Dynamics and collisions of episodic jets from black holes and accretion disk systems

In many astrophysical black hole systems, episodic jets of plasma blobs have been observed, which are much faster and more powerful than continuous jets. A magnetohydrodynamical model was proposed by Yuan et al. to study the formation of episodic jets in Sgr A＊. By taking Sgr A＊ and a stellar mass black hole as examples, we modify the model of Yuan et al. by including the effects of relativity, and further study the relativistic motion and expansion of episodic jets of plasma blobs. Then we study the collision between two consecutive ejections in the modified model, and calculate the magnetic energy released in the collision. Our results show two consecutive blobs can collide with each other, and the released magnetic energy is more than 1050 erg, which supports the idea that a gamma-ray burst is powered by the collision of episodic jets, as suggested by Yuan ＆ Zhang.

The Role of Jets in Exploding Supernovae and in Shaping their Remnants

I review studies of core collapse supernovae(CCSNe) and similar transient events that attribute major roles to jets in powering most CCSNe and in shaping their ejecta. I start with reviewing the jittering jets explosion mechanism that I take to power most CCSN explosions. Neutrino heating does play a role in boosting the jets. I compare the morphologies of some CCSN remnants to planetary nebulae to conclude that jets and instabilities are behind the shaping of their ejecta. I then discuss CCSNe that are descendants of rapidly rotating collapsing cores that result in fixed-axis jets(with small jittering) that shape bipolar ejecta. A large fraction of the bipolar CCSNe are superluminous supernovae(SLSNe). I conclude that modeling of SLSN light curves and bumps in the light curves must include jets, even when considering energetic magnetars and/or ejecta interaction with the circumstellar matter(CSM). I connect the properties of bipolar CCSNe to common envelope jets supernovae(CEJSNe) where an old neutron star or a black hole spirals-in inside the envelope and then inside the core of a red supergiant. I discuss how jets can shape the pre-explosion CSM, as in Supernova 1987A, and can power pre-explosion outbursts(precursors)in binary system progenitors of CCSNe and CEJSNe. Binary interaction also facilitates the launching of postexplosion jets.

Inference on disk-jet connection of MAXI J1836–194 from spectral analysis with the TCAF solution

Galactic transient black hole candidate(BHC)MAXI J1836–194 was discovered on 2011 Aug30,by MAXI/GSC and Swift/BAT.The source activity during this outburst continued for^3 months before entering into the quiescent state.It again became active in March 2012 and continued for another^2 months.In this paper,3-25 keV RXTE/PCA spectra from the 2011 outburst and 0.5-10.0 keV Swift/XRT data during its 2012 outburst are analyzed with the two-component advective flow(TCAF)model based fits files in XSPEC.We calculate the X-ray contributions coming from jets/outflow using a newly developed method based on the deviation of the TCAF model normalization.We also study the correlation between observed radio and estimated jet X-ray fluxes.The correlation indices(b)are found to be 1.79 and 0.61,when the 7.45 GHz Very Large Array(VLA)radio flux is correlated with the total X-ray and jet X-ray fluxes in 3-25 keV range respectively.It has been found that the jet contributes in X-rays up to a maximum of 86%during its 2011 outburst.This makes the BHC MAXI J1836–194 strongly jet dominated during the initial rising phase.

Gamma-Ray Bursts: Afterglows and Central Engines

Gamma-ray bursts (GRBs) are the most intense transient gamma-ray events in the sky; this, together with the strong evidence (the isotropic and inhomogeneous distribution of GRBs detected by BASTE) that they are located at cosmological distances, makes them the most energetic events ever known. For example, the observed radiation energies of some GRBs are equivalent to the total convertion into radiation of the mass energy of more than one solar mass. This is thousand times stronger than the energy of a supernova explosion. Some unconventional energy mechanism and extremely high conversion efficiency for these mysterious events are required. The discovery of host galaxies and association with supernovae at cosmological distances by the recently launched satellite of BeppoSAX and ground based radio and optical telescopes in GRB afterglow provides further support to the cosmological origin of GRBs and put strong constraints on their central engine. It is the aim of this article to review the possible central engines, energy mechanisms, dynamical and spectral evolution of GRBs, especially focusing on the afterglows in multi-wavebands.

Cylindrical Jet - Wind Interaction Model of Gamma-Ray Burst Afterglows

Observations on relativistic jets in radio galaxies, active galactic nuclei, and 'microquasars' revealed that many of these outflows are cylindrical, not conical. So it is worthwhile to investigate the evolution of cylindrical jets in gamma-ray bursts. We discuss afterglows from cylindrical jets in a wind environment. Numerical results as well as analytic solutions in some special cases are presented. Our light curves are steeper compared to those in the homogeneous interstellar medium case, carefully considered by Cheng, Huang & Lu. We conclude that some afterglows, used to be interpreted as isotropic fireballs in a wind environment, can be fitted as well by cylindrical jets interacting with a wind.

