About

Robert P. Kirshner is the Clowes Research Professor of Science, Emeritus at the Department of Astronomy at the Center for Astrophysics | Harvard & Smithsonian. His research interests include observations of supernovae for their intrinsic properties and their applications in cosmology, utilizing telescopes such as HST, Magellan, MMT, and the Whipple Observatory. He focuses on the use of rest frame infrared observations of Type Ia supernovae to enhance measurements of dark energy properties. Additionally, he is engaged in an ongoing Hubble Space Telescope study of SN 1987A, the brightest supernova since 1604. Professor Kirshner graduated from Harvard College in 1970 and earned a Ph.D. in Astronomy at Caltech. His early career included a postdoctoral position at the Kitt Peak National Observatory and a nine-year faculty appointment at the University of Michigan. In 1986, he joined the Harvard Astronomy Department. He served as Chairman of the Department from 1990 to 1997 and was the head of the Optical and Infrared Division of the CfA from 1997 to 2003. He also served as Master of Quincy House, one of Harvard’s undergraduate residences, from 2001 to 2007. Currently, he is the Executive Director of the Thirty Meter Telescope Project based in Mauna Kea, HI.

Research topics

• Astrophysics
• Physics
• Mathematical physics
• Astronomy
• Statistics

Selected publications

• The Compact Object and Innermost Ejecta of SN 1987A

  The Astrophysical Journal · 2025-09-22 · 2 citations

  articleOpen accessCorresponding

  Abstract The first JWST observations of SN 1987A provided clear evidence that a compact object is ionizing the innermost ejecta. Here, we analyze a second epoch of JWST NIRSpec and MIRI/Medium-Resolution Spectrometer observations to better characterize the properties of this region, aided by a higher spectral resolving power for the new NIRSpec data. We confirm the presence of the previously identified narrow lines from the central region, i.e., ([Ar vi ] 4.5292 μ m, [Ar ii ] 6.9853 μ m, [S iv ] 10.5105 μ m, and [S iii ] 18.7130 μ m), and also identify similar components in [Ca v ] 4.1585 μ m, [Cl ii ] 14.3678 μ m, and possibly [Fe ii ] 1.6440 μ m. These lines are blueshifted by ∼−250 km s −1 , while the emission region is spatially unresolved and located southeast of the center. The offset and blueshift could imply a kick velocity of 510 ± 55 km s −1 for the neutron star. We also identify [Ca iv ] 3.2068 μ m near the center, but it is displaced to the north and has a redshift of ∼700 km s −1 . We find that scattering by dust in the ejecta with a typical grain size ∼0.3 μ m can explain the [Ca iv ] properties and the absence of other narrow lines at shorter wavelengths, while dust absorption is important at λ ≳ 8 μ m. Photoionization models for a pulsar wind nebula and a cooling neutron star are both compatible with the observations, with the exception of the [Fe ii ] feature. The two models primarily differ at short wavelengths, where new lines are expected to emerge over time as the optical depth of dust in the expanding ejecta decreases.

  PublisherDOI

• Using Rest-Frame Optical and NIR Data from the RAISIN Survey to Explore the Redshift Evolution of Dust Laws in SN Ia Host Galaxies

  arXiv (Cornell University) · 2024-02-28 · 1 citations

  preprintOpen access

  ABSTRACT We use rest-frame optical and near-infrared (NIR) observations of 42 Type Ia supernovae (SNe Ia) from the Carnegie Supernova Project at low-z and 37 from the RAISIN (SNIA in the IR) Survey at high-z to investigate correlations between SN Ia host galaxy dust, host mass, and redshift. This is the first time the SN Ia host galaxy dust extinction law at high-z has been estimated using combined optical and rest-frame NIR data (YJ band). We use the BayeSN hierarchical model to leverage the data’s wide rest-frame wavelength range (extending to ∼1.0–1.2 μm for the RAISIN sample at 0.2 ≲ z ≲ 0.6). By contrasting the RAISIN and Carnegie Supernova Project (CSP) data, we constrain the population distributions of the host dust RV parameter for both redshift ranges. We place a limit on the difference in population mean RV between RAISIN and CSP of −1.16 < Δμ(RV) < 1.38 with 95 per cent posterior probability. For RAISIN we estimate μ(RV) = 2.58 ± 0.57, and constrain the population standard deviation to σ(RV) < 0.90 [2.42] at the 68 [95] per cent level. Given that we are only able to constrain the size of the low- to high-z shift in μ(RV) to ≲1.4 – which could still propagate to a substantial bias in the equation-of-state parameter w – these and other recent results motivate continued effort to obtain rest-frame NIR data at low- and high-redshifts (e.g. using the Roman Space Telescope).

