SEARCH FOR HIGH-ENERGY GAMMA-RAY EMISSION FROM TIDAL DISRUPTION EVENTS WITH THE FERMI LARGE AREA TELESCOPE

• Published in: The Astrophysical journal Vol. 825; no. 1; p. 47
• Main Authors: Peng, Fang-Kun, Tang, Qing-Wen, Wang, Xiang-Yu
• Format: Journal Article
• Language: English
• Published: United States The American Astronomical Society 01.07.2016
• Subjects: ACCELERATION; ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; BLACK HOLES; COMPARATIVE EVALUATIONS; Confidence intervals; COSMIC GAMMA BURSTS; Disruption; EMISSION; Emissions control; GALAXIES; galaxies: nuclei; GALAXY NUCLEI; GAMMA RADIATION; Gamma rays; gamma rays: galaxies; GEV RANGE; Lorentz factor; radiation mechanisms:non-thermal; RELATIVISTIC RANGE; Searching; STARS; TELESCOPES; X RADIATION; X rays
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/0004-637X/825/1/47

ABSTRACT Massive black holes at galaxy center may tear apart a star when the star passes occasionally within the disruption radius, which is the so-called tidal disruption event (TDE). Most TDEs radiate with thermal emission resulting from the acceleration disk, but three TDEs have been detected in bright nonthermal X-ray emission, which is interpreted as arising from the relativistic jets. A search for high-energy gamma-ray emission from one relativistic TDE (Swift J164449.3+573451) with the Fermi Large Area Telescope (LAT) has yielded nondetection. In this paper, we report the search for high-energy emission from the other two relativistic TDEs (Swift J2058.4+0516 and Swift J1112.2-8238) during the flare period. No significant GeV emission is found, with an upper limit fluence in the LAT energy range being less than 1% of that in X-rays. Compared with gamma-ray bursts and blazars, these TDEs have the lowest flux ratio between GeV emission and X-ray emission. The nondetection of high-energy emission from relativistic TDEs could be due to the fact that the high-energy emission is absorbed by soft photons in the source. Based on this hypothesis, upper limits on the bulk Lorentz factors, , are then obtained for the jets in these TDEs. We also search for high-energy gamma-ray emission from the nearest TDE discovered to date, ASASSN-14li. No significant GeV emission is found, and an upper limit of erg s−1 (at 95% confidence level) is obtained for the first 107 s after the disruption.