arXiv subjects

Andrew J. Levan

Publications and source records attributed to Andrew J. Levan.

At least 37 records · Page 2Linked to original sources

arXiv2025

Gamma-ray Bursts

Gamma-ray bursts are flashes of high-energy radiation lasting from a fraction of a second to several hours. Military satellites made the first detections of GRBs in the late 1960s. The $γ$-ray emission forms from shocks in a relativistic jet launched from a compact central engine. In addition to the emission of $γ$-rays, the interaction of the jet with the surrounding medium yields afterglow emission that can be observed across the electromagnetic spectrum. Redshift measurements from these afterglows place GRBs from the local to the distant Universe. The central engines of GRBs are thought to be either a hyperaccreting black hole or a highly magnetized neutron star (magnetar). There is now strong observational evidence that this central engine is created either in the core collapse of a rapidly rotating massive star or via the merger of two compact objects (neutron stars or a neutron star with a black hole). The combination of stellar scale events with extreme energies and luminosities makes GRBs powerful probes of the extreme physics involved in their production and of other areas of astrophysics and cosmology. These include as the electromagnetic counterparts of gravitational wave sources, the production and acceleration of relativistic jets, the synthesis of heavy elements, the study of the interstellar and intergalactic medium, and the identification of the collapse of early generations of stars.

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arXiv2025

JWST Spectroscopy of GRB 250702B: An Extremely Rare and Exceptionally Energetic Burst in a Dusty, Massive Galaxy at $z=1.036$

We present follow-up observations of the day-long, repeating GRB 250702B with the Near Infrared Spectrograph (NIRSpec) on board the James Webb Space Telescope (JWST). Through the identification of narrow hydrogen emission lines at a consistent redshift of $z = 1.036 \pm 0.004$, we calibrate the distance scale, and therefore the energetics, of this unique extragalactic transient. At this distance, the resulting $γ$-ray energy release is at least $E_{γ,\rm iso} = 2.2 \times 10^{54}$\,erg. We find no evidence for ongoing transient emission at the GRB position, and exclude any accompanying supernova with a luminosity comparable to the Type Ic broad-line SN 2023lcr, though we are unable to constrain fainter events. The inferred rate of such events, assuming at most one in the lifetime of {\em Fermi}, suggests that such bursts are very rare, with volumetric rates $>1,000$ times lower than normal high luminosity long GRBs and $> 10^5$ times lower than core collapse supernovae when corrected for beaming. Furthermore, we find that the host galaxy is unique amongst GRB host galaxies, and extremely rare in the general galaxy population, being extremely large, dusty and with high stellar mass. The identification of such an exotic GRB in such an unusual galaxy raises the possibility that the environment was important in the progenitor channel for this event.

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arXiv2025

The day-long, repeating GRB 250702BDE / EP250702a: A unique extragalactic transient

Gamma-ray bursts (GRBs) are singular outbursts of high-energy radiation with durations typically lasting from milliseconds to minutes and, in extreme cases, a few hours. They are attributed to the catastrophic outcomes of stellar-scale events and, as such, are not expected to recur. Here, we present observations of an exceptional GRB\,250702BDE which triggered the {\em Fermi} gamma-ray burst monitor on three occasions over several hours, and which was detected in soft X-rays by the \textit{Einstein Probe} a day before the $γ$-ray triggers (EP250702a). We present the discovery of an extremely red infrared counterpart of the event with the VLT, as well as radio observations from MeerKAT. Hubble Space Telescope observations pinpoint the source to a non-nuclear location in a host galaxy with complex morphology, implying GRB 250702BDE is an extragalactic event. The multi-wavelength counterpart is well described with standard afterglow models at a relatively low redshift $z \sim 0.2$, but the prompt emission does not readily fit within the expectations for either collapsar or merger-driven GRBs. Indeed, a striking feature of the multiple prompt outbursts is that the third occurs at an integer multiple of the interval between the first two. Although not conclusive, this could be indicative of periodicity in the progenitor system. We discuss several possible scenarios to explain the exceptional properties of the burst, which suggest that either a very unusual collapsar or the tidal disruption of a white dwarf by an intermediate-mass black hole are plausible explanations for this unprecedented GRB.

