BatAnalysis—A Comprehensive Python Pipeline for Swift BAT Time-tagged Event Data Analysis

In addition to providing the initial gamma-ray burst trigger and location, the Swift Burst Alert Telescope (BAT) will also perform an all-sky hard x-ray survey based on serendipitous pointings resulting from the study of gamma-ray bursts. BAT was designed with a very wide field-of-view (FOV) so that it can observe roughly 1/7 of the sky at any time. Since gamma-ray bursts are uniformly distributed over the sky, the final BAT survey coverage is expected to be nearly uniform. BAT's large effective area and long sky exposures will produce a 15 - 150 keV survey with up to 30 times better sensitivity than any previous hard x-ray survey (e.g. HEAO A4). Since the sensitivity of deep exposures in this energy range is systematics limited, the ultimate survey sensitivity depends on the relative sizes of the statistical and systematic errors in the data. Many careful calibration experiments were performed at NASA/Goddard Space Flight Center to better understand the BAT instrument's response to 15-150 keV gamma-rays incident from any direction within the FOV. Using radioactive sources of gamma-rays with known locations and energies, the Swift team can identify potential systematic errors in the telescope's performance and estimate the actual Swift hard x-ray survey sensitivity in flight. These calibration results will be discussed and a preliminary parameterization of the BAT instrument response will be presented. While the details of the individual BAT CZT detector response will be presented elsewhere in these proceedings, this talk will focus on the translation of the calibration experimental data into overall hard x-ray survey sensitivity.

We report on the observations of gamma-ray burst (GRB) 190114C by the Fermi Gamma-ray Space Telescope and the Neil Gehrels Swift Observatory. The prompt gamma-ray emission was detected by the Fermi GRB Monitor (GBM), the Fermi Large Area Telescope (LAT), and the Swift Burst Alert Telescope (BAT) and the long-lived afterglow emission was subsequently observed by the GBM, LAT, Swift X-ray Telescope (XRT), and Swift UV Optical Telescope. The early-time observations reveal multiple emission components that evolve independently, with a delayed power-law component that exhibits significant spectral attenuation above 40 MeV in the first few seconds of the burst. This power-law component transitions to a harder spectrum that is consistent with the afterglow emission observed by the XRT at later times. This afterglow component is clearly identifiable in the GBM and BAT light curves as a slowly fading emission component on which the rest of the prompt emission is superimposed. As a result, we are able to observe the transition from internal-shock- to external-shock-dominated emission. We find that the temporal and spectral evolution of the broadband afterglow emission can be well modeled as synchrotron emission from a forward shock propagating into a wind-like circumstellar environment. We estimate the initial bulk Lorentz factor using the observed high-energy spectral cutoff. Considering the onset of the afterglow component, we constrain the deceleration radius at which this forward shock begins to radiate in order to estimate the maximum synchrotron energy as a function of time. We find that even in the LAT energy range, there exist high-energy photons that are in tension with the theoretical maximum energy that can be achieved through synchrotron emission from a shock. These violations of the maximum synchrotron energy are further compounded by the detection of very high-energy (VHE) emission above 300 GeV by MAGIC concurrent with our observations. We conclude that the observations of VHE photons from GRB 190114C necessitates either an additional emission mechanism at very high energies that is hidden in the synchrotron component in the LAT energy range, an acceleration mechanism that imparts energy to the particles at a rate that is faster than the electron synchrotron energy-loss rate, or revisions of the fundamental assumptions used in estimating the maximum photon energy attainable through the synchrotron process.

The Swift Burst Alert Telescope (BAT) is a coded-aperture gamma-ray instrument with a large field of view that primarily operates in survey mode when it is not triggering on transient events. The survey data consist of 80-channel detector plane histograms that accumulate photon counts over periods of at least 5 minutes. These histograms are processed on the ground and are used to produce the survey data set between 14 and 195 keV. Survey data comprise >90% of all BAT data by volume and allow for the tracking of long-term light curves and spectral properties of cataloged and uncataloged hard X-ray sources. Until now, the survey data set has not been used to its full potential due to the complexity associated with its analysis and the lack of easily usable pipelines. Here, we introduce the BatAnalysis Python package, a wrapper for HEASoftpy, which provides a modern, open-source pipeline to process and analyze BAT survey data. BatAnalysis allows members of the community to use BAT survey data in more advanced analyses of astrophysical sources, including pulsars, pulsar wind nebula, active galactic nuclei, and other known/unknown transient events that may be detected in the hard X-ray band. We outline the steps taken by the Python code and exemplify its usefulness and accuracy by analyzing survey data of the Crab Nebula, NGC 2992, and a previously uncataloged MAXI transient. The BatAnalysis package allows for ∼18 yr of BAT survey data to be used in a systematic way to study a large variety of astrophysical sources.