Spectral analysis of χ class data of GRS 1915+105 using TCAF solution

The class variable source GRS 1915+105 exhibits a wide range of time variabilities on timescales of a few seconds to a few days. Depending on the count rates in different energy bands and the nature of the conventional color-color diagram, the variabilities were classified into sixteen classes that were later sequenced in ascending order of Comptonization Efficiency(CE), which is the ratio of power-law and blackbody photons. However, CE estimation is based on an empirical model which does not provide us with a comprehensive picture regarding accretion flow dynamics around the central source. In reality, the accretion flow is comprised of two components: the high angular momentum Keplerian flow in the form of a radiatively efficient disk and a low angular momentum radiatively inefficient sub-Keplerian halo enveloping the disk. These two components contribute differently to the overall flux due to the differences in their radiative efficiencies. Therefore, it is necessary to analyze the spectral behaviors and time variabilities in terms of accretion rates. In χ class, X-ray flux is steady with no significant variation, however various χsubclasses are observed at different X-ray fluxes and variations of count rates across different χ subclasses must be linked to the variation of flow parameters such as the accretion rates, be it the Keplerian disk rate and/or the low angular momentum halo rate. This motivated us to analyze the spectra of the χ class data implementing the physical Two Component Advective Flow(TCAF) solution which directly extracts these two rates from spectral fits. We find that in the χ2,4 classes, which are reportedly devoid of significant outflows, the spectra could be fitted well applying the TCAF solution alone. In the χ1,3 classes, which are always linked with outflows, a cutoff power-law model is needed in addition to the TCAF solution.At the same time, the normalization required by this model along with the variation of photon index and exponential roll-off factor provides us with information on the relative dominance of the outflow in the latter two classes. TCAF fit also supplies us with the size and location of the Compton cloud along with its optical depth. Thus by fitting with TCAF, a physical understanding of the flow geometry in different χclasses of GRS 1915+105 has been obtained.

On the Jet Structures of GRB 050820A and GRB 070125

We present the broadband numerical modeling of afterglows for two remarkably bright long gamma-ray bursts(GRBs),GRB 050820 A and GRB 070125,with a wide range of observations from the radio band to the X-ray band.In our work,we fit light curves and constrain physical parameters using a standard forward shock model from the afterglowpy Python package,considering different jet structures and the jet lateral expansion.For GRB 050820 A,the constrained jet is close to a top-hat jet with an extremely small half opening angle of about 0.015 rad,and the circumburst matter density is as small as 10^(-7)cm^(-3),which suggests that this peculiar long GRB might originate from metal-poor stars with low mass-loss rates.To explain the late time optical light curves of GRB 070125,the effects of the lateral expansion and the participation factor of electrons that are accelerated by the shock have to be taken into account.The constrained results for GRB 070125 show that the jet is also close to a top-hat jet with a half opening angle of about 0.1 rad,the viewing angle is about 0.05 rad,the circumburst density is about 10 cm^(-3),and the participation factor is about 0.1.The jet energy of the two bursts is required to be~1051–1052 erg,which can be produced by a millisecond magnetar or a hyper-accreting black hole.

Molecular Gas and Dust in the Massive Star Forming Region S 233 IR

The massive star forming region S 233 IR is observed in the molecular lines CO J = 2–1, 3–2, NH3 (1,1), (2,2) and the 870 um dust continuum. Four submillimeter continuum sources, labelled SMM 1–4, are revealed in the 870 um dust emission. The main core, SMM1, is found to be associated with a deeply embedded near infrared cluster in the northeast; while the weaker source SMM2 coincides with a more evolved cluster in the southwest. The best fit spectral energy distribution of SMM1 gives an emissivity of β = 1.6, and temperatures of 32 K and 92 K for the cold- and hot-dust components. An SMM1 core mass of 246 M☉, and a total mass of 445 M☉ are estimated from the 870 um dust continuum emission. SMM1 is found to have a temperature gradient decreasing from inside out, indicative of the presence of interior heating sources. The total outflow gas mass as traced by the CO J = 3–2 emission is estimated to be 35 M☉. Low velocity outflows are also found in the NH3 (1,1) emission. The non-thermal dominant NH3 line width as well as the substantial core mass suggest that the SMM1 core is a ``turbulent, massive dense core', in the process of forming a group or a cluster of stars. The much higher star formation efficiency found in the southwest cluster supports the suggestion that this cluster is more evolved than the northeast one. Large near infrared photometric variations found in the source PCS-IR93, a previously found highly polarized nebulosity, indicate an underlying star showing the FU Orionis type of behavior.

Large-Scale Distribution of Herbig-Haro Objects in Taurus

We report our new results on Herbig-Haro (HH) objects in the star forming region of Taurus from a wide-field survey with the 60/90 cm Schmidt telescope of the Beijing Astronomical Observatory. This survey using CCD imaging with a narrow band [SII] filter and an intermediate band [BATC10] filter covered approximately 30 square degrees in Taurus. Besides confirming the known HH Objects in the region, we discovered seven new HH candidates, and groups. Six of these are HH 701A-B, HH 702A-D, HH 703, HH 704A-D, HH 705, HH 706 and the seventh is a group, a new component of HH 319, labeled HH 319B-D. Based on the large-scale distribution of pre-main-sequence (PMS) stars in Taurus, we analyze statistically the most probable distance from the HH objects to each PMS star, from which we estimate the typical timescale of these HH objects to be between (1.3?2.0)×104 yrs; and we also obtain the birth rates of HH objects: 0.447±0.198 for Class I PMS stars, 0.360±0.222 for Class II PMS stars, and ?0.148±0.234 for Class III PMS stars.

