arXiv subjects

M. Marongiu

Publications and source records attributed to M. Marongiu.

At least 19 recordsLinked to original sources

arXiv2025

Broadband radio study of the supernova remnant Kes 73

Strong shocks occurring in supernova remnants (SNRs), and their interaction with an often anisotropic surrounding medium, make SNRs ideal laboratories for studying the production and acceleration of cosmic rays (CRs). Due to their complex morphology and phenomenology, different CR populations are expected to exist throughout the remnants, each characterized by its own energy spectrum. A comprehensive understanding of particle acceleration mechanisms and energetics in SNRs requires spatially resolved spectral and morphological studies. We want to highlight the crucial role of high-resolution radio images at high frequencies (> 10 GHz) for studying the spectral properties of different remnant regions and better constraining the models that describe their non-thermal emission from radio to $\gamma$-ray wavelengths. We studied the integrated radio spectrum of the SNR Kes 73 using single-dish observations performed with the Sardinia Radio Telescope (SRT) between 6.9 and 24.8 GHz, complemented by published data. The high-resolution map at 24.8 GHz was used to search for spatial variations in the spectral index across the remnant. We present the SRT images of Kes 73, providing the highest-frequency morphological and spectral characterization ever obtained for this source. By combining our 18.7 and 24.8 GHz maps with previously published interferometric images at 1.4 and 5 GHz, we identify a flatter spectrum in the western bright region compared to the rest of the shell. In the same region, we detect overlapping $^12$CO molecular emission and $\gamma$-ray radiation, providing strong evidence of SNR-molecular cloud interaction and enhanced CR production. We modelled the non-thermal radio to $\gamma$-ray emission from this region, favouring a lepto-hadronic scenario with a maximum electron energy of 1.1 TeV and a magnetic field strength of 25 $\mu$G.

astro-ph.HE↗

arXiv2024

Fires in the deep: The luminosity distribution of early-time gamma-ray-burst afterglows in light of the Gamow Explorer sensitivity requirements

Gamma-ray bursts (GRBs) are ideal probes of the Universe at high redshift (z > 5), pinpointing the locations of the earliest star-forming galaxies and providing bright backlights that can be used to spectrally fingerprint the intergalactic medium and host galaxy during the period of reionization. Future missions such as Gamow Explorer are being proposed to unlock this potential by increasing the rate of identification of high-z GRBs to rapidly trigger observations from 6-10 m ground telescopes, JWST, and the Extremely Large Telescopes. Gamow was proposed to the NASA 2021 Medium-Class Explorer (MIDEX) program as a fast-slewing satellite featuring a wide-field lobster-eye X-ray telescope (LEXT) to detect and localize GRBs, and a 30 cm narrow-field multi-channel photo-z infrared telescope (PIRT) to measure their photometric redshifts using the Lyman-alpha dropout technique. To derive the PIRT sensitivity requirement we compiled a complete sample of GRB optical-near-infrared afterglows from 2008 to 2021, adding a total of 66 new afterglows to our earlier sample, including all known high-z GRB afterglows. We performed full light-curve and spectral-energy-distribution analyses of these afterglows to derive their true luminosity at very early times. For all the light curves, where possible, we determined the brightness at the time of the initial finding chart of Gamow, at different high redshifts and in different NIR bands. We then followed the evolution of the luminosity to predict requirements for ground and space-based follow-up. We find that a PIRT sensitivity of 15 micro-Jy (21 mag AB) in a 500 s exposure simultaneously in five NIR bands within 1000s of the GRB trigger will meet the Gamow mission requirement to recover > 80% of all redshifts at z > 5.

astro-ph.HE↗

arXiv2024

Study of solar brightness profiles in the 18-26 GHz frequency range with INAF radio telescopes II. Evidence for coronal emission