  PublisherOA PDFDOI

• Using rest-frame optical and NIR data from the RAISIN survey to explore the redshift evolution of dust laws in SN Ia host galaxies

  Monthly Notices of the Royal Astronomical Society · 2024-04-23 · 13 citations

  articleOpen access

  ABSTRACT We use rest-frame optical and near-infrared (NIR) observations of 42 Type Ia supernovae (SNe Ia) from the Carnegie Supernova Project at low-z and 37 from the RAISIN (SNIA in the IR) Survey at high-z to investigate correlations between SN Ia host galaxy dust, host mass, and redshift. This is the first time the SN Ia host galaxy dust extinction law at high-z has been estimated using combined optical and rest-frame NIR data (YJ band). We use the BayeSN hierarchical model to leverage the data’s wide rest-frame wavelength range (extending to ∼1.0–1.2 μm for the RAISIN sample at 0.2 ≲ z ≲ 0.6). By contrasting the RAISIN and Carnegie Supernova Project (CSP) data, we constrain the population distributions of the host dust RV parameter for both redshift ranges. We place a limit on the difference in population mean RV between RAISIN and CSP of −1.16 < Δμ(RV) < 1.38 with 95 per cent posterior probability. For RAISIN we estimate μ(RV) = 2.58 ± 0.57, and constrain the population standard deviation to σ(RV) < 0.90 [2.42] at the 68 [95] per cent level. Given that we are only able to constrain the size of the low- to high-z shift in μ(RV) to ≲1.4 – which could still propagate to a substantial bias in the equation-of-state parameter w – these and other recent results motivate continued effort to obtain rest-frame NIR data at low- and high-redshifts (e.g. using the Roman Space Telescope).

  PublisherDOI

• Hubble Space Telescope images of SN 1987A: Evolution of the ejecta and the equatorial ring from 2009 to 2022

  arXiv (Cornell University) · 2024-03-21 · 2 citations

  preprintOpen access

  Supernova (SN) 1987A offers a unique opportunity to study how a spatially resolved SN evolves into a young supernova remnant (SNR). We present and analyze Hubble Space Telescope (HST) imaging observations of SN 1987A obtained in 2022 and compare them with HST observations from 2009 to 2021. These observations allow us to follow the evolution of the equatorial ring (ER), the rapidly expanding ejecta, and emission from the center over a wide range in wavelength from 2000 to 11 000 AA. The ER has continued to fade since it reached its maximum ~8200 days after the explosion. In contrast, the ejecta brightened until day ~11000 before their emission levelled off; the west side brightened more than the east side, which we attribute to the stronger X-ray emission by the ER on that side. The asymmetric ejecta expand homologously in all filters, which are dominated by various emission lines from hydrogen, calcium, and iron. From this overall similarity, we infer the ejecta are chemically well-mixed on large scales. The exception is the diffuse morphology observed in the UV filters dominated by emission from the Mg II resonance lines that get scattered before escaping. The 2022 observations do not show any sign of the compact object that was inferred from highly-ionized emission near the remnant's center observed with JWST. We determine an upper limit on the flux from a compact central source in the [O III] HST image. The non-detection of this line indicates that the S and Ar lines observed with JWST originate from the O free inner Si - S - Ar rich zone and/or that the observed [O III] flux is strongly affected by dust scattering.

  PublisherOA PDFDOI

• The Dark Energy Survey: Cosmology Results With ~1500 New High-redshift Type Ia Supernovae Using The Full 5-year Dataset

  arXiv (Cornell University) · 2024-01-05 · 37 citations

  preprintOpen access

  We present cosmological constraints from the sample of Type Ia supernovae (SN Ia) discovered during the full five years of the Dark Energy Survey (DES) Supernova Program. In contrast to most previous cosmological samples, in which SN are classified based on their spectra, we classify the DES SNe using a machine learning algorithm applied to their light curves in four photometric bands. Spectroscopic redshifts are acquired from a dedicated follow-up survey of the host galaxies. After accounting for the likelihood of each SN being a SN Ia, we find 1635 DES SNe in the redshift range $0.100.5$ SNe compared to the previous leading compilation of Pantheon+, and results in the tightest cosmological constraints achieved by any SN data set to date. To derive cosmological constraints we combine the DES supernova data with a high-quality external low-redshift sample consisting of 194 SNe Ia spanning $0.025

  PublisherOA PDFDOI

• The Dark Energy Survey: Cosmology Results with ∼1500 New High-redshift Type Ia Supernovae Using the Full 5 yr Data Set

