# Observation of the Black Widow B1957+20 millisecond pulsar binary system with the MAGIC telescopes

## TL;DR

This study used MAGIC telescopes to search for very high energy gamma-ray emission from the B1957+20 black widow pulsar binary system, setting upper limits that constrain models of particle acceleration and emission mechanisms.

## Contribution

First to provide observational upper limits on TeV gamma-ray emission from B1957+20, constraining theoretical models of high-energy processes in black widow pulsar systems.

## Key findings

- No significant steady VHE gamma-ray emission detected.
- Upper limit constrains electron acceleration efficiency below 2-10% of pulsar spin-down power.
- Limits rule out simple power-law extension of radio emission at TeV energies.

## Abstract

B1957+20 is a millisecond pulsar located in a black widow type compact binary system with a low mass stellar companion. The interaction of the pulsar wind with the companion star wind and/or the interstellar plasma is expected to create plausible conditions for acceleration of electrons to TeV energies and subsequent production of very high energy {\gamma} rays in the inverse Compton process. We performed extensive observations with the MAGIC telescopes of B1957+20. We interpret results in the framework of a few different models, namely emission from the vicinity of the millisecond pulsar, the interaction of the pulsar and stellar companion wind region, or bow shock nebula. No significant steady very high energy {\gamma}-ray emission was found. We derived a 95% confidence level upper limit of 3.0 x 10 -12 cm -2 s -1 on the average {\gamma}-ray emission from the binary system above 200 GeV. The upper limits obtained with MAGIC constrain, for the first time, different models of the high-energy emission in B1957+20. In particular, in the inner mixed wind nebula model with mono-energetic injection of electrons, the acceleration efficiency of electrons is constrained to be below ~(2-10)% of the pulsar spin down power. For the pulsar emission, the obtained upper limits for each emission peak are well above the exponential cut-off fits to the Fermi-LAT data, extrapolated to energies above 50 GeV. The MAGIC upper limits can rule out a simple power-law tail extension through the sub-TeV energy range for the main peak seen at radio frequencies.