Opening New Windows on Dark Matter in the X-ray Sky
Kerstin Perez A Rainbow of Dark Sectors ACP Winter Workshop March 22, 2021 * Photo from 33 km up in the air! Prototype GAPS balloon flight, June 2012 See poster: Field Rogers “Low-energy Cosmic Antinuclei for Dark Matter” The sky from low to high-energy
Optical, IR, UV: X-rays: Gamma-rays: FERMI HUBBLE NuSTAR + CHANDRA
HESS CHANDRA
HUBBLE + SPITZER
Accreting black holes, Stars and gas white dwarfs, neutron stars; Pulsars, supernovae, supernovae, very hot gas, active galactic nuclei scattering by cosmic rays K. Perez - MIT 2 NuSTAR: first focusing high-energy X-ray telescope
Launched June 2012
1. Two co-aligned, multilayer coated, grazing incidence focusing optics 3. CdZnTe pixel detector spectrometers 2. Deployable 10 m mast
Harrison+ (2013) arxiv:1301.7307
3 NuSTAR: first focusing high-energy X-ray telescope
• Energy Band: 3-79 keV • Angular Resolution: 58” (HPD), 18” (PSF) • Field-of-view: 12’ x 12’ • Energy resolution (FWHM): 0.4 keV at 6 keV, 0.9 keV at 60 keV • Temporal resolution: 0.1 ms • Maximum Flux Rate: 10k ct/s • ToO response: <24 hours
Harrison+ (2013) arxiv:1301.7307
4 Focus on the Galactic Center • High density of both astrophysical X- rays and dark matter 2° INTEGRAL E = 20-40 keV
E = 10-40 keV >2 Ms exposure 1.5°
G. Belanger, et al. (2006)
K. Mori+ (2015) arxiv:1510.04631
5 K. Mori+ (2015) arxiv:1510.04631 Massive, magnetically accreting population in the central ~10 pc
10-20 keV Perez+ Nature (2015) XMM Fe-Ka contours
Echoes of X-ray, cosmic-ray
Field Rogers injection in molecular clouds? (NSF grad fellow) F. Rogers et al. (in prep.)
Constraining stellar remnant populations in galactic nuclei Hong+ (2016) arXiv:1605.03882
K. Perez - MIT 6 Adapting NuSTAR as a large-aperture DM telescope
• “0-bounce” photons that bypass the optics are typically a major background 3.5 deg • Novel analysis exploits >10x increase in efficiency for slowly-varying, diffuse signal • Expands energy range up to 160 keV
0.2 0.4 0.6 0.8
• High-resolution, small field-of-view (0.05deg2), snapshots of the sky
7 X-rays from sterile neutrino dark matter
Neutrino Minimal Standard Model 3 light SM neutrinos 3 sterile neutrinos: • only interact via neutrino oscillations • two heavy (>100 GeV) explain oscillations • one lighter (~keV) can account for DM
Sterile neutrino decay can provide a clear X-ray line signature
8 The sterile neutrino landscape
Only a narrow window remains in which sterile neutrinos (in the simplest models) can constitute all of dark matter
Require *model- More mixing momentum independent with standard distribution not Abazajian, Fuller neutrinos & Patel 2001; underproduce KA 2005 small-scale structure
Require correct dark matter Less mixing with abundance standard produced in the neutrinos early universe
9 …the “3.5 keV line”?
1. A faint line detected in XMM-Newton 2. Line consistent with observations using spectra of stacked galaxy clusters many instruments and astrophysical regions
Bulbul+ (2014)
10 …the “3.5 keV line”?