The Swift Burst Alert Telescope (BAT) is a coded-aperture gamma-ray instrument with a large field of view that primarily operates in survey mode when it is not triggering on transient events. The survey data consist of 80- channel detector plane histograms that accumulate photon counts over periods of at least 5 minutes. These histograms are processed on the ground and are used to produce the survey data set between 14 and 195 keV. Survey data comprise >90% of all BAT data by volume and allow for the tracking of long-term light curves and spectral properties of cataloged and uncataloged hard X-ray sources. Until now, the survey data set has not been used to its full potential due to the complexity associated with its analysis and the lack of easily usable pipelines. Here, we introduce the BatAnalysis Python package, a wrapper for HEASoftpy, which provides a modern, opensource pipeline to process and analyze BAT survey data. BatAnalysis allows members of the community to use BAT survey data in more advanced analyses of astrophysical sources, including pulsars, pulsar wind nebula, active galactic nuclei, and other known/unknown transient events that may be detected in the hard X-ray band. We outline the steps taken by the Python code and exemplify its usefulness and accuracy by analyzing survey data of the Crab Nebula, NGC 2992, and a previously uncataloged MAXI transient. The BatAnalysis package allows for ~18 yr of BAT survey data to be used in a systematic way to study a large variety of astrophysical sources.

While waiting for new gamma-ray burst detections, the Burst Alert Telescope (BAT) on board Swift covers each day ~50% of the sky in the hard X-ray band (``Survey data''). The large field of view (FOV), high sensitivity and good angular resolution make BAT a potentially powerful all-sky hard X-ray monitor, provided that mask--related systematics can be properly accounted for. We have developed and tested a complete procedure entirely based on public Swift/BAT software tools to analyse BAT Survey data, aimed at assessing the flux and spectral variability of bright sources in the 15-150 keV energy range. Detailed tests of the capabilities of our procedure were performed focusing, in particular, on the reliability of spectral measurements over the entire BAT FOV. First, we analyzed a large set of Crab observations, spread over ~7 months. Next, we studied the case of GRO J1655-40, a strongly variable source, which experienced a 9-month long outburst, beginning on February 2005. Such an outburst was systematically monitored with the well-calibrated PCA and HEXTE instruments on board the RXTE mission. Thanks to the good BAT temporal coverage of the source, we have been able to cross-check BAT light-curves with simultaneous HEXTE ones. The Crab tests have shown that our procedure recovers both the flux and the source spectral shape over the whole FOV of the BAT instrument. Moreover, by cross-checking GRO J1655-40 light-curves obtained by BAT and HEXTE, we found the spectral and flux evolution of the outburst to be in very good agreement. Using our procedure, BAT reproduces HEXTE fluxes within a 10-15% uncertainty with a 3sigma sensitivity of ~20 mCrab for an on-axis source, thus establishing its capability to monitor the evolution of relatively bright hard X-rays sources.

Previously, we proposed a novel method to inspect the isotropy of the properties of gamma-ray bursts (GRBs), such as their duration, fluences and peak fluxes at various energy bands and different time-scales, complementary to existing studies of the spatial distribution of GRBs by other authors. The method was then applied to the Fermi Gamma-ray Burst Monitor (GBM) Burst Catalog containing 1591 GRBs. Except for one particular direction where we noticed some hints of violation from statistical isotropy, the rest of the data showed consistency with isotropy. In this work, we apply our method, with some minor modifications, to the updated Fermi GBM data sample containing 2266 GRBs, which is thus ∼40 per cent larger. We also test two other major GRB catalogues: the Burst And Transient Source Experiment (BATSE) Current GRB Catalog of the Compton Gamma Ray Observatory (CGRO), containing ∼2000 bursts, and the Swift Burst Alert Telescope (BAT) GRB Catalog, containing ∼1200 bursts. The new results using the updated data are consistent with our previous findings and we find no statistically significant anisotropic feature in the observed properties of these samples of all GRBs.

