Skip to main content
New Announcement Feature, Code of Conduct, Circular Revisions. See news and announcements

GCN Circulars

GCN Circulars are rapid astronomical bulletins submitted by and distributed to community members worldwide. They are used to share discoveries, observations, quantitative near-term predictions, requests for follow-up observations, or future observing plans related to high-energy, multi-messenger, and variable or transient astrophysical events. See the documentation for help with subscribing to or submitting Circulars.

Search for Circulars by submitter, subject, or body text (e.g. 'Fermi GRB').
To navigate to a specific circular, enter the associated Circular ID (e.g. 'gcn123', 'Circular 123', or '123').
  1. EP240426b: EP-WXT detection of a new fast X-ray transient
  2. LIGO/Virgo/KAGRA S240422ed: Archival radio detection of EP240426a
  3. LIGO/Virgo/KAGRA S240422ed: Swope Follow-up of AT2024hfq, AT2024hfr, AT2024hfs, and AT2024hfx
  4. LIGO/Virgo/KAGRA S240422ed: BOOTES-6/DPRT optical upper limits for EP240426a
  5. LIGO/Virgo/KAGRA S240422ed: GRANDMA Optical Upper Limits for EP240426a
  6. LIGO/VIRGO/KAGRA S240422ed: Historical variability for EP240426a
  7. GRB 240426A: AstroSat CZTI detection
  8. EP240426a: YAHPT optical upper limit
  9. XMM-Newton observation of EP240426a
  10. LIGO/Virgo/KAGRA S240426dl: Identification of a GW compact binary merger candidate
  11. LIGO/Virgo/KAGRA S240422ed: BOOTES-4/MET Optical Upper Limits for EP240426a
  12. LIGO/Virgo/KAGRA S240422ed: EP-FXT Detection of the Potential Opitcal Electromagnetic Counterpart AT 2024hfq Reported by DECam
  13. GRB 240414A: NOEMA detection
  14. LIGO/Virgo/KAGRA S240422ed: EP240426a possible optical detection
  15. LIGO/Virgo/KAGRA S240422ed: Continued Magellan Observations
  16. EP240426a: GMG optical upper limit
  17. LVK S240422ed: Further Swift-XRT followup of three sources
  18. LIGO/Virgo/KAGRA S240422ed: EP-FXT detection of a candidate counterpart EP240426a
  19. LIGO/Virgo/KAGRA S240426s: Identification of a GW compact binary merger candidate
  20. LIGO/Virgo/KAGRA S240422ed: Magellan Follow-up Observations of Swift/XRT candidates
  21. LIGO/Virgo/KAGRA S240422ed: Zwicky Transient Facility contuinued observations of S240422ed and candidate analysis
  22. IceCube-240424A: Upper limits from a search for additional neutrino events in IceCube
  23. LIGO/Virgo/KAGRA S240422ed: GOTO counterpart search update and AT2024hfx, AT2024hgl observations
  24. S240422ed: BlackGEM/MeerLICHT transient detection AT2024hgl/MLTJ080628.10-250116.4
  25. LIGO/Virgo/KAGRA S240422ed: PRIME near-infrared observations
  26. LIGO/Virgo/KAGRA S240422ed: 2.5m PRL Telescope follow-up of the Swift/XRT source S240422ed_X190
  27. S240422ed: MeerLICHT/BlackGEM photometry on AT2024hfx and archival ZTF detection
  28. LIGO/Virgo/KAGRA S240422ed: Second night Pan-STARRS observations of the skymap
  29. LIGO/Virgo/KAGRA S240422ed: Further near-infrared observations with Subaru/MOIRCS by J-GEM Collaboration
  30. LIGO/Virgo/KAGRA S240422ed: X-ray Upper Limits from EP-FXT for the Potential Electromagnetic Counterparts Reported by Swift and DECam
  31. LIGO/Virgo/KAGRA S240422ed: Upper limits from GECAM Observations
  32. LIGO/Virgo/KAGRA S240422ed: No significant candidates in GRANDMA and Kilonova-Catcher galaxy targeting observations
  33. LIGO/Virgo/KAGRA S240422ed: Additional DECam GW-MMADS Candidates from the first two nights of observations
  34. LIGO/Virgo/KAGRA S240422ed: ANU 2.3m followup of candidate counterparts
  35. LIGO/Virgo/KAGRA S240422ed: Magellan Spectrum of GW-MMADS Candidate AT2024hdo Indicates a Type II SN
  36. GRB 240425A: Fermi GBM Final Real-time Localization
  37. Fermi trigger No 735697285: Global MASTER-Net observations report
  38. LIGO/Virgo/KAGRA S240422ed: SRG/eROSITA archival upper limits for Swift/XRT candidates
  39. GRB 240419B: Swift-BAT refined analysis
  40. GRB 240421B: Swift-BAT refined analysis
  41. GRB 240422A: Glowbug gamma-ray detection
  42. LIGO/Virgo/KAGRA S240422ed: Archival BlackGEM/MeerLICHT detections of AT 2024hdr & AT 2024hdq
  43. LIGO/Virgo/KAGRA S240413p: DESGW DECam Follow-Up
  44. LIGO/Virgo/KAGRA S240422ed: Himalayan Chandra Telescope follow-up of the Swift/XRT source S240422ed_X101
  45. LIGO/Virgo/KAGRA S240422ed: No significant counterpart candidates in HAWC observations
  46. LIGO/Virgo/KAGRA S240422ed: Vetting of DECam Candidates Using Real-Time Resources and SAGUARO Infrastructure