1. A faint line detected in XMM-Newton 2. Line consistent with observations using spectra of stacked galaxy clusters many instruments and astrophysical regions
Bulbul+ (2014)
3. Ruled out using full ~550Ms XMM-Newton data catalog? Foster+ (2021)
Dessert+ Science (2020)
11 Perez, Ng, Beacom+ (2017)
The Galactic Center/Bulge
(+) Large dark matter density (+) Large sensitivity from unfocused FOV (–) Galactic ridge emission incl. bright Fe lines Perez, Ng, Beacom+ (2017) K. Ng, Roach, Perez+ (2019)
M31 (Andromeda Galaxy)
105 FPMA FPMB 105 FPMA FPMB )] 1 )] 1 104 M31 (Andromeda Galaxy) 104 (cts keV ⇥ Inst. + solar (cts keV Inst. + solar 103 ⇥ Inst. + solar 0-b CXB Inst. + solar 0-b CXB 3 [keV 10 0-b CXB 0-b CXB [keV dE dN 2-b M31 2-b M31
E 2-b CXB 2-b CXB dE dN 2-b M31 2-b M31 2
E 2-b CXB 2-b CXB 10 1 2 102 10 10 1.2 101 102 1.0 1.2 0.8 1.0 0.8
Data / Model 0.6 1 2 1 2 10 Data / Model 0.6 10 10 10 1 2 1 2 10 E[keV] 10 10 10 E[keV] (+) No Fe emission lines (+) surveys dark matter from both core and halo (-) emission from M31 disk Perez, Ng, Beacom+ (2017) Ng, Roach, Perez+ (2019)
M31 (Andromeda Galaxy)
(+) minimal Galactic contamination (+) near center of the dark matter halo (-) seeing deviations from instrument background model
B. Roach, Ng, Perez+ (2020)
Off-plane Galactic Center Leading sensitivity across broad mass range
• Combination of Galactic center, Andromeda (M31), and Galactic bulge give leading constraints for masses 10-50 keV • Improve on previous constraints by over an order of magnitude in some mass ranges
Kenny Ng Brandon Roach (GRAPPA) (graduate student)
Cora Hersh (Haverford undergrad à MIT EAPS Ph.D.) See also: Foster et al. A deep search for decaying dark matter with XMM-Newton arXiv:2102.02207 (2021) 15 Stars as factories for axion-like particles (ALPs)
• Axions introduced to explain why the strong interactions preserve the CP symmetry (Peccei-Quinn mechanism) • Axion-like particles generic feature of many BSM models (e.g. string theory)
Couples to fermions Couples to photons
Compton Bremsstrahlung Primakoff
Most relevant process for stars! photon axion
photon*
Image: Hubble Telescope
17 Galactic magnetic fields
photon photon axion
NuSTAR photon* photon*
Image: Hubble Telescope
Jaffe (2019)
18 Betelgeuse
1. Hot core à predicted signal in the hard X-ray range 2. No stable corona à essentially zero standard astrophysical X-ray background 3. Relatively nearby, well- studied region
Dr. Mengjiao Xiao (postdoc researcher) M. Xiao, Perez, See also: Dessert, Foster, Safdi Gianotti+ X-ray searches for Axions from Super Star Clusters, PRL (2021) PRL (2021)
Image credit: Sky & Telescope Magazine 19 Astro observations constrain light axion-like particles
predicted axion spectra
data (background subtracted) Astro observations constrain light axion-like particles
predicted axion spectra
data (background subtracted)
Xiao, Perez, Gianotti+ PRL (2021)
• No excess of events over the expected background • Limits at least ~3x deeper than CAST • Comparable to next- generation axion experiments ALPS-II and Baby-IAXO Astro observations constrain light axion-like particles
• overlapping astrophysical constraints, with separate modeling assumptions and uncertainties • builds confidence in the exclusion of this corner of parameter space
Xiao, Perez, Gianotti+ PRL (2021)
See also: Dessert, Foster, Safdi X-ray searches for Axions from Super Star Clusters, PRL (2021) Novel X-ray Optics for the International Axion Observatory
• The International Axion Observatory (IAXO) is the successor to the current leading axion solar telescope, CAST • Axions from Sun re-converted to photons in large laboratory magnetic field • The X-ray optics assembly expands the technology developed for NuSTAR, XRISM, XMM-Newton, etc.
8 X-ray optics focus signal onto low- background detectors
JCAP 1906 (2019) 047 arXiv:1904.09155
23 • NuSTAR has delivered leading sensitivity to light dark matter and stellar backgrounds to new physics • Much of this sensitivity not foreseen before launch! • Looking forward to other new windows opening on our sky Backup
25 …Elephants in the Galactic center?
Measured MWD ~ 0.9MO is much heavier than implied by low-energy X-ray surveys
Higher temperature, All looking at the same elephant…that weighs ~0.9M proportional to MWD O Measured by hard X-rays
...and different animals altogether in the Galactic bulge: cooling material, Perez, Krivonos, Wik ApJ (2020) peak emissivity <10 keV Measured by soft X-rays
Hailey, Mori, Perez+ ApJ (2016) Hong+ ApJ (2016) – Point sources in central 100 pc 26 Population changes in the Galactic bulge
NuSTAR field-of-view (Module A) NuSTAR field-of-view (Module B)
~6° INTEGRAL image in 17-60 keV overlaid with stellar mass density distribution
Perez, Krivonos, Wik. ApJ (2020) • First broad-band X-ray Galactic observations of the Galactic bulge bulge confirm spectrum dominated by non-magnetic white Cosmic X-ray Background dwarf binaries • No hard X-ray emission >20 keV • Supports conclusions from Fe emission line measurements Xu et al. 2016; Yamauchi et al. 2016; Koyama 2018; Nobukawa et al. 2016
27 Origins of Central Hard X-ray Emission?
• Massive Intermediate Polars (IPs) …but
• Millisecond pulsars with non-thermal high-energy spectrum …but previously undiscovered large population (~3000) ?
