GW230529 is the first compact binary coalescence detected by the
LIGO-Virgo-KAGRA collaboration with at least one component mass confidently in
the lower mass-gap, corresponding to the range ...3-5$M_{\odot}$. If interpreted
as a neutron star-black hole merger, this event has the most symmetric mass
ratio detected so far and therefore has a relatively high probability of
producing electromagnetic (EM) emission. However, no EM counterpart has been
reported. At the merger time $t_0$, Swift-BAT and Fermi-GBM together covered
100$\%$ of the sky. Performing a targeted search in a time window $t_0-20
\text{s},t_0+20 \text{s}$, we report no detection by the Swift-BAT and the
Fermi-GBM instruments. Combining the position-dependent $\gamma-$ray flux upper
limits and the gravitational-wave posterior distribution of luminosity
distance, sky localization and inclination angle of the binary, we derive
constraints on the characteristic luminosity and structure of the jet possibly
launched during the merger. Assuming a top-hat jet structure, we exclude at
90$\%$ credibility the presence of a jet which has at the same time an on-axis
isotropic luminosity $\gtrsim 10^{48}$ erg s$^{-1}$, in the bolometric band 1
keV-10 MeV, and a jet opening angle $\gtrsim 15$ deg. Similar constraints are
derived testing other assumptions about the jet structure profile. Excluding
GRB 170817A, the luminosity upper limits derived here are below the luminosity
of any GRB observed so far.
Gamma-ray bursts (GRBs) associated with gravitational wave events are, and will likely continue to be, viewed at a larger inclination than GRBs without gravitational wave detections. As demonstrated ...by the afterglow of GW170817, this requires an extension of the common GRB afterglow models which typically assume emission from an on-axis top hat jet. We present a characterization of the afterglows arising from structured jets, providing a framework covering both successful and choked jets. We compute new closure relations for structured jets and compare with the established relations for energy injection and refreshed shock models. The temporal slope before the jet break is found to be a simple function of the ratio between the viewing angle and effective opening angle of the jet. A numerical model to calculate synthetic light curves and spectra is publicly available as the open source Python package afterglowpy.
Kilonovae are ultraviolet, optical, and infrared transients powered by the radioactive decay of heavy elements following a neutron star merger. Joint observations of kilonovae and gravitational waves ...can offer key constraints on the source of Galactic \(r\)-process enrichment, among other astrophysical topics. However, robust constraints on heavy element production requires rapid kilonova detection (within \(\sim 1\) day of merger) as well as multi-wavelength observations across multiple epochs. In this study, we quantify the ability of 13 wide field-of-view instruments to detect kilonovae, leveraging a large grid of over 900 radiative transfer simulations with 54 viewing angles per simulation. We consider both current and upcoming instruments, collectively spanning the full kilonova spectrum. The Roman Space Telescope has the highest redshift reach of any instrument in the study, observing kilonovae out to \(z \sim 1\) within the first day post-merger. We demonstrate that BlackGEM, DECam, GOTO, the Vera C. Rubin Observatory's LSST, ULTRASAT, and VISTA can observe some kilonovae out to \(z \sim 0.1\) (\(\sim\)475 Mpc), while DDOTI, MeerLICHT, PRIME, \(Swift\)/UVOT, and ZTF are confined to more nearby observations. Furthermore, we provide a framework to infer kilonova ejecta properties following non-detections and explore variation in detectability with these ejecta parameters.
FRB 180916.J0158+65 is one of the nearest, periodically repeating, and actively bursting fast radio burst (FRB) which has been localized to the outskirts of a spiral galaxy. In this work we study the ...FRB with the hard X-ray \(14-195\) keV data from the Burst Alert Telescope (BAT) on board The Neil Gehrels Swift Observatory. BAT uses coded mask technology giving a localization of \(\lesssim 3\) arc-minute in the hard X-ray band, along with an accurate background estimation. BAT has been observing the source location in survey mode since February 2020. The survey mode observations involves background subtracted spectra, integrated over a time span ranging \(300-2000\) seconds, at the source location (from Feb 2020-Jan 2022). We analyzed all the \(\sim 230\) survey mode observations from BAT and checked for any signal in any of the observations. We did not detect any signal at \(>5\sigma\) confidence level in any of the observations. We could estimate a \(5\sigma\) upper limit on the \(14-195\) keV flux, which ranged between \(4.5\times 10^{-10} - 7.6\times 10^{-9}\, \rm erg\, cm^{-2}\, s^{-1}\). At the source distance this relates to a \(5\sigma\) upper limit on luminosity of \(5.08\times 10^{44}- 8.5\times 10^{45} \rm erg\, s^{-1}\). With this estimate, we could rule out any persistent X-ray emission, at the source location for these snapshots of BAT observations.
