Showing papers by "F. Frontera published in 2020"

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

Abstract: Context. No robust detection of prompt electromagnetic counterparts to fast radio bursts (FRBs) has yet been obtained, in spite of several multi-wavelength searches having been carried out so far. Specifically, X/γ-rays counterparts are predicted by some models.Aims. We aim to search for prompt γ-ray counterparts in the Insight-Hard X-ray Modulation Telescope (Insight-HXMT) data, taking advantage of the unique combination of the large effective area in the keV–MeV energy range, and of sub-ms time resolution.Methods. 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.Results. No convincing signal was found, and for each FRB we constrained the γ-ray isotropic-equivalent luminosity and the released energy as a function of emission timescale. For the nearest FRB source, the periodic repeater FRB 180916.J0158+65, we find Lγ, iso < 5.5 × 1047 erg s−1 over 1 s, whereas Lγ, iso < 1049 − 1051 erg s−1 for the bulk of FRBs. The same values scale up by a factor of ∼100 for a ms-long emission.Conclusions. 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 sub-luminous events, as is the case for the core-collapse of massive stars (long) or binary neutron star mergers (short) viewed off axis. Only giant flares from extragalactic magnetars at least ten times more energetic than Galactic siblings are ruled out for the nearest FRB.Key words: radiation mechanisms: non-thermal / radio continuum: stars / gamma-ray burst: general

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

Abstract: 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 $L_{\gamma,iso}<5.5\times 10^{47}$ erg/s over 1 s, whereas $L_{\gamma,iso}<10^{49}-10^{51}$ 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.

Constraining the transient high-energy activity of FRB180916.J0158+65 with Insight-HXMT followup observations.

Abstract: A link between magnetars and fast radio burst (FRB) sources has finally been established. In this context, one of the open issues is whether/which sources of extra galactic FRBs exhibit X/gamma-ray outbursts and whether it is correlated with radio activity. We aim to constrain possible X/gamma-ray burst activity from one of the nearest extragalactic FRB sources currently known over a broad energy range, by looking for bursts over a range of timescales and energies that are compatible with being powerful flares from extragalactic magnetars. We followed up the as-yet nearest extragalactic FRB source at a mere 149 Mpc distance, the periodic repeater FRB180916.J0158+65, during the active phase on February 4-7, 2020, with the Insight-Hard X-ray Modulation Telescope (HXMT). Taking advantage of the combination of broad band, large effective area, and several independent detectors available, we searched for bursts over a set of timescales from 1 ms to 1.024 s with a sensitive algorithm, that had previously been characterised and optimised. Moreover, through simulations we studied the sensitivity of our technique in the released energy-duration phase space for a set of synthetic flares and assuming different energy spectra. We constrain the possible occurrence of flares in the 1-100 keV energy band to E<10^46 erg for durations <0.1 s over several tens of ks exposure. We can rule out the occurrence of giant flares similar to the ones that were observed in the few cases of Galactic magnetars. The absence of reported radio activity during our observations does not allow us to make any statements on the possible simultaneous high-energy emission.

Constraining the transient high-energy activity of FRB 180916.J0158+65 with Insight–HXMT follow-up observations

Abstract: Context. A link has finally been established between magnetars and fast radio burst (FRB) sources. Within this context, a major issue that remains unresolved pertains to whether sources of extragalactic FRBs exhibit X/γ -ray outbursts and whether this is correlated with radio activity. If so, the subsequent goal is to identify these sources.Aims. We aim to constrain possible X/γ -ray burst activity from one of the nearest extragalactic FRB sources currently known. This is to be done over a broad energy range by looking for bursts over a range of timescales and energies that are compatible with those of powerful flares from extragalactic magnetars.Methods. We followed up on the observation of the as-yet nearest extragalactic FRB source, located at a mere 149 Mpc distance, namely, the periodic repeater FRB 180916.J0158+65. This took place during the active phase between 4 and 7 February 2020, using the Insight–Hard X-ray Modulation Telescope (Insight–HXMT). By taking advantage of the combination of broad-band wavelengths, a large effective area, and several independent detectors at our disposal, we searched for bursts over a set of timescales from 1 ms to 1.024 s with a sensitive algorithm that had been previously characterised and optimised. Moreover, through simulations, we studied the sensitivity of our technique in the released energy-duration phase space for a set of synthetic flares and assuming a range of different energy spectra.Results. We constrain the possible occurrence of flares in the 1−100 keV energy band to E erg for durations Δ t We can rule out the occurrence of giant flares similar to the ones that were observed in the few cases of Galactic magnetars. The absence of reported radio activity during our observations prevents us from making any determinations regarding the possibility of simultaneous high-energy emission.