• Bremsstrahlung and inverse Compton from Sgr A* particle outflows interacting with dense molecular material (Dogiel et al. 2015) … but no correlation with radio or radiation density models?
K. Perez - MIT 28 Point Sources in the inner 100 pc
• 70 hard (3-79 keV) X-ray point sources in a 0.6 deg2 region around Sgr A* with a total exposure of 1.7 Ms • 7 sources in the Sgr B2 field with 300 ks • Sensitive to ~4x1032 erg s-1 in 3-10 keV and ~8x1032 erg s-1 in 10-40 keV
NuSTAR 10-40 keV Trial Map J. Hong+ (2016) arxiv:1605.03882 NuSTAR point sources indicate heavy mCVs
• The NuSTAR (10-40 keV) J. Hong+ (2016) arxiv:1605.03882 and Chandra (0.5-8 keV) distributions match if the average spectra are Γ~1.5- 2 or kT ~ 20-50 keV
• High percentage with Fe lines (60%) and hard spectra support dominant mCV population
• High plasma temperature translates to MWD > 0.8MO • Consistent with average white dwarf mass measured by SDSS
K. Perez - MIT 30 Adapting NuSTAR as a large-aperture DM telescope
• “0-bounce” photons that bypass the optics are typically a major background 3.5 deg • Novel analysis exploits >10x increase in efficiency for slowly-varying, diffuse signal
0.2 0.4 0.6 0.8
31 Population changes in the Galactic bulge?
Xu (2016); Yamauchi+ (2016); Yuasa et al. (2012) ß Previous high-energy (>10keV) Nobukawa+ (2016); Koyama+ (2018) measurements of bulge and ridge indicate dominated by IPs
But recent low-energy (<10keV) Fe lines and continuum indicate dominated by quiescent dwarf novae~6° à
Perez, Krivonos, and Wik arXiv:1909.05916 (2019) Purely soft spectrum, no emission >20 keV
Supports dominated by dwarf novae, with no evidence of additional hard IP component
32 The sterile neutrino landscape Only a narrow window remains in which sterile neutrinos (in the simplest models) can constitute all of dark matter
Sterile neutrinos are *model- fermions, limits phase space independent distribution in a galaxy Abazajian, Fuller & Patel 2001; mDM > ~1 keV KA 2005
Require momentum distribution not underproduce small-scale structure
Require correct dark matter abundance be produced in the early universe
33 0-bounce technique allows leap-forward in sensitivity
NuSTAR Bullet Cluster
Total exposure: 0.6 Ms
(+) Huge DM mass in FOV
(–) Large astro. background (–) DM in focused FOV only
34 0-bounce technique allows leap-forward in sensitivity
NuSTAR Blank-sky
Total exposure: 7.5 Ms
(+) Long exposure (+) Low astro. background (+) Large sensitivity from unfocused FOV
(–) Low DM density
35 NuSTAR’s NEW “view” of the Galactic Center . INTEGRAL image in 17-60 keV
Module B Module A
4:00:00.0 2:00:00.0 0:00:00.0 358:00:00.0 356:00:00.0
Projected stellar mass density -3:00:00.0 1:00:00.0 3:00:00
0 0.05 0.15 0.35 0.74 1.5 3.1 6.2 13 25 365 We detect a line! (OK, lots of them…)
Galactic Bulge X-ray Emission: Cosmic X-ray Population of accreting stellar remnant binaries Background
A 3.5 keV (background) signal
• Set line flux limits: how much DM flux could we add without breaking the spectral fit? • Conservative method: allow DM line to assume full strength of any known line 37 Low astro emission reveals instrumental background
Good fit quality, but we are starting to see systematic deviations from the NuSTAR background model due to low astrophysical emission.
38 Towards closing the sterile neutrino window?
• >50 Ms (!!) NuSTAR catalog allows improved instrumental background model, increased sensitivity especially at low mass • Work underway with authors of NuSTAR background model (D. Wik, Utah)
Prospects for Micro-X rocket: Prospects for XRISM Satellite:
Figueroa-Feliciano+ 1506.05519
Bulbul et al. ApJ arXiv:1402.2301
39 Novel X-ray Optics for the International Axion Observatory
8 X-ray optics focus signal onto low- background detectors
SPIE Vol. 7473, p.107-114 (2009)
Expanding the NuSTAR slumped-glass technique to larger radii, lower cost
40