First results of X-shooter observations of IGR sources
aa r X i v : . [ a s t r o - ph . H E ] F e b First results of X-shooter observations of IGRsources
P. Goldoni ∗ † APC, Univ. Paris Diderot, CNRS/IN2P3, CEA/IRFU, Obs. de Paris, Sorbonne Paris Cité, FranceE-mail: [email protected]
S. Chaty
Laboratoire AIM (UMR-E 9005 CEA/DSM-CNRS-Université Paris Diderot), Irfu/Serviced’Astrophysique, CEA-Saclay and Institut Universitaire de France, 103, bd Saint Michel, Paris,France
A. Goldwurm
APC, Univ. Paris Diderot, CNRS/IN2P3, CEA/IRFU, Obs. de Paris, Sorbonne Paris Cité, France
A. Coleiro
Laboratoire AIM (UMR-E 9005 CEA/DSM-CNRS-Université Paris Diderot), Irfu/Serviced’Astrophysique, CEA-Saclay
X-shooter is a second generation ESO-VLT instrument that had its first light in October 2009. It isa single object medium-resolution spectrograph whose main feature is the capability of coveringsimultaneously in a single observation the range from 3000 to 24000 Angstrom. This uniquecapability is very well suited to investigate the complex spectra of the optical counterparts ofX/gamma ray sources which usually display signatures of different components in emission andabsorption. In July 2012 we observed with X-shooter a small sample of counterparts of brightIGR sources in order to better determine their physical properties. We present the first results ofthese observations. ’An INTEGRAL view of the high-energy sky (the first 10 years)’ 9th INTEGRAL Workshop and celebrationof the 10th anniversary of the launch,October 15-19, 2012Bibliotheque Nationale de France, Paris, France ∗ Speaker. † Based on observations collected at the European Organization for Astronomical Research in the Southern Emi-sphere, Chile under Program P089.D-0056(A) c (cid:13) Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlikeLicence. http://pos.sissa.it/ irst results of X-shooter observations of IGR sources
P. Goldoni
1. Introduction
INTEGRAL has discovered several bright sources in the Galactic plane, they are usually di-vided in two groups: obscured sources and SFXTs [2]. Their study is difficult due to their distance(> 1-15 kpc), absorption (line-of-sight and intrinsic) and the crowded fields in which they are found.Since their first discovery, several of them have been identified as High Mass X-ray Binaries. Thevast majority of them are quite bright in infrared and faint in the visible range due to extremelyhigh absorption (A(V) almost always greater than 10). Therefore the spectroscopic observationshave almost always been performed in infrared and for some of these sources, no visible spectrumis available. This is a problem because the best diagnostics of the properties of the primary starsuch as rotation, metallicity and mass loss lie in the visible and ultraviolet domains (see e.g. [8]). For the sources that do have visible spectra, they are not simultaneous with the infrared oneswhich may make the comparison unreliable due to the intrinsic variability of the primary star atleast concerning the emission features.The X-shooter spectrograph [17] with its exceptional wavelength range and its high sensitivityis very well placed to investigate on these matters allowing to monitor the known NIR spectrumwhile exploring the VIS and UVB spectrum whenever possible. In principle the comparison of thesimultaneous visible and infrared diagnostics should allow to constrain strongly the properties ofthe primary star. Moreover the line of sight absorption can be studied thoroughly by measuringthe total reddening with the SED and measuring the equivalent width and, for identified lines, theDoppler shifts of ISM absorption features. We asked for 2.5 nights of French GTO time to observea sample of eleven IGR sources in order to perform a first test of X-shooter capabilities on thesesources. We aimed at observing all the sources of the sample at least twice to check for variablefeatures. Unfortunately, due to bad weather, we could observe only one night and therefore onlyseven sources could be observed once. Here we report on the first results of these observations forthree of the sources in our sample.
