High energy emission processes in OJ 287 during 2009 flare

Abstract

The broadband spectrum of a BL Lac object, OJ 287, from radio to γ-rays obtained during a major γ-ray flare detected by Fermi in 2009 are studied to understand the high energy emission mechanism during this episode. Using a simple one-zone leptonic model, incorporating synchrotron and inverse Compton emission processes, we show that the explanation of high energy emission from X-rays to γ-rays, by considering a single emission mechanism, namely, synchrotron self-Compton (SSC) or external Compton (EC) requires unlikely physical conditions. However, a combination of both SSC and EC mechanisms can reproduce the observed high energy spectrum satisfactorily. Using these emission mechanisms we extract the physical parameters governing the source and its environment. Our study suggests that the emission region of OJ 287 is surrounded by a warm infrared (IR) emitting region of ∼ 250 K. Assuming this region as a spherical cloud illuminated by an accretion disk, we obtain the location of the emission region to be ∼ 9 pc. This supports the claim that the γ-ray emission from OJ 287 during the 2009 flare arises from a location far away from the central engine as deduced from millimeter-gamma ray correlation study and very long baseline array images.

A Multi-Wavelength View of OJ 287 Activity in 2015–2017: Implications of Spectral Changes on Central-Engine Models and MeV-GeV Emission Mechanism

“…Subsequently, Qian [98] argued that NIR-optical break is actually a shift in synchrotron peak and is in tune with the shift observed in HE SED peak while Oikonomou et al [99] has proposed a hadronic scenario for the MeV-GeV. However, as shown in Kushwaha et al [100], the SED corresponding to the impact flare has similar NIR and X-ray emission and lacks any spectral change vis-a-vis 2009 jet SEDs [28]. This rules out Qian [98] interpretation and also the previous EC-IR explanation for the MeV-GeV emission [100].…”

“…28]. Using ν * ∼ 7.2 × 10 15 Hz from Pihajoki [eq 68; 95] results ν p ∼ 2.2 × 10 22 Hz assuming δ = Γ and γ b = 2000 [28,60] while the observed HE SED peak is at ∼ 10 24 Hz [60]. An additional clue against a dominant contribution of bremsstrahlung photons in IC is that the MeV-GeV spectral profile remains as it was during the 2015 QPOO [27] even after the disappearance of the NIR-optical spectral break around March 3, 2016 (MJD 57455; fig.…”

“…The observed spectra cover all the possible spectral phases. In addition to its typical LBL spectra described by a power-law 28,30,60,73,74], it has shown a flat [Γ ∼ 1; 27,28, 63,75], extremely soft Γ > 2 [27,69,73, and references therein] as well as mixture of these [27,74,76]. Interestingly, most of the extremely soft spectral state seems to have been around (within a few years) the period of optical outbursts claimed to be thermal bremsstrahlung emission [44,77].…”

“…OJ 287 has shown variability on all time scales (e.g. minutes-to-hours: [59,78], days: [28,59], months-to-years: [41,59,62], decades: [43,61]) across the entire electromagnetic spectrum [e.g. 27,28, ].…”

A helical jet model for OJ287

“…It could also be 58.3 + 1.4 yr, i.e., with a shift of one half of the cycle period. However, the distance of the optically emitting region is more likely to be around 1.4 × Γ lyr than 60 × Γ lyr from the center (Agudo et al 2012a;Kushwaha et al 2013). Moreover, the rather abrupt jump of the optical polarization by ∼90 degrees around 1995 occurs only in the model with the shorter time delay (Fig.…”