We present the first Swift Ultra-Violet/Optical Telescope (UVOT) gamma-ray burst (GRB) afterglow catalog. The catalog contains data from over 64,000 independent UVOT image observations of 229 GRBs first detected by Swift, the High Energy Transient Explorer 2 (HETE2), the INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL), and the Interplanetary Network (IPN). The catalog covers GRBs occurring during the period from 2005 Jan 17 to 2007 Jun 16 and includes ~86% of the bursts detected by the Swift Burst Alert Telescope (BAT). The catalog provides detailed burst positional, temporal, and photometric information extracted from each of the UVOT images. Positions for bursts detected at the 3-sigma-level are provided with a nominal accuracy, relative to the USNO-B1 catalog, of ~0.25 arcseconds. Photometry for each burst is given in three UV bands, three optical bands, and a 'white' or open filter. Upper limits for magnitudes are reported for sources detected below 3-sigma. General properties of the burst sample and light curves, including the filter-dependent temporal slopes, are also provided. The majority of the UVOT light curves, for bursts detected at the 3-sigma-level, can be fit by a single power-law, with a median temporal slope (alpha) of 0.96, beginning several hundred seconds after the burst trigger and ending at ~1x10^5 s. The median UVOT v-band (~5500 Angstroms) magnitude at 2000 s for a sample of "well" detected bursts is 18.02. The UVOT flux interpolated to 2000 s after the burst, shows relatively strong correlations with both the prompt Swift BAT fluence, and the Swift X-ray flux at 11 hours after the trigger.

We present observations of the early X-ray emission for a sample of 40 gamma-ray bursts (GRBs) obtained using the Swift satellite, for which the narrow-field instruments were pointed at the burst within 10 minutes of the trigger. Using data from the Burst Alert Telescope and the X-Ray Telescope, we show that the X-ray light curve can be well described by an exponential that relaxes into a power law, often with flares superimposed. The transition time between the exponential and the power law provides a physically defined timescale for the burst duration. In most bursts, the power law breaks to a shallower decay within the first hour, and a late emission "hump" is observed, which can last for many hours. In other GRBs the hump is weak or absent. The observed variety in the shape of the early X-ray light curve can be explained as a combination of three components: prompt emission from the central engine, afterglow, and the late hump. In this scenario, afterglow emission begins during or soon after the burst, and the observed shape of the X-ray light curve depends on the relative strengths of the emission due to the central engine and that of the afterglow. There is a strong correlation such that those GRBs with stronger afterglow components have brighter early optical emission. The late emission hump can have a total fluence equivalent to that of the prompt phase. GRBs with the strongest late humps have weak or no X-ray flares.

The transition from prompt to afterglow emission is one of the most exciting and least understood phases in gamma-ray bursts (GRBs). Correlations among optical, X-ray, and gamma-ray emission in GRBs have been explored, to attempt to answer whether the earliest optical emission comes from internal and/or external shocks. We present optical photometric observations of GRB 180325A collected with the TAROT and RATIR ground-based telescopes. These observations show two strong optical flashes with separate peaks at ∼50 and ∼120 s, followed by a temporally extended optical emission. We also present X-rays and gamma-ray observations of GRB 180325A, detected by the Burst Alert Telescope and X-ray Telescope, on the Neil Gehrels Swift observatory, which both observed a narrow flash at ∼80 s. We show that the prompt gamma-ray and X-ray early emission shares similar temporal and spectral features consistent with internal dissipation within the relativistic outflow (e.g., by internal shocks or magnetic reconnection), while the early optical flashes are likely generated by the reverse shock that decelerates the ejecta as it sweeps up the external medium.

