M. Stanbro

Fermi GBM Observations of LIGO Gravitational Wave event GW150914

With an instantaneous view of 70% of the sky, the Fermi Gamma-ray Burst Monitor (GBM) is an excellent partner in the search for electromagnetic counterparts to gravitational-wave (GW) events. GBM observations at the time of the Laser Interferometer Gravitational-wave Observatory (LIGO) event GW150914 reveal the presence of a weak transient above 50 keV, 0.4 s after the GW event, with a false-alarm probability of 0.0022 (2.9(sigma)). This weak transient lasting 1 s was not detected by any other instrument and does not appear to be connected with other previously known astrophysical, solar, terrestrial, or magnetospheric activity. Its localization is ill-constrained but consistent with the direction of GW150914. The duration and spectrum of the transient event are consistent with a weak short gamma-ray burst (GRB) arriving at a large angle to the direction in which Fermi was pointing where the GBM detector response is not optimal. If the GBM transient is associated with GW150914, then this electromagnetic signal from a stellar mass black hole binary merger is unexpected. We calculate a luminosity in hard X-ray emission between 1 keV and 10 MeV of 1.8(sup +1.5, sub -1.0) x 10(exp 49) erg/s. Future joint observations of GW events by LIGO/Virgo and Fermi GBM could reveal whether the weak transient reported here is a plausible counterpart to GW150914 or a chance coincidence, and will further probe the connection between compact binary mergers and short GRBs.

An Ordinary Short Gamma-Ray Burst with Extraordinary Implications: Fermi-GBM Detection of GRB 170817A

On August 17, 2017 at 12:41:06 UTC the Fermi Gamma-ray Burst Monitor (GBM) detected and triggered on the short gamma-ray burst GRB 170817A. Approximately 1.7 s prior to this GRB, the Laser Interferometer Gravitational-Wave Observatory (LIGO) triggered on a binary compact merger candidate associated with the GRB. This is the first unambiguous coincident observation of gravitational waves and electromagnetic radiation from a single astrophysical source and marks the start of gravitational-wave multi-messenger astronomy. We report the GBM observations and analysis of this ordinary short GRB, which extraordinarily confirms that at least some short GRBs are produced by binary compact mergers.

Characteristics of Thunderstorms That Produce Terrestrial Gamma Ray Flashes

AbstractGround-based lightning detection systems geolocated 877 terrestrial gamma ray flashes (TGFs) from a sample of 2,279 TGFs detected with the Fermi Gamma Ray Burst Monitor (GBM). From these accurate geolocations, 24 TGFs are found within the Next Generation Weather Radar (NEXRAD) operational range in the Gulf of Mexico, the Caribbean, and the Pacific near Guam. NEXRAD-enhanced echo-top (EET) data show that these 24 TGFs are consistently adjacent to high-altitude regions of the storms. The high EET values suggest that there is likely a detection–selection effect, in which the gamma rays from lower-altitude TGFs are attenuated by the atmosphere so that such TGFs fall below the detection threshold of current space-based detectors. The vertical integrated liquid density (VILD) values and the volume scan reflectivities Z show that these 24 TGFs originate from storms of a wide range of convective strengths. Convective available potential energy (CAPE) values from reanalysis also vary widely, providing addi...

Compton scattering in terrestrial gamma-ray flashes detected with the Fermi gamma-ray burst monitor

Max-Planck-Institut fur extraterrestrische Physik, Giessenbachstrasse 1, 85748 Garching, Germany(Received 30 June 2014; published 20 August 2014)Terrestrial gamma-ray flashes (TGFs) are short intense flashes of gamma rays associated with lightningactivity in thunderstorms. Using Monte Carlo simulations of the relativistic runaway electron avalanche(RREA) process, theoretical predictions for the temporal and spectral evolution of TGFs are compared toobservations made with the Gamma-ray Burst Monitor (GBM) on board the Fermi Gamma-ray SpaceTelescope. Assuming a single source altitude of 15 km, a comparison of simulations to data is performedfor a range of empirically chosen source electron variation time scales. The data exhibit a clear softeningwith increased source distance, in qualitativeagreement with theoretical predictions. The simulated spectrafollow this trend in the data, but tend to underestimate the observed hardness. Such a discrepancy mayimply that the basic RREA model is not sufficient. Alternatively, a TGF beam that is tilted with respect tothe zenith could produce an evolution with source distance that is compatiblewith the data. Based on theseresults, we propose that the source electron distributions of TGFs observed by GBM vary on time scales ofat least tens of microseconds, with an upper limit of ∼100 μs.

The spectroscopy of individual terrestrial gamma-ray flashes: Constraining the source properties

We report on the spectral analysis of individual Terrestrial Gamma-ray Flashes (TGFs) observed with the Fermi Gamma-ray Burst Monitor (GBM). The large GBM TGF sample provides 46 events suitable for individual spectral analysis: sufficiently bright, localized by ground-based radio, and with the gamma rays reaching a detector unobstructed. These TGFs exhibit diverse spectral characteristics that are hidden when using summed analysis methods. We account for the low counts in individual TGFs by using Poisson likelihood, and we also consider instrumental effects. The data are fit with models obtained from Monte Carlo simulations of the large scale Relativistic Runaway Electron Avalanche (RREA) model, including propagation through the atmosphere. Source altitudes ranging from 11.6 to 20.2 km are simulated. Two beaming geometries were considered: In one, the photons retain the intrinsic distribution from scattering (narrow), and in the other, the photons are smeared into a wider beam (wide). Several TGFs are well fit only by narrow models, while others favor wide models. Large-scale RREA models can accommodate both narrow and wide beams, with narrow beams suggest large-scale RREA in organized electric fields while wide beams may imply converging or diverging electric fields. Wide beams are also consistent with acceleration in the electric fields of lightning leaders, but the TGFs that favor narrow beam models appear inconsistent with some lightning leader models.

On the interpretation of the Fermi-GBM transient observed in coincidence with LIGO gravitational-wave event GW150914

The weak transient detected by the Fermi Gamma-ray Burst Monitor (GBM) 0.4 s after GW150914 has generated much speculation regarding its possible association with the black-hole binary merger. Investigation of the GBM data by Connaughton et al. (2016) revealed a source location consistent with GW150914 and a spectrum consistent with a weak, short Gamma-Ray Burst. Greiner et al. (2016) present an alternative technique for fitting background-limited data in the low-count regime, and call into question the spectral analysis and the significance of the detection of GW150914-GBM presented in Connaughton et al. (2016). The spectral analysis of Connaughton et al. (2016) is not subject to the limitations of the low-count regime noted by Greiner et al. (2016). We find Greiner et al. (2016) used an inconsistent source position and did not follow the steps taken in Connaughton et al. (2016) to mitigate the statistical shortcomings of their software when analyzing this weak event. We use the approach of Greiner et al. (2016) to verify that our original spectral analysis is not biased. The detection significance of GW150914-GBM is established empirically, with a False Alarm Rate (FAR) of

Terrestrial gamma ray flashes due to particle acceleration in tropical storm systems

\sim 10^{-4}

Distribution of CO2 in Saturn's Atmosphere from Cassini/cirs Infrared Observations

~Hz. A post-trials False Alarm Probability (FAP) of

Fermi GBM Observations of GRB 150101B: A Second Nearby Event with a Short Hard Spike and a Soft Tail

2.2 \times 10^{-3}

Electric field change measurements of a terrestrial gamma ray flash

(