Jet Break Research Articles

THE DIVERSE BROADBAND LIGHT CURVES OFSWIFTGAMMA-RAY BURSTS REPRODUCED WITH THE CANNONBALL MODEL

Two radiation mechanisms, inverse Compton scattering (ICS) and synchrotron radiation (SR), suffice within the cannonball (CB) model of long gamma ray bursts (LGRBs) and X-ray flashes (XRFs) to provide a very simple and accurate description of their observed prompt emission and afterglows. Simple as they are, the two mechanisms and the burst environment generate the rich structure of the light curves at all frequencies and times. This is demonstrated for 33 selected Swift LGRBs and XRFs, which are well sampled from early until late time and faithfully represent the entire diversity of the broad-band light curves of Swift LGRBs and XRFs. Their prompt gamma-ray and X-ray emission is dominated by ICS of `glory' light. During their fast decline phase, ICS is taken over by SR, which dominates their broad-band afterglow. The pulse shape and spectral evolution of the gamma-ray peaks and the early-time X-ray flares, and even the delayed optical `humps' in XRFs, are correctly predicted. The `canonical' and non-canonical X-ray light curves and the chromatic behaviour of the broad-band afterglows are well reproduced. In particular, in canonical X-ray light curves, the initial fast decline and rapid softening of the prompt emission, the transition to the plateau phase, the subsequent gradual steepening of the plateau to an asymptotic power-law decay, and the transition from chromatic to achromatic behaviour of the light curves agrees well with those predicted by the CB model. The Swift early-time data on XRF 060218 are inconsistent with a black-body emission from a shock break-out through a stellar envelope. Instead, they are well described by ICS of glory light by a jet breaking out from SN2006aj.

Testing the blast wave model withSwiftGRBs

The complex structure of the light curves of Swift Gamma-Ray Bursts (GRBs) has made the identification of breaks, and the interpretation of the blast wave caused by the burst, more difficult than in the pre-Swift era. We aim to identify breaks, which are possibly hidden, and to constrain the blast wave parameters; electron energy distribution, p, density profile of the circumburst medium, k, and the continued energy injection index, q. We do so by comparing the observed multiwavelength light curves and X-ray spectra of our sample to the predictions of the blast wave model. We can successfully interpret all of the bursts in our sample of 10, except two, within this framework and we can estimate, with confidence, the electron energy distribution index for 6 of the sample. Furthermore, we identify jet breaks in a number of the bursts. A statistical analysis of the distribution of p reveals that, even in the most conservative case of least scatter, the values are not consistent with a single, universal value. The values of k suggest that the circumburst density profiles are not drawn from only one of the constant density or wind-like media populations.

Asymptotic solution of slender viscous jet break-up

The break-up of a slender viscous jet is examined using the Needham-Leach asymptotic method. This method enables the calculation of the large time asymptotic structure of the model evolution equations using matched asymptotic expansions. An equation which describes the dynamics of non-linear travelling waves at large times is derived using this method. In particular, the wave speed, wavelength, growth rate and frequency of these travelling waves are determined. This provides information on how the jet breaks up, the region of break-up and the possibility for multiple break-up points. Also, this method gives information on how non-linear jets may be controlled.