We report observations of the optical counterpart of the long gamma-ray burst (LGRB) GRB 221009A. Due to the extreme rarity of being both nearby (\(z = 0.151\)) and highly energetic ...(\(E_{\gamma,\mathrm{iso}} \geq 10^{54}\) erg), GRB 221009A offers a unique opportunity to probe the connection between massive star core collapse and relativistic jet formation across a very broad range of \(\gamma\)-ray properties. Adopting a phenomenological power-law model for the afterglow and host galaxy estimates from high-resolution Hubble Space Telescope imaging, we use Bayesian model comparison techniques to determine the likelihood of an associated SN contributing excess flux to the optical light curve. Though not conclusive, we find moderate evidence (\(K_{\rm{Bayes}}=10^{1.2}\)) for the presence of an additional component arising from an associated supernova, SN 2022xiw, and find that it must be substantially fainter (\(<\) 67% as bright at the 99% confidence interval) than SN 1998bw. Given the large and uncertain line-of-sight extinction, we attempt to constrain the supernova parameters (\(M_{\mathrm{Ni}}\), \(M_{\mathrm{ej}}\), and \(E_{\mathrm{KE}}\)) under several different assumptions with respect to the host galaxy's extinction. We find properties that are broadly consistent with previous GRB-associated SNe: \(M_{\rm{Ni}}=0.05\) - \(0.25 \, \rm{M_\odot}\), \(M_{\rm{ej}}=3.5\) - \(11.1 \, \rm{M_\odot}\), and \(E_{\rm{KE}} = (1.6\) - \(5.2) \times 10^{52} \, \rm{erg}\). We note that these properties are weakly constrained due to the faintness of the supernova with respect to the afterglow and host emission, but we do find a robust upper limit on the \(M_{\rm{Ni}}\) of \(M_{\rm{Ni}}<0.36\, \rm{M_\odot}\). Given the tremendous range in isotropic gamma-ray energy release exhibited by GRBs (7 orders of magnitude), the SN emission appears to be decoupled from the central engine in these systems.
Using deep and high-cadence gamma-ray burst (GRB) afterglow data from RATIR, we observe a sharp and achromatic light curve break 12.6 days after the GRB, accompanied by an approximately achromatic ...bump. Fitting of the optical, NIR, and X-ray data suggest a very narrow (2 degree) jet which remains collimated at late-time. We argue that the sharp light curve bump suggests an edge brightened jet, perhaps emitting only during a brief period of lateral jet expansion. The lightcurve also exhibits a gradual spectral evolution lasting \(>10\) days. The evolution of the flux can be modeled as \(\textrm{Flux} \sim \big(\frac{t}{20 \textrm{days}}\big)^\alpha \big(\frac{\lambda}{800 \textrm{nm}}\big)^\beta\), with a temporal slope \(\alpha=-0.956 \pm 0.003\) and a gradually time-varying spectral slope \(\beta = (0.60 \pm 0.07)+(0.26 \pm 0.06) \textrm{log}\big(\frac{t}{20 \rm{days}}\big)\).
Kilonovae are a rare class of astrophysical transients powered by the radioactive decay of nuclei heavier than iron, synthesized in the merger of two compact objects. Over the first few days, the ...kilonova evolution is dominated by a large number of radioactive isotopes contributing to the heating rate. On timescales of weeks to months, its behavior is predicted to differ depending on the ejecta composition and merger remnant. However, late-time observations of known kilonovae are either missing or limited. Here we report observations of a luminous red transient with a quasi-thermal spectrum, following an unusual gamma-ray burst of long duration. We classify this thermal emission as a kilonova and track its evolution up to two months after the burst. At these late times, the recession of the photospheric radius and the rapidly-decaying bolometric luminosity (\(L_{\rm bol}\propto t^{-2.7\pm 0.4}\)) support the recombination of lanthanide-rich ejecta as they cool.
