The Swift mission, scheduled for launch in 2004, is a multiwavelength observatory for gamma-ray burst (GRB) astronomy. It is a first-of-its-kind autonomous rapid-slewing satellite for transient astronomy and pioneers the way for future rapid-reaction and multiwavelength missions. It will be far more powerful than any previous GRB mission, observing more than 100 bursts yr � 1 and performing detailed X-ray and UV/optical afterglow observations spanning timescales from 1 minute to several days after the burst. The objectives are to (1) determine the origin of GRBs, (2) classify GRBs and search for new types, (3) study the interaction of the ultrarelativistic outflows of GRBs with their surrounding medium, and (4) use GRBs to study the early universe out to z >10. The mission is being developed by a NASA-led international collaboration. It will carry three instruments: a newgeneration wide-field gamma-ray (15‐150 keV) detector that will detect bursts, calculate 1 0 ‐4 0 positions, and trigger autonomous spacecraft slews; a narrow-field X-ray telescope that will give 5 00 positions and perform spectroscopy in the 0.2‐10 keV band; and a narrow-field UV/optical telescope that will operate in the 170‐ 600 nm band and provide 0B3 positions and optical finding charts. Redshift determinations will be made for most bursts. In addition to the primary GRB science, the mission will perform a hard X-ray survey to a sensitivity of � 1m crab (� 2;10 � 11 ergs cm � 2 s � 1 in the 15‐150 keV band), more than an order of magnitude better than HEAO 1 A-4. A flexible data and operations system will allow rapid follow-up observations of all types of

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The Swift Gamma-Ray Burst Mission

Supermassive black holes (BHs) have been found in 85 galaxies by dynamical modeling of spatially resolved kinematics. The Hubble Space Telescope revolutionized BH research by advancing the subject from its proof-of-concept phase into quantitative studies of BH demographics. Most influential was the discovery of a tight correlation between BH mass and the velocity dispersion σ of the bulge component of the host galaxy. Together with similar correlations with bulge luminosity and mass, this led to the widespread belief that BHs and bulges coevolve by regulating each other's growth. Conclusions based on one set of correlations from in brightest cluster ellipticals to in the smallest galaxies dominated BH work for more than a decade. New results are now replacing this simple story with a richer and more plausible picture in which BHs correlate differently with different galaxy components. A reasonable aim is to use this progress to refine our understanding of BH-galaxy coevolution. BHs with masses of 105−106M...

https://www.annualreviews.org/doi/suppl/10.1146/annurev-astro-082708-101811/suppl_file/aa51_kormendy_supmat.pdf

Coevolution (Or Not) of Supermassive Black Holes and Host Galaxies

On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of $\sim 1.7\,{\rm{s}}$ with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg2 at a luminosity distance of ${40}_{-8}^{+8}$ Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 $\,{M}_{\odot }$. An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at $\sim 40\,{\rm{Mpc}}$) less than 11 hours after the merger by the One-Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over ~10 days. Following early non-detections, X-ray and radio emission were discovered at the transient's position $\sim 9$ and $\sim 16$ days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC 4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta.

