MAGIC search for VHEγ-ray emission from AE Aquarii in a multiwavelength context

Abstract

Context. It has been claimed that the nova-like cataclysmic variable AE Aquarii (AE Aqr) is a very-high-energy (VHE, E > 100 GeV) source both on observational and theoretical grounds. Aims. We search for VHE γ-ray emission from AE Aqr during different states of the source at several wavelengths to confirm or rule out previous claims of detection of γ-ray emission from this object. Methods. We report on observations of AE Aqr performed by MAGIC. The source was observed during 12 h as part of a multiwavelength campaign carried out between May and June 2012 covering the optical, X-ray, and γ-ray ranges. Besides MAGIC, the other facilities involved were the KVA, Skinakas, and Vidojevica telescopes in the optical and Swift in X-rays. We calculated integral upper limits coincident with different states of the source in the optical. We computed upper limits to the pulsed emission limiting the signal region to 30% of the phaseogram and we also searched for pulsed emission at different frequencies applying the Rayleigh test. Results. AE Aqr was not detected at VHEs during the multiwavelength campaign. We establish integral upper limits at the 95% confidence level for the steady emission assuming the differential flux proportional to a power-law function dφ/dE ∝ E −Γ , with a Crab-like photon spectral index of Γ = 2.6. The upper limit above 200 GeV is 6.4 × 10 −12 cm −2 s −1 and above 1 TeV is 7.4 × 10 −13 cm −2 s −1 . We obtained an upper limit for the pulsed emission of 2.6 × 10 −12 cm −2 s −1 for energies above 200 GeV. Applying the Rayleigh test for pulsed emission at different frequencies we did not find any significant signal. Conclusions. Our results indicate that AE Aqr is not a VHE γ-ray emitter at the level of emission previously claimed. We have established the most constraining upper limits for the VHE γ-ray emission of AE Aqr.

Search for Gamma-Ray Emission From Ae Aquarii With Seven Years of Fermi Lat Observations

“…In this model, particles could be accelerated to relativistic energies by the huge potential differences in the clumpy ring, leading to a gamma-ray luminosity ∼ 10 34 erg s −1 during bursts, which is equal to the total spin down power. The upper limits to the steady gamma-ray luminosity measured by MAGIC (∼ 6.8 × 10 30 erg s −1 above 200 GeV, Aleksić et al 2014) and our present analysis in the 100 MeV-300 GeV energy range are both several orders of magnitude lower than this model prediction. It is not likely that the model proposed by Meintjes & de Jager (2000) could account for the gamma-ray emission of ae, unless the episodes of gamma-ray emission are much more sporadic than expected, an assumption that seems ad hoc and unattractive.…”

“…A 1-min long pulsating TeV burst was reported from ae by Bowden et al (1992). However, following these early observations, campaigns with the more sensitive Whipple Observatory (Lang et al 1998) and the MAGIC telescopes (Aleksić et al 2014) have shown no evidence for any steady, pulsed, or episodic TeV emission of ae at any epoch. A negative result of a search for gamma-ray emission from ae in the 0.1-1 GeV band was achieved with the Compton Gamma-ray Observatory (Schlegel et al 1995).…”

The detection of pulsed emission at the spin period of the white dwarf in AE Aquarii in MeerKAT and Fermi-LAT data

“…The follow−up studies using other Cherenkov telescopes resulted in no detection of any gamma−ray emission (e.g. [16]). However, the discovery of hard X−rays [17,18] with a spectrum that resembles a power−law, rekindled the notion that WDs are potential particle accelerators and hence possible gamma−ray sources.…”

Exploring the nature of AE Aquarii at higher energies using Sazuku and Fermi-LAT

“…The MAGIC telescope was utilised during follow-up studies, but again no evidence of any steady TeV gamma-ray emission was found [19]. In 2012 a multi-wavelength campaign using optical, UV, X-ray (Swift) and gamma-ray (MAGIC) telescopes was conducted [20,21]. No significant detections for steady TeV as well as variable (33.08 and 16.54 s pulsed) .…”

“…TeV emission were found. Upper-limit values of 6.39 × 10 −12 cm −2 s −1 above 250 GeV and 7.401 × 10 −13 cm −2 s −1 above 1 TeV for a power-law spectrum with a slope of -2.6 resulted from the campaign [20,21]. Fortunately the advent of space-based telescopes such as Fermi and AGILE increased the amount of data available to utilise in the search for steady, pulsed or episodic γ-ray emission from this enigmatic source.…”