Review: <i>The Buried Past: An Archaeological History of Philadelphia</i>, by John L. Cotter, Daniel G. Roberts, and Michael Parrington

Potter, Parker B.

doi:10.2307/3378360

Cited by 13 publications

(23 citation statements)

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“…While we have fitted Mrk 421 with an accelerating jet, Potter & Cotter (2013b) (based on the model of Potter & Cotter 2013a) found they can model it by a significant deceleration. We stress, however, that our fits were intended to illustrate the possibility of reproducing soft radio-to-IR spectra by changing bulk Lorentz factor and are neither self-consistent nor unique.…”

Section: Comparison With Datamentioning

confidence: 89%

“…We could have, in fact, fit Mrk 421 with a decelerating jet and Mrk 501 with an accelerating one. Furthermore, we note that Potter & Cotter (2013b) managed to obtain a good fit to the soft radio spectrum of Mrk 421 by assuming it was optically thin synchrotron emission. For that emission, changing the bulk Lorentz factor does not change the slope of the observed spectrum (unlike the case of partially selfabsorbed emission) and thus the deceleration used in that model does not affect the value of α.…”

Section: Comparison With Datamentioning

confidence: 98%

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Variable jet Lorentz factors can explain soft self-absorbed radio spectra of accreting black holes

Zdziarski

2019

Monthly Notices of the Royal Astronomical Society: Letters

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We study the effect of variable jet bulk Lorentz factors, i.e., either jet acceleration or deceleration, on partially synchrotron self-absorbed radio spectra from cores of radio-loud active galactic nuclei and black-hole binaries in the hard state. In about a half of quasars and radio galaxies, their core radio spectra are observed to be soft, i.e., have the spectral index of α < 0. If they are emitted by jets with constant Lorentz factors, that softness implies deposition of large amounts of energy at large distances from the centre. We show here that such soft spectra can be explained without that energetic requirement by emission of jets with the Doppler factor increasing with the distance. This can happen for either jet acceleration or deceleration, depending on the jet viewing angle. We find our model can explain the quiescent radio to X-ray spectra of the BL Lac objects Mrk 421 and Mrk 501.

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Section: Comparison With Datamentioning

confidence: 89%

Section: Comparison With Datamentioning

confidence: 98%

Variable jet Lorentz factors can explain soft self-absorbed radio spectra of accreting black holes

Zdziarski

2019

Monthly Notices of the Royal Astronomical Society: Letters

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“…Here, we find a continuous acceleration is necessary to account for the observed spectra with α < 0. Our approach is also different from that of Potter & Cotter (2012, 2013a,b, 2015, who considered numerical jet models. Instead, we here model the jet using a kinetic equation and obtain analytical solutions.…”

Section: Introductionmentioning

confidence: 97%

“…In order to mitigate the problem of the large adiabatic losses, a number of authors, e.g., Kaiser (2006), Pe'er & Casella (2009) and Potter & Cotter (2012, 2013a considered the presence of adiabatic losses as optional, and studied jet models both with and without adiabatic losses. Some others developed jet models with acceleration and radiative losses but without including adiabatic losses at all, e.g., Hervet, Boisson & Sol (2015).…”

Section: Introductionmentioning

confidence: 99%

“…The issue of the nature of adiabatic losses is discussed, in particular, in Potter & Cotter (2012, who argued that both the bulk velocity and the electron internal energy may remain constant in a conical jet of constant speed. Potter & Cotter (2015) considered the possibility that adiabatic losses are converted into radial bulk motion, which is then immediately converted back into electron acceleration.…”

Section: Introductionmentioning

confidence: 99%

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The effect of adiabatic losses on spectra of stationary jets and the origin of soft radio spectra of accreting black hole sources

Zdziarski

Stawarz

Sikora

2019

Monthly Notices of the Royal Astronomical Society

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It has been suggested that adiabatic energy losses are not effective in stationary jets, where the jet expansion is not associated with net work. Here, we study jet solutions without them, assuming that adiabatic losses are balanced by electron reacceleration. The absence of effective adiabatic losses makes electron advection along the jet an important process, and we solve the electron kinetic equation including that process. We find analytical solutions for the case of conical jets with advection and synchrotron losses. We show that accounting for adiabatic losses in the case of sources showing soft partially self-absorbed spectra with the spectral index of α < 0 in the radio-to-IR regime requires deposition of large amounts of energy at large distances in the jet. On the other hand, such spectra can be accounted for by advection of electrons in the jet. We compare our results to the quiescent spectrum of the blazar Mrk 421. We find its soft radio-IR spectrum can be fitted either by a model without adiabatic losses and advection of electrons or by one with adiabatic losses, but the latter requires injection of a very large power at large distances.

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An active state of the BL Lacertae object Markarian 421 detected by INTEGRAL in April 2013

Pian¹,

Türler²,

Fiocchi³

et al. 2014

A&A

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Aims. Multiwavelength variability of blazars offers indirect, but very effective, insight into their powerful engines and on the mechanisms through which energy is propagated from the centre down the jet. The BL Lac object Mkn 421 is a TeV emitter, a bright blazar at all wavelengths, and therefore an excellent target for variability studies. Methods. We activated INTEGRAL observations of Mkn 421 in an active state on 16-21 April 2013, and complemented them with Fermi-LAT data. Results. We obtained well sampled optical, soft, and hard X-ray light curves that show the presence of two flares and time-resolved spectra in the 3.5-60 keV (JEM-X and IBIS/ISGRI) and 0.1-100 GeV (Fermi-LAT) ranges. The average flux in the 20-100 keV range is 9.1 × 10 −11 erg s −1 cm −2 (∼4.5 mCrab) and the nuclear average apparent magnitude, corrected for Galactic extinction, is V 12.2. In the time-resolved X-ray spectra, which are described by broken power laws and, marginally better, by log-parabolic laws, we see a hardening that correlates with flux increase, as expected in refreshed energy injections in a population of electrons that later cool via synchrotron radiation. The hardness ratios between the JEM-X fluxes in two different bands and between the JEM-X and IBIS/ISGRI fluxes confirm this trend. During the observation, the variability level increases monotonically from the optical to the hard X-rays, while the large LAT errors do not allow a significant assessment of the MeV-GeV variability. The cross-correlation analysis during the onset of the most prominent flare suggests a monotonically increasing delay of the lower frequency emission with respect to that at higher frequency, with a maximum time-lag of about 70 min, that is however not well constrained. The spectral energy distributions from the optical to the TeV domain were compared to homogeneous models of blazar emission based on synchrotron radiation and synchrotron self-Compton scattering. They represent a satisfactory description, except in the state corresponding to the LAT softest spectrum and highest flux. Conclusions. Multiwavelength variability of Mkn 421 can be very complex, with patterns changing from epoch to epoch down to intra-day timescales, depending on the emission state. This makes accurate monitoring of this source during bright hard X-ray states necessary and calls for the elaboration of multicomponent, multizone, time-dependent models.

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Review: The Buried Past: An Archaeological History of Philadelphia, by John L. Cotter, Daniel G. Roberts, and Michael Parrington

Cited by 13 publications

References 0 publications

Variable jet Lorentz factors can explain soft self-absorbed radio spectra of accreting black holes

Variable jet Lorentz factors can explain soft self-absorbed radio spectra of accreting black holes

The effect of adiabatic losses on spectra of stationary jets and the origin of soft radio spectra of accreting black hole sources

An active state of the BL Lacertae object Markarian 421 detected by INTEGRAL in April 2013

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