[Paper Review] The MAGIC Telescope and the Observation of Gamma Ray Bursts

D. Bastieri, N. Galante+5 more|arXiv (Cornell University)|Apr 14, 2005

Gamma-ray bursts and supernovae3 citations

TL;DR

The MAGIC Telescope, with its sub-100 GeV energy threshold and sub-20-second slewing capability, is positioned to detect prompt high-energy gamma-ray emission from Gamma Ray Bursts (GRBs) when triggered by alerts from the GCN network. It is projected to observe 0.5 to 2 GRBs per year due to its low duty cycle (~10%) and fast response, making it a key instrument for early high-energy GRB studies.

ABSTRACT

The MAGIC Telescope, now taking data with an energy threshold well below 100 GeV, will soon be able to take full advantage of the fast slewing capability of its altazimuthal mount. Exploiting the link with the GCN network, the MAGIC Telescope could be one of the first ground-based experiments able to see the prompt emission of Gamma Ray Bursts in the few tens of GeV region.

Motivation & Objective

• To demonstrate MAGIC Telescope’s capability to observe prompt high-energy gamma-ray emission from GRBs.
• To quantify the observability of GRBs given MAGIC’s operational constraints, including duty cycle and response time.
• To evaluate the impact of slewing delay on the number of detectable GRBs using realistic observational parameters.
• To validate MAGIC’s performance through early observations of standard sources like the Crab Nebula and Mkn 421.
• To establish MAGIC as a complementary ground-based Cherenkov telescope for high-energy GRB follow-up, especially below 100 GeV.

Proposed method

• Utilizes the Imaging Atmospheric Cherenkov Technique (IACT) to detect Cherenkov light from extensive air showers initiated by high-energy gamma rays.
• Employs Hillas parameters (alpha and size) to reconstruct shower direction and energy, enabling source detection and background suppression.
• Applies the Li-Ma formula to calculate significance (Nσ) of potential GRB signals, incorporating effective area and background rates.
• Models GRB flux using extrapolated BATSE power-law spectra, corrected for cosmological absorption via γγ → e⁺e⁻ interactions.
• Calculates duty cycle based on observational constraints: solar/zenith angle, lunar avoidance, humidity <80%, wind <10 m/s.
• Integrates slewing time (<20 s), GCN alert latency (~2 s), and satellite trigger delay to estimate total response delay and its impact on observable GRBs.

Experimental results

Research questions

• RQ1 Can MAGIC detect prompt high-energy gamma-ray emission from GRBs below 100 GeV using fast-slewing capabilities?
• RQ2 What fraction of GRB alerts can MAGIC actually observe, given its duty cycle and sky access constraints?
• RQ3 How does reducing the total response delay (from GRB onset to observation) affect the number of observable GRBs?
• RQ4 What is the expected detection significance (Nσ > 5) for GRBs under MAGIC’s sensitivity and background conditions?
• RQ5 How does the zenith angle dependence of the duty cycle and GRB rate affect the annual number of observable GRBs?

Key findings

• MAGIC successfully detected the Crab Nebula and Mkn 421 in high state, with signals exceeding 5σ, confirming its operational readiness and sensitivity below 100 GeV.
• The telescope achieved a sub-100 GeV energy threshold, enabling observation of low-energy gamma-ray emission from transient sources.
• The duty cycle for GRB observations is approximately 10%, constrained by weather, solar, and lunar conditions.
• Reducing the total response delay from 1 minute to 15 seconds increases the number of observable GRBs by a factor of 5.
• Due to the combined effects of duty cycle and delay, MAGIC is expected to observe between 0.5 and 2 GRBs per year with significance above 5σ.
• The effective area of MAGIC reaches ~10⁵ m² at 100 GeV and ~10⁴ m² at 50 GeV, supporting high-sensitivity detection in the tens of GeV range.