arXiv subjects

Daniela Hadasch

Publications and source records attributed to Daniela Hadasch.

12 recordsLinked to original sources

arXiv2026

Extreme Transients in Gamma Rays

Extreme gamma-ray transients represent some of the most energetic and physically constraining phenomena in high-energy astrophysics. They are characterized by rapid, large-amplitude variability and by physical conditions approaching fundamental limits on particle acceleration, cooling, and compactness. In this review, we focus on transients detected above around 100 MeV and define extreme events as either those involving catastrophic transformations of astrophysical systems (such as stellar explosions, compact-object mergers, and tidal-disruption events) or those exhibiting evidence for particle acceleration operating in an extreme regime. These systems are powered by the rapid release of gravitational, magnetic, nuclear, or kinetic energy, with shocks and magnetic reconnection playing a central role in producing ultra-relativistic particle populations and non-thermal radiation. We summarize observational and theoretical diagnostics that constrain the size, magnetization, and Lorentz factor of the emitting region, including variability timescales, luminosity-timescale correlations, and spectral evolution across the MeV-TeV domain. We further review the complementary capabilities of space-borne gamma-ray instruments, ground-based Cherenkov and air-shower observatories in detecting short-lived, high-energy outbursts. Extreme transient classes discussed include gamma-ray bursts, novae, rapidly variable emission from extragalactic and Galactic jets. Also, because of its extreme aspects, we include flaring emission detected from the Crab Nebula. While each type of these flares poses interesting challenges for phenomenology and theory of these sources, together, these events form the landscape of extreme gamma-ray variability.

astro-ph.HE↗

arXiv2026

Temporal evolution of the periodic GeV signal from 4FGL J1913.2+0512 and analysis of the SS 433 / W50 lobes

SS 433 is a microquasar whose relativistic jets precess every ~162 days, providing a laboratory for jet-interstellar medium interactions. We present a comprehensive analysis of 16 years of Fermi Large Area Telescope data (August 2008-September 2024) of the SS 433/W50 field, using events in the 0.3-300 GeV range and employing pulsar gating to mitigate contamination from the bright nearby pulsar PSR J1907+0602. We detect the GeV source 4FGL J1913.2+0512 (TS = 45, where TS denotes the likelihood-ratio Test Statistic) with a power-law spectrum (photon index 2.61 +- 0.08) and confirm a GeV excess at the western lobe (TS = 17). The eastern lobe of SS 433 is hinted at with lower significance. One additional GeV excess, Fermi J1909.6+0552 (TS = 20; TS = 28 over 0.1-300 GeV), located outside the SS 433 / W50 system, is revealed after gating. Exposure-corrected Lomb-Scargle periodograms and precessional phase-folded light curves show a ~162-day modulation in 4FGL J1913.2+0512. This periodicity is prominent during the first 10 years of the mission (2008-2018) but disappears thereafter, with the phase-folded flux concentrated in precessional phases 0.0-0.5. Over the full 16-year dataset, the modulation remains detectable but with reduced significance, consistent with dilution by the later non-modulated epoch. These results indicate that the efficiency and/or geometry of gamma-ray production in the SS 433 environment evolves on multi-year timescales.

astro-ph.HE↗

arXiv2023

Resource-aware Research on Universe and Matter: Call-to-Action in Digital Transformation

Given the urgency to reduce fossil fuel energy production to make climate tipping points less likely, we call for resource-aware knowledge gain in the research areas on Universe and Matter with emphasis on the digital transformation. A portfolio of measures is described in detail and then summarized according to the timescales required for their implementation. The measures will both contribute to sustainable research and accelerate scientific progress through increased awareness of resource usage. This work is based on a three-days workshop on sustainability in digital transformation held in May 2023.

physics.comp-ph↗

arXiv2022

Calibration and performance of the readout system based on switched capacitor arrays for the Large-Sized Telescope of the Cherenkov Telescope Array