/pdf/multi-messenger-observations-of-a-binary-neutron-star-merger-3g2lxan5gn.pdf

Multi-messenger observations of a binary neutron star merger

On 2017 August 17, the gravitational-wave event GW170817 was observed by the Advanced LIGO and Virgo detectors, and the gamma-ray burst (GRB) GRB 170817A was observed independently by the Fermi Gamma-ray Burst Monitor, and the Anti-Coincidence Shield for the Spectrometer for the International Gamma-Ray Astrophysics Laboratory. The probability of the near-simultaneous temporal and spatial observation of GRB 170817A and GW170817 occurring by chance is $5.0\times {10}^{-8}$. We therefore confirm binary neutron star mergers as a progenitor of short GRBs. The association of GW170817 and GRB 170817A provides new insight into fundamental physics and the origin of short GRBs. We use the observed time delay of $(+1.74\pm 0.05)\,{\rm{s}}$ between GRB 170817A and GW170817 to: (i) constrain the difference between the speed of gravity and the speed of light to be between $-3\times {10}^{-15}$ and $+7\times {10}^{-16}$ times the speed of light, (ii) place new bounds on the violation of Lorentz invariance, (iii) present a new test of the equivalence principle by constraining the Shapiro delay between gravitational and electromagnetic radiation. We also use the time delay to constrain the size and bulk Lorentz factor of the region emitting the gamma-rays. GRB 170817A is the closest short GRB with a known distance, but is between 2 and 6 orders of magnitude less energetic than other bursts with measured redshift. A new generation of gamma-ray detectors, and subthreshold searches in existing detectors, will be essential to detect similar short bursts at greater distances. Finally, we predict a joint detection rate for the Fermi Gamma-ray Burst Monitor and the Advanced LIGO and Virgo detectors of 0.1–1.4 per year during the 2018–2019 observing run and 0.3–1.7 per year at design sensitivity.

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Gravitational Waves and Gamma-Rays from a Binary Neutron Star Merger: GW170817 and GRB 170817A

New large-scale CO surveys of the first and second Galactic quadrants and the nearby molecular cloud complexes in Orion and Taurus, obtained with the CfA 1.2 m telescope, have been combined with 31 other surveys obtained over the past two decades with that instrument and a similar telescope on Cerro Tololo in Chile, to produce a new composite CO survey of the entire Milky Way. The survey consists of 488,000 spectra that Nyquist or beamwidth ( °) sample the entire Galactic plane over a strip 4°-10° wide in latitude, and beamwidth or ° sample nearly all large local clouds at higher latitudes. Compared with the previous composite CO survey of Dame et al. (1987), the new survey has 16 times more spectra, up to 3.4 times higher angular resolution, and up to 10 times higher sensitivity per unit solid angle. Each of the component surveys was integrated individually using clipping or moment masking to produce composite spatial and longitude-velocity maps of the Galaxy that display nearly all of the statistically significant emission in each survey but little noise. The composite maps provide detailed information on individual molecular clouds, suggest relationships between clouds and regions widely separated on the sky, and clearly display the main structural features of the molecular Galaxy. In addition, since the gas, dust, and Population I objects associated with molecular clouds contribute to the Galactic emission in every major wavelength band, the precise kinematic information provided by the present survey will form the foundation for many large-scale Galactic studies. A map of molecular column density predicted from complete and unbiased far-infrared and 21 cm surveys of the Galaxy was used both to determine the completeness of the present survey and to extrapolate it to the entire sky at |b| 5°), X shows little systematic variation with latitude from a mean value of (1.8 ± 0.3) × 1020 cm-2 K-1 km-1 s. Given the large sky area and large quantity of CO data analyzed, we conclude that this is the most reliable measurement to date of the mean X value in the solar neighborhood.