One of the most important objectives of solar physics is the physical understanding of the solar atmosphere, the structure of which is also described in terms of the density (N) and temperature (T) distributions of the atmospheric matter. Several multi-frequency analyses show that the characteristics of these distributions are still debated, especially for the outer coronal emission. We aim to constrain the T and N distributions of the solar atmosphere through observations in the centimetric radio domain. We employ single-dish observations from two of the INAF radio telescopes at the K-band frequencies (18 - 26 GHz). We investigate the origin of the significant brightness temperature ($T_B$) level that we detected up to the upper corona ($\sim 800$ Mm of altitude with respect to the photospheric solar surface). To probe the physical origin of the atmospheric emission and to constrain instrumental biases, we reproduced the solar signal by convolving specific 2D antenna beam models. The analysis of the solar atmosphere is performed by adopting a physical model that assumes the thermal bremsstrahlung as the emission mechanism, with specific T and N distributions. The modelled $T_B$ profiles are compared with those observed by averaging solar maps obtained during the minimum of solar activity (2018 - 2020). The T and N distributions are compatible (within $25\%$ of uncertainty) with the model up to $\sim 60$ Mm and $\sim 100$ Mm of altitude, respectively. The analysis of the role of the antenna beam pattern on our solar maps proves the physical nature of the atmospheric emission in our images up to the coronal tails seen in our $T_B$ profiles. The challenging analysis of the coronal radio emission at higher altitudes, together with the data from satellite instruments will require further multi-frequency measurements.

astro-ph.SR↗

arXiv2024

Study of solar brightness profiles in the 18-26 GHz frequency range with INAF radio telescopes I: solar radius

The Sun is an extraordinary workbench, from which several fundamental astronomical parameters can be measured with high precision. Among these parameters, the solar radius $R_{\odot}$ plays an important role in several aspects, such as in evolutionary models. Despite the efforts in obtaining accurate measurements of $R_{\odot}$, the subject is still debated and measurements are puzzling and/or lacking in many frequency ranges. We aimed to determine the mean, equatorial, and polar radii of the Sun ($R_c$, $R_{eq}$, and $R_{pol}$) in the frequency range 18.1 - 26.1 GHz. We employed single-dish observations from the newly-appointed Medicina "Gavril Grueff" Radio Telescope and the Sardinia Radio Telescope (SRT) throughout 5 years, from 2018 to mid-2023, in the framework of the SunDish project for solar monitoring. Two methods to calculate the radius at radio frequencies are considered and compared. To assess the quality of our radius determinations, we also analysed the possible degrading effects of the antenna beam pattern on our solar maps, using two 2D-models. We carried out a correlation analysis with the evolution of the solar cycle through the calculation of Pearson's correlation coefficient $ρ$. We obtained several values for the solar radius - ranging between 959 and 994 arcsec - and $ρ$, with typical errors of a few arcsec. Our $R_{\odot}$ measurements, consistent with values reported in literature, suggest a weak prolatness of the solar limb ($R_{eq}$ > $R_{pol}$), although $R_{eq}$ and $R_{pol}$ are statistically compatible within 3$σ$ errors. The correlation analysis using the solar images from Grueff shows (1) a positive correlation between the solar activity and the temporal variation of $R_c$ (and $R_{eq}$) at all observing frequencies, and (2) a weak anti-correlation between the temporal variation of $R_{pol}$ and the solar activity at 25.8 GHz.

