Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userA tale of two transients: GW170104 and GRB170105A
87
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We present multi-wavelength follow-up campaigns by the AstroSat-CZTI and GROWTH collaborations to search for an electromagnetic counterpart to the gravitational wave event GW170104. At the time of the GW170104 trigger, the AstroSat CZTI field-of-view covered 50.3% of the sky localization. We do not detect any hard X-ray (>100 keV) signal at this time, and place an upper limit of $approx 4.5 times 10^{-7}~{rm erg~cm}^{-2}{rm~s}^{-1}$ for a 1,s timescale. Separately, the ATLAS survey reported a rapidly fading optical source dubbed ATLAS17aeu in the error circle of GW170104. Our panchromatic investigation of ATLAS17aeu shows that it is the afterglow of an unrelated long, soft GRB~170105A, with only a fortuitous spatial coincidence with GW170104. We then discuss the properties of this transient in the context of standard long GRB afterglow models.
rate research
Read More
We highlight similarities between recently discovered Rotating Radio Transients and X-ray Dim Isolated Neutron Stars. In particular, it is shown that X-ray Dim Isolated Neutron Stars have a birthrate comparable to that of Rotating Radio Transients. On the contrary, magnetars have too low a formation rate to account for the bulk of the radio transient population. The consequences of the recent detection of a thermal X-ray source associated with one of the Rotating Radio Transients on the proposed scenarios for these sources are also discussed.
We used data from the INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL) to set upper-limits on the ${gamma}$-ray and hard X-ray prompt emission associated with the gravitational wave event GW170104, discovered by the LIGO/Virgo collaboration. The unique omni-directional viewing capability of the instruments on-board INTEGRAL allowed us to examine the full 90% confidence level localization region of the LIGO trigger. Depending on the particular spectral model assumed and the specific position within this region, the upper limits inferred from the INTEGRAL observations range from F${gamma}$=1.9x10-7 erg cm-2 to F${gamma}$=10-6 erg cm-2 (75 keV - 2 MeV energy range). This translates into a ratio between the prompt energy released in ${gamma}$-rays along the direction to the observer and the gravitational wave energy of E${gamma}$/EGW <2.6x10-5 . Using the INTEGRAL results, we can not confirm the ${gamma}$-ray proposed counterpart to GW170104 by the AGILE team with the MCAL instrument. The reported flux of the AGILE/MCAL event, E2, is not compatible with the INTEGRAL upper limits within most of the 90% LIGO localization region. There is only a relatively limited portion of the sky where the sensitivity of the INTEGRAL instruments was not optimal and the lowest allowed fluence estimated for E2 would still be compatible with the INTEGRAL results. This region was also observed independently by Fermi/GBM and AstroSAT, from which, as far as we are aware, there are no reports of any significant detection of a prompt high-energy event.
We introduce a minimalist dynamical model of wealth evolution and wealth sharing among $N$ agents as a platform to compare the relative merits of altruism and individualism. In our model, the wealth of each agent independently evolves by diffusion. For a population of altruists, whenever any agent reaches zero wealth (that is, the agent goes bankrupt), the remaining wealth of the other $N-1$ agents is equally shared among all. The population is collectively defined to be bankrupt when its total wealth falls below a specified small threshold value. For individualists, each time an agent goes bankrupt (s)he is considered to be dead and no wealth redistribution occurs. We determine the evolution of wealth in these two societies. Altruism leads to more global median wealth at early times; eventually, however, the longest-lived individualists accumulate most of the wealth and are richer and more long lived than the altruists.
The Galactic Center (GC) has been long known to host gamma-ray emission detected to >10 TeV. HESS data now points to two plausible origins: the supermassive black hole (perhaps with >PeV cosmic rays and neutrinos) or high-energy electrons from the putative X-ray pulsar wind nebula G359.95-0.04 observed by Chandra and NuSTAR. We show that if the magnetic field experienced by PWN electrons is near the several mG ambient field strength suggested by radio observations of the nearby GC magnetar SGR J1745-29, synchrotron losses constrain the TeV gamma-ray output to be far below the data. Accounting for the peculiar geometry of GC infrared emission, we also find that the requisite TeV flux could be reached if the PWN is ~1 pc from Sgr A* and the magnetic field is two orders of magnitude weaker, a scenario that we discuss in relation to recent data and theoretical developments. Otherwise, Sgr A* is left, which would then be a PeV link to other AGN.
We present a detailed multi-wavelength analysis of two short Gamma-Ray Bursts (sGRBs) detected by the Neil Gehrels Swift Observatory: GRB 160624A at $z=0.483$ and GRB 200522A at $z=0.554$. These sGRBs demonstrate very different properties in their observed emission and environment. GRB 160624A is associated to a late-type galaxy with an old stellar population ($approx$3 Gyr) and moderate on-going star formation ($approx$1 $M_{odot}$ yr$^{-1}$). Hubble and Gemini limits on optical/nIR emission from GRB 160624A are among the most stringent for sGRBs, leading to tight constraints on the allowed kilonova properties. In particular, we rule out any kilonova brighter than AT2017gfo, disfavoring large masses of wind ejecta ($lesssim$0.03 $M_odot$). In contrast, observations of GRB 200522A uncovered a luminous ($L_textrm{F125W}approx 10^{42}$ erg s$^{-1}$ at 2.3~d) and red ($r-Happrox 1.3$ mag) counterpart. The red color can be explained either by bright kilonova emission powered by the radioactive decay of a large amount of wind ejecta (0.03 $M_odot$ $lesssim$ $M$ $lesssim$ 0.1 $M_odot$) or moderate extinction, $E(B-V)approx0.1-0.2$ mag, along the line of sight. The location of this sGRB in the inner regions of a young ($approx$0.1 Gyr) star-forming ($approx$2-6 $M_{odot}$ yr$^{-1}$) galaxy and the limited sampling of its counterpart do not allow us to rule out dust effects as contributing, at least in part, to the red color.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
