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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"

26370 results found.

  1. GRB 250821A: NOT z-band upper limit
  2. GRB 250821A: KAIT optical upper limit
  3. GRB 250821A: Swift-XRT refined Analysis
  4. GRB 250821B: Fermi GBM Detection
  5. GRB 250821B: BALROG localization (Fermi Trigger / GRB 250821672)
  6. GRB 250821A: Enhanced Swift-XRT position
  7. GRB 250821A: Swift/UVOT Upper Limits
  8. EP250821a: Rapidly fading optical source detected in Las Cumbres followup
  9. EP250821a: Swift XRT and UVOT counterpart detection
  10. LIGO/Virgo/KAGRA S250818k: GOTO counterpart search and upper limits
  11. EP250821a: Preliminary analysis of the EP-WXT and EP-FXT observations
  12. GRB 250821A: LCOGT Optical Upper Limits
  13. GRB 250814A: CMO SAI and SAO RAS izJ observations.
  14. GRB 250821A: Swift detection of a burst
  15. LIGO/Virgo/KAGRA S250818k: WFST pre-discovery limits and follow-up observations of AT 2025ulz
  16. EP250821a: Einstein Probe detection of an X-ray transient
  17. GRB 250819A: SVOM/GRM observation of a possible “long” duration type I burst
  18. LIGO/Virgo/KAGRA S250818k: WINTER J-band observations of AT 2025ulz
  19. LIGO/Virgo/KAGRA S250818k: ATLAS pre-discovery limits for AT2025ulz
  20. GRB 250814A: Swift/UVOT Upper Limits
  21. GRB 250813B: Swift/UVOT Upper Limit
  22. IPN triangulation of GRB 250816A (short)
  23. IPN triangulation of GRB 250814C (short)
  24. IPN triangulation of GRB 250804B (short)
  25. GRB 250818B: Kilonova-Catcher optical afterglow detection
  26. LIGO/Virgo/KAGRA S250818k: AstroSat CZTI non-detection and upper limits
  27. LIGO/Virgo/KAGRA S250818k: Upper limits from Fermi-GBM Observations
  28. LIGO/Virgo/KAGRA S250818k: Updated Sky localization and EM Bright Classification
  29. LIGO/Virgo/KAGRA S250818k: Pan-STARRS pre-detection limits for AT2025ulz
  30. LIGO/Virgo/KAGRA S250818k: Properties of the low-significance GW compact binary merger candidate potentially associated with AT 2025ulz
  31. GRB 250818B: Swift/UVOT Detection
  32. GRB 250818B: optical afterglow detection with Lesedi (GOTO25fzq)
  33. GRB 250818B: SAO RAS optical observations
  34. GRB 250818A: Swift-XRT refined Analysis
  35. GRB 250818B: EP-FXT counterpart detection
  36. GRB 250818A: Swift-BAT refined analysis
  37. GRB 250818B: KAIT optical observations
  38. GRB 250818A: Swift/UVOT Upper Limits
  39. LIGO/Virgo/KAGRA S250818t: Updated Sky localization
  40. GRB 250818A: Enhanced Swift-XRT position
  41. GRB 250813B: SVOM/ECLAIRs refined analysis
  42. GRB 250818A: Fermi GBM Observation
  43. LIGO/Virgo/KAGRA S250818k: Coverage and upper limits from MAXI/GSC observations
  44. GRB 250814A: Further GRAWITA TNG NIR observations
  45. GRB 250818B: Swift-XRT afterglow detection
  46. GRB 250818B: SVOM detection of a short burst
  47. LIGO/Virgo/KAGRA S250818t: Identification of a GW compact binary merger candidate
  48. GRB 250818A: Swift detection of a burst
  49. sb25081602: Swift-XRT observations
  50. GRB 250816A: SVOM/GRM observation of a short burst
  51. GRB 250814A: Swift-BAT refined analysis
  52. GRB 250813B: Liverpool Telescope optical upper limits
  53. GRB 250814A: Further COLIBRÍ optical upper limit
  54. GRB 250814A: detection of the afterglow candidate with Liverpool Telescope
  55. GRB 250814A: GRAWITA TNG NIR observations
  56. GRB 250814A: Mondy optical observations of the candidate counterpart to LVK S250814bg
  57. GRB 250813B: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  58. GRB250814A: TRT optical upper limits
  59. GRB 250814B: SVOM/GRM observation
  60. LIGO/Virgo/KAGRA S250813k: Swift XRT observations, 2 X-ray sources
  61. GRB 250813B: SVOM/GRM observation
  62. GRB 250814A: P200/WIRC observations of the afterglow candidate
  63. GRB 250814A: possible optical afterglow candidate at Spanish observatories
  64. GRB 250814A: KAIT optical upper limit
  65. GRB 250814A: Swift-XRT refined Analysis
  66. GRB 240814A: Fermi GBM Observation
  67. GRB 250814A: Possible afterglow candidate from P200/WIRC
  68. GRB 250813B: Fermi GBM Observation
  69. GRB 250814A: Optical observations with MDM Hiltner 2.4m telescope
  70. GRB 250814A: J-band upper limit from WINTER
  71. IceCube-250813A: Upper limits from a search for additional neutrino events in IceCube
  72. GRB 250813B: NOT observations of the optical afterglow
  73. GRB 250814A: COLIBRÍ optical upper limit
  74. GRB 250813A: AstroSat CZTI detection
  75. LIGO/Virgo/KAGRA S250814bg: Identification of a GW compact binary merger candidate possibly associated with GRB 250814A detected by Fermi GBM and Swift BAT
  76. GRB 250814A: DDOTI Optical Upper Limit
  77. GRB 250813B: EP-FXT counterpart detection
  78. Fermi-LAT Gamma-ray Observations of IceCube-250813A
  79. GRB 250813B: Swift-XRT afterglow detection
  80. GRB 250814A: Swift detection of a burst coincident with a subthreshold GW trigger
  81. GRB 250813B: SVOM/COLIBRÍ (FM-GFT) optical observations
  82. GRB 250813B: SVOM detection of a bright long burst (Correction for GCN 41352).
  83. GRB 250813B: SVOM detection of a bright long burst
  84. LIGO/Virgo/KAGRA S250813k: NED Galaxies in the 4-Update Localization Volume
  85. LIGO/Virgo/KAGRA S250813k: Updated Sky localization
  86. EP250812a: Nickel optical upper limit
  87. GRB 250812A: VLT X-shooter spectroscopic redshift confirmation z = 2.571
  88. EP250812a: NOT, NTT, and GS observations
  89. GRB 250812A: Swift/UVOT Detection
  90. EP250812a: COLIBRÍ detection of the VT candidate and evidence of flattening
  91. EP250812a: Liverpool Telescope upper limits
  92. EP250812a: refined analysis of the EP-WXT and EP-FXT observations
  93. LIGO/Virgo/KAGRA S250813k: Identification of a GW compact binary merger candidate
  94. GRB 250812A: EP-FXT counterpart detection
  95. GRB 250807B: Swift-BAT refined analysis
  96. EP 250812a: GOTO optical upper limit
  97. GRB 250812A: Kilonova-Catcher optical afterglow detection
  98. EP250812a: Swift-XRT counterpart detection
  99. GRB 250812A: SVOM/COLIBRÍ (FM-GFT) optical observations
  100. EP250812a: Einstein Probe detection of an X-ray transient

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