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Register a new userSub-luminous X-ray Bursters Unveiled with INTEGRAL
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In 2005 March 22nd, the INTEGRAL satellite caught a type-I X-ray burst from the unidentified source XMMU J174716.1-281048, serendipitously discovered with XMM-Newton in 2003. Based on the type-I X-ray burst properties, we derived the distance of the object and suggested that the system is undergoing a prolonged accretion episode of many years. We present new data from a Swift/XRT campaign which strengthen this suggestion. AX J1754.2-2754 was an unclassified source reported in the ASCA catalogue of the Galactic Centre survey. INTEGRAL observed a type-I burst from it in 2005, April 16th. Recently, a Swift ToO allowed us to refine the source position and establish its persistent nature.
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GRB031203 was a very low apparent luminosity gamma-ray burst (GRB). It was also the first GRB with a dust-scattered X-ray halo. The observation of the halo allowed us to infer the presence of a large soft X-ray fluence in the total burst output. It has, however, also been claimed that GRB031203 was intrinsically sub-energetic, representative of a class of spectrally hard, low-energy bursts quite different from other GRBs. Reanalysis of the available data confirms our original finding that GRB031203 had a very large soft X-ray component, the time of which can be constrained to within a few minutes after the burst, implying that while GRB031203 did indeed have a very low apparent luminosity, it was also very soft. Notions propagated in the literature regarding the uncertainties in the determination of the soft X-ray fluence from the halo data and on the available constraints from the hard X-ray data are addressed: the properties of the scattering dust along the line of sight (grain sizes, precise location and the geometry) are determined directly from the high quality X-ray data so that there is little uncertainty about the scatterer; constraints on the X-ray lightcurve from the Integral spacecraft at the time of the soft X-ray blast are not complete because of a slew in the spacecraft pointing shortly after the burst. Claims that GRB031203 was intrinsically under-energetic and that it represents a deviation from the luminosity-peak energy relation do not appear to be substantiated by the data, regardless of whether the soft X-ray component is declared part of the prompt emission or the afterglow. We conclude that the difference between the soft and hard X-ray spectra from XMM-Newton and Integral indicate that a second soft pulse probably occurred in this burst as has been observed in other GRBs, notably GRB050502B.
We present results of a ground-based near-infrared campaign with Palomar TripleSpec, Keck NIRSPEC, and Gemini GNIRS to target two samples of reddened active galactic nucleus (AGN) candidates from the 31 deg$^2$ Stripe 82 X-ray survey. One sample, which is $sim$89% complete to $K<16$ (Vega), consists of eight confirmed AGNs, four of which were identified with our follow-up program, and is selected to have red $R-K$ colors ($>4$, Vega). The fainter sample ($K>17$, Vega) represents a pilot program to follow-up four sources from a parent sample of 34 that are not detected in the single-epoch SDSS catalog and have {it WISE} quasar colors. All twelve sources are broad-line AGNs (at least one permitted emission line has a FWHM exceeding 1300 km s$^{-1}$) and span a redshift range $0.59 < z < 2.5$. Half the ($R-K$)-selected AGNs have features in their spectra suggestive of outflows. When comparing these sources to a matched sample of blue Type 1 AGNs, we find the reddened AGNs are more distant ($z > 0.5$) and a greater percentage have high X-ray luminosities ($L_{rm X,full} > 10^{44}$ erg s$^{-1}$). Such outflows and high luminosities may be consistent with the paradigm that reddened broad-line AGNs represent a transitory phase in AGN evolution as described by the major merger model for black hole growth. Results from our pilot program demonstrate proof-of-concept that our selection technique is successful in discovering reddened quasars at $z > 1$ missed by optical surveys.
The remnant of the supernova of 1006 AD, the remnant first showing evidence for the presence of X-ray synchrotron emission from shock-accelerated electrons, was observed for ~1000 ksec with INTEGRAL for the study of electron acceleration to very high energies. The aim of the observation was to characterize the synchrotron emission, and attempt to detect non-thermal bremsstrahlung, using the combination of IBIS and JEM-X spatial and spectral coverage. The source was detected with JEM-X between 2.4 and 8.4 keV bands, and not detected with either ISGRI or SPI above 20 keV. The ISGRI upper limit is about a factor of four above current model predictions, but confirms the presence of steepening in the power-law extrapolated from lower energies (< 4 keV).
We have discovered three certain (SAX J1324.5-6313, 2S 1711-339 and SAX J1828.5-1037) and two likely (SAX J1818.7+1424 and SAX J2224.9+5421) new thermonuclear X-ray burst sources with the BeppoSAX Wide Field Cameras, and observed a second burst ever from a sixth one (2S 0918-549). Four of them (excluding 2S 1711-339 and 2S 0918-549) are newly detected X-ray sources from which we observed single bursts, but no persistent emission. We observe the first 11 bursts ever from 2S 1711-339; persistent flux was detected during the first ten bursts, but not around the last burst. A single burst was recently detected from 2S 0918-549 by Jonker et al.(2001); we observe a second burst showing radius expansion, from which a distance of 4.2 kpc is derived. According to theory, bursts from very low flux levels should last ~100 s. Such is indeed the case for the last burst from 2S 1711-339, the single burst from SAX J1828.5-1037 and the two bursts from 2S 0918-549, but not for the bursts from SAX J1324.5-6313, SAX J1818.7+1424 and SAX J2224.9+5421. The bursts from the latter sources all last ~20 s. We suggest that SAX J1324.5-6313, SAX J1818.7+1424, SAX J1828.$-1037 and SAX J2224.9+5421 are members of the recently proposed class of bursters with distinctively low persistent flux levels, and show that the galactic distribution of this class is compatible with that of the standard low-mass X-ray binaries.
New observations suggest that high redshift quasars can be turned into Gamma Ray Bursters and BL Lacertids by interaction with absorbing clouds in their vicinity.
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