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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"

25841 results found.

  1. GRB 250823A: Enhanced Swift-XRT position
  2. GRB 250823A: LCOGT Optical Detection
  3. GRB 250823A: Swift detection of a burst
  4. Konus-Wind detection of GRB 250821B
  5. LIGO/Virgo/KAGRA S250818k: HST nIR detection of AT 2025ulz
  6. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Optical Detection of AT2025ulz
  7. LIGO/Virgo/KAGRA S250818k: 3 GHz MeerKAT observations of AT2025ulz
  8. IPN triangulation of GRB 250821B (long/bright)
  9. GRB 250821A: Kilonova-Catcher optical upper limits
  10. EP250821a: Swift/XRT counterpart fading
  11. GRB 250812A: SVOM/ECLAIRs refined analysis
  12. LIGO/Virgo/KAGRA S250818k: Pan-STARRS coverage of the skymap and candidate counterparts
  13. GRB 250821A: VLT/FORS2 Optical Observation
  14. GRB 250821B: SVOM/GRM observation
  15. EP250821a: SVOM/VT optical observation
  16. GRB 250821A: NOT z-band upper limit
  17. GRB 250821A: KAIT optical upper limit
  18. GRB 250821A: Swift-XRT refined Analysis
  19. GRB 250821B: Fermi GBM Detection
  20. GRB 250821B: BALROG localization (Fermi Trigger / GRB 250821672)
  21. GRB 250821A: Enhanced Swift-XRT position
  22. GRB 250821A: Swift/UVOT Upper Limits
  23. EP250821a: Rapidly fading optical source detected in Las Cumbres followup
  24. EP250821a: Swift XRT and UVOT counterpart detection
  25. LIGO/Virgo/KAGRA S250818k: GOTO counterpart search and upper limits
  26. EP250821a: Preliminary analysis of the EP-WXT and EP-FXT observations
  27. GRB 250821A: LCOGT Optical Upper Limits
  28. GRB 250814A: CMO SAI and SAO RAS izJ observations.
  29. GRB 250821A: Swift detection of a burst
  30. LIGO/Virgo/KAGRA S250818k: WFST pre-discovery limits and follow-up observations of AT 2025ulz
  31. LIGO/Virgo/KAGRA S250818k: EP/FXT observation of AT 2025ulz
  32. EP250821a: Einstein Probe detection of an X-ray transient
  33. GRB 250819A: SVOM/GRM observation of a possible “long” duration type I burst
  34. LIGO/Virgo/KAGRA S250818k: WINTER J-band observations of AT 2025ulz
  35. LIGO/Virgo/KAGRA S250818k: ATLAS pre-discovery limits for AT2025ulz
  36. GRB 250814A: Swift/UVOT Upper Limits
  37. GRB 250813B: Swift/UVOT Upper Limit
  38. IPN triangulation of GRB 250816A (short)
  39. IPN triangulation of GRB 250814C (short)
  40. IPN triangulation of GRB 250804B (short)
  41. GRB 250818B: Kilonova-Catcher optical afterglow detection
  42. LIGO/Virgo/KAGRA S250818k: AstroSat CZTI non-detection and upper limits
  43. GRB 250818B: Liverpool Telescope optical detections
  44. LIGO/Virgo/KAGRA S250818k: Upper limits from Fermi-GBM Observations
  45. LIGO/Virgo/KAGRA S250818k: Updated Sky localization and EM Bright Classification
  46. LIGO/Virgo/KAGRA S250818k: Properties of the low-significance GW compact binary merger candidate potentially associated with AT 2025ulz
  47. GRB 250818B: Swift/UVOT Detection
  48. GRB 250818B: SAO RAS optical observations
  49. GRB 250818A: Swift-XRT refined Analysis
  50. GRB 250818B: EP-FXT counterpart detection
  51. GRB 250818B: KAIT optical observations
  52. GRB 250818A: Swift/UVOT Upper Limits
  53. GRB 250818A: Enhanced Swift-XRT position
  54. GRB 250813B: SVOM/ECLAIRs refined analysis
  55. GRB 250818A: Fermi GBM Observation
  56. LIGO/Virgo/KAGRA S250818k: Coverage and upper limits from MAXI/GSC observations
  57. GRB 250814A: Further GRAWITA TNG NIR observations
  58. GRB 250818B: Swift-XRT afterglow detection
  59. GRB 250818B: SVOM detection of a short burst
  60. LIGO/Virgo/KAGRA S250818t: Identification of a GW compact binary merger candidate
  61. GRB 250818A: Swift detection of a burst
  62. sb25081602: Swift-XRT observations
  63. GRB 250816A: SVOM/GRM observation of a short burst
  64. SVOM/sb25081602: detection of a likely X-ray transient
  65. GRB 250813B: Liverpool Telescope optical upper limits
  66. GRB 250814A: Further COLIBRÍ optical upper limit
  67. GRB 250814A: detection of the afterglow candidate with Liverpool Telescope
  68. GRB 250814A: GRAWITA TNG NIR observations
  69. GRB 250814A: Mondy optical observations of the candidate counterpart to LVK S250814bg
  70. GRB 250813B: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  71. GRB250814A: TRT optical upper limits
  72. GRB 250814B: SVOM/GRM observation
  73. LIGO/Virgo/KAGRA S250813k: Swift XRT observations, 2 X-ray sources
  74. GRB 250813B: SVOM/GRM observation
  75. GRB 250814A: P200/WIRC observations of the afterglow candidate
  76. GRB 250814A: possible optical afterglow candidate at Spanish observatories
  77. GRB 250814A: KAIT optical upper limit
  78. GRB 250814A: Swift-XRT refined Analysis
  79. GRB 240814A: Fermi GBM Observation
  80. GRB 250814A: Possible afterglow candidate from P200/WIRC
  81. GRB 250813B: Fermi GBM Observation
  82. GRB 250814A: Optical observations with MDM Hiltner 2.4m telescope
  83. GRB 250814A: J-band upper limit from WINTER
  84. IceCube-250813A: Upper limits from a search for additional neutrino events in IceCube
  85. GRB 250813B: NOT observations of the optical afterglow
  86. Subject GRB 250813B: SVOM/MXT refined analysis
  87. GRB 250814A: COLIBRÍ optical upper limit
  88. GRB 250813A: AstroSat CZTI detection
  89. LIGO/Virgo/KAGRA S250814bg: Identification of a GW compact binary merger candidate possibly associated with GRB 250814A detected by Fermi GBM and Swift BAT
  90. GRB 250814A: DDOTI Optical Upper Limit
  91. GRB 250813B: EP-FXT counterpart detection
  92. Fermi-LAT Gamma-ray Observations of IceCube-250813A
  93. GRB 250813B: Swift-XRT afterglow detection
  94. GRB 250814A: Swift detection of a burst coincident with a subthreshold GW trigger
  95. GRB 250813B: SVOM/COLIBRÍ (FM-GFT) optical observations
  96. GRB 250813B: SVOM detection of a bright long burst (Correction for GCN 41352).
  97. GRB 250813B: SVOM detection of a bright long burst
  98. EP250812a: Nickel optical upper limit
  99. GRB 250812A: VLT X-shooter spectroscopic redshift confirmation z = 2.571
  100. EP250812a: NOT, NTT, and GS observations

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