A Search for Pulsar Companions Around Extremely Low Mass White Dwarfs 14th BONN workshop 1 7 F e b . 2 0 2 0 Tilemachos M. Athanasiadis Supervisors: Dr. John Antoniadis, Prof. Dr. Michael Kramer
• Usually • Single star evolution needs more than a Hubble time to create a LMWD 50% of the LMWDs of ~0.4M ☉ are expected to exist in binaries • or ELM WDs should exist • Possible dark companions: Another WD • Black hole • • Optical surveys have discovered LMWDs and through optical spectroscopy orbital parameters are measured.
LMWD+MSPs are ideal for through timing of the MSP and optical spectroscopy of the LMWD (for example Antoniadis et al. 2013). Very few NS mass measurements are currently available. Observational among the double-degenerate population. This information is a crucial missing input in stellar- evolution and population synthesis models.
Outline PROJECTS ELM follow-up Survey Effelsberg GAIA follow-up Survey Effelsberg GAIA follow-up Survey Arecibo
• ELM survey target selection: • Sloan Digital Sky Survey (SDSS) photometric catalog by color. Objects with • • Our target selection: • ELM WDs in binaries with a dark companion with mass > 0.8 M ☉ . for MSP companions observed by M. Berezina & L. Spitler (Effelsberg-2014) • For these systems there are also spectroscopic observations .
Athanasiadis et al. 2020 (in prep.)
90 min 30 min P orb *10% • The 3 most compact systems was observed J0751-0141 J+A J+A A for 90 minutes each. • 5 systems was observed multiple times J0755+4800 n.o. A - for 30 minutes per session. J0755+4906 J+A J+A A • SIGPROC: Acceleration (A) and/or Jerk (J) search applied based on the orbital period. J0811+0225 n.o. A - • Acceleration and jerk range based on J1233+1602 n.o. J+A A each system • DM range: 0-100 (calc. based on NE2001) J1443+1509 n.o. J+A A J1741+6526 J+A J+A A J2132+0754 n.o. A - Our SIGPROC-PRESTO pipeline are based on the HTRU-N pipeline (M. Cruces)
• Inject simulated pulsar signals into real Effelsberg noise. • We have used that tool to have a better understanding of the sensitivity of our survey. • ~0.1 mJy error before RFI mitigation • ~0.05 mJy error after RFI mitigation
We simulate 10000 companions for MONTE CARLO SIMULATION OF COMPANIONS FOR EACH SYSTEM every LMWD in a specific distance d assuming a (GAIA) percentance of NSs within the using random Luminosity companions based on (S v d 2 ) from distribution the mass function ( Gonthier 2018) Flux density S v using random P spin from Compare S v with the survey Flux density S v distribution sensitivity as function of P s Spin period P s (Lorimer 2015) using a beaming fraction Flux density S v model Spin period P s (Tauris & Manchester 1998) Beaming DETECTION RATE Assumption: The acceleration range that we use in Probability for each our search is enough to detect the systems that we system to host a NS. are looking for.
Athanasiadis et al. (paper A) Athanasiadis et al. (paper A) Athanasiadis et al. 2020A Flux Density (mJy) Flux Density (mJy)
Flux Density (mJy) Flux Density (mJy) Athanasiadis et al. 2020A
Probability of P NS P NS detection mass func after obs Athanasiadis et al. 2020A
Precise proper motions for 1.5 billion objects in the Galaxy. ~500,000 WDs with hydrogen atmospheres, ~30,000 LMWDs with M < 0.25 solar masses EFFELSBERG GAIA FOLLOW UP SURVEY Well known and small distances (<1.5 kpc) Telescope Effelsberg Radio Telescope Different astrometric properties (due to the Receiver 7-beam receiver (21 cm) supernova kick) : Targets 104 selected GAIA white dwarfs high proper motion high galactic latitudes Obs. time 2x30 min Sensitivity 0.125 mJy
Athanasiadis et al. 2020b NS fraction is the percentance of the LMWD/NS binaries compared to other double GAIA follow up survey degenerate binaries. 104 targets Upper limit: P NS < 0.031 Binomial distribution: det N L ~ ( 1 P P ) NS Upper limit based on van Leewen et al. ELM follow up survey 8 targets 2007: Upper limit: P NS < 0.35 1 / N 1 1 / 2 P 0 . 0073 GAIA NS P survey det 1 / N 1 1 / 2 ELM P 0 . 09 survey NS P det
• We have strong motivation to search for radio pulsars at the positions of low mass white dwarfs. • Both detections and non-detections are useful: Detection > Precise NS mass measurements • • Non-detections > Constraints on the LMWD/NS population • Survey sensitivity, beaming fraction and distance are the most important factors regarding the detection rate. • Based on our results, we expect the fraction of LMWD/NS systems to be close to zero and not higher than ~3%.