Magnetic acceleration of ultrarelativistic jets in gamma-ray burst sources

We present numerical simulations of axi symmetric, magnetically driven outflows that reproduce the inferred properties of ultrarelativistic gamma-ray burst (GRB) jets. These results extend our previous simulations of outflows accelerated to moderately relativistic speeds, which are applicable to jets of active galactic nuclei. In contrast to several recent investigations, which have employed the magnetodynamics approximation, our numerical scheme solves the full set of equations of special relativistic, ideal magnetohydrodynamics, which enables us to explicitly calculate the jet velocity and magnetic-to-kinetic energy conversion efficiency - key parameters of interest for astrophysical applications. We confirm that the magnetic acceleration scheme remains robust into the ultrarelativistic regime, as previously indicated by semi-analytic self-similar solutions. We find that all current-carrying outflows exhibit self-collimation and consequent acceleration near the rotation axis, but that unconfined outflows lose causal connectivity across the jet and therefore do not collimate or accelerate efficiently in their outer regions. We show that magnetically accelerated jets confined by an external pressure that varies as z -α (0 1), and we obtain analytic expressions for the one-to-one correspondence between the pressure distribution and the asymptotic jet shape. We demonstrate that the acceleration efficiency of jets with paraboloidal streamlines is ≥50 per cent, with the numerical value being higher the lower the initial magnetization. We derive asymptotic analytic expressions for the acceleration of initially cold outflows along paraboloidal streamlines and verify that they provide good descriptions of the simulated flows. Our modelled jets (corresponding to 3/2 < a < 3) attain Lorentz factors Γ ≥ 10 2 on scales ∼ 10 10 -10 12 cm, consistent with the possibility that long/soft GRB jets are accelerated within envelopes of collapsing massive stars, and r ≥ 30 on scales ∼9 x 10 8 -3 x 10 10 cm, consistent with the possibility that short/hard GRB jets are accelerated on scales where they can be confined by moderately relativistic winds from accretion discs. We also find that Γθ v ∼ 1 for outflows that undergo an efficient magnetic-to-kinetic energy conversion, where θ v is the opening half-angle of the poloidal streamlines. This relation implies that the γ-ray emitting components of GRB outflows accelerated in this way are very narrow, with θ v ≤ 1° in regions where Γ ≥ 100, and that the afterglow light curves of these components would either exhibit a very early jet break or show no jet break at all.

GRB 060605: multi-wavelength analysis of the first GRB observed using integral field spectroscopy

The long and relatively faint gamma-ray burst GRB 060605 detected by Swift/BAT lasted about 20 sec. Its afterglow could be observed with Swift/XRT for nearly 1 day, while Swift/UVOT could detect the afterglow during the first 6 hours after the event. Here, we report on integral field spectroscopy of its afterglow performed with PMAS /PPak mounted at the Calar Alto 3.5 m telescope. In addition, we report on a detailed analysis of XRT and UVOT data and on the results of deep late-time VLT observations that reveal the GRB host galaxy. We find t hat the burst occurred at a redshift of z=3.773, possibly associated with a faint, RC = 26.4± 0.3 host. Based on the optical and X-ray data, we deduce information on the SED of the afterglow, the position of the cooling frequency in the SED, the nature of the circumburst environment, its collimation factor, and its energetics. We find that the GRB fi reball was expanding into a constant-density medium and that the explosion was collimated with a narrow half-opening angle of about 2.4 degrees. The initial Lorentz factor of the fireball was about 250; however, its beaming-corrected energy release in the gamma-ray band was comparably low. The optical, X-ray afterglow, on the other hand, was rather luminous. Finally, we find that the data are consistent withi n the error bars with an achromatic evolution of the afterglo w during the suspected jet break time at about 0.27 days after the burst.

OBSERVATIONS OF THE NAKED-EYE GRB 080319B: IMPLICATIONS OF NATURE'S BRIGHTEST EXPLOSION

The first gamma-ray burst (GRB) confirmed to be bright enough to be seen with the naked eye, GRB 080319B at redshift z = 0.937, allowed for exquisite follow-up observations across the electromagnetic spectrum. We present our detailed optical and infrared observations of the afterglow, consisting of over 5000 images starting 51 s after the GRB trigger, in concert with our own analysis of the Swift data. The event is extreme not only in observed properties but intrinsically: it was the most luminous event ever recorded at optical and infrared wavelengths and had an exceedingly high isotropic-equivalent energy release in gamma-rays. At early times, the afterglow evolution is broadly consistent with being reverse-shock dominated, but then is subsumed by a forward shock at around 1000 s. The overall spectral energy distribution, spanning from ultraviolet through near-infrared wavelengths, shows no evidence for a significant amount of dust extinction in the host frame. The afterglow evolution, however, is highly chromatic: starting at about 1000 s the index shifts blueward before shifting back to the red at late times. In our deepest late-time observations, we find tentative evidence for an optical jet break and a luminous supernova. Finally, we examine the detectability of such events with current and future facilities and find that such an event could be detected in gamma-rays by BAT out to z = 10.7 (8 sigma), while the nominal EXIST sensitivity would allow detection to z ~ 32. At K band, this source would have been easily detected with meter-class telescopes to z ~ 17.