The Cherenkov Telescope Array (CTA) is the next-generation ground-based very-high-energy gamma-ray observatory. The Large-Sized Telescope (LST) of CTA is designed to detect gamma rays between 20 GeV and a few TeV with a 23-meter diameter mirror. We have developed the focal plane camera of the first LST, which has 1855 photomultiplier tubes (PMTs) and the readout system which samples a PMT waveform at GHz with switched capacitor arrays, Domino Ring Sampler ver4 (DRS4). To measure the precise pulse charge and arrival time of Cherenkov signals, we developed a method to calibrate the output voltage of DRS4 and the sampling time interval, as well as an analysis method to correct the spike noise of DRS4. Since the first LST was inaugurated in 2018, we have performed the commissioning tests and calibrated the camera. We characterised the camera in terms of the charge pedestal under various conditions of the night sky background, the charge resolution of each pixel, the charge uniformity of the whole camera, and the time resolutions with a test pulse and calibration laser.

astro-ph.IM↗

arXiv2018

VHE observations of binary systems performed with the MAGIC telescopes

The improvement on the Imaging Air Cherenkov Technique (IACT) led to the discovery of a new type of sources that can emit at very high energies: the gamma-ray binaries. Only six systems are part of this exclusive class. We summarize the latest results from the observations performed with the MAGIC telescopes on different systems as the gamma-ray binary LS I +61$^{\circ}$ 303 and the microquasars SS433, V404 Cygni and Cygnus X-1, which are considered potential VHE gamma-ray emitters. The binary system LS I +61$^{\circ}$ 303 has been observed by MAGIC in a long-term monitoring campaign. We show the newest results of our search for super-orbital variability also in context of contemporaneous optical observations. Besides, we will present the results of the only super-critical accretor known in our galaxy: SS 433. We will introduce the VHE results achieved with MAGIC after 100 hours of observations on the microquasar Cygnus X-1 and report on the microquasar V404 Cyg, which has been observed with MAGIC after it went through a series of exceptional X-ray outbursts in June 2015.

astro-ph.HE↗

arXiv2017

MAGIC VHE Gamma-Ray Observations Of Binary Systems

There are several types of Galactic sources that can potentially accelerate charged particles up to GeV and TeV energies. We present here the results of our observations of the source class of gamma-ray binaries and the subclass of binary systems known as novae with the MAGIC telescopes. Up to now novae were only detected in the GeV range. This emission can be interpreted in terms of an inverse Compton process of electrons accelerated in a shock. In this case it is expected that protons in the same conditions can be accelerated to much higher energies. Consequently they may produce a second component in the gamma-ray spectrum at TeV energies. The focus here lies on the four sources: nova V339 Del, SS433, LS I +61 303 and V404 Cygni. The binary system LS I +61 303 was observed in a long-term monitoring campaign for 8 years. We show the newest results on our search for superorbital variability, also in context with contemporaneous optical observations. Furthermore, we present the observations of the only super-critical accretion system known in our galaxy: SS433. Finally, the results of the follow-up observations of the microquasar V404 Cygni during a series of outbursts in the X-ray band and the ones of the nova V339 Del will be discussed in these proceedings.

astro-ph.HE↗

arXiv2015

Development of the photomultiplier tube readout system for the first Large-Sized Telescope of the Cherenkov Telescope Array

The Cherenkov Telescope Array (CTA) is the next generation ground-based very high energy gamma-ray observatory. The Large-Sized Telescope (LST) of CTA targets 20 GeV -- 1 TeV gamma rays and has 1855 photomultiplier tubes (PMTs) installed in the focal plane camera. With the 23 m mirror dish, the night sky background (NSB) rate amounts to several hundreds MHz per pixel. In order to record clean images of gamma-ray showers with minimal NSB contamination, a fast sampling of the signal waveform is required so that the signal integration time can be as short as the Cherenkov light flash duration (a few ns). We have developed a readout board which samples waveforms of seven PMTs per board at a GHz rate. Since a GHz FADC has a high power consumption, leading to large heat dissipation, we adopted the analog memory ASIC "DRS4". The sampler has 1024 capacitors per channel and can sample the waveform at a GHz rate. Four channels of a chip are cascaded to obtain deeper sampling depth with 4096 capacitors. After a trigger is generated in a mezzanine on the board, the waveform stored in the capacitor array is subsequently digitized with a low speed (33 MHz) ADC and transferred via the FPGA-based Gigabit Ethernet to a data acquisition system. Both a low power consumption (2.64 W per channel) and high speed sampling with a bandwidth of $>$300 MHz have been achieved. In addition, in order to increase the dynamic range of the readout we adopted a two gain system achieving from 0.2 up to 2000 photoelectrons in total. We finalized the board design for the first LST and proceeded to mass production. Performance of produced boards are being checked with a series of quality control (QC) tests. We report the readout board specifications and QC results.