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arXiv2025

A kinematically constrained kick distribution for isolated neutron stars

The magnitudes of the velocity kicks that neutron stars (NSs) obtain at their formation have long been a topic of discussion. In previous work, a novel method was proposed to determine kicks based on the eccentricity of Galactic trajectories. We applied this method to the isolated pulsars with known parallax in order to kinematically constrain the NS natal kick distribution. We assumed the velocity vectors of the pulsars to be distributed isotropically in the local standard of rest frame, and for each pulsar we sampled 100 velocities taking into account this assumption. These velocity vectors were used to trace back the trajectories of the NSs through the Galaxy and estimate their eccentricity. Then, we simulated kicked objects in order to evaluate the relationship between kick magnitude and Galactic eccentricity, which was used to infer the kicks corresponding to the estimated eccentricities. The resulting kick distributions indeed show a bimodal structure for young pulsars and our fits resemble the ones from literature well. However, for older pulsars the bimodality vanishes and instead we find a log-normal kick distribution peaking at ~200 km/s and a median of ~400 km/s. We also compare our methods to literature that suggests natal kicks are significantly higher and follow a Maxwellian with $σ=265$ km/s. We cannot reproduce these results using their sample and distance estimates, and instead find kicks that are consistent with our proposed distribution. We conclude that our kinematically constrained kick distribution is well-described by a log-normal distribution with $μ=6.38$ and $σ=1.01$, normalised between 0 and 1000 km/s. This analysis reveals no evidence for bimodality in the larger sample, and we suggest that the bimodality found by existing literature may be caused by their relatively small sample size.

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arXiv2025

The kangaroo's first hop: the early fast cooling phase of EP250108a/SN 2025kg

Fast X-ray transients (FXTs) are a rare and poorly understood population of events. Previously difficult to detect in real time, the launch of the Einstein Probe with its wide field X-ray telescope has led to a rapid expansion in the sample and allowed the exploration of these transients across the electromagnetic spectrum. EP250108a is a recently detected example linked to an optical counterpart, SN 2025kg, or 'the kangaroo'. Together with a companion paper (Rastinejad et al. 2025), we present our observing campaign and analysis of this event. In this letter, we focus on the early evolution of the optical counterpart over the first six days, including our measurement of the redshift of $z=0.17641$. We find that the source is well-modelled by a rapidly expanding cooling blackbody. We show the observed X-ray and radio properties are consistent with a collapsar-powered jet that is low energy ($\lesssim10^{51}$ erg) and/or fails to break out of the dense material surrounding it. While we examine the possibility that the optical emission emerges from the shock produced as the supernova ejecta expand into a dense shell of circumstellar material, due to our X-ray and radio inferences, we favour a model where it arises from a shocked cocoon resulting from the trapped jet. This makes SN 2025kg one of the few examples of this currently observationally rare event.

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arXiv2025

First joint absorption and T$_e$-based metallicity measured in a GRB host galaxy at $z=4.28$ using JWST/NIRSpec

We present the first gamma-ray burst (GRB) host galaxy with a measured absorption line and electron temperature (T$_e$) based metallicity, using the temperature sensitive [OIII]$λ$4363 auroral line detected in the JWST/NIRSpec spectrum of the host of GRB 050505 at redshift $z=4.28$. We find that the metallicity of the cold interstellar gas, derived from the absorption lines in the GRB afterglow, of 12 + log(O/H)$\sim 7.7$ is in reasonable agreement with the temperature-based emission line metallicity in the warm gas of the GRB host galaxy, which has values of 12 + log(O/H) = 7.80$\pm$0.19 and 7.96$\pm$0.21 for two common indicators. When using strong emission line diagnostics appropriate for high-z galaxies and sensitive to ionisation parameter, we find good agreement between the strong emission line metallicity and the other two methods. Our results imply that, for the host of GRB050505, mixing between the warm and the cold ISM along the line of sight to the GRB is efficient, and that GRB afterglow absorption lines can be a reliable tracer of the metallicity of the galaxy. If confirmed with a large sample, this suggest that metallicities determined via GRB afterglow spectroscopy can be used to trace cosmic chemical evolution to the earliest cosmic epochs and in galaxies far too faint for emission line spectroscopy, even for JWST.

