The broad-band radio spectrum of LSI+61303 in outburst

Abstract

Aims: Our aim is to explore the broad-band radio continuum spectrum of LSI+61303 during its outbursts by employing the available set of secondary focus receivers of the Effelsberg 100 m telescope. Methods: The clear periodicity of the system LSI+61303 allowed observations to be scheduled covering the large radio outburst in March-April 2012. We observed LSI+61303 on 14 consecutive days at 2.6, 4.85, 8.35, 10.45, 14.3, 23, and 32 GHz with a cadence of about 12 hours followed by two additional observations several days later. Based on these observations we obtained a total of 24 quasi-simultaneous broad-band radio spectra. Results: During onset, the main flare shows an almost flat broad-band spectrum, most prominently seen on March 27, 2012, where - for the first time - a flat spectrum (alpha=0.00+/-0.07, S nu^alpha) is observed up to 32 GHz (9 mm wavelength). The flare decay phase shows superimposed 'sub-flares' with the spectral index oscillating between -0.4 and -0.1 in a quasi-regular fashion. Finally, the spectral index steepens during the decay phase, showing optically thin emission with values alpha $\sim$ -0.5 to -0.7. Conclusions: The radio characteristics of LSI+61303 compare well with those of the microquasars XTE J1752-223 and Cygnus X-3. In these systems the flaring phase is actually also composed of a sequence of outbursts with clearly different spectral characteristics: a first outburst with a flat/inverted spectrum followed by a bursting phase of optically thin emission.

4 pages, 3 figures, accepted for publication in A&A

References in corpus (8)

• Gamma-ray binaries: pulsars in disguise ?
• Accretion vs colliding wind models for the gamma-ray binary LS I +61 303: an assessment
• Testing the inverse-Compton catastrophe scenario in the intra-day variable blazar S5 0716+71, III. Rapid and correlated flux density variability from radio to sub-mm bands
• Multi-wavelength observations of the binary system PSR B1259-63/LS 2883 around the 2010-2011 periastron passage
• The 2000 Periastron Passage of PSR B1259-63
• Long-term periodicity in LSI+61303 as beat frequency between orbital and precessional rate
• Intrinsic physical properties and Doppler boosting effects in LSI+61303
• Discovery of a periodical apoastron GeV peak in LS I +61°303

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• Evidence for periodic accretion-ejection in LSI+61303
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• Understanding the periodicities in radio and GeV emission from LS I+61303
• A Precessing Jet Scenario for the Multi-Wavelength Long-Term Modulation of LS I +61${}^{\circ }$303
• Orbital and superorbital variability of LS I +61 303 at low radio frequencies with GMRT and LOFAR
• Hour time-scale QPOs in the X-ray and radio emission of LS I +61${}^{\circ }$303
• Owens Valley Radio Observatory monitoring of LS I +61°303 completes three cycles of the super-orbital modulation
• Rapid X-ray variability of the gamma-ray binary LS I+61 303
• Radio/X-ray correlations and variability in the X-ray binary LS I +61°303