astro-ph.SR↗

arXiv2022

The role of the magnetic fields in GRB outflows

Gamma-ray bursts (GRBs) are bright extragalactic flashes of gamma-ray radiation and briefly the most energetic explosions in the Universe. Their catastrophic origin (the merger of compact objects or the collapse of massive stars) drives the formation of a newborn compact remnant (black hole or magnetar) that powers two highly relativistic jets. To distinguish between magnetized and baryonic jet models and ultimately determine the power source for these energetic explosions, our team studies the polarization of the light during the first minutes after the explosion (using novel instruments on fully autonomous telescopes around the globe) to directly probe the magnetic field properties in these extragalactic jets. This technology allowed the detection of highly polarized optical light in GRB 120308A and confirmed the presence of mildly magnetized jets with large-scale primordial magnetic fields in a reduced sample of GRBs (e.g. GRB 090102, GRB 110205A, GRB 101112A, GRB 160625B). Here we discuss the observations of the most energetic and first GRB detected at very high TeV energies, GRB 190114C, which opens a new frontier in GRB magnetic field studies suggesting that some jets can be launched highly magnetized and that the collapse and destruction of these magnetic fields at very early times may have powered the explosion itself. Additionally, our most recent polarimetric observations of the jet of GRB 141220A indicate that, when the jetted ejected material is decelerated by the surrounding environment, the magnetic field amplification mechanisms at the front shock (needed to generate the observed synchrotron emission) produce small magnetic domains. These measurements validate theoretical expectations and contrast with previous observations that suggest large magnetic domains in collisionless shocks (i.e. GRB 091208B).

astro-ph.HE↗

arXiv2022

A short gamma-ray burst from a proto-magnetar remnant

The contemporaneous detection of gravitational waves and gamma rays from the GW170817/GRB 170817A, followed by kilonova emission a day after, confirmed compact binary neutron-star mergers as progenitors of short-duration gamma-ray bursts (GRBs), and cosmic sources of heavy r-process nuclei. However, the nature (and lifespan) of the merger remnant and the energy reservoir powering these bright gamma-ray flashes remains debated, while the first minutes after the merger are unexplored at optical wavelengths. Here, we report the earliest discovery of bright thermal optical emission associated with the short GRB 180618A with extended gamma-ray emission, with ultraviolet and optical multicolour observations starting as soon as 1.4 minutes post-burst. The spectrum is consistent with a fast-fading afterglow and emerging thermal optical emission at 15 minutes post-burst, which fades abruptly and chromatically (flux density $F_ν \propto t^{-α}$, $α=4.6 \pm 0.3$) just 35 minutes after the GRB. Our observations from gamma rays to optical wavelengths are consistent with a hot nebula expanding at relativistic speeds, powered by the plasma winds from a newborn, rapidly-spinning and highly magnetized neutron star (i.e. a millisecond magnetar), whose rotational energy is released at a rate $L_{\rm th} \propto t^{-(2.22\pm 0.14)}$ to reheat the unbound merger-remnant material. These results suggest such neutron stars can survive the collapse to a black hole on timescales much larger than a few hundred milliseconds after the merger, and power the GRB itself through accretion. Bright thermal optical counterparts to binary merger gravitational wave sources may be common in future wide-field fast-cadence sky surveys.

astro-ph.HE↗

arXiv2022

Solar observations with single-dish INAF radio telescopes: continuum imaging in the 18-26 GHz range

We present a new solar radio imaging system implemented through the upgrade of the large single-dish telescopes of the Italian National Institute for Astrophysics (INAF), not originally conceived for solar observations. During the development and early science phase of the project (2018-2020), we obtained about 170 maps of the entire solar disk in the 18-26 GHz band, filling the observational gap in the field of solar imaging at these frequencies. These solar images have typical resolutions in the 0.7-2 arcmin range and a brightness temperature sensitivity <10 K. Accurate calibration adopting the Supernova Remnant Cas A as a flux reference, provided typical errors <3% for the estimation of the quiet-Sun level components and for active regions flux measurements. As a first early science result of the project, we present a catalog of radio continuum solar imaging observations with Medicina 32-m and SRT 64-m radio telescopes including the multi-wavelength identification of active regions, their brightness and spectral characterization. The interpretation of the observed emission as thermal bremsstrahlung components combined with gyro-magnetic variable emission pave the way to the use of our system for long-term monitoring of the Sun. We also discuss useful outcomes both for solar physics (e.g. study of the chromospheric network dynamics) and space weather applications (e.g. flare precursors studies).