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arXiv2025

Multi-messenger Gravitational Lensing

We introduce the rapidly emerging field of multi-messenger gravitational lensing - the discovery and science of gravitationally lensed phenomena in the distant universe through the combination of multiple messengers. This is framed by gravitational lensing phenomenology that has grown since the first discoveries in the 20th century, messengers that span 30 orders of magnitude in energy from high energy neutrinos to gravitational waves, and powerful "survey facilities" that are capable of continually scanning the sky for transient and variable sources. Within this context, the main focus is on discoveries and science that are feasible in the next 5-10 years with current and imminent technology including the LIGO-Virgo-KAGRA network of gravitational wave detectors, the Vera C. Rubin Observatory, and contemporaneous gamma/X-ray satellites and radio surveys. The scientific impact of even one multi-messenger gravitational lensing discovery will be transformational and reach across fundamental physics, cosmology and astrophysics. We describe these scientific opportunities and the key challenges along the path to achieving them. This article is the introduction to the Theme Issue of the Philosophical Transactions of The Royal Society A on the topic of Multi-messenger Gravitational Lensing, and describes the consensus that emerged at the associated Theo Murphy Discussion Meeting in March 2024.

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arXiv2025

EP240801a/XRF 240801B: An X-ray Flash Detected by the Einstein Probe and Implications of its Multiband Afterglow

We present multiband observations and analysis of EP240801a, a low-energy, extremely soft gamma-ray burst (GRB) discovered on August 1, 2024 by the Einstein Probe (EP) satellite, with a weak contemporaneous signal also detected by Fermi/GBM. Optical spectroscopy of the afterglow, obtained by GTC and Keck, identified the redshift of $z = 1.6734$. EP240801a exhibits a burst duration of 148 s in X-rays and 22.3 s in gamma-rays, with X-rays leading by 80.61 s. Spectral lag analysis indicates the gamma-ray signal arrived 8.3 s earlier than the X-rays. Joint spectral fitting of EP/WXT and Fermi/GBM data yields an isotropic energy $E_{γ,\rm{iso}} = (5.57^{+0.54}_{-0.50})\times 10^{51}\,\rm{erg}$, a peak energy $E_{\rm{peak}} = 14.90^{+7.08}_{-4.71}\,\rm{keV}$, a fluence ratio $\rm S(25-50\,\rm{keV})/S(50-100\,\rm{keV}) = 1.67^{+0.74}_{-0.46}$, classifying EP240801a as an X-ray flash (XRF). The host-galaxy continuum spectrum, inferred using Prospector, was used to correct its contribution for the observed outburst optical data. Unusual early $R$-band behavior and EP/FXT observations suggest multiple components in the afterglow. Three models are considered: two-component jet model, forward-reverse shock model and forward-shock model with energy injection. Both three provide reasonable explanations. The two-component jet model and the energy injection model imply a relatively small initial energy and velocity of the jet in the line of sight, while the forward-reverse shock model remains typical. Under the two-component jet model, EP240801a may resemble GRB 221009A (BOAT) if the bright narrow beam is viewed on-axis. Therefore, EP240801a can be interpreted as an off-beam (narrow) jet or an intrinsically weak GRB jet. Our findings provide crucial clues for uncovering the origin of XRFs.

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arXiv2024

A study on late time UV-emission in core collapse supernovae and the implications for the peculiar transient AT2018cow

Over time, core-collapse supernova (CCSN) spectra become redder due to dust formation and cooling of the SN ejecta. A UV detection of a CCSN at late times thus indicates an additional physical process such as interaction between the SN ejecta and the circumstellar material, or viewing down to the central engine of the explosion. Both these models have been proposed to explain the peculiar transient AT2018cow, a luminous fast blue optical transient that has been detected in the UV 2-4 years after the event with only marginal fading over this time period. To identify if the late-time UV detection of AT2018cow could indicate that it is a CCSN, we investigate if CCSNe are detected in the UV between 2-5 years after the explosion. We use a sample of 51 nearby (z<0.065) CCSNe observed with the Hubble Space Telescope within 2-5 years of discovery. We measure their brightness, or determine an upper limit on the emission through an artificial star experiment if there is no detection. For two CCSNe we detect a point source within the uncertainty region of the SN position. Both have a low chance alignment probability with bright objects within their host galaxies and are thus likely related to the SNe. Comparing the absolute UV magnitude of AT2018cow to the absolute UV magnitudes of the two potential SN detections, there is no evidence that a late-time UV detection of AT2018cow is atypical for interacting SNe. However, when limiting to CCSNe closer than AT2018cow, we see that it is brighter than the upper limits on most non-detections. Combined with a very small late time photospheric radius of AT2018cow, this leads us to conclude that AT2018cow's late-time UV detection was not driven by interaction. It suggests instead that we are possibly viewing the inner region of the explosion. Such properties are naturally expected in tidal disruption models and are less straightforward in supernova scenarios.

