TeV gamma-ray observations of SS-433 and a survey of the surrounding field with the HEGRA IACT-System

Abstract

Abstract. We present results of a search for TeV γ-ray emission from the microquasar SS-433 and the surrounding region covering a ∼8 • × 8 • field of view. Analysis of data taken with the HEGRA stereoscopic system of imaging atmosphericČerenkov imaging telescopes reveals no evidence of steady or variable emission from any position. Observation times of over 100 h have been achieved in central parts of the field of view. We set 99% confidence level upper limits to a number of a-priorichosen objects of interest, including SS-443 and its interaction regions, 32 pulsars, 3 supernova remnants and the GeV source GeV J1907+0537. Our upper limit of 3.2% Crab flux (for energies E > 0.8 TeV) for the eastern-lobe region e3 of SS-433 permits, after comparison with X-ray fluxes, a lower limit of B ≥ 19 µG on the post-shocked magnetic field in this region. An ensemble upper limit at 0.3% Crab flux (E > 0.7 TeV) from a subset (11) of the 32 pulsars implies a maximum of 4.5% of the spin-down pulsar power is available for TeV γ-ray production. For one of the SNR in our FoV, 3C 396, recent Chandra observations suggest that a central pulsar-driven wind nebula may be the source of X-ray emission. Our upper limit implies that a maximum of 0.1% of the spin-down power from the central source of 3C 396 would be available for TeV γ-rays.

Dissecting the Cygnus region with TeV gamma rays and neutrinos

“…It is intriguing that a Whipple observation of this region showed an excess of gamma-ray-like events over the entire field of view, which was deemed unlikely to be due to a bright, extended source [40]. A number of interesting objects are located near this area, perhaps the foremost being the microquasar SS 433 and its SNR, W50, from which no TeV emission was discovered by HEGRA [41]. Other systems worth noting are SNR G40.5-0.5 [42], HMXB 4U 1909+07 [43], candidate SNR 041.3-01.3 [44], and a prominent molecular cloud complex [45].…”

Constraints on particle acceleration in SS433/W50 from MAGIC and H.E.S.S. observations

“…The application of this model to SS 433/W50 yielded fluxes at the level of ∼10 −13 erg cm −2 s −1 for E > 250 GeV for an assumed distance to the system of 5.5 kpc (Bordas et al 2010), which are roughly at the level of the upper limits reported here. However, as noted in Aharonian & Atoyan (1998) (see also discussion in Petre 1999 andAharonian et al 2005), electrons accelerated at the interaction region shock interface could lose most of their energy mainly through synchrotron emission for ambient magnetic fields at or above ∼ 10 µG, preventing an effective channelling through IC scattering that is relevant for the production of gamma rays at high and very high energies. The integral flux upper limits for the interaction regions shown in Table 2, together with the assumption that the same high-energy electron population is responsible for the observed (synchrotron) X-ray emission and the putative gamma-ray fluxes, can be used to constrain the magnetic fields present in the shocked SS 433 jets/ISM interaction regions.…”

“…analyses were optimized assuming a source radius (θ-cut) of 0.05 • , 0.17 • , 0.25 • , 0.07 • , and 0.07 • for e1, e2, e3, w1, and w2, respectively, derived from the extension of these regions observed at X-ray energies (see e.g. Safi-Harb & Ögelman 1997; Safi-Harb & Petre 1999; Aharonian et al 2005, and references therein).…”

“…The integral flux upper limits for the interaction regions shown in Table 2, together with the assumption that the same high-energy electron population is responsible for the observed (synchrotron) X-ray emission and the putative gamma-ray fluxes, can be used to constrain the magnetic fields present in the shocked SS 433 jets/ISM interaction regions. Rowell & HEGRA Collaboration (2001) (see also Aharonian et al 2005) make use of HEGRA upper limits obtained for the e3 interaction region (Φ HEGRA ≤ 2.1 × 10 −12 ph cm −2 s −1 ) and the predictions by Aharonian et al (1997) to derive a lower limit on the post-shock magnetic field in this region of ∼ 13 µG. Using the upper limits reported here, a more constraining lower limit on the magnetic field of 20-25 µG is obtained.…”

“…At VHEs, SS 433/W50 remains so far undetected. Upper limits have been reported by the CANGAROO-II and HEGRA Collaborations, at the level of 2-3% of the Crab nebula flux above 800 GeV (Hayashi et al 2009;Aharonian et al 2005), following extended observation campaigns including both the central system and the jet/medium interaction regions. The selected dates of these observations, however, did not account for the gamma-ray absorption affecting the inner system.…”