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Swift follow-up confirms S4 1030+61 as the counterpart of 1FGL J1033.8+6048

ATEL # 2628; F. D'Ammando (INAF - IASF Palermo), K. V. Sokolovsky (MPIfR/ASC Lebedev), S. Ciprini (Perugia University and ASI-INAF, Italy) on behalf of the Fermi Large Area Telescope Collaboration and L. Vetere (PSU)
on 19 May 2010; 21:56 UT
Distributed as an Instant Email Notice (Request for Observations)
Password Certification: Filippo D'Ammando (

Subjects: Optical, Ultra-Violet, X-ray, Gamma Ray, Request for Observations
Referred to by ATEL #: 3062

Following the Fermi-LAT detection of a GeV flare from 1FGL J1033.8+6048 on 2010 May 14 (ATel #2622), Swift Target of Opportunity observations were performed on May 17 in order to identify which of the two suggested flat-spectrum radio quasars is associated with the flaring gamma-ray source: S4 1030+61 or GB6 J1032+6051 (separated by 7'). Of these two candidates S4 1030+61 was found in a high X-ray and UV/optical state, while GB6 J1032+6051 was in a low state below the detection limit in both bands.

The Swift/XRT spectrum of S4 1030+61 can be fit (0.3-10 keV) with an absorbed power law model with a column density consistent with the Galactic value in the direction of the source (n_H = 6.58e19 cm^-2, Kalberla et al. 2005) and a photon index of 1.46+/-0.16. The corresponding unabsorbed 0.3-10 keV flux is (2.2+/-0.3)e-12 erg cm^-2 s^-1. Comparison with the flux of S4 1030+61 observed by XRT on 2009 March 7, (6.0+/-1.6)e-13 erg cm^-2 s^-1, shows an increase by a factor of 3.5.

Multicolor Swift/UVOT observations found S4 1030+61 in a flaring state (V=15.87+/-0.03), about 3 magnitudes brighter than on 2009 March 7 in all six UV and optical filters.

The Swift observation identifies S4 1030+61 as the counterpart of 1FGL J1033.8+6048, as already suggested by the recent detection of its optical (ATel #2623) and near-infrared (ATel #2625) outburst with the ground-based telescopes.

In consideration of the ongoing activity of this source we encourage further multiwavelength observations. Multi-frequency (5-43 GHz) VLBA as well as additional Swift observations of S4 1030+61 are planned. For this source the Fermi LAT contact persons are E. Wallace ( and K. Sokolovsky (

We thank the Swift team for their rapid scheduling of these observations.

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R. E. Rutledge , Editor
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