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arXiv2024

Rubin ToO 2024: Envisioning the Vera C. Rubin Observatory LSST Target of Opportunity program

The Legacy Survey of Space and Time (LSST) at Vera C. Rubin Observatory is planned to begin in the Fall of 2025. The LSST survey cadence has been designed via a community-driven process regulated by the Survey Cadence Optimization Committee (SCOC), which recommended up to 3% of the observing time to carry out Target of Opportunity (ToO) observations. Experts from the scientific community, Rubin Observatory personnel, and members of the SCOC were brought together to deliver a recommendation for the implementation of the ToO program during a workshop held in March 2024. Four main science cases were identified: gravitational wave multi-messenger astronomy, high energy neutrinos, Galactic supernovae, and small potentially hazardous asteroids possible impactors. Additional science cases were identified and briefly addressed in the documents, including lensed or poorly localized gamma-ray bursts and twilight discoveries. Trigger prioritization, automated response, and detailed strategies were discussed for each science case. This document represents the outcome of the Rubin ToO 2024 workshop, with additional contributions from members of the Rubin Science Collaborations. The implementation of the selection criteria and strategies presented in this document has been endorsed in the SCOC Phase 3 Recommendations document (PSTN-056). Although the ToO program is still to be finalized, this document serves as a baseline plan for ToO observations with the Rubin Observatory.

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arXiv2024

The Redshift of GRB 190829A/ SN 2019oyw: A Case Study of GRB-SN Evolution

The nearby long gamma-ray burst (GRB) 190829A was observed using the HST/WFC3/IR grisms about four weeks to 500 days after the burst. We find the spectral features of its associated supernova, SN 2019oyw, are redshifted by several thousands km/s compared to the redshift of the large spiral galaxy on which it is superposed. This velocity offset is seen in several features but most clearly in Ca II NIR triplet $λλ$ 8498, 8542, 8662 (CaIR3). We also analyze VLT/FORS and X-shooter spectra of the SN and find strong evolution with time of its P-Cygni features of CaIR3 from the blue to the red. However, comparison with a large sample of Type Ic-BL and Ic SNe shows no other object with the CaIR3 line as red as that of SN 2019oyw were it at the z = 0.0785 redshift of the disk galaxy. This implies that SN 2019oyw is either a highly unusual SN or is moving rapidly with respect to its apparent host. Indeed, using CaIR3 we find the redshift of SN 2019oyw is 0.0944 <= z <= 0.1156. The GRB-SN is superposed on a particularly dusty region of the massive spiral galaxy; therefore, while we see no sign of a small host galaxy behind the spiral, it could be obscured. Our work provides a surprising result on the origins of GRB 190829A, as well as insights into the time evolution of GRB-SNe spectra and a method for directly determining the redshift of a GRB-SN using the evolution of strong spectral features such as CaIR3.

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arXiv2024

The Einstein Probe transient EP240414a: Linking Fast X-ray Transients, Gamma-ray Bursts and Luminous Fast Blue Optical Transients

Detections of fast X-ray transients (FXTs) have been accrued over the last few decades. However, their origin has remained mysterious. There is now rapid progress thanks to timely discoveries and localisations with the Einstein Probe mission. Early results indicate that FXTs may frequently, but not always, be associated with gamma-ray bursts (GRBs). Here, we report on the multi-wavelength counterpart of FXT EP240414a, which has no reported gamma-ray counterpart. The transient is located 25.7~kpc in projection from a massive galaxy at $z=0.40$. We perform comprehensive photometric and spectroscopic follow-up. The optical light curve shows at least three distinct emission episodes with timescales of $\sim 1, 4$ and 15 days and peak absolute magnitudes of $M_R \sim -20$, $-21$, and $-19.5$, respectively. The optical spectrum at early times is extremely blue, inconsistent with afterglow emission. It may arise from the interaction of both jet and supernova shock waves with the stellar envelope and a dense circumstellar medium, as has been suggested for some Fast Blue Optical Transients (LFBOTs). At late times, the spectrum evolves to a broad-lined~Type~Ic supernova, similar to those seen in collapsar long-GRBs. This implies that the progenitor of EP240414a is a massive star creating a jet-forming supernova inside a dense envelope, resulting in an X-ray outburst with a luminosity of $\sim 10^{48}$ erg s$^{-1}$, and the complex observed optical/IR light curves. If correct, this argues for a causal link between the progenitors of long-GRBs, FXTs and LFBOTs.