A unifying view of gamma-ray burst afterglows

We selected a sample of 33 Gamma Ray Bursts (GRBs) detected by Swift, with known redshift and optical extinction at the host frame. For these, we constructed the de-absorbed and K-corrected X-ray and optical rest frame light curves. These are modelled as the sum of two components: emission from the forward shock due to the interaction of a fireball with the circum-burst medium and an additional component, treated in a completely phenomenological way. The latter can be identified, among other possibilities, as emission produced by a long lived central engine with mechanisms similar to those responsible for the production of the standard early prompt radiation. Apart from flares or re-brightenings, that we do not model, we find a good agreement with the data, despite of their complexity and diversity. Although based in part on a phenomenological model with a relatively large number of free parameters, we believe that our findings are a first step towards the construction of a more physical scenario. Our approach allows us to interpret the behaviour of the optical and X-ray afterglows in a coherent way, by a relatively simple scenario. Within this context it is possible to explain why sometimes no jet break is observed; why, even if a jet break is observed, it is often chromatic; why the steepening after the jet break time is often shallower than predicted. Finally, the decay slope of the late prompt emission after the shallow phase is found to be remarkably similar to the time profile expected by the accretion rate of fall-back material (i.e. proportional to t^{-5/3}), suggesting that this can be the reason why the central engine can be active for a long time.

Jet breaks at the end of the slow decline phase ofSwiftGRB light curves

The Swift mission has discovered an intriguing feature of gamma-ray burst (GRBs) afterglows, a phase of shallow decline of the flux in the X-ray and optical light curves. This behaviour is typically attributed to energy injection into the burst ejecta. At some point this phase ends, resulting in a break in the light curve, which is commonly interpreted as the cessation of the energy injection. In a few cases, however, while breaks in the X-ray light curve are observed, optical emission continues its slow flux decline. This behaviour suggests a more complex scenario. In this paper, we present a model that invokes a double component outflow, in which narrowly collimated ejecta are responsible for the X-ray emission while a broad outflow is responsible for the optical emission. The narrow component can produce a jet break in the X-ray light curve at relatively early times, while the optical emission does not break due to its lower degree of collimation. In our model both components are subject to energy injection for the whole duration of the follow-up observations. We apply this model to GRBs with chromatic breaks, and we show how it might change the interpretation of the GRBs canonical light curve. We also study our model from a theoretical point of view, investigating the possible configurations of frequencies and the values of GRB physical parameters allowed in our model.

乱流境界層中に噴出した気流からの気泡分離機構に関する研究 : 連続気柱からの気泡分離(流体工学,流体機械)

A theoretical and experimental consideration is conducted to investigate the bubble separation from an air injected into a liquid turbulent boundary layer. There exist three patterns of bubble separation dependent on the jet velocity, i.e., (a) single bubble, (b) ccalescent bubble, and (c) continuous jet. First, the critical jet velocity from (a) to (b) is theoretically estimated from the condition that the jet from the nozzle overtakes the rear end of the separated bubble which shrinks due to the action of surface tension. The calculated results roughly reproduce the experimental results observed by the high-speed video camera. The process of bubble separation from the continuous jet (c) can be classified into two patterns, i.e., (i) the bubble separates from the swell at the front end of jet, (ii) the jet breaks due to the instability on the liquid-gas interface. The separated bubble diameter of pattern (i) is theoretically determined by considering the force balance at the front end of jet between surface tension, drag from the frees stream and virtual mass force. Also the bubble diameter of pattern (ii) is calculated from the most unstable wavelength of Rayleigh instability. Both theoretical results agree well with those obtained experimentally.

Time-resolved spectral correlations of long-duration γ-ray bursts

For a sample of long γ-ray bursts (GRBs) with known redshift, we study the distribution of the evolutionary tracks on the rest-frame luminosity-peak energy L iso −E′ p diagram. We are interested in exploring the extension of the ‘Yonetoku’ correlation to any phase of the prompt light curve, and in verifying how the high-signal prompt duration time, T′ f , in the rest frame correlates with the residuals of such correlation. For our purpose, we separately analyse two samples of time-resolved spectra corresponding to 32 GRBs with peak fluxes F p > 1.8 phot cm −2 s −1 from the Swift-BAT detector, and seven bright GRBs from the Compton Gamma-ray Observatory (CGRO)-BATSE detector previously processed by Kaneko et al. After constructing the L iso −E′ p diagram, we discuss the relevance of selection effects, finding that they could significantly affect the correlation. However, we find that these effects are much less significant in the L iso T′ f −E′ p diagram, where the intrinsic scatter reduces significantly. We apply further corrections in order to reduce the intrinsic scatter even more. For the subsamples of GRBs (seven from Swift and five from CGRO) with measured jet break time, t j , we analyse the effects of correcting L iso by jet collimation. We find that (i) the scatter around the correlation is reduced, and (ii) this scatter is dominated by the internal scatter of the individual evolutionary tracks. These results suggest that the time-integrated ‘Amati’ and ‘Ghirlanda’ correlations are consequences of the time-resolved features, not of selection effects, and therefore call for a physical origin. We finally remark the relevance of looking inside the nature of the evolutionary tracks.