https://iopscience.iop.org/article/10.1086/318388/pdf

The Milky Way in Molecular Clouds: A New Complete CO Survey

We investigate the rates at which energy is supplied to individual p-modes as a function of their frequencies
v and angular degrees l. The observationally determined rates are compared with those calculated on the hypothesis that the modes are stochastically excited by turbulent convection. The observationally determined excitation rate is assumed to be equal to the product of the mode's energy
E and its (radian) line width Г. We obtain E from the mode's mean square surface velocity with the aid of its
velocity eigenfunction. We assume that Г measures the mode's energy decay rate, even though quasi-elastic
scattering may dominate true absorption. At fixed l, EГ rises as v^7 at low v, reaches a peak at v ≈ 3.5 mHz,
and then declines as v^(-4•4) at higher v. At fixed v, EГ exhibits a slow decline with increasing l. To calculate energy input rates, P_ α, we rely on the mixing-length model of turbulent convection. We find entropy fluctuations to be about an order of magnitude more effective than the Reynolds stress in exciting p-modes. The calculated P_ α mimic the v^7 dependence of EГ at low v and the v^(-4•4) dependence at high v. The break of 11.4 powers in the v-dependence of EГ across its peak is attributed to a combination of (1) the reflection of high-frequency acoustic waves just below the photosphere where the scale height drops precipitously and (2) the absence of energy-bearing eddies with short enough correlation times to excite high-frequency modes. Two parameters associated with the eddy correlation time are required to match the
location and shape of the break. The appropriate values of these parameters, while not unnatural, are poorly
constrained by theory. The calculated P_ α can also be made to fit the magnitude of EГ with a reasonable value
for the eddy aspect ratio. Our results suggest a possible explanation for the decline of mode energy with increasing l at fixed v. Entropy fluctuations couple to changes in volume associated with the oscillation mode. These decrease with decreasing n at fixed v, becoming almost zero for the ƒ-mode.

Excitation of solar p-modes

We carry out a numerical hydrodynamical modeling for the evolution of a relativistic collimated outflow as it interacts with the surrounding medium and calculate the light curve resulting from synchrotron emission of the shocked fluid. The hydrodynamic equations are reduced to one-dimensional by assuming axial symmetry and integrating over the radial profile of the flow, thus considerably reducing the computation time. We present results for a number of different initial jet structures, including several different power laws and a Gaussian profile for the dependence of the energy per unit solid angle, � , and the Lorentz factor, C, on the angle from the jet symmetry axis. Our choice of parameters for the various calculations is motivated by the current knowledge of relativistic outflows from gamma-ray bursts and the observed afterglow light curves. Comparison of the light curves for different jet profiles with gamma-ray burst afterglow observations provides constraints on the jet structure. One of the main results we find is that the transverse fluid velocity in the comoving frame (vt) and the speed of sideways expansion for smooth jet profiles is typically much smaller than the speed of sound (cs) throughout much of the evolution of the jet; vt approaches cs when C along the

/pdf/the-evolution-of-a-structured-relativistic-jet-and-gamma-ray-5e2n86220b.pdf

The evolution of a structured relativistic jet and gamma-ray burst afterglow light curves

We model the radio, optical, and X-ray emission for the afterglows of GRB 980703, GRB 990123, GRB 990510, and GRB 991216, within the framework of relativistic jets, to determine their physical parameters. The models that yield acceptable fits to the data have jet energies mostly between 1050 and 1051 ergs and initial opening angles between 1° and 4°. The external medium density is uncertain by at least 1 order of magnitude in each case, being around 10-3 cm-3 for GRB 980703 and GRB 990123, ~10-1 cm-3 for GRB 990510, and ~3 cm-3 for GRB 991216. If the jets are uniform (i.e., there are no angular gradients of the energy per solid angle), then the 20 keV-1 MeV radiative efficiency during the GRB phase must have been at least 2%-3% for GRB 990510, 20% for GRB 990123, and 30% for GRB 991216.

https://iopscience.iop.org/article/10.1086/321388/pdf

Jet Energy and Other Parameters for the Afterglows of GRB 980703, GRB 990123, GRB 990510, and GRB 991216 Determined from Modeling of Multifrequency Data