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arXiv2024

Kinematic constraints on the ages and kick velocities of Galactic neutron star binaries

The systems creating binary neutron stars (BNSs) experience systemic kicks when one of the components goes supernova. The combined magnitude of these kicks is still a topic of debate, and has implications for the eventual location of the transient resulting from the merger of the binary. For example, the offsets of short-duration gamma-ray bursts (SGRBs) resulting from BNS mergers depend on the BNS kicks. We investigated Galactic BNSs, and traced their motion through the Galaxy. This enabled us to estimate their kinematic ages and construct a BNS kick distribution, based on their Galactic trajectories. We used the pulsar periods and their derivatives to estimate the characteristic spin-down ages of the binaries. Moreover, we used a Monte Carlo estimation of their present-day velocity vector in order to trace back their trajectory and estimate their kinematic ages. These trajectories, in turn, were used to determine the eccentricity of their Galactic orbit. Based on simulations of kicked objects in the Galactic potential, we investigated the relationship between this eccentricity and kick velocity, in order to constrain the kicks imparted to the binaries at birth. We find that the Galactic BNSs are likely older than $\sim40$ Myr, which means their current (scalar) galactocentric speeds are not representative of their initial kicks. However, we find a close relationship between the eccentricity of a Galactic trajectory and the experienced kick. Using this relation, we constrained the kicks of the Galactic BNSs, depending on the kind of isotropy assumed in estimating their velocity vectors. These kick velocities are well-described by a log-normal distribution peaking around $\sim40-50$ km/s, and coincide with the peculiar velocities of the binaries at their last disc crossing.

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arXiv2024

Redshifts of candidate host galaxies of four fast X-ray transients using VLT/MUSE

Fast X-ray transients (FXTs) are X-ray flares lasting minutes to hours. Multi-wavelength counterparts to these FXTs have been proven hard to find. As a result distance measurements are through indirect methods such as host galaxy identification. The three main models proposed for FXTs; supernova shock breakout emission (SN SBO), binary neutron star (BNS) mergers and tidal dirsuption events (TDEs) of an intermediate mass black hole (IMBH) disrupting a white dwarf (WD), have a different associated L$_{X, peak}$. Therefore obtaining the distance to FXTs will be a powerful probe to investigate the nature of these FXTs. We use VLT/MUSE observations of a sample of FXTs to report the redshift of between 13 and 22 galaxies per FXT and use these redshifts to calculate the distance, L$_{X, peak}$ and the projected offsets. We find L$_{X, peak}>10^{44}$ erg s$^{-1}$ if we assume any of the sources with a redshift measurement is the true host galaxy of the corresponding FXT. For XRT 100831 we find a very faint galaxy within the 1$σ$ uncertainty region with a chance alignment probability of 0.04. For XRT 060207 we find a candidate host galaxy at z = 0.939 with a low chance alignment probability. However, we also report the detection of a late-type star within the 3$σ$ uncertainty region with a similar chance alignment probability. For the remaining FXTs we find no sources within their 3$σ$ uncertainty regions. We rule out a SN SBO nature for all FXTs based on L$_{X, peak}$ and the projected offsets. For XRT 100831 we conclude the detected galaxy within the 1$σ$ uncertainty position is likely to be the host galaxy of this FXT. From the available information, we are not able to determine if XRT 060207 originated from the galaxy found within 1$σ$ of the FXT position or was due to a flare from the late-type star detected within the 3$σ$ uncertainty region.

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arXiv2024

Deceleration of kicked objects due to the Galactic potential

Various stellar objects experience a velocity kick at some point in their evolution. These include neutron stars and black holes at their birth or binary systems when one of the two components goes supernova. For most of these objects, the magnitude of the kick and its impact on the object dynamics remains a topic of debate. We investigate how kicks alter the velocity distribution of objects born in the Milky Way disc, both immediately after the kick and at later times, and whether these kicks are encoded in the observed population of Galactic neutron stars. We simulate the Galactic trajectories of point masses on circular orbits in the disc after being perturbed by an isotropic kick, with a Maxwellian distribution of magnitudes with $σ=265$ km/s. Then, we simulate the motion of these point masses for $200$ Myr. These trajectories are then evaluated, either for the Milky Way population as a whole or for those passing within two kiloparsecs of the Sun, to get the time evolution of the velocities. During the first $20$ Myr, the bulk velocity of kicked objects becomes temporarily aligned to the cylindrical radius, implying an anisotropy in the velocity orientations. Beyond this age, the velocity distribution shifts toward lower values and settles to a median of $\sim200$ km/s. Around the Sun, the distribution also loses its upper tail, primarily due to unbound objects escaping the Galaxy. We compare this to the velocities of Galactic pulsars and find that pulsars show a similar evolution with characteristic age. The shift of the velocity distribution is due to bound objects spending most of their orbits at larger radii after the kick. They are, therefore, decelerated by the Galactic potential. We find the same deceleration to be predicted for nearby objects and the total population and conclude it is also observed in Galactic pulsars.