astro-ph.SR↗

arXiv2022

Radio data challenge the broadband modelling of GRB160131A afterglow

Context. Gamma-ray burst (GRB) afterglows originate from the interaction between the relativistic ejecta and the surrounding medium. Consequently, their properties depend on several aspects: radiation mechanisms, relativistic shock micro-physics, circumburst environment, and the structure and geometry of the relativistic jet. While the standard afterglow model accounts for the overall spectral and temporal evolution for a number of GRBs, its validity limits emerge when the data set is particularly rich and constraining, especially in the radio band. Aims. We aimed to model the afterglow of the long GRB160131A (redshift $z = 0.972$), for which we collected a rich, broadband, and accurate data set, spanning from $6\times10^{8}$ to $7\times10^{17}$ Hz in frequency, and from 330 s to 160 days post burst in time. Methods. We modelled the spectral and temporal evolution of this GRB afterglow through two approaches: the adoption of empirical functions to model optical/X-rays data set, later assessing their compatibility with the radio domain; the inclusion of the entire multi-frequency data set simultaneously through the Python package named sAGa (Software for AfterGlow Analysis), to come up with an exhaustive and self-consistent description of the micro-physics, geometry, and dynamics of the afterglow. Results. From deep broadband analysis (from radio to X-ray frequencies) of the afterglow light curves, GRB160131A outflow shows evidence of jetted emission. Moreover, we observe dust extinction in the optical spectra, and energy injection in the optical/X-ray data. Radio spectra are characterised by several peaks, that could be due to either interstellar scintillation (ISS) effects or a multi-component structure. Conclusions. The inclusion of radio data in the broadband set of GRB160131A makes a self-consistent modelling hardly attainable within the standard model of GRB afterglows.

astro-ph.HE↗

arXiv2021

Coherence scale of magnetic fields generated in early-time forward shocks of GRBs

We report the earliest-ever detection of optical polarization from a GRB forward shock (GRB 141220A), measured $129.5-204.3\,$s after the burst using the multi-colour RINGO3 optical polarimeter on the 2-m fully autonomous robotic Liverpool Telescope. The temporal decay gradient of the optical light curves from $86\,$s to $\sim 2200\,$s post-burst is typical of classical forward shocks with $α= 1.091 \pm 0.008$. The low optical polarization $P_{BV} = 2.8_{- 1.6} ^{+ 2.0} \, \%$ (2$σ$) at mean time $\sim 168\,$s post-burst is compatible with being induced by the host galaxy dust ($A_{V, {\rm HG}}= 0.71 \pm 0.15 \,$mag), leaving low polarization intrinsic to the GRB emission itself -- as theoretically predicted for forward shocks and consistent with previous detections of low degrees of optical polarization in GRB afterglows observed hours to days after the burst. The current sample of early-time polarization data from forward shocks suggests polarization from (a) the Galactic and host galaxy dust properties (i.e. $P \sim 1\%-3\%$), (b) contribution from a polarized reverse shock (GRB deceleration time, jet magnetization) or (c) forward shock intrinsic polarization (i.e. $P \leq 2\%$), which depends on the magnetic field coherence length scale and the size of the observable emitting region (burst energetics, circumburst density).

astro-ph.HE↗

arXiv2021

Low frequency view of GRB 190114C reveals time varying shock micro-physics

We present radio and optical afterglow observations of the TeV-bright long Gamma Ray Burst (GRB) 190114C at a redshift of $z=0.425$, which was detected by the MAGIC telescope. Our observations with ALMA, ATCA, and uGMRT were obtained by our low frequency observing campaign and range from $\sim1$ to $\sim140$ days after the burst and the optical observations were done with three optical telescopes spanning up to $\sim25$ days after the burst. Long term radio/mm observations reveal the complex nature of the afterglow, which does not follow the spectral and temporal closure relations expected from the standard afterglow model. We find that the microphysical parameters of the external forward shock, representing the share of shock-created energy in the non-thermal electron population and magnetic field, are evolving with time. The inferred kinetic energy in the blast-wave depends strongly on the assumed ambient medium density profile, with a constant density medium demanding almost an order of magnitude higher energy than in the prompt emission, while a stellar wind-driven medium requires approximately the same amount energy as in prompt emission.

