is detected in some
sources, most notably the jet of M87. I briefly discuss why different hot spots
emit X-rays by different emission mechanisms and the nature of the synchrotron
spectra.Comment: To be published in the proceedings of the Bologna conference ``The
Physics of Relativistic Jets in the Chandra and XMM Era'', New Astronomy
Revie
The radio-ultraviolet spectral energy distribution of the jet in 3C273
We present deep VLA and HST observations of the large-scale jet in 3C 273
matched to 0.3" resolution. The observed spectra show a significant flattening
in the infrared-ultraviolet wavelength range. The jet's emission cannot
therefore be assumed to arise from a single electron population and requires
the presence of an additional emission component. The observed smooth
variations of the spectral indices along the jet imply that the physical
conditions vary correspondingly smoothly. We determine the maximum particle
energy for the optical jet using synchrotron spectral fits. The slow decline of
the maximum energy along the jet implies particle reacceleration acting along
the entire jet. In addition to the already established global anti-correlation
between maximum particle energy and surface brightness, we find a weak positive
correlation between small-scale variations in maximum particle energy and
surface brightness. The origin of these conflicting global and local
correlations is unclear, but they provide tight constraints for reacceleration
models.Comment: 28 pages, lots of figures, accepted for publication in A&
A Magnetohydrodynamic Model of the M87 Jet I: Superluminal Knot Ejections from HST-1 as Trails of Quad Relativistic MHD Shocks
This is the first in a series of papers that introduces a new paradigm for
understanding the jet in M87: a collimated relativistic flow in which strong
magnetic fields play a dominant dynamical role. Here wefocus on the flow
downstream of HST-1 - an essentially stationary flaring feature that ejects
trails of superluminal components. We propose that these components are quad
relativistic magnetohydrodynamic shock fronts (forward/reverse fast and slow
modes) in a narrow jet with a helically twisted magnetic structure. And we
demonstrate the properties of such shocks with simple one-dimensional numerical
simulations. Quasi-periodic ejections of similar component trails may be
responsible for the M87 jet substructures observed further downstream on 100 -
1,000 pc scales. This new paradigm requires the assimilation of some new
concepts into the astrophysical jet community, particularly the behavior of
slow/fast-mode waves/shocks and of current-driven helical kink instabilities.
However, the prospects of these ideas applying to a large number of other jet
systems may make this worth the effort.Comment: 7 pages, 4 figures, Accepted for Publication in Ap
A cosmic ray cocoon along the X-ray jet of M87?
Relativistic jets propagating through an ambient medium must produce some
observational effects along their side boundaries because of interactions
across the large velocity gradient. One possible effect of such an interaction
would be a sheared magnetic field structure at the jet boundaries, leading to a
characteristic radio polarization pattern. As proposed by Ostrowski, another
effect can come from the generation of a high energy cosmic ray component at
the boundary, producing dynamic effects on the medium surrounding the jet and
forming a cocoon dominated by cosmic rays with a decreased thermal gas
emissivity. We selected this process for our first attempt to look for the
effects of this type of interaction. We analyzed the Chandra X-ray data for the
radio galaxy M87 in order to verify if the expected regions of diminished
emissivity may be present near the spectacular X-ray jet in this source. The
detailed analysis of the data, merged from 42 separate observations, shows
signatures of lower emissivity surrounding the jet. In particular we detect an
intensity dip along the part of the jet, which would be approximately 150 pc x
2 kpc in size, if situated along the jet which is inclined toward us. Due to a
highly non-uniform X-ray background in the central region we are not able to
claim the discovery of a cosmic ray cocoon around the M87 jet: we only have
demonstrated that the data show morphological structures which could be
accounted for if a cosmic ray cocoon exists.Comment: 8 pages, 8 pictures accepted for publication in MNRA
Variability Timescales in the M87 Jet: Signatures of E-Squared Losses, Discovery of a Quasi-period in HST-1, and the Site of TeV Flaring
We investigate the variability timescales in the jet of M87 with two goals.
The first is to use the rise times and decay times in the radio, ultraviolet
and X-ray lightcurves of HST-1 to constrain the source size and the energy loss
mechanisms affecting the relativistic electron distributions. HST-1 is the
first jet knot clearly resolved from the nuclear emission by Chandra and is the
site of the huge flare of 2005. We find clear evidence for a
frequency-dependent decrease in the synchrotron flux being consistent with
E-squared energy losses. Assuming that this behavior is predominantly caused by
synchrotron cooling, we estimate a value of 0.6 mG for the average magnetic
field strength of the HST-1 emission region, a value consistent with previous
estimates of the equipartition field. In the process of analyzing the first
derivative of the X-ray light curve of HST-1, we discovered a quasi-periodic
oscillation which was most obvious in 2003 and 2004 prior to the major flare in
2005. The four cycles observed have a period of order 6 months. The second goal
is to search for evidence of differences between the X-ray variability
timescales of HST-1 and the unresolved nuclear region (diameter <0.6"). These
features, separated by more than 60 pc, are the two chief contenders for the
origin of the TeV variable emissions observed by HESS in 2005 and by MAGIC and
VERITAS in 2008. The X-ray variability of the nucleus appears to be at least
twice as rapid as that of the HST-1 knot. However, the shortest nuclear
variability timescale we can measure from the Chandra data (<= 20 days) is
still significantly longer than the shortest TeV variability of M87 reported by
the HESS and MAGIC telescopes (1-2 days).Comment: Accepted for publication in the Astrophysical Journal. 16 pages
including 9 figures, some in colo
Flaring X-ray Emission from HST-1, a Knot in the M87 Jet
We present Chandra X-ray monitoring of the M87 jet in 2002, which shows that
the intensity of HST-1, an optical knot 0.8" from the core, increased by a
factor of two in 116 days and a factor of four in 2 yrs. There was also a
significant flux decrease over two months, with suggestive evidence for a
softening of the spectrum. From this variability behavior, we argue that the
bulk of the X-ray emission of HST-1 comes from synchrotron emission. None of
the other conceivable emission processes can match the range of observed
characteristics. By estimating synchrotron model parameters for various bulk
relativistic velocities, we demonstrate that a model with a Doppler factor,
delta, in the range 2 to 5 fits our preliminary estimates of light travel time
and synchrotron loss timescales.Comment: 4 pages with 3 embedded figures; 1 of which is color but prints ok in
b/w. Accepted for publication in the ApJ
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