Planck confirms SWIFT J1508.6-4953 / PMN J1508-4953 to be a flat-spectrum radio source

ATel #4183; M. Tuerler, R. Walter, C. Ferrigno (ISDC, University of Geneva, Switzerland)
on 18 Jun 2012; 13:39 UT
Credential Certification: Carlo Ferrigno (Carlo.Ferrigno@unige.ch)

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Landi et al. (ATel #4167) suggested that SWIFT J1508.6-4953 could be a flat spectrum radio quasar (FSRQ). Evidence for this is the association of this hard X-ray source detected both by Swift/BAT and INTEGRAL/IBIS with the radio source PMN J1508-4953 and a GeV source detected by Fermi. The hard photon index (Γ<2) of the associated Swift/XRT source together with the steeper Fermi spectrum (Γ>2) further suggests the blazar to be low-frequency peaked.

Using the HEAVENS web interface provided by the ISDC (http://isdc.unige.ch/heavens/) we obtained the Planck spectrum of this source as reported in the Early Release Compact Source Catalog (Planck collaboration 2011, A&A 536, A7). Planck has detected a positionally consistent source at four different frequencies: 30 GHz, 70 GHz, 100 GHz and 143 GHz. The Planck source names, coordinates, positional error and associated fluxes in the four separate frequency catalogs are:

 
Planck Identification      Freq.       RA       DEC    Pos. Err     Flux 
                          (GHz)      (deg)     (deg)   (arcmin)     (Jy) 
PLCKERC030 G324.37+07.16    30       227.14   -49.92     5.3      0.68±0.12 
PLCKERC070 G324.39+07.19    70       227.15   -49.87     0.9      1.26±0.17 
PLCKERC100 G324.39+07.17   100       227.15   -49.89     1.0      1.11±0.08 
PLCKERC143 G324.39+07.17   143       227.15   -49.89     0.7      0.92±0.06 

The Planck spectrum constructed with these values has an overall spectral index of about α = 0.1 (defined by F_ν ∝ ν^α) typical of a flat spectrum radio source (α > -0.5). This flat spectrum extends further towards lower-frequencies as measured for PMN J1508-4953 by the Australia Telescope 20 GHz Survey (AT20G): S_20GHz = 0.94 Jy, S_8.6GHz = 0.65 Jy, S_4.8GHz = 0.39 Jy (Massardi et al. 2008, MNRAS 384, 775).

The flat (or slightly convex) flux density spectrum measured over almost two decades in radio frequencies confirms that the source is a FSRQ or, alternatively, a low-frequency peaked BL Lac (LBL), depending on the presence or not of broad emission lines in the optical spectrum.

HEAVENS web interface