  The Astrophysical Journal Letters · 2024-09-01 · 352 citations

  articleOpen access

  Abstract We present cosmological constraints from the sample of Type Ia supernovae (SNe Ia) discovered and measured during the full 5 yr of the Dark Energy Survey (DES) SN program. In contrast to most previous cosmological samples, in which SNe are classified based on their spectra, we classify the DES SNe using a machine learning algorithm applied to their light curves in four photometric bands. Spectroscopic redshifts are acquired from a dedicated follow-up survey of the host galaxies. After accounting for the likelihood of each SN being an SN Ia, we find 1635 DES SNe in the redshift range 0.10 &lt; z &lt; 1.13 that pass quality selection criteria sufficient to constrain cosmological parameters. This quintuples the number of high-quality z &gt; 0.5 SNe compared to the previous leading compilation of Pantheon+ and results in the tightest cosmological constraints achieved by any SN data set to date. To derive cosmological constraints, we combine the DES SN data with a high-quality external low-redshift sample consisting of 194 SNe Ia spanning 0.025 &lt; z &lt; 0.10. Using SN data alone and including systematic uncertainties, we find Ω M = 0.352 ± 0.017 in flat ΛCDM. SN data alone now require acceleration ( q 0 &lt; 0 in ΛCDM) with over 5 σ confidence. We find <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">Ω</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">M</mml:mi> </mml:mrow> </mml:msub> <mml:mo>,</mml:mo> <mml:mi>w</mml:mi> <mml:mo stretchy="false">)</mml:mo> <mml:mo>=</mml:mo> <mml:mo stretchy="false">(</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>0.264</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.096</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.074</mml:mn> </mml:mrow> </mml:msubsup> <mml:mo>,</mml:mo> <mml:mo>−</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>0.80</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.16</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.14</mml:mn> </mml:mrow> </mml:msubsup> <mml:mo stretchy="false">)</mml:mo> </mml:math> in flat w CDM. For flat w 0 w a CDM, we find <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">Ω</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">M</mml:mi> </mml:mrow> </mml:msub> <mml:mo>,</mml:mo> <mml:msub> <mml:mrow> <mml:mi>w</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>0</mml:mn> </mml:mrow> </mml:msub> <mml:mo>,</mml:mo> <mml:msub> <mml:mrow> <mml:mi>w</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>a</mml:mi> </mml:mrow> </mml:msub> <mml:mo stretchy="false">)</mml:mo> <mml:mo>=</mml:mo> <mml:mo stretchy="false">(</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>0.495</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.043</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.033</mml:mn> </mml:mrow> </mml:msubsup> <mml:mo>,</mml:mo> <mml:mo>−</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>0.36</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.30</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.36</mml:mn> </mml:mrow> </mml:msubsup> <mml:mo>,</mml:mo> <mml:mo>−</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>8.8</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>4.5</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>3.7</mml:mn> </mml:mrow> </mml:msubsup> <mml:mo stretchy="false">)</mml:mo> </mml:math> , consistent with a constant equation of state to within ∼2 σ . Including Planck cosmic microwave background, Sloan Digital Sky Survey baryon acoustic oscillation, and DES 3 × 2pt data gives (Ω M , w ) = (0.321 ± 0.007, −0.941 ± 0.026). In all cases, dark energy is consistent with a cosmological constant to within ∼2 σ . Systematic errors on cosmological parameters are subdominant compared to statistical errors; these results thus pave the way for future photometrically classified SN analyses.

  PublisherDOI

• Deep <i>JWST</i>/NIRCam imaging of Supernova 1987A

  Monthly Notices of the Royal Astronomical Society · 2024-06-25 · 9 citations

  articleOpen access

  ABSTRACT JWST/NIRCam obtained high angular resolution (0.05–0.1 arcsec), deep near-infrared 1–5 $\mu$m imaging of Supernova (SN) 1987A taken 35 yr after the explosion. In the NIRCam images, we identify: (1) faint H2 crescents, which are emissions located between the ejecta and the equatorial ring, (2) a bar, which is a substructure of the ejecta, and (3) the bright 3–5 $\mu$m continuum emission exterior to the equatorial ring. The emission of the remnant in the NIRCam 1–2.3 $\mu$m images is mostly due to line emission, which is mostly emitted in the ejecta and in the hotspots within the equatorial ring. In contrast, the NIRCam 3–5 $\mu$m images are dominated by continuum emission. In the ejecta, the continuum is due to dust, obscuring the centre of the ejecta. In contrast, in the ring and exterior to the ring, synchrotron emission contributes a substantial fraction to the continuum. Dust emission contributes to the continuum at outer spots and diffuse emission exterior to the ring, but little within the ring. This shows that dust cooling and destruction time-scales are shorter than the synchrotron cooling time-scale, and the time-scale of hydrogen recombination in the ring is even longer than the synchrotron cooling time-scale. With the advent of high sensitivity and high angular resolution images provided by JWST/NIRCam, our observations of SN 1987A demonstrate that NIRCam opens up a window to study particle-acceleration and shock physics in unprecedented details, probed by near-infrared synchrotron emission, building a precise picture of how an SN evolves.

