FACT - First Energy Spectrum from a SiPM Cherenkov Telescope

Ahnen, M. L.; Balbo, Matteo; Bergmann, Matthias; Biland, A.; Bockermann, Christian; Bretz, T.; Brügge, Kai; Buß, Jens; Dorner, D.; Einecke, S.; Freiwald, Jan; Hempfling, Christina; Hildebrand, D.; Hughes, G.; Lustermann, W.; Mannheim, K.; Meier, K.; Morik, Katharina; Mueller, S.; Neise, Dominik; Neronov, A.; Noethe, Maximilian; Overkemping, A.; Paravac, Aleksander; Pauß, F.; Rhode, W.; Thaele, J.; Toscano, S.; Vogler, P.; Walter, R.; Wilbert, Aylin

doi:10.22323/1.236.0707

Cited by 7 publications

(10 citation statements)

References 11 publications

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“…The work on fluxes from FACT are ongoing. As shown in [15], the spectrum of the Crab Nebula measured with FACT is consistent with the measurements of other instruments.…”

Section: Discussionsupporting

confidence: 86%

FACT - TeV Flare Alerts Triggering Multi-Wavelength Observations

Dorner¹,

Ahnen²,

Balbo³

et al. 2016

Proceedings of the 34th International Cosmic Ray Conference — PoS(ICRC2015)

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Active galactic nuclei show variability on time scales ranging from minutes to decades. The radiation from these extreme objects spans many orders of magnitude along the whole electromagnetic spectrum. The spectral energy distribution shows two peaks, where for the subgroup of blazars the first peak is in the radio to X-ray regime, while the second peak is in the gamma-ray regime. Due to the extreme variability and the wide spectral range, simultaneous multi-wavelength observations are vital to understand the underlying physics. Furthermore, long-term monitoring is crucial to obtain an unbiased data sample. While for the measurements of the low-energy peak, many instruments are available, the data at TeV energies are sparse. The First G-APD Cherenkov Telescope (FACT) is a gamma-ray telescope dedicated to the long-term monitoring of bright TeV blazars. Operational since October 2011, it has collected more than three years of data from a dedicated sample of sources. The results of an automatic quick look analysis are publicly available on a website the same night. Based on this, other instruments are informed in case of a high flux state and target-of-opportunity observations are carried out. In the previous year, seven flare alerts have been sent to the community and several periods of strong variability have been observed for the blazars Mrk 421 and Mrk 501.

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“…The work on fluxes from FACT are ongoing. As shown in [15], the spectrum of the Crab Nebula measured with FACT is consistent with the measurements of other instruments.…”

Section: Discussionsupporting

confidence: 86%

FACT - TeV Flare Alerts Triggering Multi-Wavelength Observations

Dorner¹,

Ahnen²,

Balbo³

et al. 2016

Proceedings of the 34th International Cosmic Ray Conference — PoS(ICRC2015)

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“…To evaluate the performance of FACT with respect to energy bias, energy resolution, and energy range, an analysis of data of the Crab Nebula was performed [3]. Overall, 87.6 h of data with zenith angles below 30 • and under dark night and good observation conditions were analysed.…”

Section: Physics Performance Of Factmentioning

confidence: 99%

“…The evaluation of the energy bias and energy resolution is based on this estimated energy. Unfolded energy spectrum, scaled with the square of the energy E of the Crab Nebula [3], compared to HEGRA [8] and MAGIC [9].…”

Section: Physics Performance Of Factmentioning

confidence: 99%

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Long-Term Monitoring of Bright Blazars in the Multi-GeV to TeV Range with FACT

et al. 2017

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Blazars like Markarian 421 or Markarian 501 are active galactic nuclei (AGN), with their jets orientated towards the observer. They are among the brightest objects in the very high energy (VHE) gamma ray regime (>100 GeV). Their emitted gamma-ray fluxes are extremely variable, with changing activity levels on timescales between minutes, months, and even years. Several questions are part of the current research, such as the question of the emission regions or the engine of the AGN and the particle acceleration. A dedicated longterm monitoring program is necessary to investigate the properties of blazars in detail. A densely sampled and unbiased light curve allows for observation of both high and low states of the sources, and the combination with multi-wavelength observation could contribute to the answer of several questions mentioned above. FACT (First G-APD Cherenkov Telescope) is the first operational telescope using silicon photomultiplier (SiPM, also known as Geigermode-Avalanche Photo Diode, G-APD) as photon detectors. SiPM have a very homogenous and stable longterm performance, and allow operation even during full moon without any filter, leading to a maximal duty cycle for an Imaging Air Cherenkov Telescope (IACT). Hence, FACT is an ideal device for such a longterm monitoring of bright blazars. A small set of sources (e.g., Markarian 421, Markarian 501, 1ES 1959+650, and 1ES 2344+51.4) is currently being monitored. In this contribution, the FACT telescope and the concept of longterm monitoring of bright blazars will be introduced. The results of the monitoring program will be shown, and the advantages of densely sampled and unbiased light curves will be discussed.

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“…With a reflective area of 9.5 sqm and the excellent photon detection efficiency of SiPMs, a trigger threshold of 350 GeV is reached. The current analysis provides an analysis threshold of 750 GeV [4].…”

Section: Factmentioning

confidence: 99%

First study of combined blazar light curves with FACT and HAWC

Dorner¹,

Lauer

Adam³

et al. 2017

AIP Conference Proceedings

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Abstract. For studying variable sources like blazars, it is crucial to achieve unbiased monitoring, either with dedicated telescopes in pointing mode or survey instruments. At TeV energies, the High Altitude Water Cherenkov (HAWC) observatory monitors approximately two thirds of the sky every day. It uses the water Cherenkov technique, which provides an excellent duty cycle independent of weather and season. The First G-APD Cherenkov Telescope (FACT) monitors a small sample of sources with better sensitivity, using the imaging air Cherenkov technique. Thanks to its camera with silicon-based photosensors, FACT features an excellent detector performance and stability and extends its observations to times with strong moonlight, increasing the duty cycle compared to other imaging air Cherenkov telescopes. As FACT and HAWC have overlapping energy ranges, a joint study can exploit the longer daily coverage given that the observatories' locations are offset by 5.3 hours. Furthermore, the better sensitivity of FACT adds a finer resolution of features on hour-long time scales, while the continuous duty cycle of HAWC ensures evenly sampled long-term coverage. Thus, the two instruments complement each other to provide a more complete picture of blazar variability. In this presentation, the first joint study of light curves from the two instruments will be shown, correlating long-term measurements with daily sampling between air and water Cherenkov telescopes. The presented results focus on the study of the variability of the bright blazars Mrk 421 and Mrk 501 during the last two years featuring various flaring activities.

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FACT - First Energy Spectrum from a SiPM Cherenkov Telescope

Cited by 7 publications

References 11 publications

FACT - TeV Flare Alerts Triggering Multi-Wavelength Observations

FACT - TeV Flare Alerts Triggering Multi-Wavelength Observations

Long-Term Monitoring of Bright Blazars in the Multi-GeV to TeV Range with FACT

First study of combined blazar light curves with FACT and HAWC

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