  47. LIGO/Virgo/KAGRA S240422ed: No significant candidates in GRANDMA/FRAM Observations
  48. IceCube-240424A - IceCube observation of a high-energy neutrino candidate track-like event
  49. LIGO/Virgo/KAGRA S240422ed: X-ray Upper Limits from EP-WXT for the Potential Electromagnetic Counterparts Reported by Swift and DECam
  50. LIGO/Virgo/KAGRA S240422ed: MOSFIRE spectroscopy of the DECam GW-MMADS candidate AT 2024hdn
  51. LIGO/Virgo/KAGRA S240422ed: ATCA follow-up of candidate counterparts
  52. LIGO/Virgo/KAGRA S240422ed: MOSFIRE imaging of the DECam GW-MMADS candidate AT 2024hdm
  53. LIGO/Virgo S240422ed: Swift-XRT detection of 3 possible counterparts
  54. LIGO/Virgo/KAGRA S240422ed: Early X-ray Upper Limits from EP-WXT for the LVK Sky Localization Region
  55. LIGO/Virgo/KAGRA S240422ed: J-band non-detection of Mag24a
  56. LIGO/Virgo/KAGRA S240422ed: Continued Imaging of Mag24a
  57. LIGO/Virgo/KAGRA S240422ed: Archival DECaPSs2 observations of the field of Mag24a
  58. LIGO/Virgo/KAGRA S240422ed: DECam GW-MMADS Candidates
  59. LIGO/Virgo/KAGRA S240422ed: Potential Magellan candidates from GCN 36263 are unrelated.
  60. LIGO/Virgo/KAGRA S240422ed: NOT J-band upper limit on the Swift/XRT source S240422ed_X61
  61. LIGO/Virgo/KAGRA S240422ed: X-ray Upper Limits from EP-WXT for the Three Potential Electromagnetic Counterparts Reported So Far
  62. GRB 240421B: GRBAlpha detection
  63. IceCube Alert 240424.08: Global MASTER-Net observations report
  64. LIGO/Virgo/KAGRA S240422ed: Magellan Detection of a Potential Electromagnetic Counterpart
  65. LIGO/Virgo/KAGRA S240422ed: SAGUARO upper limits from CSS
  66. LIGO/Virgo/KAGRA S240422ed: Subaru/MOIRCS near-infrared observations by J-GEM Collaboration
  67. LIGO/Virgo/KAGRA S240422ed: LAST optical observations
  68. LIGO/Virgo/KAGRA S240422ed: Potential Candidates from Magellan galaxy-based search
  69. LIGO/Virgo/KAGRA S240422ed: WINTER J-band upper limits on the Swift/XRT source S240422ed_X61
  70. IceCube-240419A: Upper limits from a search for additional neutrino events in IceCube
  71. LIGO/Virgo/KAGRA S240421ar: Updated Sky localization
  72. LIGO/Virgo/KAGRA S240422ed: GW-MMADS DECam upper limits on the Swift/XRT source S240422ed_X61
  73. LIGO/Virgo/KAGRA S240422ed: no candidate counterparts from Pan-STARRS observations of the skymap
  74. LIGO/Virgo/KAGRA S240422ed: GOTO counterpart search
  75. LIGO/Virgo/KAGRA S240422ed: No Counterparts in DDOTI/OAN Optical Observations
  76. GRB 240419A: Swift-BAT refined analysis
  77. GRB 240418A: Swift-BAT refined analysis
  78. LXT240402A/GRB240402B: Chandra X-ray detection
  79. LIGO/Virgo/KAGRA S240423br: Retraction of GW compact binary merger candidate
  80. LIGO/Virgo/KAGRA S240422ed: no candidate counterparts from ATLAS observations
  81. GRB 240419A: Possible ATCA radio detection
  82. GRB 240421B: ATCA radio observations
  83. LIGO/Virgo/KAGRA S240422ed: WINTER near-infrared J-band observations
  84. LIGO/Virgo S240422ed: No counterpart candidates in INTEGRAL SPI-ACS prompt observation
  85. LIGO/Virgo/KAGRA S240422ed: Zwicky Transient Facility observations and candidates
  86. LIGO/Virgo/KAGRA S240422ed: GW-MMADS DECam observations
  87. LIGO/Virgo/KAGRA S240422ed: Magellan Observations
  88. LIGO/Virgo/KAGRA S240422ed: Updated NED Galaxies in the Localization Volume
  89. LIGO/Virgo/KAGRA S240422ed: AstroSat CZTI non-detection and upper limits
  90. LIGO/Virgo/KAGRA S240422ed: Upper limits from Fermi-GBM Observations
  91. LIGO/Virgo/KAGRA S240422ed: Updated Sky localization and EM Bright Classification
  92. LIGO/Virgo/KAGRA S240421ar: Upper limits from Swift/BAT-GUANO
  93. LIGO/Virgo/KAGRA S240422ed: Coverage and upper limits from MAXI/GSC observations
  94. LIGO/Virgo/KAGRA S240422ed: MeerLICHT and BlackGEM observations report
  95. LIGO/Virgo/KAGRA S240422ed: Identification of a GW compact binary merger candidate
  96. LIGO/Virgo/Kagra S240422ed: NED Galaxies in the Localization Volume
  97. LIGO/Virgo/KAGRA S240422ed: Global MASTER-Net observations report
  98. Fermi trigger No 735470374: Global MASTER-Net observations report
  99. GRB 240421A: Glowbug gamma-ray detection
  100. GRB 240414A: radio detection with the VLA

Advanced

Download all Circulars as a .tar.gz archive:
Questions or comments?
Contact GCN directly.
Have you found a bug in GCN?
Open an issue.
Want to contribute code to GCN?
Get involved on GitHub.

gcn.nasa.gov

A service of the Astrophysics Science Division at NASA Goddard Space Flight Center

Looking for U.S. government information and services? Visit USA.gov