Neutron star mergers produce a substantial amount of fast-moving ejecta, expanding outwardly for years after the merger. The interaction of these ejecta with the surrounding medium may produce a weak ...isotropic radio remnant, detectable in relatively nearby events. We use late-time radio observations of short duration gamma-ray bursts (sGRBs) to constrain this model. Two samples of events were studied: four sGRBs that are possibly in the local (<200 Mpc) universe were selected to constrain the remnant non-thermal emission from the sub-relativistic ejecta, whereas 17 sGRBs at cosmological distances were used to constrain the presence of a proto-magnetar central engine, possibly re-energezing the merger ejecta. We consider the case of GRB~170817A/GW170817, and find that in this case the early radio emission may be quenched by the jet blast-wave. In all cases, for ejecta mass range of M_ej \lesssim 10^{-2} (5 * 10^{-2}) M_sun, we can rule out very energetic merger ejecta E_ej \gtrsim 5 * 10^{52}(10^{53}) erg, thus excluding the presence of a powerful magnetar as a merger remnant.
FRB180301 is one of the most actively repeating fast radio bursts (FRBs) which has shown polarization angle changes in its radio burst emission, an indication for their likely origin in the ...magnetosphere of a highly-magnetized neutron star. We carried out a multi-wavelength campaign with the FAST radio telescope and NICER X-ray observatory to investigate any possible X-ray emission temporally coincident with the bright radio bursts. The observations took place on 2021 March 4, 9 and 19. We detected five bright radio bursts with FAST, four of which were strictly simultaneous with the NICER observations. The peak flux-density of the radio bursts ranged between \(28-105\) mJy, the burst fluence between \(27-170\) mJy-ms, and the burst durations between \(1.7-12.3\) ms. The radio bursts from FRB~180301 exhibited complex time domain structure, and sub-pulses were detected in individual bursts, with no significant circular polarisation. The linear degree of polarisation in L-band reduced significantly compared to the 2019 observations. We do not detect any X-ray emission in excess of the background during the 5ms, 10ms, 100ms, 1sec and 100sec time intervals at/around the radio-burst barycenter-corrected arrival times, at a \(>5\sigma\) confidence level. The \(5\sigma\) upper limits on the X-ray a) persistent flux is \(<7.64\times 10^{-12}\, \rm erg\, cm^{-2}\, s^{-1}\) , equivalent to \(L_{\rm X}<2.50 \times 10^{45} \rm erg\, s^{-1}\) and b) 5 ms fluence is \(<2\times 10^{-11} \rm erg\, cm^{-2}\), at the radio burst regions. Using the \(5\) ms X-ray fluence upper limit, we can estimate the radio efficiency \(\eta_{R/X} \equiv L_{\rm Radio}/L_{\rm X-ray} \gtrsim 10^{-8}\). The derived upper limit on \(\eta_{R/X}\) is consistent with both magnetospheric models and synchrotron maser models involving relativistic shocks.
IC443 is a supernova remnant located in a quite complex environment since it interacts with nearby clouds. Indications for the presence of overionized plasma have been found though the possible ...physical causes of overionization are still debated. Moreover, because of its peculiar position and proper motion, it is not clear if the pulsar wind nebula (PWN) within the remnant is the relic of the IC443 progenitor star or just a rambling one seen in projection on the remnant. Here we address the study of IC443 plasma in order to clarify the relationship PWN-remnant, the presence of overionization and the origin of the latter. We analyzed two \emph{XMM-Newton} observations producing background-subtracted, vignetting-corrected and mosaicked images in two different energy bands and we performed a spatially resolved spectral analysis of the X-ray emission. We identified an elongated (jet-like) structure with Mg-rich plasma in overionization. The head of the jet is interacting with a molecular cloud and the jet is aligned with the position of the PWN at the instant of the supernova explosion. Interestingly, the direction of the jet of ejecta is somehow consistent with the direction of the PWN jet. Our discovery of a jet of ejecta in IC443 enlarge the sample of core-collapse SNRs with collimated ejecta structures. IC443's jet is the first one which shows overionized plasma, possibly associated with the adiabatic expansion of ejecta. The match between the jet's direction and the original position of the PWN strongly supports the association between the neutron star and IC443.
