INTEGRAL survey of the Cassiopeia region in hard X rays

Abstract

We report on the results of a deep 1.6 Ms INTEGRAL observation of the Cassiopeia region performed from December 2003 to February 2004. Eleven sources were detected with the imager IBIS-ISGRI at energies above 20 keV, including three new hard X-ray sources. Most remarkable is the discovery of hard X-ray emission from the anomalous X-ray pulsar 4U 0142+61, which shows emission up to ∼150 keV with a very hard power-law spectrum with photon index Γ = 0.73 ± 0.17. We derived flux upper limits for energies between 0.75 MeV and 30 MeV using archival data from the Compton telescope COMPTEL. In order to reconcile the very hard spectrum of 4U 0142+61 measured by INTEGRAL with the COMPTEL upper limits, the spectrum has to bend or break between ∼75 keV and ∼750 keV. 1E 2259+586, another anomalous X-ray pulsar in this region, was not detected. INTEGRAL and COMPTEL upper limits are provided. The new INTEGRAL sources are IGR J00370+6122 and IGR J00234+6144. IGR J00370+6122 is a new supergiant X-ray binary with an orbital period of 15.665 ± 0.006 days, derived from RXTE All-Sky Monitor data. Archival BeppoSAX Wide-Field Camera data yielded four more detections. IGR J00234+6144 still requires a proper identification. Other sources for which INTEGRAL results are presented are high-mass X-ray binaries 2S 0114+650, γ Cas, RX J0146.9+6121 and 4U 2206+54, intermediate polar V709 Cas and 1ES 0033+595, an AGN of the BL-Lac type. For each of these sources the hard X-ray spectra are fitted with different models and compared with earlier published results.

The first multi-wavelength campaign of AXP 4U 0142+61 from radio to hard X-rays

“…The INTE-GRAL spectrum is in agreement with previously found results, however, thanks to the high effective exposure in this dedicated observation the maximum energy up to which 4U 0142+61 could be detected is now higher, namely 230 keV. The spectrum, described with a power-law model with photon index Γ = 0.79 ± 0.10 and luminosity 8.7 × 10 34 erg s −1 (20-100 keV, d = 3.6 kpc) can be compared with the spectral results reported earlier by den Hartog et al (2006) using an independent data set: Γ = 0.73 ± 0.17 and luminosity 8.5 × 10 34 erg s −1 (20-100 keV, d = 3.6 kpc). Kuiper et al (2006) derived Γ = 1.05 ± 0.11 and luminosity 8.1 × 10 34 erg s −1 (20-100 keV, d = 3.6 kpc).…”

“…For 4U 0142+61, the best fit parameters are a black-body temperature of kT ∼ 0.4 keV and a power-law photon index of Γ ∼ 3.4. 4U 0142+61 was detected by den Hartog et al (2006) in hard X-rays up to 150 keV in 1.6 Ms of INTEGRAL observations (see also Kuiper et al 2006). The 20-150 keV flux was measured to be (9.7 ± 0.9) × 10 −11 erg cm −2 s −1 .…”

“…Assuming that the hard X-ray flux is stable, a spectral break has to occur in the hard X-ray regime below ∼750 keV in order for the spectrum not to be in conflict with the COMP-TEL upper limits. den Hartog et al (2006) and Kuiper et al (2006) were not able to measure such a break, but a hint was found with a 2.3σ fit improvement when a high-energy cutoff was added to the power-law model by . The indication for the cutoff was found at an energy of 73 ± 15 keV.…”

Unveiling soft gamma-ray repeaters with INTEGRAL

“…Hard X-ray emission has been detected from three AXPs with INTEGRAL: 1E 1841-045 [35], 4U 0142+61 [11] and 1RXS J170849-400910 [42]. The presence of pulsations seen with RXTE up to ∼200 keV in 1E 1841-045 ( [19]) proofs that the hard Xray emission originates from the AXP and not from the associated supernova remnant Kes 73.…”

Observations of the magnetars 4U 0142+61 and 1E 2259+586 with the MAGIC telescopes

“…2). In the case of 4U 0142+61, the 0.1-200 keV data are from XMM-Newton-PN and INTEGRAL-ISGRI (Rea et al 2007a;den Hartog et al 2008;Gonzalez et al 2010) plotted together with the 2σ COMPTEL upper limits (den Kuiper et al 2006). For 1E 2259+586 we show data points from XMMNewton-PN (Woods et al 2004) together with COMPTEL upper limits .…”