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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').
Advanced Search

To narrow the search results, use advanced search syntax. This allows for specifying which circular field to search (submitter, subject, and/or body). For additional information, refer to the advanced search documentation.

Advanced Search Examples (click to copy):

subject:"Swift"
body:"GRB"
submitter:"Judith Racusin"
  1. IPN triangulation of GRB 250816A (short)
  2. IPN triangulation of GRB 250814C (short)
  3. IPN triangulation of GRB 250804B (short)
  4. GRB 250818B: FTW optical and NIR observations show reddening of the counterpart
  5. GRB 250818B: Kilonova-Catcher optical afterglow detection
  6. LIGO/Virgo/KAGRA S250818k: AstroSat CZTI non-detection and upper limits
  7. GRB 250818B: Liverpool Telescope optical detections
  8. LIGO/Virgo/KAGRA S250818k: Upper limits from Fermi-GBM Observations
  9. LIGO/Virgo/KAGRA S250818k: Updated Sky localization and EM Bright Classification
  10. LIGO/Virgo/KAGRA S250818k: Pan-STARRS pre-detection limits for AT2025ulz
  11. GRB 250818A: AstroSat CZTI detection
  12. LIGO/Virgo/KAGRA S250818k: Properties of the low-significance GW compact binary merger candidate potentially associated with AT 2025ulz
  13. LIGO/Virgo/KAGRA S250818k: Keck I LRIS spectroscopy of ZTF25abjmnps (AT2025ulz)
  14. GRB 250818B: Swift/UVOT Detection
  15. Fermi Gamma-ray Burst Monitor trigger 777342746/250820022 is not a GRB
  16. LIGO/Virgo/KAGRA S250818k: FTW Fast reddening of AT 2025ulz
  17. GRB 250820A: Fermi GBM Final Real-time Localization
  18. GRB 250818B: optical afterglow detection with Lesedi (GOTO25fzq)
  19. GRB 250818B: TRT Optical Observation
  20. Fermi GRB 250816A: Global MASTER-Net observations report
  21. GRB 250818B: SAO RAS optical observations
  22. Swift GRB 250818A: Global MASTER-Net observations report
  23. GRB 250818B: NOT optical observations
  24. GRB 250818A: Swift-XRT refined Analysis
  25. GRB 250818B: EP-FXT counterpart detection
  26. GRB 250818A: Swift-BAT refined analysis
  27. Fermi Gamma-ray Burst Monitor trigger 777251788/250818970 is not a GRB
  28. LIGO/Virgo/KAGRA S250818k: FTW optical and NIR observations of AT 2025ulz
  29. GRB 250818C: Fermi GBM Final Real-time Localization
  30. GRB 250818B: Keck redshift of the optical afterglow
  31. Fermi trigger No 776849714: Global MASTER-Net observations report
  32. GRB 250818B: KAIT optical observations
  33. GRB 250818A: Swift/UVOT Upper Limits
  34. LIGO/Virgo/KAGRA S250818t: Updated Sky localization
  35. LIGO/Virgo/KAGRA S250818k: Candidates from the Zwicky Transient Facility
  36. GRB 250818A: Enhanced Swift-XRT position
  37. GRB 250813B: SVOM/ECLAIRs refined analysis
  38. GRB 250818A: Fermi GBM Observation
  39. LIGO/Virgo/KAGRA S250818k: Coverage and upper limits from MAXI/GSC observations
  40. GRB 250818B: SVOM/VT optical observation
  41. GRB 250814A: Further GRAWITA TNG NIR observations
  42. GRB 250818B: Swift-XRT afterglow detection
  43. GRB 250818B: GOTO optical counterpart candidate
  44. GRB 250818B: SVOM detection of a short burst
  45. LIGO/Virgo/KAGRA S250818t: Identification of a GW compact binary merger candidate
  46. GRB 250818A: Swift detection of a burst
  47. GRB 250818A: Fermi GBM Final Real-time Localization
  48. sb25081602: Swift-XRT observations
  49. GRB 250816A: SVOM/GRM observation of a short burst
  50. SVOM/sb25081602: detection of a likely X-ray transient
  51. Fermi GRB 250814B: Global MASTER-Net observations report
  52. GRB 250816A: Fermi GBM Final Real-time Localization
  53. GRB 250814A: Swift-BAT refined analysis
  54. GRB 250815A: Fermi GBM Final Localization
  55. GRB 250813B: Liverpool Telescope optical upper limits
  56. GRB 250814A: Further COLIBRÍ optical upper limit
  57. GRB 250814A: detection of the afterglow candidate with Liverpool Telescope
  58. GRB 250814A: GRAWITA TNG NIR observations
  59. GRB 250812A: SVOM/VT optical continued observation
  60. GRB 250814A: Mondy optical observations of the candidate counterpart to LVK S250814bg
  61. GRB 250813B: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  62. GRB250814A: TRT optical upper limits
  63. GRB 250814B: SVOM/GRM observation
  64. GRB 250814C: SVOM/GRM observation of a short burst
  65. LIGO/Virgo/KAGRA S250813k: Swift XRT observations, 2 X-ray sources
  66. GRB 250813B: SVOM/GRM observation
  67. GRB 250814A: P200/WIRC observations of the afterglow candidate
  68. GRB 250814A: possible optical afterglow candidate at Spanish observatories
  69. GRB 250814A: KAIT optical upper limit
  70. GRB 250814A: Swift-XRT refined Analysis
  71. GRB 240814A: Fermi GBM Observation
  72. GRB 250814A: Possible afterglow candidate from P200/WIRC
  73. GRB 250813B: Fermi GBM Observation
  74. GRB 250814A: Optical observations with MDM Hiltner 2.4m telescope
  75. Fermi trigger No 776818276: Global MASTER-Net observations report
  76. Swift GRB250814.32: Global MASTER-Net observations report
  77. GRB 250814A: J-band upper limit from WINTER
  78. IceCube-250813A: Upper limits from a search for additional neutrino events in IceCube
  79. GRB 250813B: NOT observations of the optical afterglow
  80. GRB 250813B: SVOM/VT optical observations
  81. Subject GRB 250813B: SVOM/MXT refined analysis
  82. GRB 250814A: COLIBRÍ optical upper limit
  83. GRB 250814B: Fermi GBM Final Real-time Localization
  84. GRB 250813A: AstroSat CZTI detection
  85. LIGO/Virgo/KAGRA S250814bg: Identification of a GW compact binary merger candidate possibly associated with GRB 250814A detected by Fermi GBM and Swift BAT
  86. GRB 250813B: VLT X-shooter spectroscopic redshift z = 1.752
  87. GRB 250814A: DDOTI Optical Upper Limit
  88. GRB 250813B: EP-FXT counterpart detection
  89. Fermi-LAT Gamma-ray Observations of IceCube-250813A
  90. GRB 250813B: Swift-XRT afterglow detection
  91. GRB 250814A: Swift detection of a burst coincident with a subthreshold GW trigger
  92. GRB 250814A: Fermi GBM Final Real-time Localization
  93. GRB 250813B: SVOM/COLIBRÍ (FM-GFT) optical observations
  94. GRB 250813B: Ondrejov D50 fast decay
  95. GRB 250813B: SVOM detection of a bright long burst (Correction for GCN 41352).
  96. GRB 250813B: Ondrejov D50 optical afterglow detection
  97. GRB 250813B: SVOM detection of a bright long burst
  98. LIGO/Virgo/KAGRA S250813k: NED Galaxies in the 4-Update Localization Volume
  99. LIGO/Virgo/KAGRA S250813k: Updated Sky localization
  100. EP250812a: Nickel optical upper limit

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