The Rapidly Flaring Afterglow of the Very Bright and Energetic GRB 070125

We report on multiwavelength observations, ranging from X-ray to radio wave bands, of the IPN-localized gamma-ray burst GRB 070125. Spectroscopic observations reveal the presence of absorption lines due to O I, Si II, and C IV, implying a likely redshift of z = 1.547. The well-sampled light curves, in particular from 0.5 to 4 days after the burst, suggest a jet break at 3.7 days, corresponding to a jet opening angle of similar to 7.0 degrees, and implying an intrinsic GRB energy in the 1-10,000 keV band of around E-gamma = (6.3-6.9) x 10(51) ergs (based on the fluences measured by the gamma-ray detectors of the IPN). GRB 070125 is among the brightest afterglows observed to date. The SED implies a host extinction of A(V) < 0. 9 mag. Two rebrightening episodes are observed, one with excellent time coverage, showing an increase in flux of 56% in similar to 8000s. The evolution of the afterglow light curve is achromatic at all times. Late-time observations of the afterglow do not show evidence for emission from an underlying host galaxy or supernova. Any host galaxy would be subluminous, consistent with current GRB host galaxy samples. Evidence for strong Mg II absorption features is not found, which is perhaps surprising in view of the relatively high redshift of this burst and the high likelihood for such features along GRB-selected lines of sight.

A Comprehensive Study of GRB 070125, A Most Energetic Gamma‐Ray Burst

We present a comprehensive multiwavelength analysis of the bright, long duration gamma-ray burst GRB 070125, comprised of observations in $\gamma$-ray, X-ray, optical, millimeter and centimeter wavebands. Simultaneous fits to the optical and X-ray light curves favor a break on day 3.78, which we interpret as the jet break from a collimated outflow. Independent fits to optical and X-ray bands give similar results in the optical bands but shift the jet break to around day 10 in the X-ray light curve. We show that for the physical parameters derived for GRB 070125, inverse Compton scattering effects are important throughout the afterglow evolution. While inverse Compton scattering does not affect radio and optical bands, it may be a promising candidate to delay the jet break in the X-ray band. Radio light curves show rapid flux variations, which are interpreted as due to interstellar scintillation, and are used to derive an upper limit of $2.4 \times 10^{17}$ cm on the radius of the fireball in the lateral expansion phase of the jet. Radio light curves and spectra suggest a high synchrotron self absorption frequency indicative of the afterglow shock wave moving in a dense medium. Our broadband modeling favors a constant density profile for the circumburst medium over a wind-like profile ($R^{-2}$). However, keeping in mind the uncertainty of the parameters, it is difficult to unambiguously distinguish between the two density profiles. Our broadband fits suggest that \event is a burst with high radiative efficiency ($> 60 %$).

Go Long, Go Deep: Finding Optical Jet Breaks for Swift -Era GRBs with the LBT

Using the 8.4m Large Binocular Telescope, we observed six GRB afterglows from 2.8 hours to 30.8 days after the burst triggers to systematically probe the late time behaviors of afterglows including jet breaks, flares, and supernova bumps. We detected five afterglows with Sloan r' magnitudes ranging from 23.0-26.3 mag. The depth of our observations allows us to extend the temporal baseline for measuring jet breaks by another decade in time scale. We detected two jet breaks and a third candidate, all of which are not detectable without deep, late time optical observations. In the other three cases, we do not detect the jet breaks either because of contamination from the host galaxy light, the presence of a supernova bump, or the intrinsic faintness of the optical afterglow. This suggests that the basic picture that GRBs are collimated is still valid and that the apparent lack of Swift jet breaks is due to poorly sampled afterglow light curves, particularly at late times.