We consider wave generation by turbulent convection in a plane parallel, stratified atmosphere that sits in a
gravitational field, g. The atmosphere consists of two semi-infinite layers, the lower adiabatic and polytropic
and the upper isothermal. The adiabatic layer supports a convective energy flux given by mixing length theory; F_c ~ pv^3_H, where p is mass density and v_H is the velocity of the energy bearing turbulent eddies. Acoustic waves with ω > ω_(ɑc) and gravity waves with ω < 2k_h H_iωb propagate in the isothermal layer whose acoustic cutoff frequency, ω_(ac), and Brunt-Vaisala frequency, ω_b, satisfy ω^2_(ɑc) = yg/4H_i and ω^2_b = (y-1)g/yH_i, where y and H_i denote the adiabatic index and scale height. The atmosphere traps acoustic waves in upper part of the adiabatic layer (p-modes) and gravity waves on the interface between the adiabatic and isothermal layers (f-modes). These modes obey the dispersion relation ω^2≈2/m gk_h(n + m/2), for ω < ω_(ɑc). Here, m is the polytropic index, k_h is the magnitude of the horizontal wave vector, and n is the
number of nodes in the radial displacement eigenfunction; n = 0 for f-modes. Wave generation is concentrated at the top of the convection zone since the turbulent Mach number, M =
v_H/c, peaks there; we assume M_t « 1. The dimensionless efficiency, η, for the conversion of the energy carried
by convection into wave energy is calculated to be η~M_t^(5/12) for p-modes,f-modes, and propagating acoustic
waves, and η~M, for propagating gravity waves. Most of the energy going into p-modes, f-modes, and propagating
acoustic waves is emitted by inertial range eddies of size h ~ M_t^(3/2)H_t, at ω ~ ω_(ɑc) and k_h ~ 1/H_t. The
energy emission into propagating gravity waves is dominated by energy bearing eddies of size ~ H_t and is concentrated at ω ~ v_t/H_t ~ M_t ω_(ɑc) and k_h ~ 1/H_t. We find the power input to individual p-modes, E_p, to vary as ω<^(2m^2+7m-3)/(m+3) at frequencies ω « v_t/H_t. Libbrecht has shown that the amplitudes and linewidths of the solar p-modes imply E_p ∝ ω^8 for ω « 2 x 10^(-2) s^(-1). The theoretical exponent matches the observational one for m ≈ 4, a value obtained from the density profile in the upper part of the solar convection zone. This agreement supports the hypothesis that the solar p-modes are stochastically excited by turbulent convection.

/pdf/wave-generation-by-turbulent-convection-26nbf652mg.pdf

Wave generation by turbulent convection

We carry out a numerical hydrodynamical modeling for the evolution of a relativistic collimated outflow, as it interacts with the surrounding medium, and calculate the light-curve resulting from synchrotron emission of the shocked fluid. The hydrodynamic equations are reduced to 1-D by assuming axial symmetry and integrating over the radial profile of the flow, thus considerably reducing the computation time. We present results for a number of different initial jet structures, including several different power-laws and a Gaussian profile for the dependence of the energy per unit solid angle, $\epsilon$, and the Lorentz factor, $\Gamma$, on the angle from the jet symmetry axis. Our choice of parameters for the various calculations is motivated by the current knowledge of relativistic outflows from gamma-ray bursts and the observed afterglow light-curves. Comparison of the light curves for different jet profiles with GRB afterglow observations provides constraints on the jet structure. One of the main results we find is that the transverse fluid velocity in the comoving frame ($v_t$) and the speed of sideways expansion, for smooth jet profiles, is typically much smaller than the speed of sound ($c_s$) throughout much of the evolution of the jet; $v_t$ approaches $c_s$ when $\Gamma$ along the jet axis becomes of order a few (for large angular gradient of $\epsilon$, $v_t\sim c_s$ while $\Gamma$ is still large). This result suggests that the dynamics of relativistic structured jets may be reasonably described by a simple analytic model where $\epsilon$ is independent of time, as long as $\Gamma$ along the jet-axis is larger than a few.

Pawan Kumar

Papers

Excitation of solar p-modes

The evolution of a structured relativistic jet and gamma-ray burst afterglow light curves

Jet Energy and Other Parameters for the Afterglows of GRB 980703, GRB 990123, GRB 990510, and GRB 991216 Determined from Modeling of Multifrequency Data

Wave generation by turbulent convection

The Evolution of a Structured Relativistic Jet and GRB Afterglow Light-Curves