Gamma-ray bursts (GRBs) are the most luminous transient events with short intense flashes that have been detected in random directions in the sky once or twice per day. Their durations have been measured in seconds, especially short GRBs with duration of < 2 sec. The Ultra-Fast Flash Observatory (UFFO) space mission aims to detect the earliest moments of an explosion which presents the nature of GRBs, resulting into the enhancement of GRB mechanism understanding. The UFFO consists of a couple of wide Field-of-View (FOV) trigger telescopes, a narrow-FOV Slewing Mirror Telescope (SMT) for the fast measurement of the UV-optical photons from GRBs, and a gamma-ray monitor for energy measurement. The triggering is done by the UFFO burst Alert & Trigger telescope (UBAT) using the hard X-ray from GRBs and the UV/optical Trigger Assistant Telescope (UTAT) using the UV/optical photons from GRBs. The UBAT monitors the sky for GRB, and determines their position with sufficient accuracy (10' at 7.0σ) for follow-up UV/optical observations with the SMT. The primary trigger telescope is based on a fast recognition of position using hard X-ray from GRBs. Whereas the fastest previous experiment, the SWIFT observatory, rarely observed GRB in less than 60 seconds after trigger, the UFFO is designed to begin the UV/optical observations in less than a few seconds after trigger. The SMT uses the novel approach of steering our telescope beam using the rotatable mirror, instead of re-orienting the instrument platform like SWIFT and other previous instruments. The UFFO pathfinder is scheduled to launch into orbit on 2011 November by the Lomonosov spacecraft. This pathfinder is the scaled-down version of UFFO in order to make the first systematic study of early UV/optical light curves, including the rise phase of GRBs. It contains two instruments of UBAT and SMT. It only allows the payload mass of 20 kg and the power consumption of 20 W. The SMT has a fast rotatable mirror, a modified Ritchey-Chretien telescope with the aperture size of 10 cm diameter, and an image intensifier readout by CCD. The UBAT is using a coded-mask aperture for position detection and their X-ray photons are readout by LYSO crystals and Multi-Anode photomultiplier tubes (MAPMTs) with the effective active area size of 191.1 cm2. With this design, we expect UBAT to trigger ∼44 GRBs/yr and expect SMT to detect ∼10 GRBs/yr.

To draw inferences about gamma-ray burst (GRB) source populations based on Swift observations, it is essential to understand the detection efficiency of the Swift burst alert telescope (BAT). This study considers the problem of modeling the Swift/BAT triggering algorithm for long GRBs, a computationally expensive procedure, and models it using machine learning algorithms. A large sample of simulated GRBs from Lien et al. is used to train various models: random forests, boosted decision trees (with AdaBoost), support vector machines, and artificial neural networks. The best models have accuracies of ≳97% (≲3% error), which is a significant improvement on a cut in GRB flux, which has an accuracy of 89.6% (10.4% error). These models are then used to measure the detection efficiency of Swift as a function of redshift z, which is used to perform Bayesian parameter estimation on the GRB rate distribution. We find a local GRB rate density of n 0 &sim; 0.48 &minus; 0.23 &plus; 0.41 Gpc &minus; 3 yr &minus; 1 ?> with power-law indices of n 1 &sim; 1.7 &minus; 0.5 &plus; 0.6 ?> and n 2 &sim; &minus; 5.9 &minus; 0.1 &plus; 5.7 ?> for GRBs above and below a break point of z 1 &sim; 6.8 &minus; 3.2 &plus; 2.8 ?> . This methodology is able to improve upon earlier studies by more accurately modeling Swift detection and using this for fully Bayesian model fitting.

From Day 325, 2004 (launch) through Day 101, 2010, there is a total of 3 anomalies on the Swift Instrument Module (IM) Thermal Control System (TCS). Two are concerned with the Burst Alert Telescope (BAT) loop heat pipe (LHP) heater circuits. On Day 90, 2010, the primary heater circuit of the BAT LHP #0 compensation chamber (CC) failed to power on by the Power Converter Box (PCB). It caused a rapid decrease in the CC temperature and activated its secondary heater circuit which had a 2oC lower heater controller set point. The 2oC difference in temperature set points between the LHP #0 CC and LHP #1 CC led to thermal instability in the entire LHP thermal system and Blocks. After the LHP #0 CC secondary heater controller set point was increased to that of LHP #1, thermal stability has been restored and the temperatures of the LHP thermal system and Blocks are nominal. On Day 97, 2005, a failure in temperature controllability of the BAT LHP #1 CC primary heater circuit caused temperature excursions that led to a LHP #1 shut down. It had no impact on Gamma Ray Burst (GRB) detection because LHP #0 was nominal. After LHP #1 was started up and its primary heat controller was disabled on Day 98, both LHPs had been nominal until Day 90, 2010. On Day 337, 2004, the X-Ray Telescope (XRT) thermo-electric cooler (TEC) power supply (PS) suffered a single point failure. The charge-coupled device (CCD) has been cooled by the radiator passively to -50oC or colder most of the time. The CCD temperature meets the main objective of pinpointing GRB afterglow positions. With these 3 anomalies overcome, the IM TCS is nominal after more than 5 years in flight. Redundancy in thermal control hardware and electronics boxes that supply power to thermal control hardware is highly recommended to prevent a mission single point failure.