2. Observations and Data Reduction
The main observations consisted of four different pointings of 300 s each taken using thenodding along the slit technique with an offset of 5 arcsec between pointings in a standard ABBAsequence. In order to avoid saturation, all the exposures on the NIR arm and some of those in theVIS arm were split in shorter integrations. All of these pointings were performed using narrow slits(0.5 ′′ for the UVB arm, 0.7 ′′ for the VIS arm and 0.6 ′′ for the NIR arm) (see table 1 for details).Each source was also briefly observed with a wide (5.0 ′′ ) slit to estimate the slit losses. A telluricA0V star was observed before each source and a flux standard was observed in the beginning ofthe night.The spectra were reduced using the X-shooter pipeline [6, 9]. We used the pipeline to buildcalibration files (master bias, wavelength solution...) from daytime calibration observations. Af-terwards we performed bias and dark subtraction followed by division by a master flat field. Theorders were then extracted, rectified in wavelength-slit space and then shifted and added to sub-tract the sky contribution. The resulting 2D order spectra were then merged to produce the final 2Dspectrum and the 1D spectrum was extracted using a PSF-weighing scheme in IDL. The 1D spectra2 irst results of X-shooter observations of IGR sources P. Goldoni were subsequently normalized. Flux calibrations and telluric corrections have not been performedyet.
Table 1:
Summary of the narrow slit observations for the three sources presented here. Four independentpointings of 300s each were performed in a standard nodding ABBA sequence. Each pointing in the NIRarm was split in 20 independent exposures each one with up to 6 independent integrations that are averagedby the detector. The exposure time is given as N(exposure) x N(integrations) x (Detector Integration Timeor DIT).
Source Name Coordinates Exptime (s) Slit Width ( ′′ )(J2000) UVB, VIS, NIR UVB, VIS, NIRIGR J16465 − ′′ , 0.7 ′′ , 0.6 ′′ IGR J18483 − ′′ , 0.7 ′′ , 0.6 ′′ IGR J16418 − ′′ , 0.7 ′′ , 0.6 ′′
3. IGR J16465 − This source has been classified as a supergiant of spectral type B0-B1 ([11],[2]) or O9.5 [13].Spectroscopic observations have been performed from the U (3900 Å) to the K band. We clearlydetect IGR J16465 − a feature (not shown)and several He I features. Figure 1:
Left: Section of the UVB spectrum of IGR J16465 − − ∼ In figure 1 we show the first I band spectrum of IGR J16465 − irst results of X-shooter observations of IGR sources P. Goldoni
Figure 2:
Left: section of the I band spectrum of IGR J18483 − ∼ − g lines in absorption. The HeI 10830 Å emission line has a slightly asymmetric profile whichmay be of P Cygni type however a nore careful analysis is required. The feature at 10780 Å proposed as apossible DIB by [7] is also present. More quantitatively, we estimated the spectral type with the properties of the Paschen lines usingthe approach of [1]. We measured the equivalent width of the Paschen-11 and Paschen-17 linesobtaining ∼ ∼ ∼ ∼ ∼ ∼ ∼
4. IGR J18483 − IGR J18483 − − a line is visible, similar to [5].From the I band spectrum in Figure 2 we measured the equivalent width of the Paschen-11 andPaschen-17 lines obtaining respectively 2.1 Å and 0.6 Å thus validating the spectral classifica-tion by [15]. We detect the 8620 Å DIB with EW ∼ ∼ ∼ irst results of X-shooter observations of IGR sources P. Goldoni
Figure 3:
Left: Section of the I band spectrum of IGR J16418 − − g mainly in absorption. They alsoshow small emission bumps consistent with the presence of moderate winds. The absorption feature notmarked between He I 21614 Å and Brackett g is a telluric feature.
5. IGR J16418 − IGR J16418 − ∼ ∼ g . Their equivalent widths arerespectively ∼ ∼
6. Conclusions
We have presented the first results of our X-shooter observations of a sample of IGR sources.Taking advantage of the unprecedented spectral coverage, we could compare the results in dif-ferent spectral domains. On this basis we suggest that IGR J16465 − − − irst results of X-shooter observations of IGR sources P. Goldoni
However in two of three cases the extinction estimations we obtain are compatible with publishedones only if we assume non standard extinction curves.
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