astro-ph.HE↗

arXiv2020

New high-frequency radio observations of the Cygnus Loop supernova remnant with the Italian radio telescopes

Supernova remnants (SNRs) represent a powerful laboratory to study the Cosmic-Ray acceleration processes at the shocks, and their relation to the properties of the circumstellar medium. With the aim of studying the high-frequency radio emission and investigating the energy distribution of accelerated electrons and the magnetic field conditions, we performed single-dish observations of the large and complex Cygnus Loop SNR from 7.0 to 24.8 GHz with the Medicina and the Sardinia Radio Telescope, focusing on the northern filament (NGC 6992) and the southern shell. Both regions show a spectrum well fitted by a power-law function ($S\proptoν^{-α}$), with spectral index $α=0.45\pm0.05$ for NGC 6992 and $α=0.49\pm0.01$ for the southern shell and without any indication of a spectral break. The spectra are significantly flatter than the whole Cygnus Loop spectrum ($α=0.54\pm0.01$), suggesting a departure from the plain shock acceleration mechanisms, which for NGC 6992 could be related to the ongoing transition towards a radiative shock. We model the integrated spectrum of the whole SNR considering the evolution of the maximum energy and magnetic field amplification. Through the radio spectral parameters, we infer a magnetic field at the shock of 10 $μ$G. This value is compatible with a pure adiabatic compression of the interstellar magnetic field, suggesting that the amplification process is currently inefficient.

astro-ph.HE↗

arXiv2020

Energy spread minimization in a beam-driven plasma wakefield accelerator

Next-generation plasma-based accelerators can push electron bunches to gigaelectronvolt energies within centimetre distances. The plasma, excited by a driver pulse, generates large electric fields that can efficiently accelerate a trailing witness bunch making possible the realization of laboratory-scale applications ranging from high-energy colliders to ultra-bright light sources. So far several experiments have demonstrated a significant acceleration but the resulting beam quality, especially the energy spread, is still far from state of the art conventional accelerators. Here we show the results of a beam-driven plasma acceleration experiment where we used an electron bunch as a driver followed by an ultra-short witness. The experiment demonstrates, for the first time, an innovative method to achieve an ultra-low energy spread of the accelerated witness of about 0.1%. This is an order of magnitude smaller than what has been obtained so far. The result can lead to a major breakthrough toward the optimization of the plasma acceleration process and its implementation in forthcoming compact machines for user-oriented applications.

physics.acc-ph↗

arXiv2020

Methods for detection and analysis of weak radio sources with single-dish radio telescopes

The detection of mJy/sub-mJy point sources is a significant challenge for single-dish radio telescopes. Detection or upper limits on the faint afterglow from GRBs or other sources at cosmological distances are important means of constraining the source modeling. Using the Sardinia Radio Telescope (SRT), we compare the sensitivity and robustness of three methods applied to the detection of faint radio sources from raster maps around a known source position: the smart quick-look method, the source extraction method (typical of high-energy astronomy), and the fit with a 2-D Gaussian. We developed a Python code specific for the analysis of point-like radio sources applied to the SRT C-band (6.9 GHz) observations of both undetected sources (GRB afterglows of 181201A and 190114C) and the detected Galactic X-ray binary GRS 1915+105. Our comparative analysis of the different detection methods made extensive use of simulations as a useful complement to actual radio observations. The best method for the SRT data analysis is the fit with a 2-D Gaussian, as it pushes down the sensitivity limits of single-dish observations -- with respect to more traditional techniques -- to ~ 1.8 mJy, improving by ~ 40 % compared with the initial value. This analysis shows that -- especially for faint sources -- good maps of the scanned region pre- or post-outburst are essential.