Compton-thick active galactic nuclei (AGN) arguably constitute the most elusive class of sources, as they are absorbed by large column densities above 1024 cm−2. These extreme absorptions hamper the detection of the central source even in hard X-ray energies. In this work, we use both Neil Gehrels Swift and NuSTAR observations to derive the most accurate yet Compton-thick AGN luminosity function. We first compiled a sample of candidate Compton-thick AGN (NH = 1024 − 25 cm−2) detected in the Swift Burst Alert Telescope (BAT) all-sky survey in the 14–195 keV band. We confirmed that they are Compton-thick sources by using the NuSTAR follow-up observations already presented in the literature. Our sample is composed of 44 sources, consistent with a column density of 1024 − 1025 cm−2 at the 90% confidence level. These sources have intrinsic luminosities higher than L10 − 50 keV ∼ 3 × 1041 erg s−1 and are found up to a redshift of z = 0.05 (≈200 Mpc). We derived the luminosity function of Compton-thick AGN using a Bayesian methodology where both the full column density and the luminosity distributions are taken into account. The faint end of the luminosity function is flat, having a slope of γ1 = 0.01−0.74+0.51, rather arguing against a numerous population of low luminosity Compton-thick AGN. Based on our luminosity function, we estimate that the fraction of Compton-thick AGN relative to the total number of AGN is of the order of 24 ± 5%, which is in agreement with previous estimates in the local Universe based on BAT samples.

Repeating and apparently non-repeating fast radio bursts (FRBs) differ qualitatively and are produced by distinct classes of sources. Apparently non-repeating FRBs must actually repeat many times in their lifetimes because there are insufficient catastrophic events to explain their rate. Yet no such infrequent repetitions, in contrast to the frequent activity of FRBs known to repeat, have been observed, constraining their repetition rates. The large gap in energy between FRB 200428 and its much weaker repetitions resembles the large gap in energy between rare giant outbursts of soft gamma repeaters (SGRs) and their lesser outbursts. This phenomenological similarity suggests that the sources of apparently non-repeating FRBs are related to SGRs. Apparently non-repeating FRBs are associated with SGR outbursts more energetic than the 2020 April 28 outburst of SGR 1935+2154 associated with FRB 200428 but less energetic than the 2004 outburst of SGR 1806−20 that had no associated FRB. At 20–1000 times its actual distance, FRB 200428 would have been an apparent non-repeater.

We report on the discovery by the Swift Gamma-Ray Burst Explorer of the black hole candidate Swift J1539.2-6227 and the subsequent course of an outburst beginning in November 2008 and lasting at least seven months. The source was discovered during normal observations with the Swift Burst Alert Telescope (BAT) on 2008 November 25. An extended observing campaign with the Rossi X-Ray Timing Explorer (RXTE) and Swift provided near-daily coverage over 176 days, giving us a good opportunity to track the evolution of spectral and timing parameters with fine temporal resolution through a series of spectral states. The source was first detected in a hard state during which strong low-frequency quasi-periodic oscillations (QPOs) were detected. The QPOs persisted for about 35 days and a signature of the transition from the hard to soft intermediate states was seen in the timing data. The source entered a short-lived thermal state about 40 days after the start of the outburst. There were variations in spectral hardness as the source flux declined and returned to a hard state at the end of the outburst. The progression of spectral states and the nature of the timing features provide strong evidence that Swift J1539.2-6227 is a candidate black hole in a low-mass X-ray binary system.