Search for High-Energy Gamma-Ray Emission From Tidal Disruption Events With the Fermi Large Area Telescope

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,  G 30, 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 ( -) Ĺ 0.1 10 GeV 4.4 10 42 erg s −1(at 95% confidence level) is obtained for the first 10 7 s after the disruption.

Jets from Tidal Disruption Events

“…In the years after its discovery, SW1644 has been extensively observed in radio (Zauderer et al, 2011;Berger et al, 2012;Zauderer et al, 2013;Cendes et al, 2014;Yang et al, 2016;Wiersema et al, 2012;Eftekhari et al, 2018), infrared/optical (Levan et al, 2016;Wiersema et al, 2012) and X-rays (Saxton et al, 2012;Reis et al, 2012;Zauderer et al, 2013;Mangano et al, 2016;Eftekhari et al, 2018;Levan et al, 2016). Upper limits were also provided by VERITAS (Aliu et al, 2011), MAGIC (Aleksić et al, 2013) and Fermi LAT (Omodei et al, 2011;Peng et al, 2016) above ∼ 50 MeV.…”

“…In the high-energy gamma-ray band (0.1(1 + z)-10(1 + z) GeV), Fermi LAT provides stringent constraints on the jet gamma-ray luminosity 6 , i.e. L LAT < 1 × 10 46 erg s −1 within the first day, < 3 × 10 45 erg s −1 within the first 8.5 days, and < 5×10 44 erg s −1 within the first 85 days (Peng et al, 2016). In the very-high-energy gamma-ray band (0.1-1 TeV), MAGIC provided constraints νL ν (0.14(1 + z) TeV) < 5 × 10 45 erg s −1 , νL ν (0.32(1 + z) TeV) < 1.6 × 10 45 erg s −1 , νL ν (0.65(1 + z) TeV) < 4 × 10 44 erg s −1 within the first 13 10 10 10 12 10 14 10 16 10 18 10 20 10 22 10 24 10 26 rest-frame ν Figure 7: Comparison between the SEDs of jetted TDEs with the blazar sequence from Ghisellini et al (2017), which considers a larger sample with more complete multiwavelength data than the original version by Fossati et al (1998).…”

The Long Term Evolution of ASASSN-14li

“…This is in contrast with ASASSN-14ae, in which the He ii λ4686 line became stronger relative to the Balmer lines as the event progressed (Brown et al 2016). Unlike the two other ASASSN TDEs, ASASSN-14li showed strong X-ray emission, and, due to it's proximity, was the target of several groundbased (Alexander et al 2016;van Velzen et al 2016;Romero-Cañizales et al 2016), space-based (Miller et al 2015;Cenko et al 2016;Peng, Tang & Wang 2016;Jiang et al 2016), and theoretical efforts (Krolik et al 2016;Kochanek 2016a).…”

Capabilities beyond Gamma Rays

“…C) X-ray, optical, and radio transients: So far, dozens of candidate TDEs have been observed in the optical and/or X-ray bands, but only a handful of them have been identified as relativistic TDEs with jets [261,296,297]. Although searches for a few such objects in the GeV [296,333] and TeV [334,335] bands have been negative, systematic and comprehensive studies of TDEs at these energies have yet to be conducted. Only a small number of SSB events have been discovered to date in the optical and/or X-ray bands [262], with proper coverage lacking above GeV.…”