astro-ph.IM↗

arXiv2020

Lowly polarized light from a highly magnetized jet of GRB 190114C

We report multi-color optical imaging and polarimetry observations of the afterglow of the first TeV- detected gamma-ray burst, GRB 190114C, using RINGO3 and MASTER II polarimeters. Observations begin 31 s after the onset of the GRB and continue until $\sim 7000\,$s post-burst. The light curves reveal a chromatic break at $\sim 400- 500\,$s, with initial temporal decay $α= 1.669 \pm 0.013$ flattening to $α\sim 1$ post-break, which we model as a combination of reverse and forward-shock components, with magnetization parameter $R_{\rm B} \sim 70$. The observed polarization degree decreases from $7.7 \pm 1.1\%$ to $2-4\%$ during $52-109\,$s post-burst and remains steady at this level for the subsequent $\sim 2000$-s, at constant position angle. Broadband spectral energy distribution modeling of the afterglow confirms GRB 190114C is highly obscured (A$_{\rm v, HG} = 1.49 \pm 0.12 \,$mag; N$_{\rm H, HG}= (9.0 \pm 0.3) \times 10^{22}\,$cm$^{-2}$). We interpret the measured afterglow polarization as intrinsically low and dominated by dust, in contrast to ${\rm P} >10\%$ measured previously for other GRB reverse shocks, with a small contribution from polarized prompt photons in the first minute. We test whether 1st and higher-order inverse Compton scattering in a magnetized reverse shock can explain the low optical polarization and the sub-TeV emission but conclude neither is explained in the reverse shock Inverse Compton model. Instead, the unexpectedly low intrinsic polarization degree in GRB 190114C can be explained if large-scale jet magnetic fields are distorted on timescales prior to reverse shock emission.

astro-ph.HE↗

arXiv2020

A search for prompt gamma-ray counterparts to fast radio bursts in the Insight-HXMT data

No robust detection of prompt electromagnetic counterparts to fast radio bursts (FRBs) has yet been obtained, in spite of several multi-wavelength searches carried out so far. Specifically, X/gamma-ray counterparts are predicted by some models. We planned on searching for prompt gamma-ray counterparts in the Insight-Hard X-ray Modulation Telescope (Insight-HXMT) data, taking advantage of the unique combination of large effective area in the keV-MeV energy range and of sub-ms time resolution. We selected 39 FRBs that were promptly visible from the High-Energy (HE) instrument aboard Insight-HXMT. After calculating the expected arrival times at the location of the spacecraft, we searched for a significant excess in both individual and cumulative time profiles over a wide range of time resolutions, from several seconds down to sub-ms scales. Using the dispersion measures in excess of the Galactic terms, we estimated the upper limits on the redshifts. No convincing signal was found and for each FRB we constrained the gamma-ray isotropic-equivalent luminosity and the released energy as a function of emission timescale. For the nearest FRB source, the periodic repeater FRB180916.J0158+65, we find $L_{γ,iso}<5.5\times 10^{47}$ erg/s over 1 s, whereas $L_{γ,iso}<10^{49}-10^{51}$ erg/s for the bulk of FRBs. The same values scale up by a factor of ~100 for a ms-long emission. Even on a timescale comparable with that of the radio pulse itself no keV-MeV emission is observed. A systematic association with either long or short GRBs is ruled out with high confidence, except for subluminous events, as is the case for core-collapse of massive stars (long) or binary neutron star mergers (short) viewed off axis. Only giant flares from extra-galactic magnetars at least ten times more energetic than Galactic siblings are ruled out for the nearest FRB.

astro-ph.HE↗

arXiv2019

A cumulative search for hard X/$γ$-Ray emission associated with fast radio bursts in Fermi/GBM data