Simulations of ultrarelativistic magnetodynamic jets from gamma-ray burst engines

Long-duration gamma-ray bursts (GRBs) require an engine capable of driving a jet of plasma to ultrarelativistic bulk Lorentz factors of up to several hundred and into narrow opening angles of a few degrees. We use global axisymmetric stationary solutions of magnetically-dominated (force-free) ultrarelativistic jets to test whether the popular magnetic-driving paradigm can generate the required Lorentz factors and opening angles. Our global solutions are obtained via time-dependent relativistic ideal magnetodynamical numerical simulations which follow the jet from the central engine to beyond six orders of magnitude in radius. Our model is primarily motivated by the collapsar model, in which a jet is produced by a spinning black hole or neutron star and then propagates through a massive stellar envelope. We find that the size of the presupernova progenitor star and the radial profile of pressure inside the star determine the terminal Lorentz factor and opening angle of the jet. At the radius where the jet breaks out of the star, our well-motivated fiducial model generates a Lorentz factor $\gamma\sim 400$ and a half-opening angle $\theta_j\sim 2^\circ$, consistent with observations of many long-duration GRBs. Other models with slightly different parameters give $\gamma$ in the range 100 to 5000 and $\theta_j$ from $0.1^\circ$ to $10^\circ$, thus reproducing the range of properties inferred for GRB jets. A potentially observable feature of some of our solutions is that the maximum Poynting flux in the jet is found at $\theta \sim \theta_j$ with the jet power concentrated in a hollow cone, while the maximum in the Lorentz factor occurs at an angle $\theta$ substantially smaller than $\theta_j$ also in a hollow cone. [abridged]

A Level-Set Method for Simulation of a Thermal Inkjet Process

A numerical approach is presented for computing a thermal inkjet process, in which bubble growth and collapse acts as a driving mechanism for ink droplet ejection. The liquid–vapor and liquid–air interfaces are tracked by a level-set method which is modified to include the effect of phase change at the liquid–vapor interface and is extended to treat the contact angle condition at an immersed solid surface. The compressibility effect of a bubble is also included in the analysis to account for the high vapor pressure caused by instantaneous bubble nucleation. The whole process of the thermal inkjet, including jet breaking, satellite droplet formation, and ink refill, as well as bubble growth and collapse, is simulated without employing a simplified bubble growth model.

Gamma‐Ray Burst Energetics in theSwiftEra

We examine the rest-frame energetics of 76 gamma-ray bursts (GRBs) with known redshift that were detected by the Swift spacecraft and monitored by the satellite's X-Ray Telescope (XRT). Using the bolometric fluence values estimated by Butler and coworkers and the last XRT observation for each event, we set a lower limit to their collimation-corrected energy Eγ and find that 68% of our sample is at high enough redshift and/or low enough fluence to accommodate a jet break occurring beyond the last XRT observation and still be consistent with the pre-Swift Eγ distribution for long GRBs. We find that relatively few of the X-ray light curves for the remaining events show evidence for late-time decay slopes that are consistent with that expected from post-jet break emission. The breaks in the X-ray light curves that do exist tend to be shallower and occur earlier than the breaks previously observed in optical light curves, yielding a Eγ distribution that is far lower than the pre-Swift distribution. If these early X-ray breaks are not due to jet effects, then a small but significant fraction of our sample have lower limits to their collimation-corrected energy that place them well above the pre-Swift Eγ distribution. Either scenario would necessitate a much wider post-Swift Eγ distribution for long cosmological GRBs compared to the narrow standard energy deduced from pre-Swift observations. We note that almost all of the pre-Swift Eγ estimates come from jet breaks detected in the optical whereas our sample is limited entirely to X-ray wavelengths, furthering the suggestion that the assumed achromaticity of jet breaks may not extend to high energies.

Are the missing X-ray breaks in gamma-ray burst afterglow light curves merely hidden?