astro-ph.IM↗

arXiv2013

The MAGIC telescopes DAQ software and the on-the-fly online analysis client

In this contribution we describe the design of the Data AcQuisition (DAQ) and online analysis software of the MAGIC telescopes after the 2012 upgrade. Although the final stereo trigger requires coincidence between the two telescopes, the actual data acquisition is performed independently, producing two separate data streams. Events are first readout and built from the front-end electronics and then stored in the DAQs' internal ring buffer for further processing: pre-calibration and signal extraction. The pixel signals, previously used only for data quality monitoring, are now also sent "on-the-fly" to the centralized online analysis program MOLA, which acts as a single client for the two DAQ data streams, and uses this information to provide preliminary high level analysis results. The integrated DAQ and online analysis programs allows an immediate feedback in case of a rapid gamma-ray flare of the pointed astrophysical source.

astro-ph.IM↗

arXiv2012

Unveiling the super-orbital modulation of LSI +61 303 in X-rays

We found evidence for the super-orbital modulation in the X-ray emission of LS I +61 303 from the longest monitoring date by the RXTE. The time evolution of the modulated fraction in the orbital light curves can be well fitted with a sinusoidal function having a super-orbital period of 1667 days. However, we have found a 281.8+/-44.6 day shift between the super-orbital variability found at radio frequencies and our X-ray data. We also find a super-orbital modulation in the maximum count rate of the orbital light curves, compatible with the former results, including the shift.

astro-ph.HE↗

arXiv2011

Unveiling the super-orbital modulation of LS I +61 303 in X-rays

From the longest monitoring of LS I +61 303 done to date by the Rossi X-ray Timing Explorer (RXTE) we found evidence for the long-sought, years- long modulation in the X-ray emission of the source. The time evolution of the modulated fraction in the orbital lightcurves can be well fitted with a sinusoidal function having a super-orbital period of 1667 days, the same as the one reported in non-contemporaneous radio measurements. However, we have found a 281.8 \pm 44.6 days shift between the super-orbital variability found at radio frequencies extrapolated to the observation time of our campaign and what we found in the super-orbital modulation of the modulated fraction of our X-ray data. We also find a super-orbital modulation in the maximum count rate of the orbital lightcurves, compatible with the former results, including the shift.

astro-ph.HE↗

arXiv2011

Long-term X-ray monitoring of LS I +61 303: analysis of spectral variability and flares

We report on the full analysis of a Rossi X-ray Timing Explorer (RXTE) Proportional Counter Array (PCA) monitoring of the γ-ray binary system LS I +61 303. The data set covers 42 contiguous cycles of the system orbital motion. Analyzing this X-ray monitoring dataset, the largest to date for this source, we report on the variability of the orbital profile and the spectral distribution, and provide strong evidence for an anti-correlation between flux and spectral index (the higher the flux, the harder the spectral index). Furthermore, we present the analysis of two newly discovered ks-timescale flares, which present significant variability also on shorter timescales, and tend to occur at orbital phases between 0.6-0.9. However, a detailed timing analysis of the flares does not show any coherent or quasi-coherent (QPO) structure in their power spectra. We also investigated the possible appearance of the radio super-orbital modulation at X-rays energies, but we could not unambiguously detect such modulation in the system flux history, nor in the evolution of its orbital modulation fraction.

astro-ph.HE↗

arXiv2010

Variability in the orbital profiles of the X-ray emission of the gamma-ray binary LS I +61 303

We report on the analysis of Rossi X-ray Timing Explorer (RXTE) Proportional Counter Array (PCA) monitoring observations of the $γ$-ray binary system LS I +61 303, covering 35 full cycles of its orbital motion. This constitutes the largest continuous X-ray monitoring dataset analyzed to date for this source. Such an extended analysis allows us to report: a) the discovery of variability in the orbital profiles of the X- ray emission, b) the existence of a few (recent) short flares on top of the overall behavior typical of the source, which, given the PCA field-of-view, may or may not be associated with LS I +61 303, and c) the determination of the orbital periodicity using soft X-ray data alone.

astro-ph.HE↗