Search Publications
New Parallaxes of Galactic Cepheids from Spatially Scanning the Hubble Space Telescope: Implications for the Hubble Constant
Casertano, Stefano; Anderson, Jay; Filippenko, Alexei V. +8 more
We present new measurements of the parallax of seven long-period (≥10 days) Milky Way (MW) Cepheid variables (SS CMa, XY Car, VY Car, VX Per, WZ Sgr, X Pup, and S Vul) using one-dimensional astrometric measurements from spatial scanning of Wide-Field Camera 3 on the Hubble Space Telescope (HST). The observations were obtained at ∼6 month intervals…
GRB 170817A Associated with GW170817: Multi-frequency Observations and Modeling of Prompt Gamma-Ray Emission
Lyutikov, M.; Minaev, P. Yu.; Pozanenko, A. S. +7 more
We present our observations of electromagnetic transients associated with GW170817/GRB 170817A using optical telescopes of Chilescope observatory and Big Scanning Antenna (BSA) of Pushchino Radio Astronomy Observatory at 110 MHz. The Chilescope observatory detected an optical transient of ∼19m on the third day in the outskirts of the ga…
Gamma-Ray Burst Jet Breaks Revisited
Zhang, Bing; Lin, Da-Bin; Li, Jing +4 more
Gamma-ray Burst (GRB) collimation has been inferred with the observations of achromatic steepening in GRB light curves, known as jet breaks. Identifying a jet break from a GRB afterglow light curve allows a measurement of the jet opening angle and true energetics of GRBs. In this paper, we re-investigate this problem using a large sample of GRBs t…
Characteristics of Late-phase >100 MeV Gamma-Ray Emission in Solar Eruptive Events
White, S. M.; Dennis, B. R.; Murphy, R. J. +5 more
We characterize and catalog 30 solar eruptive events observed by the Fermi Large Area Telescope (LAT) having late-phase >100 MeV γ-ray emission (LPGRE), identified 30 yr ago in what were called long-duration gamma-ray flares. We show that LPGRE is temporally and spectrally distinct from impulsive phase emission in these events. The spectra are …
On the Rate and on the Gravitational Wave Emission of Short and Long GRBs
Rodriguez, J.; Wang, Y.; Barres de Almeida, U. +13 more
On the ground of the large number of gamma-ray bursts (GRBs) detected with cosmological redshift, we classified GRBs in seven subclasses, all with binary progenitors which emit gravitational waves (GWs). Each binary is composed of combinations of carbon-oxygen cores (COcore), neutron stars (NSs), black holes (BHs), and white dwarfs (WDs…
Onset of Photospheric Impacts and Helioseismic Waves in X9.3 Solar Flare of 2017 September 6
Kosovichev, Alexander G.; Sharykin, Ivan N.
The X9.3 flare of 2017 September 6, was the most powerful flare of Solar Cycle 24. It generated strong white-light emission and multiple helioseismic waves (sunquakes). By using data from the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory as well as hard X-ray (HXR) data from the KONUS instrument on board the WIND s…
Can a Bright and Energetic X-Ray Pulsar Be Hiding Amid the Debris of SN 1987A?
Esposito, Paolo; Rea, Nanda; Matsuura, Mikako +3 more
The mass of the stellar precursor of supernova (SN) 1987A and the burst of neutrinos observed at the moment of the explosion are consistent with the core-collapse formation of a neutron star. However, no compelling evidence for the presence of a compact object of any kind in SN 1987A has been found yet in any band of the electromagnetic spectrum, …
Fermi Transient J1544-0649: A Flaring Radio-weak BL Lac
Ubertini, Pietro; Bazzano, Angela; Panessa, Francesca +6 more
On 2017 May 15, the FERMI/LAT gamma-ray telescope observed a transient source not present in any previous high-energy catalog: J1544-0649. It was visible for two consecutive weeks, with a flux peak on May 21. Subsequently observed by a Swift/XRT follow-up starting on May 26, the X-ray counterpart position was coincident with the optical transient …
Period Analysis of Seven Field ab-type RR Lyrae Stars Based on O - C Diagrams: Cyclic Variations and Long-term Period Changes
Qian, S. -B.; Zhu, L. -Y.; Li, L. -J.
Using the times of light maximum collected from the GEOS RR Lyrae database and determined from sky surveys, we utilize the O - C method to study the period variations of seven field ab-type RR Lyrae stars. The time coverage of data for most stars is more than 100 years, allowing us to investigate period changes over a large time span. We find that…
The Influence of Stellar Spin on Ignition of Thermonuclear Runaways
Galloway, Duncan K.; Kuulkers, Erik; Chenevez, Jérôme +8 more
Runaway thermonuclear burning of a layer of accumulated fuel on the surface of a compact star provides a brief but intense display of stellar nuclear processes. For neutron stars accreting from a binary companion, these events manifest as thermonuclear (type-I) X-ray bursts, and recur on typical timescales of hours to days. We measured the burst r…