Gamma-ray burst afterglow observations in the Swift era have a perceived lack of achromatic jet breaks compared to the BeppoSAX, or pre-Swift era. Specifically, relatively few breaks, consistent with jet breaks, are observed in the X-ray light curves of these bursts. If these breaks are truly missing, it has serious consequences for the interpretation of GRB jet collimation and energy requirements, and the use of GRBs as cosmological tools. Here we address the issue of X-ray breaks that are possibly `hidden' and hence the light curves are misinterpreted as being single power laws. We do so by synthesising XRT light curves and fitting both single and broken power laws, and comparing the relative goodness of each fit via Monte Carlo analysis. Even with the well sampled light curves of the Swift era, these breaks may be left misidentified, hence caution is required when making definite statements on the absence of achromatic breaks.

Study on jet breakup behavior at core disruptive accident for fast breeder reactor

It is important to estimate the cooling possibility of the molten jet in coolant during a core disruptive accident (CDA) of a fast breeder reactor (FBR). In the present study, the molten jet of U-alloy78 simulating the core material is injected into the water simulating the coolant. The visual data of the molten jet breakup behavior is observed by using the high-speed video camera. The front velocity of the molten jet is estimated by using the image processing technique from the visual data. It shows that the front velocity of the molten jet can be divided into three time regions. In the first region, the front velocity of the molten jet increases. In the second region, the front velocity of the molten jet suddenly decreases. In the third region, the front velocity of the molten jet keeps at low and steady. In first region, the column diameter of the molten jet decreases with the passage of time. At the location between first region and second region, the column of the molten jet breaks up and disappears. In the present study, the jet breakup length is defined as the distance from the water surface to the location where the jet column disappears. The results show that the jet breakup length depends on the injection nozzle diameter, but does not depend on the jet penetration velocity. This tendency agrees with the prediction by Epstein's equation. After the experiment, the solidified fragments are collected and the mass median diameter is measured. The mass median diameter is compared with the existing theories. Furthermore, a model to estimate the cooling possibility during a CDA of a FBR is constructed, reflecting the above-mentioned results.

A Comprehensive Analysis ofSwiftXRT Data. III. Jet Break Candidates in X‐Ray and Optical Afterglow Light Curves

The Swift XRT data for 179 GRBs (050124 to 070129) and the optical afterglow data for 57 pre- and post-Swift GRBs are analyzed to explore whether the observed breaks in the afterglow light curves can be interpreted as jet breaks, as well as their implications for jet energetics. We find that no burst is included in our Platinum sample, in which the data fully satisfy the jet break criteria. By relaxing one or more of the requirements for a jet break, candidates to various degrees are identified. In the X-ray band, 42 of 103 well-sampled X-ray light curves have a decay slope greater than or similar to 1.5 in the postbreak segment (the Bronze sample), and 27 of these also satisfy the closure relations of the forward-shock models (Silver sample). The numbers of Bronze and Silver candidates in the optical light curves are 27 and 23, respectively. The X-ray break time is earlier than that in the optical bands. Among 13 bursts having both optical and X-ray light curves, only seven have an achromatic break, and even in these cases, only in one band do the data satisfy the closure relations (Gold sample). These results raise concerns about interpreting the breaks as jet breaks and further inferring GRB energetics. Assuming that the Silver and Gold breaks are jet breaks, we derive jet opening angles (theta(j)) and kinetic energies (E(K)) or lower limits on them and find that the EK distribution is much more scattered than the pre-Swift sample, but a tentative anticorrelation between theta(j) and E(K,iso) is found, indicating that the E(K) could still be quasi-universal.

Inkjet printing - the physics of manipulating liquid jets and drops

Over the last 30 years inkjet printing technology has been developed for many applications including: product date codes, mailing shots, desktop printing, large-area graphics and, most recently, the direct writing of materials to form electronic, biological, polymeric and metallic devices. The new non-graphical applications require higher print rates, better resolution and higher reliability while printing more complex, non-Newtonian and heavily solids-loaded liquids. This makes the understanding of the physics involved in the precise manipulation of liquid jets and drops ever more important. The proper understanding and control of jet formation and subsequent motion of the jetted materials requires physical studies into material properties at very high shear rates, acoustic modes in print heads, instabilities of jets, drop formation, drop motion, stretching of fluid ligaments, the role of polymers in jet break up, electrical charging of drops and the aerodynamic and electrostatic interaction of jets and drops in flight. Techniques for observation, measurement and analysis are evolving to assist these studies. This paper presents some examples of the application of physics to understanding and implementing inkjet printing, including recent work at the Cambridge Inkjet Research Centre.