Flat spectrum radio quasars (FSRQs) can suffer strong absorption above E = 25/(1+z) GeV, due to gamma-gamma interaction if the emitting region is at sub-parsec scale from the super-massive black hole (SMBH). Gamma-ray flares from these astrophysical
sources can investigate the location of the high-energy emission region and the physics of the radiating processes. We present a remarkable gamma-ray flaring activity from FSRQ PKS 2023-07 during April 2016, as detected by both AGILE and Fermi satellites. An intensive multi-wavelength campaign, triggered by Swift, covered the entire duration of the flaring activity, including the peak gamma-ray activity. We report the results of multiwavelength observations of the blazar. We found that, during the peak emission, the most energetic photon had an energy of 44 GeV, putting strong constraints on the opacity of the gamma-ray dissipation region. The overall Spectral Energy Distribution (SED) is interpreted in terms of leptonic models for blazar jet, with the emission site located beyond the Broad Line Region (BLR).
MWC 656 (= HD 215227) was recently discovered to be the first binary system composed of a Be star and a black hole (BH). We observed it with textit{XMM-Newton}, and detected a faint X-ray source compatible with the position of the optical star, thus
proving it to be the first Be/BH X-ray binary. The spectrum analysis requires a model fit with two components, a black body plus a power law, with $k_{rm B}T = 0.07^{+0.04}_{-0.03}$~keV and a photon index $Gamma= 1.0pm0.8$, respectively. The non-thermal component dominates above $simeq$0.8 keV. The obtained total flux is $F(0.3$--$5.5~{rm keV}) = (4.6^{+1.3}_{-1.1})times10^{-14}$ erg cm$^{-2}$ s$^{-1}$. At a distance of $2.6pm0.6$~kpc the total flux translates into a luminosity $L_{rm X} = (3.7pm1.7)times10^{31}$ erg s$^{-1}$. Considering the estimated range of BH masses to be 3.8--6.9 $M_{odot}$, this luminosity represents $(6.7pm4.4)times10^{-8}~L_{rm Edd}$, which is typical of stellar-mass BHs in quiescence. We discuss the origin of the two spectral components: the thermal component is associated with the hot wind of the Be star, whereas the power law component is associated with emission from the vicinity of the BH. We also find that the position of MWC~656 in the radio versus X-ray luminosity diagram may be consistent with the radio/X-ray correlation observed in BH low-mass X-ray binaries. This suggests that this correlation might also be valid for BH high-mass X-ray binaries (HMXBs) with X-ray luminosities down to $sim10^{-8} L_{rm Edd}$. MWC~656 will allow the accretion processes and the accretion/ejection coupling at very low luminosities for BH~HMXBs to be studied.
The variable gamma-ray source HESS J0632+057 is an excellent candidate for a gamma-ray binary. The putative binary system was discovered as a point-like VHE gamma-ray source by HESS. Later measurements by VERITAS yielding no detection, provided evide
nce for variable emission in the gamma-ray domain. A variable X-ray source as well as a Be star (MWC 148) are found at the location of the gamma-ray source. Recently a periodic X-ray outburst occurring about every 320 days was reported by Swift (ATel 3152). The putative binary system was observed by the MAGIC stereo system in 2010 and 2011. Our measurements demonstrate significant activity in the gamma-ray (E > 200 GeV) band in February 2011. Our detection of the system occurred during an X-ray outburst reported by Swift. Here we present the obtained light curve and spectrum during this outburst and put them into context with the X-ray measurements.