Context. Fast Radio Bursts (FRBs) are millisecond-long bursts uniquely detected at radio frequencies. FRB 131104 is the only case for which a $γ$-ray transient positionally and temporally consistent was claimed. This high-energy transient had a duration of $\sim400$~s and a 15-150~keV fluence $S_γ\sim4\times10^{-6}$ erg $\mathrm{cm}^{-2}$. However, the association with the FRB is still debated. Aims. We aim at testing the systematic presence of an associated transient high-energy counterpart throughout a sample of the FRB population. Methods. We used an approach like that used in machine learning methodologies to accurately model the highly-variable Fermi/GBM instrumental background on a time interval comparable to the duration of the proposed $γ$-ray counterpart of FRB 131104. A possible $γ$-ray signal is then constrained considering sample average lightcurves. Results. We constrain the fluence of the possible $γ$-ray signal in the 8-1000 keV band down to $6.4 \times 10^{-7}$ ($7.1 \times 10^{-8}$) erg cm$^{-2}$ for a 200-s (1-s) integration time. Furthermore, we found the radio-to-gamma fluence ratio to be $η>10^{8}$ Jy ms erg$^{-1}$ cm$^2$. Conclusions. Our fluence limits exclude $\sim 94\%$ of Fermi/GBM detected long gamma-ray bursts and $\sim 96\%$ of Fermi/GBM detected short gamma-ray bursts. In addition, our limits on the radio-to-gamma fluence ratio point to a different emission mechanism from that of magnetar giant flares. Finally, we exclude a $γ$-ray counterpart as fluent as the one possibly associated with FRB 131104 to be a common feature of FRBs.

astro-ph.HE↗

arXiv2019

A search for gamma-ray prompt emission associated with the Lorimer Burst FRB010724

No transient electromagnetic emission has yet been found in association to fast radio bursts (FRBs), the only possible exception (3sigma confidence) being the putative gamma-ray signal detected in Swift/BAT data in the energy band 15-150 keV at the time and position of FRB131104. Systematic searches for hard X/gamma-ray counterparts to other FRBs ended up with just lower limits on the radio/gamma-ray fluence ratios. In 2001, at the time of the earliest discovered FRBs, the BeppoSAX Gamma-Ray Burst Monitor (GRBM) was one of the most sensitive open sky gamma-ray monitors in the 40-700~keV energy band. During its lifetime, one of the FRBs with the highest radio fluence ever recorded, FRB010724 (800 +- 400 Jy ms), also known as the Lorimer burst, was promptly visible to the GRBM. Upon an accurate modeling of the GRBM background, eased by its equatorial orbit, we searched for a possible gamma-ray signal in the first 400 s following the FRB, similar to that claimed for FRB131104 and found no significant emission down to a 5-sigma limit in the range (0.24-4.7)x10^-6 erg cm^-2 (corresponding to 1 and 400 s integration time, respectively), in the energy band 40-700 keV. This corresponds to eta = F_radio/F_gamma>10^{8-9} Jy ms erg^-1 cm^2, i.e. the deepest limit on the ratio between radio and gamma-ray fluence, which rules out a gamma-ray counterpart similar to that of FRB131104. We discuss the implications on the possible mechanisms and progenitors that have been proposed in the literature, also taking into account its relatively low dispersion measure (375 +- 3 pc cm^-3) and an inferred redshift limit of z<0.4.

astro-ph.HE↗

arXiv2019

A robotic pipeline for fast GRB followup with the Las Cumbres observatory network

In the era of multi-messenger astronomy the exploration of the early emission from transients is key for understanding the encoded physics. At the same time, current generation networks of fully-robotic telescopes provide new opportunities in terms of fast followup and sky coverage. This work describes our pipeline designed for robotic optical followup of gamma-ray bursts with the Las Cumbres Observatory network. We designed a Python code to promptly submit observation requests to the Las Cumbres Observatory network within 3 minutes of the receipt of the socket notice. Via Telegram the pipeline keeps the users informed, allowing them to take control upon request. Our group was able to track the early phases of the evolution of the optical output from gamma-ray bursts with a fully-robotic procedure and here we report the case of GRB180720B as an example. The developed pipeline represent a key ingredient for any reliable and rapid (minutes timescale) robotic telescope system. While successfully utilized and adapted for LCO, it can also be adapted to any other robotic facilities.

astro-ph.IM↗