TARGET SELECTION: High tranverse velocities High galactic latitudes Cross-matched with 3FGL Fermi catalog (<0.5 o positional difference) ARECIBO GAIA FOLLOW UP SURVEY Telescope Arecibo Radio Telescope Receiver L-wide (1.15-1.73 GHz) Targets 42 selected GAIA white dwarfs (some with Fermi counterparts) Obs. time 15 min Sensitivity 0.016 mJy for a 2ms pulsar at DM=100pc/cm 3
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BACKUP SLIDES
Beaming fraction model for MSPs MSPs are considered to have large beaming fraction values Tauris & Manchester (1998) Consistent with Kramer et al 1999 MSPs
• P det = N MSPs /N NS Athanasiadis et al. 2020 • We simulate a population of NS companions for a LMWD in different (well known) parallaxes. • We calculate how many pulsars the survey would have detected. • For systems with parallax higher than 0.5 mas (d<2kpc) the P det is constant. • P det cannot go higher than ~90% due to the beaming fraction.
• For each NS companion (MSP candidate), we assume a random: from a spin distribution based on Lorimer 2015 . based on Tauris & Manchester 1998. (based on Gonthier et al. 2018) within the distance error based on MSPs GAIA DR2. • From the Luminosity (L) and distance (r) we calculate the : (L/4πr 2 ) • Comparing the flux density with the sensitivity of the survey provide us with the Lorimer (2008)
Athanasiadis et al. (paper A) Athanasiadis et al. (paper A)
Li et al. 2019 Li et al. 2019
• Possible companions of LMWDs: Another WD • • Neutron star Black hole • • No hydrogen shell flashes occur during the ELM WD cooling stage in contrast with more massive WDs. In the latter case the hydrogen-rich envelope is loosing mass, therefore they have thiner envelopes. • • WDs have thicker envelopes which allow for significantly higher stable hydrogen burning rates, ELM WDs are much more luminous than their more massive companions (Driebe et al. 1999) . •
Athanasiadis et al. (paper A)
Athanasiadis et al. (paper A) Athanasiadis et al. (paper A)
EFFELSBERG GAIA FOLLOW UP SURVEY Telescope Effelsberg Radio Telescope The DATA are archived and easily accesible on Receiver 7-beam receiver (21 cm) HERCULES cluster. Targets 104 selected GAIA white dwarfs Useful scripts for easy retrieval and reprocessing Obs. time 2x30 min Sensitivity 0.125 mJy Acceleration-Jerk on 30 min observ. Acceleration search on 10 min FFA with acceleration search observations (in coop. with T. Gautam) Sensitive to systems with Porb > 5 hours Sensitive to systems with Period range: Porb > 1,6 hours 0.5-30 seconds Acceleration range: ± 100 km/s 2 Acceleration range: ± 500 km/s 2 random discoveries Jerk range: ± 4cm/s 3 DM range: 0-2000 Single pulse search (PRESTO) DM range: 0-2000 Our SIGPROC-PRESTO pipelines are based on the HTRU-N pipeline (M. Cruces)
Test pulsars Known MSPS-WD systems observed as tests of the pipeline: Binary Period DM P_orb S1400 (ms) (pc*cm^-3) (hours) (mJy) J2053+4650 12.58 98.08 2.4 J1738+0333 5.85 33.77 8.5 0.67 J0751+1807 3.47 30.24 6.3 3.2 J0348+0432 3.9 40.46 2.4
Acceleration range We need to be sure that the acceleration range that we use is enough for the objects that we are looking for. (Handbook, Lorimer & Kramer) Acceleration range depends on masses and the orbital period: Red: MSP+WD (1+0.25 solar masses) Green: NS+NS (1+2 solar masses) Black: BH+BH (10+10 solar masses) Athanasiadis et al. 2019 (in prep.)
Expected Orbital Periods (MSPs+He WDs) Tauris et al. 1999
ARECIBO OBSERVATIONS PART II Graphical example of our selection method. Clustering based on a gaussian mixture model based on their transverse velocity and galactic latitude. Our algorithm clusters nearby GAIA LMWDs into 4 distinct in the galactic latitute/velocity plane. Known MSPs (in green) belong exclusively in two of these clusters.
Luminosity distribution for MSPs Based on all-sky surveys carried out in the 90s and for pulsars observed at 430 MHz within 1.5 kpc of the Sun. Severe undersampling of low- luminosity pulsars. The observed (dashed line) and corrected (solid line) luminosity distribution for MSPs. Power law with a slope of -1 Lorimer 2008
• For every system: • Known parameters: orbital period, mass function • For random orientations: MC simulation of companions neutron stars 1.4 < M < 2.5 Ozel & Freire 2016 Athanasiadis et al. (paper A)
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