2020A&A...640A.124P


C.D.S. - SIMBAD4 rel 1.7 - 2020.10.26CET14:37:58

2020A&A...640A.124P - Astronomy and Astrophysics, volume 640A, 124-124 (2020/8-1)

The EXOD search for faint transients in XMM-Newton observations: Method and discovery of four extragalactic Type I X-ray bursters.

PASTOR-MARAZUELA I., WEBB N.A., WOJTOWICZ D.T. and VAN LEEUWEN J.

Abstract (from CDS):


Context. The observations carried out with XMM-Newton have produced a very extensive X-ray source catalogue in which the standard pipeline determines the variability of sufficiently bright sources through χ2 and fractional variability tests. Faint sources, however, are not automatically checked for variability, and this means that faint, short timescale transients are overlooked. From dedicated X-ray searches, as well as optical and radio archive searches, we know that some such dim sources can still be identified with high confidence.
Aims. Our goal is to find new faint, fast transients in XMM-Newton EPIC-pn observations. To that end we created the EPIC-pn XMM-Newton outburst detector (EXOD) algorithm, which we run on the EPIC-pn full-frame data available in the 3XMM-DR8 catalogue.
Methods. In EXOD, we computed the variability of the whole field of view by first binning in time the counts detected in each pixel of the detector. We next computed the difference between the median and maximal number of counts in each time bin and pixel to detect variability. We applied EXOD to 5751 observations in the full frame mode and compared the variability of the detected sources to the standard χ2 and Kolmogorov-Smirnov (KS) variability tests.
Results. The algorithm is able to detect periodic and aperiodic variability, with both short and long flares. Of the sources detected by EXOD, 60-95% are also shown to be variable by the standard χ2 and KS tests. EXOD computes the variability over the entire field of view faster than the light curve generation takes for all the individual sources. We detect a total of 2961 X-ray variable sources. After removing the spurious detections, we obtain a net number of 2536 variable sources. Of these we investigate the nature of 35 sources with no previously confirmed classification. Amongst the new sources, we find stellar flares and AGNs, in addition to four extragalactic type I X-ray bursters that double the known neutron-star population in M 31.
Conclusions. This algorithm is a powerful tool for the prompt detection of interesting variable sources in XMM-Newton observations. EXOD also detects fast transients that other variability tests would classify as non-variable due to their short duration and low number of counts. This is of increasing importance for the multi-messenger detection of transient sources. Finally, EXOD allows us to identify the nature of compact objects through their variability and to detect rare compact objects. We demonstrate this through the discovery of four extragalactic neutron-star low-mass X-ray binaries, doubling the number of known neutron stars in M 31.

Abstract Copyright: © ESO 2020

Journal keyword(s): methods: data analysis - X-rays: general - X-rays: binaries - X-rays: bursts - stars: flare

Status at CDS : Tables of objects will be appraised for possible ingestion in SIMBAD.

Simbad objects: 19

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Number of rows : 19

N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2020
#notes
1 CXOM31 J004210.9+411248 X 00 42 10.917 +41 12 48.05           ~ 8 0
2 [ZGV2011] 27 LXB 00 42 12.17 +41 17 58.6           ~ 2 0
3 M 31 G 00 42 44.330 +41 16 07.50 4.86 4.36 3.44     ~ 11053 1
4 [ZGV2011] 23 LXB 00 43 07.51 +41 20 19.4           ~ 2 0
5 FRB 110214 rB 01 21 17.0 -49 47 11           ~ 14 0
6 NGC 752 OpC 01 57 41 +37 47.1           ~ 543 0
7 WISEA J051237.57-161925.2 PM* 05 12 37.5100534646 -16 19 24.308982942           ~ 2 0
8 FRB 121102 rB 05 32 09.60 +33 05 13.4           ~ 360 0
9 Cl* NGC 2632 HSHJ 283 * 08 39 41.6615276590 +19 29 00.618567822           M6V 13 0
10 V* V1129 Cen bL* 12 39 07.8949564904 -45 33 44.148062587   9.99 9.65 9.46   F2V 19 0
11 2MASX J13020015+2746579 AGN 13 02 00.1380286789 +27 46 57.858881675   15.4       ~ 61 0
12 2MASS J16415078-4532253 HXB 16 41 50.7854893198 -45 32 25.452141297           O8.5(sg?) 93 2
13 LSQ J172554.8-643839 CV* 17 25 54.8 -64 38 39           ~ 3 0
14 2XMM J173046.8+521847 AG? 17 30 46.85 +52 18 47.1           ~ 2 0
15 [SKM2002] 27 LXB 17 45 35.65 -29 01 34.0           ~ 156 1
16 NAME Gal Center reg 17 45 40.04 -29 00 28.1           ~ 11760 0
17 CXOU J174610.8-290019 X 17 46 10.81 -29 00 19.8           ~ 3 0
18 RX J1914.4+2456 XB* 19 14 26.09 +24 56 44.6           ~ 123 0
19 NAME Sgr 1935+2154 * 19 34 55.68 +21 53 48.2           ~ 104 1

    Equat.    Gal    SGal    Ecl

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2020.10.26-14:37:58

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