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arXiv2024

The fast X-ray transient EP240315a: a z ~ 5 gamma-ray burst in a Lyman continuum leaking galaxy

The nature of the minute-to-hour long Fast X-ray Transients (FXTs) localised by telescopes such as Chandra, Swift, and XMM-Newton remains mysterious, with numerous models suggested for the events. Here, we report multi-wavelength observations of EP240315a, a 1600 s long transient detected by the Einstein Probe, showing it to have a redshift of z=4.859. We measure a low column density of neutral hydrogen, indicating that the event is embedded in a low-density environment, further supported by direct detection of leaking ionising Lyman-continuum. The observed properties are consistent with EP240315a being a long-duration gamma-ray burst, and these observations support an interpretation in which a significant fraction of the FXT population are lower-luminosity examples of similar events. Such transients are detectable at high redshifts by the Einstein Probe and, in the (near) future, out to even larger distances by SVOM, THESEUS, and Athena, providing samples of events into the epoch of reionisation.

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arXiv2024

Multi-messenger prospects for black hole - neutron star mergers in the O4 and O5 runs

The existence of merging black hole-neutron star (BHNS) binaries has been ascertained through the observation of their gravitational wave (GW) signals. However, to date, no definitive electromagnetic (EM) emission has been confidently associated with these mergers. Such an association could help unravel crucial information on these systems, for example, their BH spin distribution, the equation of state (EoS) of NS and the rate of heavy element production. We model the multi-messenger (MM) emission from BHNS mergers detectable during the fourth (O4) and fifth (O5) observing runs of the LIGO-Virgo-KAGRA GW detector network, in order to provide detailed predictions that can help enhance the effectiveness of observational efforts and extract the highest possible scientific information from such remarkable events. Our methodology is based on a population synthesis-approach, which includes the modelling of the signal-to-noise ratio of the GW signal in the detectors, the GW-inferred sky localization of the source, the kilonova (KN) optical and near-infrared light curves, the relativistic jet gamma-ray burst (GRB) prompt emission peak photon flux, and the GRB afterglow light curves in the radio, optical and X-ray bands. The resulting prospects for BHNS MM detections during O4 are not promising, with a GW detection rate of $15.0^{+15.4}_{-8.8}$ yr$^{-1}$, but joint MM rates of $\sim 10^{-1}$ yr$^{-1}$ for the KN and $\sim 10^{-2}$ yr$^{-1}$ for the jet-related emission. In O5 we find an overall increase in expected detection rates by around an order of magnitude, owing to both the enhanced sensitivity of the GW detector network, and the coming online of future EM facilities. Finally, we discuss direct searches for the GRB radio afterglow with large-field-of-view instruments as a new possible follow-up strategy in the context of ever-dimming prospects for KN detection.

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arXiv2023

The Galactic neutron star population II -- Systemic velocities and merger locations of binary neutron stars

The merger locations of binary neutron stars (BNSs) encode their galactic kinematics and provide insights into their connection to short gamma-ray bursts (SGRBs). In this work, we use the sample of Galactic BNSs with measured proper motions to investigate their kinematics and predict their merger locations. Using a synthetic image of the Milky Way and its Galactic potential we analyse the BNS mergers as seen from an extragalactic viewpoint and compare them to the location of SGRBs on and around their host galaxies. We find that the Galactocentric transverse velocities of the BNSs are similar in magnitude and direction to those of their Local Standards of Rest, which implies that the present-day systemic velocities are not isotropically oriented and the peculiar velocities might be as low as those of BNS progenitors. Both systemic and peculiar velocities fit a lognormal distribution, with the peculiar velocities being as low as $\sim 22-157$ km s$^{-1}$. We also find that the observed BNS sample is not representative of the whole Galactic population, but rather of systems born around the Sun's location with small peculiar velocities. When comparing the predicted BNS merger locations to SGRBs, we find that they cover the same range of projected offsets, host-normalized offsets, and fractional light. Therefore, the spread in SGRB locations can be reproduced by mergers of BNSs born in the Galactic disk with small peculiar velocities, although the median offset match is likely a coincidence due to the biased BNS sample.

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