  PublisherOA PDFDOI

• Measuring the ejecta velocities of type Ia supernovae from the pan-STARRS1 medium deep survey

  Monthly Notices of the Royal Astronomical Society · 2024-07-01 · 10 citations

  articleOpen access

  ABSTRACT There is growing evidence that Type Ia supernovae (SNe Ia) may originate from multiple explosion channels. Previous studies have indicated that the ejecta velocity of SNe Ia is one powerful tool to discriminate between different channels. In this work, we study ∼400 confirmed SNe Ia discovered by the Pan-STARRS1 Medium Deep Survey (PS1-MDS), and obtain a sample of ∼50 SNe Ia that have near-peak $\mathrm{Si}\, {\small II}\, \lambda 6355$ velocity ($v_{\mathrm{Si}\, {\small II}}$) measurements. We investigate the relationships between $v_{\mathrm{Si}\, {\small II}}$ and various parameters, including SN light-curve width, colour, host galaxy properties, and redshift. No significant trends are identified between $v_{\mathrm{Si}\, {\small II}}$ and light-curve parameters. Regarding the host-galaxy properties, we see a significant trend that high-velocity (HV) SNe Ia ($v_{\mathrm{Si}\, {\small II}}\gtrsim 12000$ km s$^{-1}$) tend to reside in more massive galaxies compared to normal velocity (NV) SNe Ia ($v_{\mathrm{Si}\, {\small II}}\lt 12000$ km s$^{-1}$) when combining both the PS1-MDS data set and those from previous low-z studies. While we do not see a significant trend between $v_{\mathrm{Si}\, {\small II}}$ and redshift, HV SNe Ia appear to be more prevalent in low-z samples than in high-z samples. We discuss several possibilities that could potentially contribute to this trend. Furthermore, we investigate the potential bias on SN Ia distances and find no significant difference in Hubble residuals between HV and NV subgroups.

  PublisherOA PDFDOI

• Fund two extremely large US telescopes

  Science · 2024-02-15

  letterCorresponding
  PublisherDOI

• 1991T-like Supernovae*

  The Astrophysical Journal Supplement Series · 2024-07-01 · 14 citations

  articleOpen access

  Abstract Understanding the nature of the luminous 1991T-like supernovae (SNe) is of great importance to SN cosmology as they are likely to have been more common in the early Universe. In this paper, we explore the observational properties of 1991T-like SNe to study their relationship to other luminous, slow-declining Type Ia supernovae (SNe Ia). From the spectroscopic and photometric criteria defined in Phillips et al., we identify 17 1991T-like SNe from the literature. Combining these objects with 10 1991T-like SNe from the Carnegie Supernova Project-II, the spectra, light curves, and colors of these events, along with their host galaxy properties, are examined in detail. We conclude that 1991T-like SNe are closely related in essentially all of their UV, optical, and near-infrared properties—as well as their host galaxy parameters—to the slow-declining subset of Branch core-normal SNe and to the intermediate 1999aa-like events, forming a continuum of luminous SNe Ia. The overriding difference between these three subgroups appears to be the extent to which 56 Ni mixes into the ejecta, producing the premaximum spectra dominated by Fe iii absorption, the broader UV light curves, and the higher luminosities that characterize the 1991T-like events. Nevertheless, the association of 1991T-like SNe with the rare Type Ia circumstellar material SNe would seem to run counter to this hypothesis, in which case 1991T-like events may form a separate subclass of SNe Ia, possibly arising from single-degenerate progenitor systems.

  PublisherOA PDFDOI

Recent grants

• Understanding Supernovae for Cosmology & Themselves

  NSF · $500k · 2015–2018

• Supernovae and Supernova Cosmology

  NSF · $866k · 2009–2013

• Understanding Supernovae for Cosmology and for Themselves

  NSF · $563k · 2006–2009

• Understanding Supernovae for Cosmology and for Themselves

  NSF · $1.0M · 2012–2017

Frequent coauthors

• P. Challis

  Center for Astrophysics Harvard & Smithsonian

  510 shared

• T. Matheson

  NSF’s NOIRLab

  416 shared

• R. J. Foley

  332 shared

• P. Garnavich

  University of Notre Dame

  272 shared

• A. V. Filippenko

  University of California, Berkeley

  250 shared

• Saurabh W. Jha

  248 shared

• Adam G. Riess

  Space Telescope Science Institute

  213 shared

• N. B. Suntzeff

  Texas A&M University

  207 shared

Education

• Ph.D., Astronomy

  Harvard University

  1979

• B.A., Physics

  Harvard University

  1974