Near-Infrared Observations of the Massive Star Forming Region IRAS 23151+5912

Near-infrared images and K-band spectroscopy of the massive star-formingregion IRAS 23151+5912 are presented. The JHK′ images reveal an embedded infrared clusterassociated with infrared nebula, and the H_2 (2.12 μm) narrowband image provides for the first timeevidence of outflow activity associated with the cluster. That the cluster is young can be shown bythe high percentage of infrared excess sources and the outflow activity. We suggest an age of thecluster of ～ 10~6 yr. Eight young stars are found in the bright nebular core around IRAS23151+5912. By the color-magnitude diagrams of the cluster, we found five high-mass YSOs and fourintermediate-mass YSOs in the cluster. Eight H_2 emission features are discovered in the region witha scattered and non-axisymmetric distribution, indicating the existence of multiple outflows drivenby the cluster. Diffuse H_2 emission detected to the north and to the west of the cluster mayresult from UV leakage of the cluster. Brγ, H_2, and CIV emission lines are found in the K-bandspectrum of the brightest source, NIRS 19, indicating the presence of envelope, stellar wind, andshock in the circumstellar environment. We have estimated an O7-O9 spectral type for the centralmassive YSO (20 ～ 30 solar mass), with an age of less than 1 x 10~6 yr.

Fallback in bipolar planetary nebulae?

The subclass of bipolar Planetary Nebulae(PNe)exhibits well-defined low-power outflows and some shows shock-related equatorial spiderweb structures and hourglass structures surrounding these outflows.These structures are distinctly different from the phenomena associated with spherical and elliptical PNe and suggest a non-standard way to simultaneously energise both kinds of structures.This paper presents evidence from the published literature on bipolar PN Hb 12 and other sources in support of an alternative scenario for energising these structures by means of accretion from material shells deposited during earlier post-AGB and pre-PNe evolutionary stages.In addition to energising the bipolar outflow,a sub-Eddington accretion scenario could hydrodynamically explain the spiderweb and outer hourglass structures as oblique shockwaves for guiding the accreting material into the equatorial region of the source.Estimates of the accretion rate resulting from fallback-related spherical accretion could indeed help to drive a low-power outflow and contribute to the total luminosity of these sources.

Effect of Conversion Efficiency on Gamma-Ray Burst Energy

Beaming effect makes it possible that gamma-ray bursts have a standardenergy, but the gamma-ray energy release is sensitive to some parameters. Our attention is focusedon the effect of the gamma ray conversion efficiency (η_γ), which may range between 0.01 and 0.9,and which probably has a random value for different GRBs under certain conditions. Making use of theafterglow data from the literature, we carried out a complete correction to the conical openingangle formula. Within the framework of the conical jet model, we ran a simple Monte Carlo simulationfor random values of η_γ, and found that the gamma-ray energy release is narrowly clustered,whether we use a constant value of η_γ or random values for different gamma-ray bursts.

Near-Infrared Imaging Observations of the Orion A-W Star Forming Region

We carried out near-infrared imaging observations of the Ori A-W region using the Italian 1.5 m TIRGO infrared telescope at Gornergrat. A group of infrared objects is visible on the K band image, including an IRAS source (IRS 1). From its IRAS flux density the IRAS luminosity is derived to be 45L⊙, which shows that IRS 1 is a low-mass protostar. By superimposing the position of the VLA H2O maser on the K image, we can identify the less evolved object IRS 1 as the excitation source of the H2O maser, within a projected distance of 470AU. This would be evidence that the maser effect is associated with the youngest phase of stellar evolution. The first probable HH object candidate in the Ori A-W region is discovered from the H2S(1)1-0 observation. Comparing the position of the H2O maser with the direction of the molecular hydrogen emission in the region, we suggest that the observed H2O maser could be tracing the circumstellar disk of IRS 1.

A Search for High-velocity Gas Associated H_2O Masers and Ultracompact HII Regions

With the objective of studying the relationships between high-velocity gas and water maser emissions the results of a search from 95 IRAS sources for high-velocity gas associated with star forming molecular clouds are reported. 21 sources have been identified as molecular outflow candidates.

Constraint on the counter-jet emission in gamma-ray burst afterglows from GRB 980703

We present a numerical investigation of emission from the receding jet of gamma-ray bursts.It is found that the peak time of the receding jet emission is significantly affected by synchrotron self-absorption in radio wavelengths.However,the receding jet component is generally very weak.It is observable mainly for those nearby events in a dense environment.Although GRB 980703 has been observed in radio wavelengths for more than 1000 days,we argue that the receding jet emission still has not been detected for this event.Actually,it is completely submerged by the host galaxy.